Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Exploiting whole genome sequence variants in cattle breeding : Unraveling the distribution of genetic variants and role of rare variants in genomic evaluation
    Zhang, Qianqian - \ 2017
    Wageningen University. Promotor(en): H. Bovenhuis; M.S. Lund, co-promotor(en): G. Sahana; M. Calus; B. Guldbrandtsen. - Wageningen : Wageningen University - ISBN 9788793643147 - 249
    cattle - genomes - genetic variation - inbreeding - homozygosity - longevity - quantitative traits - animal breeding - animal genetics - rundvee - genomen - genetische variatie - inteelt - homozygotie - gebruiksduur - kwantitatieve kenmerken - dierveredeling - diergenetica

    The availability of whole genome sequence data enables to better explore the genetic mechanisms underlying different quantitative traits that are targeted in animal breeding. This thesis presents different strategies and perspectives on utilization of whole genome sequence variants in cattle breeding. Using whole genome sequence variants, I show the genetic variation, recent and ancient inbreeding, and genome-wide pattern of introgression across the demographic and breeding history in different cattle populations. Using the latest genomic tools, I demonstrate that recent inbreeding can accurately be estimated by runs of homozygosity (ROH). This can further be utilized in breeding programs to control inbreeding in breeding programs. In chapter 2 and 4, by in-depth genomic analysis on whole genome sequence data, I demonstrate that the distribution of functional genetic variants in ROH regions and introgressed haplotypes was shaped by recent selective breeding in cattle populations. The contribution of whole genome sequence variants to the phenotypic variation partly depends on their allele frequencies. Common variants associated with different traits have been identified and explain a considerable proportion of the genetic variance. For example, common variants from whole genome sequence associated with longevity have been identified in chapter 5. However, the identified common variants cannot explain the full genetic variance, and rare variants might play an important role here. Rare variants may account for a large proportion of the whole genome sequence variants, but are often ignored in genomic evaluation, partly because of difficulty to identify associations between rare variants and phenotypes. I compared the powers of different gene-based association mapping methods that combine the rare variants within a gene using a simulation study. Those gene- based methods had a higher power for mapping rare variants compared with mixed linear models applying single marker tests that are commonly used for common variants. Moreover, I explored the role of rare and low-frequency variants in the variation of different complex traits and their impact on genomic prediction reliability. Rare and low-frequency variants contributed relatively more to variation for health-related traits than production traits, reflecting the potential of improving prediction reliability using rare and low-frequency variants for health-related traits. However, in practice, only marginal improvement was observed using selected rare and low-frequency variants when combined with 50k SNP genotype data on the reliability of genomic prediction for fertility, longevity and health traits. A simulation study did show that reliability of genomic prediction could be improved provided that causal rare and low-frequency variants affecting a trait are known.

    Comparative genomics and trait evolution in Cleomaceae, a model family for ancient polyploidy
    Bergh, Erik van den - \ 2017
    Wageningen University. Promotor(en): M.E. Schranz; Y. van de Peer. - Wageningen : Wageningen University - ISBN 9789463431705 - 106
    capparaceae - genomics - polyploidy - evolution - genomes - reproductive traits - flowers - colour - glucosinolates - genetic variation - biosystematics - taxonomy - identification - capparaceae - genomica - polyploïdie - evolutie - genomen - voortplantingskenmerken - bloemen - kleur - glucosinolaten - genetische variatie - biosystematiek - taxonomie - identificatie

    As more and more species have been sequenced, evidence has been piling up for a fascinating phenomenon that seems to occur in all plant lineages: paleopolyploidy. Polyploidy has historically been a much observed and studied trait, but until recently it was assumed that polyploids were evolutionary dead-ends due to their sterility. However, many studies since the 1990’s have challenged this notion by finding evidence for ancient genome duplications in many genomes of current species. This lead to the observation that all seed plants share at least one ancestral polyploidy event. Another polyploidy event has been proven to lie at the base of all angiosperms, further signifying the notion that ancient polyploidy is widespread and common. These findings have led to questions regarding the apparent disadvantages that can be observed in a first generation polyploid. If these disadvantages can be overcome however, duplication of a genome also presents an enormous potential for evolutionary novelty. Duplicated copies of genes are able to acquire changes that can lead to specialization of the duplicated pair into two functions (subfunctionalization) or the development of one copy towards an entirely new function (neofunctionalization).

    Currently, most research towards polyploidy has focused on the economically and scientifically important Brassicaceae family containing the model plant Arabidopsis thaliana and many crops such as cabbage, rapeseed, broccoli and turnip. In this thesis, I lay the foundations for the expansion of this scope to the Cleomaceae, a widespread cosmopolitan plant family and a sister family of Brassicaceae. The species within Cleomaceae are diverse and exhibit many scientifically interesting traits. They are also in a perfect position phylogenetically to draw comparisons with the much more studied Brassicaceae. I describe the Cleomaceae and their relevance to polyploid research in more detail in the Introduction. I then describe the important first step towards setting up the genetic framework of this family with the sequencing of Tarenaya hassleriana in Chapter 1.

    In Chapter 2, I have studied the effects of polyploidy on the development of C4 photosynthesis by comparing the transcriptome of C3 photosynthesis based species Tarenaya hassleriana with the C4 based Gynandropsis gynandra. C4 photosynthesis is an elaboration of the more common C3 form of photosynthesis that concentrates CO2 in specific cells leading to decreased photorespiration by the RuBisCO and higher photosynthetic efficieny in low CO2 environments. I find that polyploidy has not led to sub- or neofunctionalization towards the development of this trait, but instead find evidence for another important phenomenon in postpolyploid evolution: the dosage balance hypothesis. This hypothesis states that genes which are dependent on specific dosage levels of their products will be maintained in duplicate; any change in their function would lead to dosage imbalance which would have deleterious effects on their pathway. We show that most genes involved in photosynthesis have returned to single copy in G. gynandra and that the changes leading to C4 have mostly taken place at the expression level confirming current assumptions on the development of this trait.

    In Chapter 3, I have studied the effects of polyploidy on an important class of plant defence compounds: glucosinolates. These compounds, sometimes referred to as ‘mustard oils’, play an important role in the defence against herbivores and have radiated widely in Brassicaceae to form many different ‘flavors’ to deter specific herbivores. I show that in Cleomaceae many genes responsible for these compounds have benefited from the three rounds of polyploidy that T. hassleriana has undergone and that many duplicated genes have been retained. We also show that more than 75% is actively expressed in the plant, proving that the majority of these duplications has an active function in the plant.

    Finally, in Chapter 4 I investigate a simple observation made during experiments with T. hassleriana in the greenhouse regarding the variation in flower colour between different individuals: some had pink flowers and some purple. Using LC-PDA mass spectrometry we find that the two colours are caused by different levels of two anthocyanin pigments, with cyanidin dominating in the purple flowers and pelargonidin being more abundant in pink flowers. Through sequence comparison and synteny analysis between A. thaliana and T. hassleriana we find the orthologs of the genes involved in this pathway. Using a Genotyping by Sequencing method on a cross between these two flower colours, we produce a collection of SNP markers on the reference genome. With these SNPs, we find two significant binary trait loci, one of which corresponds to the location of the F3’H ortholog which performs the conversion of a pelargonidin precursor to a cyanidin precursor.

    In the General Conclusion, I combine all findings of the previous chapters and explain how they establish part of a larger species framework to study ancient polyploidy in angiosperms. I then put forth what these findings can mean for possible future research and the directions that are worth to be explored further.

    From species to trait evolution in Aethionema (Brassicaceae)
    Mohammadin, Setareh - \ 2017
    Wageningen University. Promotor(en): M.E. Schranz. - Wageningen : Wageningen University - ISBN 9789463431385 - 125
    brassicaceae - evolution - rna - genomes - genetic diversity - phytogeography - glucosinolates - quantitative trait loci - next generation sequencing - brassicaceae - evolutie - rna - genomen - genetische diversiteit - plantengeografie - glucosinolaten - loci voor kwantitatief kenmerk - next generation sequencing

    The plant family Brassicaceae (or crucifers) is an economically important group that includes many food crops (e.g. cabbages and radishes), horticultural species (e.g. Draba, Iberis, Lunaria), and model plant species (particularly Arabidopsis thaliana). Because of the fundamental importance of A. thaliana to plant biology, it makes the Brassicaceae an ideal system for comparative genomics and to test wider evolutionary, ecological and speciation hypotheses. One such hypothesis is the ‘Whole Genome Duplication Radiation Lag Time’ (WGD-RLT) model for the role of polyploidy on the evolution of important plant families such as the Brassicaceae. The WGD-RLT model indicates a higher rate of diversification of a core-group compared to its sister group, due to a lag time after a whole genome duplication event that made it possible for novel traits or geo- or ecological events to increase the core groups diversification rate.

    Aethionema is the species-poor sister genus of the core Brassicaceae and hence is at an important comparative position to analyse trait and genomic evolution of the species-rich core group. Aethionema species occur mainly in the western Irano-Turanian region, which is concordantly the biodiversity hotspot of the Brassicaceae family. Moreover comparing Aethionema to the Brassicaceae core group can help us to understand and test the ‘WGD-RLT’ model. However to be able to do so we first need to know more about Aethionema. In this thesis, I investigated various levels of evolutionary change (from macro, to micro to trait evolution) within the genus Aethionema, with a major focus the emerging model species Aethionema arabicum.

    Next generation sequencing has made it possible to use the genomes of many species in a comparative framework. However, the formation of proteins and enzymes, and in the end the phenotype of the whole plant, relies on transcription from particular regions of the genome including genes. Hence, the transcriptome makes it possible to assess the functional parts of the genome. However, the functional part of the genome not only relies on the protein coding genes. Gene regulatory elements like promoters and long non-coding RNAs function as regulators of gene expression and hence are involved in increasing or decreasing transcription. In Chapter 2 I used the transcriptome of four different Aethionema species to understand the lineage specificity of these long non-coding RNAs. Moreover in a comparison with the Brassicaceae core group and Brassicaceae’s sister family the Cleomaceae I show that although the position of long non-coding RNAs can be conserved, their sequences do not have to be.

    Most of the Aethionema species occur in the Irano-Turanian region, a politically instable region, making it hard for scientist to collect from. However the natural history collections made throughout the last centuries are a great resource. Combing these collections with the newest sequencing techniques, e.g. next generation sequencing, have allowed me to infer the phylogeny of ~75% of the known Aethionema species in a time calibrated and historical biogeographical framework. Hence, I was able to establish that Aethionema species likely originated from the Anatolian Diagonal and that major geological events like the uplift of the Turkish and Iranian plateau have had a hand in their speciation (Chapter 3).

    To examine species-level processes I sequenced and analysed transcriptomes of eight Ae. arabicum accessions coming from Cyprus, Iran and Turkey to investigate population structure, genetic diversity and local adaptation (Chapter 4). The most prominent finding was a ploidy difference between the Iranian and Turkish/Cypriotic lines, whereby the former were (allo)tetraploid and the latter diploid. The tetraploid Iranian lines seem to have one set of alleles from the Turkish/Cypriotic gene-pool. However we do not know where the other alleles come from. In addition to the differences in ploidy level there are also differences in glucosinolate defence compounds between these two populations (Iranian vs Turkish/Cypriotic), with the Iranian lines lacking the diversity and concentration of indolic glucosinolates that the Turkish/Cypriotic lines have. This chapter serves as a good resource and starting point for future research in the region, maybe by using the natural history collections that are at hand.

    Glucosinolates (i.e. mustard oils) are mainly made by Brassicales species, with their highest structural diversity in the Brassicaceae. In Chapter 5, I examined two Ae. arabicum lines (CYP and TUR) and their recombinant inbred lines to assess glucosinolate composition in different tissues and throughout the plants development. The levels of glucosinolates in the leaves changed when Ae. arabicum went from vegetative to a reproductive state. Moreover, a major difference in glucosinolate content (up to 10-fold) between CYP and TUR indicates a likely regulatory pathway outside of the main glucosinolate biosynthesis pathway. Multi-trait and multi-environment QTL analyses based on leaves, reproductive tissues and seeds identified a single major QTL. Fine mapping this region reduced the interval to only fifteen protein coding genes, including the two most intriguing candidates: FLOWERING LOCUS C (FLC) and the sulphate transporter SULTR2;1. These findings show an interesting correlation between development and defence.

    Finally, Chapter 6 gives a final discussion of this thesis and its results. It brings the different topics together, put them in a bigger picture and look forward to new research possibilities.

    The transcriptome as early marker of diet-related health : evidence in energy restriction studies in humans
    Bussel, Inge P.G. van - \ 2017
    Wageningen University. Promotor(en): Sander Kersten, co-promotor(en): Lydia Afman. - Wageningen : Wageningen University - ISBN 9789463430678 - 194
    energy restricted diets - energy intake - gene expression - genomes - proteins - endurance - food composition - human nutrition research - energiearme diëten - energieopname - genexpressie - genomen - eiwitten - uithoudingsvermogen - voedselsamenstelling - voedingsonderzoek bij de mens

    Background: Nutrition research is facing several challenges with respect to finding diet related health effects. The effects of nutrition on health are subtle, show high interindividual variations in response, and can take long before they become visual. Recently, the definition of health has been redefined as an organism’s ability to adapt to challenges and ‘this definition’ can be extended to metabolic health. In the metabolic context the ability to adapt has been named ‘phenotypic flexibility’. A potential new tool to magnify the effects of diet on health is the application of challenge tests. Combined with a comprehensive tool such as transcriptomics, the study of challenge tests before and after an intervention might be able to test a change in phenotypic flexibility. A dietary intervention well-known to improve health through weight loss is energy restriction (ER). ER can be used as a model to examine the potential of challenge tests in combination with transcriptomics to magnify diet-induced effects on health. As opposed to ER, caloric restriction (CR) is a reduction in energy intake aimed at improving health and life span in non-obese subjects and not directly aimed at weight loss. In this thesis, we aimed to investigate the use of the transcriptome as an early and sensitive marker of diet-related health.

    Methods: First we studied the consequences of age on the effects of CR on the peripheral blood mononuclear cells (PBMCs) transcriptome. For that purpose, we compared the changes in gene expression in PBMCs from old men with the changes in gene expression in PBMCs from young men upon three weeks of 30% CR. To study the effect of a change in dietary composition during ER, we compared the changes in gene expression upon a 12 weeks high protein 25% ER diet with the changes in gene expression upon a 12 weeks normal protein 25% ER diet in white adipose tissue (WAT). Next, we investigated the added value of measuring the PBMC transcriptome during challenge tests compared to measuring the PBMC transcriptome in the fasted state to magnify the effects of ER on health. This was investigated by measuring the changes in gene expression upon an oral glucose tolerance test (OGTT) and upon a mixed meal test (MMT), both before and after 12 weeks of 20% ER. Finally, we determined the differences between a challenge test consisting of glucose alone, the OGTT, or consisting of glucose plus other macronutrients, the MMT, on the PBMC transcriptome in diet-related health.

    Results: We observed that the transcriptome of PBMCs of healthy young men had a higher responsiveness in immune response pathways compared to the transcriptome of PBMCs of aged men upon CR (chapter 2). Also, we showed that upon a normal protein-ER diet the transcriptome of WAT showed a decrease in pathways involved in immune response and inflammasome, whereas no such effect was found upon a high protein-ER diet. These effect were observed while parameters such as weight loss, glucose, and waist circumference did not change due to the different protein quantities (chapter 3). 12 weeks of 20% ER was shown to increase phenotypic flexibility as reflected by a faster and more pronounced downregulation of OXPHOS, cell adhesion, and DNA replication during the OGTT compared to the control diet (chapter 4). Finally, two challenge tests consisting of either glucose (OGTT) or glucose plus fat and protein (MMT), were shown to result in a larger overlap than difference in the changes in gene expression of PBMCs (chapter 5).

    Conclusions: Based on the differential changes in gene expression upon CR at different ages, we concluded that age is an important modulator in the response to CR. As a high protein ER diet induced transcriptional changes seemed to reflect less beneficial health effects than a normal protein ER diet we concluded that the diet composition is important in the health-effect of ER as measured by the transcriptome. Based on the faster PBMCs changes in gene expression during an OGTT upon 12 weeks of 20% ER, we concluded that the PBMC transcriptome combined with a challenge test can reflect changes in phenotypic flexibility. This makes challenge tests a suitable tool to study diet-related health effects. Finally, based on the changes in gene expression of the MMT and OGTT, we conclude that glucose in a challenge test is the main denominator of the postprandial changes in gene expression in the first two hours. Overall, these results lead to the conclusion that the transcriptome, especially in combination with challenges test, can be used as an early marker of diet-related health. The direct relation to health still needs to be investigated, but the possibility to use the transcriptome as an early marker of diet-related health gives rise to a better understanding of the effects of nutrition on health.

    Selection for pure- and crossbred performance in Charolais
    Vallée-Dassonneville, Amélie - \ 2017
    Wageningen University. Promotor(en): Johan van Arendonk; Henk Bovenhuis. - Wageningen : Wageningen University - ISBN 9789463430180 - 151
    charolais - cattle - animal breeding - crossbreeding - crossbreds - selection - beef cattle - genomes - genetic parameters - charolais - rundvee - dierveredeling - kruisingsfokkerij - kruising - selectie - vleesvee - genomen - genetische parameters

    Two categories of beef production exist; i.e. (i) purebred animals from a beef sire and a beef dam and (ii) crossbred animals from a beef sire and a dairy dam.

    For the purebred beef production, there is a growing interest to include behavior and type traits in the breeding goal. Heritabilities for behavior traits, estimated using subjective data scored by farmers, range from 0.02 to 0.19. Heritabilities for type traits range from 0.02 to 0.35. Results show that there are good opportunities to implement selection for behavior traits using a simple on-farm recording system to allow collection of large data set, and for type traits in Charolais. A genome-wide association study detected 16 genomic regions with small effect on behavior and type traits. This suggests that behavior and type traits are influenced by many genes each explaining a small part of the genetic variance.

    The two main dairy breeds mated to Charolais sires for crossbred beef production in France are Montbéliard and Holstein. The genetic correlation between the same trait measured on Montbéliard x Charolais and on Holstein x Charolais was 0.99 for muscular development, 0.96 for birth weight; and 0.91 for calving difficulty, 0.80 for height, and 0.70 for bone thinness. Thus, for these last three traits, results show evidence for re-ranking of Charolais sires depending on whether they are mated to Montbéliard or Holstein cows. When using genomic prediction, the Montbéliard x Charolais and Holstein x Charolais populations could be combined into a single reference population to increase size and accuracy of genomic prediction. Results indicate that the higher the genetic correlation is between the two crossbred populations, the higher the gain in accuracy is achieved when combining the two populations into a single reference.

    The selection of Charolais sires to produce purebred or crossbred animals is made through distinct breeding programs. An alternative could be to combine selection into one breeding program. Decision for combining or keeping breeding programs separate is determined by the correlation between the breeding objectives, the selection intensity, the difference in level of genetic merit, the accuracy of selection, and the recent implementation of genomic evaluation. Considering all parameters and based on estimations for selection on birth weight, I recommend combining both breeding programs because this will lead to higher genetic gain, and might simplify operating organization and reduce associated costs.

    Utilization of complete chloroplast genomes for phylogenetic studies
    Ramlee, Shairul Izan Binti - \ 2016
    Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Rene Smulders; Theo Borm. - Wageningen : Wageningen University - ISBN 9789462579354 - 186
    phylogenetics - genomes - chloroplasts - models - solanum - orchidaceae - phylogenomics - dna sequencing - fylogenetica - genomen - chloroplasten - modellen - solanum - orchidaceae - phylogenomica - dna-sequencing

    Chloroplast DNA sequence polymorphisms are a primary source of data in many plant phylogenetic studies. The chloroplast genome is relatively conserved in its evolution making it an ideal molecule to retain phylogenetic signals. The chloroplast genome is also largely, but not completely, free from other evolutionary processes such as gene duplication, concerted evolution, pseudogene formation and genome rearrangements. The conservation of the chloroplast genome sequence allows designing primers targeting regions conserved well beyond species boundaries, and amplification of these targets.

    The small size together with their high copy number in leaf cells greatly facilitates chloroplast genome sequencing. In this thesis, chloroplast phylogenomics was conducted using complete chloroplast DNA genomes obtained by a newly developed method of de novo assembly. The method was not only cost-effective but also has the potential to extract a wealth of useful information of thousands of chloroplast genomes from Whole Genome Shotgun (WGS) data. We used k-mer frequency tables to identify and extract the chloroplast reads from the WGS reads and assemble these using a highly integrated and automated custom pipeline. This pipeline includes steps aimed at optimizing assemblies and filling gaps that are left due to coverage variation in the WGS dataset. The pipeline enabled successful de novo assembly across a range of nuclear genome sizes, from Solanum lycopersicon (tomato, 0.9 Gb) to Paphiopedilum heryanum (slipper orchid, 35 Gb).

    The pipeline is suitable for studying structural variation in the chloroplast genome, as opposed to the common procedure of read mapping against a reference genome. To support the putative rearrangements, a flexible assembly quality comparison tool was created that combines and visualizes read mapping and alignment results in a two-dimensional plot. We have evaluated the ability of this tool using the de novo assemblies of S. lycopersicon and P. henryanum chloroplasts. The results show that not only we can immediately select the best of two options, but also determine the location of specific artefacts.

    In order to explore and evaluate the utility of complete chloroplast phylogenomics, tomato and Paphiopedilum spp were used to conduct phylogenetic inferences based on the complete chloroplast genome. In total 84 tomato chloroplast genomes within the section Lycopersicon were assembled and phylogenetic trees produced. The analyses revealed that next to the chloroplast regions and spacers traditionally used for phylogenetics, additional regions of protein coding and non-coding DNA may be exploited for intraspecific phylogenetic studies. In particular, more than 50% of all phylogenetically relevant information could be included by just using four genes (ycf1, ndhF, ndhA, and ndhH), of which 34% in ycf1 alone. The topology of the phylogenetic tree inferred from ycf1 was the same as that of trees based on all other protein coding genes, although with lower bootstrap values. The phylogenetic analyses based on 32 complete Paphiopedilum spp. chloroplast genomes confirmed the division of the genus into three subgenera Parvisepalum, Brachypetalum and Paphiopedilum. The division of five sections of subgenus Paphiopedilum was also recovered. The de novo assemblies revealed several structural rearrangements including gene loss and inversion. In addition, the chloroplast genome of Paphiopedilum has experienced extreme IR expansion that has included part of or the entire SSC region, resulting in larger IR regions than commonly observed among monocots.

    In conclusion, WGS data offer opportunities to generate partial or entire chloroplast genomes for phylogenetic studies. Species discrimination can be achieved already with partial data (subsets of genes), but evolutionarily young lineages may require more informative characters. Therefore, it is expected that many complete chloroplast genomes will be produced in the years to come. While generating these genomes, the urge for de novo assembly of chloroplast genomes rather than mapping against reference genomes is adamant in order to also uncover structural rearrangements in chloroplast genome.

    Antibodies and longevity of dairy cattle : genetic analysis
    Klerk, B. de - \ 2016
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Jan van der Poel; Bart Ducro. - Wageningen : Wageningen University - ISBN 9789462577589 - 134
    dairy cattle - dairy cows - antibodies - longevity - genetic analysis - breeding value - genomes - genetic improvement - animal genetics - melkvee - melkkoeien - antilichamen - gebruiksduur - genetische analyse - fokwaarde - genomen - genetische verbetering - diergenetica

    The dairy sector has a big impact on food production for the growing world population and contributes substantially to the world economy. In order to produce food in a sustainable way, dairy cows need to be able to produce milk without problems and as long as possible. Therefore, breeding programs focuses on improvement of important traits for dairy cows. In order to improve desirable traits and obtain genetic gain there is a constant need for optimization of breeding programs and search for useful parameters to include within breeding programs. Over the last several decades, breeding in dairy cattle mainly focused on production and fertility traits, with less emphasis on health traits. Health problems, however, can cause substantial economic losses to the dairy industry. The economic losses, together with the rising awareness of animal welfare, increased herd size, and less attention for individual animals, have led to an increased need to focus more on health traits. Longevity is strongly related to disease resistance, since a more healthy cow will live a longer productive life (longevity). The identification of biomarkers and the detection of genes controlling health and longevity, would not only greatly enhance the understanding of such traits but also offer the opportunity to improve breeding schemes. The objectives of this thesis therefore were 1) to find an easy measurable disease resistance related biomarker in dairy cows, 2) identify the relation between antibodies and longevity, 3) identify genomic regions that are involved with antibody production/expression. In this thesis antibodies are investigated as parameter for longevity. Antibodies might be a novel parameter that enables selection of cows with an improved ability to stay healthy and to remain productive over a longer period of time. In this thesis antibodies bindiging the naive antigen keyhole limpet hemocyanin (KLH) were assumed to be natural antibodies. Antibodies binding bacteria-derived antigens lipoteichoic acid (LTA), lipopolysaccharide (LPS) and peptidoglycan (PGN) were assumed to be specific antibodies. In chapter 2 it was shown that levels of antibodies are heritable (up to h2 = 0.23). Additionally, antibody levels measured in milk and blood are genetically highly correlated (± 0.80) for the two studied isotypes (IgG and IgM). On the other hand, phenotypically, natural antibodies (from both IgG and IgM isotype) measured in milk cannot be interpreted as the same trait (phenotypic correlation = ± 0.40). In chapter 3 and 4 it was shown that levels of antibodies (both natural-and specific antibodies) showed a negative relation with longevity: first lactation cows with low IgM or IgG levels were found to have a longer productive life. When using estimated breeding values for longevity, only a significant relation was found between natural antibody level (IgM binding KLH) and longevity. Lastly chapter 5 reports on a genome-wide-association study (GWAS), to detect genes contributing to genetic variation in natural antibody level. For natural antibody isotype IgG, genomic regions with a significant association were found on chromosome 21 (BTA). These regions included genes have impact on in isotype class switching (from IgM to IgG). The gained knowledge on relations between antibodies and longevity and the gained insight on genes responsible for natural antibodies level make antibodies potential interesting biomarkers for longevity.

    Conservation genetics of the frankincense tree
    Bekele, A.A. - \ 2016
    Wageningen University. Promotor(en): Frans Bongers, co-promotor(en): Rene Smulders; K. Tesfaye Geletu. - Wageningen : Wageningen University - ISBN 9789462576865 - 158
    boswellia - genomes - dna sequencing - tropical forests - genetic diversity - genetic variation - genetics - forest management - plant breeding - boswellia - genomen - dna-sequencing - tropische bossen - genetische diversiteit - genetische variatie - genetica - bosbedrijfsvoering - plantenveredeling

    Boswellia papyrifera is an important tree species of the extensive Combretum-Terminalia dry tropical forests and woodlands in Africa. The species produces a frankincense which is internationally traded because of its value as ingredient in cosmetic, detergent, food flavor and perfumes productions, and because of its extensive use as incense during religious and cultural ceremonies in many parts of the world. The forests in which B. papyrifera grows are increasingly overexploited at the expense of the economic benefit and the wealth of ecological services they provide. Populations of B. papyrifera have declined in size and are increasingly fragmented. Regeneration has been blocked for the last 50 years in most areas and adult productive trees are dying. Projections showed a 90% loss of B. papyrifera trees in the coming 50 years and a 50% loss of frankincense production in 15 years time.

    This study addressed the conservation genetics of B. papyrifera. Forty six microsatellite (SSR) markers were developed for this species, and these genetic markers were applied to characterize the genetic diversity pattern of 12 B. papyrifera populations in Ethiopia. Next to this, also the generational change in genetic diversity and the within-population genetic structure (FSGS) of two cohort groups (adults and seedlings) were studied in two populations from Western Ethiopia. In these populations seedlings and saplings were found and natural regeneration still takes place, a discovery that is important for the conservation of the species.

    Despite the threats the populations are experiencing, ample genetic variation was present in the adult trees of the populations, including the most degraded populations. Low levels of population differentiation and isolation-by-distance patterns were detected. Populations could be grouped into four genetic clusters: the North eastern (NE), Western (W), North western (NW) and Northern (N) part of Ethiopia. The clusters corresponded to environmentally different conditions in terms of temperature, rainfall and soil conditions. We detected a low FSGS and found that individuals are significantly related up to a distance of 60-130 m.

    Conservation of the B. papyrifera populations is urgently needed. The regeneration bottlenecks in most existing populations are an urgent prevailing problem that needs to be solved to ensure the continuity of the genetic diversity, species survival and sustainable production of frankincense. Local communities living in and around the forests should be involved in the use and management of the forests. In situ conservation activities will promote gene flow among fragmented populations and scattered remnant trees, so that the existing level of genetic diversity may be preserved. Geographical distance among populations is the main factor to be considered in sampling for ex situ conservation. A minimum of four conservation sites for B. papyrifera is recommended, representing each of the genetic clusters. Based on the findings of FSGS analyses, seed collection for ex situ conservation and plantation programmes should come from trees at least 100 m, but preferably 150 m apart.

    Mining microbiota signatures in human intestinal tract metagenomes
    Tims, S. - \ 2016
    Wageningen University. Promotor(en): Michiel Kleerebezem; Willem de Vos, co-promotor(en): Erwin Zoetendal. - Wageningen : Wageningen University - ISBN 9789462576933 - 264
    gastrointestinal microbiota - intestines - genomes - man - hosts - host guest relations - dna microarrays - gastrointestinal diseases - inflammatory bowel diseases - irritable colon - prebiotics - body mass index - oligosaccharides - microbiota van het spijsverteringskanaal - darmen - genomen - mens - gastheren (dieren, mensen, planten) - relaties tussen gastheer en gast - dna microarrays - maagdarmziekten - chronische darmontstekingen - prikkelbaar colon - prebiotica - quetelet index - oligosacchariden
    Genetic diversity and evolution in Lactuca L. (Asteraceae) : from phylogeny to molecular breeding
    Wei, Z. - \ 2016
    Wageningen University. Promotor(en): Eric Schranz. - Wageningen : Wageningen University - ISBN 9789462576148 - 210
    lactuca sativa - leafy vegetables - phylogeny - genetic diversity - domestication - molecular breeding - genomes - dna - quantitative trait loci - evolution - lactuca sativa - bladgroenten - fylogenie - genetische diversiteit - domesticatie - moleculaire veredeling - genomen - dna - loci voor kwantitatief kenmerk - evolutie

    Cultivated lettuce (Lactuca sativa L.) is an important leafy vegetable worldwide. However, the phylogenetic relationships between domesticated lettuce and its wild relatives are still not clear. In this thesis, I focus on the phylogenetic relationships within Lactuca L., including an analysis of the wild Lactuca species that are endemic to Africa for the first time. The genetic variation of responses to salinity in a recombinant inbred line population, derived from a cross between the lettuce crop (L. sativa ‘Salinas’) and wild species (L. serriola), was investigated and the candidate gene in the identified QTL regions was further studied.

    In Chapter 1, I introduce and discuss topics related to genetic diversity and evolution in Lactuca, including an overview of lettuce cultivars and uses, its hypothesized domestication history, the taxonomic position of Lactuca, current status of molecular breeding in lettuce and mechanisms of salinity tolerance in plants, especially the High-affinity K+ Transporter (HKT) gene family.

    In Chapter 2, the most extensive molecular phylogenetic analysis of Lactuca was constructed based on two chloroplast genes (ndhF and trnL-F), including endemic African species for the first time. This taxon sampling covers nearly 40% of the total Lactuca species endemic to Africa and 34% of all Lactuca species. DNA sequences from all the subfamilies of Asteraceae in Genbank and those generated from Lactuca herbarium samples were used to elucidate the monophyly of Lactuca and the affiliation of Lactuca within Asteracaeae. Based on the subfamily tree, 33 ndhF sequences from 30 species and 79 trnL-F sequences from 48 species were selected to infer phylogenetic relationships within Lactuca using Randomized Axelerated Maximum Likelihood (RAxML) and Bayesian Inference (BI) analyses. In addition, biogeographical, chromosomal and morphological character states were analysed based on the Bayesian tree topology. The results showed that Lactuca contains two distinct phylogenetic clades - the crop clade and the Pterocypsela clade. Other North American, Asian and widespread species either form smaller clades or mix with the Melanoseris species in an unresolved polytomy. The newly sampled African endemic species probably should be excluded from Lactuca and treated as a new genus.

    In Chapter 3, twenty-seven wild Lactuca species and four outgroup species were sequenced using next generation sequencing (NGS) technology. The sampling covers 36% of total Lactuca species and all the important geographical groups in the genus. Thirty chloroplast genomes, including one complete (partial) large single copy region (LSC), one small single copy region (SSC), one inverted repeat (IR) region, and twenty-nine nuclear ribosomal DNA sequences (containing the internal transcribed spacer region ) were successfully assembled and analysed. A methodology paper for which I am co-author, but is not included in this thesis, of the sequencing pipeline was published: ‘Herbarium genomics: plastome sequence assembly from a range of herbarium specimens using an Iterative Organelle Genome Assembly (IOGA) pipeline’. These NGS data helped resolve deeper nodes in the phylogeny within Lactuca and resolved the polytomy from Chapter 2. The results showed that there are at least four main groups within Lactuca: the crop group, the Pterocypsela group, the North American group and the group containing widely-distributed species. I also confirmed that the endemic African species should be removed and treated as a new genus.

    In Chapter 4, quantitative trait loci (QTLs) related to salt-induced changes in Root System Architecture (RSA) and ion accumulation were determined using a recombinant inbred line population derived from a cross between cultivated lettuce and wild lettuce. I measured the components of RSA by replicated lettuce seedlings grown on vertical agar plates with different NaCl concentrations in a controlled growth chamber environment. I also quantified the concentration of sodium and potassium in replicates of greenhouse-grown plants watered with 100 mM NaCl. The results identified a total of fourteen QTLs using multi-trait linkage analysis, including three major QTLs associated with general root development (qRC9.1), root growth in salt stress condition (qRS2.1), and ion accumulation (qLS7.2).

    In Chapter 5, one of the identified QTL regions (qLS7.2) reported in Chapter 4 was found to contain a homolog of the HKT1 from Arabidopsis thaliana. I did a phylogenetic analysis of Lactuca HKT1-like protein sequences with other published HKT protein sequences and determined transmembrane and pore segments of lettuce HKT1;1 alleles, according to the model proposed for AtHKT1;1. Gene expression pattern and level of LsaHKT1;1 (L. sativa ‘Salinas’) and LseHKT1;1 (L. serriola) in root and shoot were investigated in plants growing hydroponically over a time-course. The measurements of Na+ and K+ contents were sampled at the same time as the samples used for gene expression test. In addition, I examined the 5’ promoter regions of the two genotypes. The results showed low expression levels of both HKT1;1 alleles in Lactuca root and relatively higher expression in shoot, probably due to the negative cis-regulatory elements of HKT1 alleles found in Lactuca promoter regions. Significant allelic differences were found in HKT1;1 expression in early stage (0-24 hours) shoots in and in late stage (2-6 days) roots. shoot HKT1;1 expression/root HKT1;1 expression was generally consistent with the ratios of Na+/K+ balance in the relevant tissues (shoot Na+/K+ divided by root Na+/K+).

    In Chapter 6, I summarize and discuss the results from previous chapters briefly. The implications of Chapter 2 and 3 for Lactuca phylogenetics are discussed, including some key characters for the diagnosis of species within Lactuca, the use of herbarium DNA for NGS technology, and perspectives into Lactuca phylogeny. Future perspectives of genome-wide association mapping for lettuce breeding were also discussed. Lastly, I propose to integrate phylogenetic approaches into investigations of allelic differences in lettuce, not just associated with salinity stress but also with other stressed and beneficial characters, both within and between species.

    Natural genetic variation in Arabidopsis thaliana photosynthesis
    Flood, P.J. - \ 2015
    Wageningen University. Promotor(en): Maarten Koornneef, co-promotor(en): Mark Aarts; Jeremy Harbinson. - Wageningen : Wageningen University - ISBN 9789462575004 - 278
    arabidopsis thaliana - genetische variatie - fotosynthese - genomen - chlorofyl - fenotypen - arabidopsis thaliana - genetic variation - photosynthesis - genomes - chlorophyll - phenotypes

    Oxygenic photosynthesis is the gateway of the sun’s energy into the biosphere, it is where light becomes life. Genetic variation is the fuel of evolution, without it natural selection is powerless and adaptation impossible. In this thesis I have set out to study a relatively unexplored field which sits at the intersection of these two topics, namely natural genetic variation in plant photosynthesis. To begin I reviewed the available literature (Chapter 2), from this it became clear that the main bottleneck restricting progress was the lack of high-throughput phenotyping platforms for photosynthesis. To address this an automated high-throughput chlorophyll fluorescence phenotyping system was developed, which could measure 1440 plants in less than an hour for ΦPSII, a measure of photosynthetic efficiency (Chapter 3). Using this phenotyping platform I screened five populations of Arabidopsis thaliana. Three of these populations resulted from bi-parental crosses and segregated for only two genomes, using these I conducted family mapping (Chapter 4). The final two populations were composed of natural, field collected, accessions and were analysed using a genome wide association approach (Chapter 5). The family mapping approach had greater statistical power due to within population replication and the genome wide association approach had higher mapping resolution due to historical recombination. Both approaches were used to identify genomic regions (loci) which were responsible for some of the variation in photosynthesis observed. The number and average effect of these loci was used to infer the genetic architecture of photosynthesis as a highly complex polygenic trait for which there are many loci of very small effect. In addition to screening these large populations a smaller subset of 18 lines was assayed for natural variation in phosphorylation of photosystem II (PSII) proteins in response to changing light (Chapter 6). This exploratory study indicated that this process shows considerable variation and may be important for adaptation of the photosynthetic apparatus to photosynthetic extremes. The genetic mapping studies just described, focus exclusively on genetic variation in the nuclear genome, whilst this contains the majority of the plants genetic information there is also a store of genetic information in the chloroplast and mitochondria. These genetic repositories contain genes which are essential for photosynthesis and energy metabolism. Any variation in these genes could have a large impact on photosynthesis. To study natural variation in these genomes I developed a new population of reciprocal nuclear-organellar hybrids (cybrids) which could be used to study the effect of genetic variation in organelles whilst controlling for nuclear genetic variation (Chapter 7). Preliminary results indicate that this resource will be of great use in disentangling natural genetic variation in nucleo-organelle interactions. Finally I looked at one chloroplast encoded photosynthetic mutation in more detail (Chapter 8). This mutation had evolved in response to herbicide application and had spread along British railways. When studying this population of resistant plants I found empirical evidence for organelle mediated nuclear genetic hitchhiking. This is a previously undescribed evolutionary phenomenon and is likely to be quite common. In conclusion there is an abundance of genetic variation in photosynthesis which can be used to improve the trait for agriculture and provide insights into novel evolutionary phenomena in the field.

    Using natural variation to unravel the dynamic regulation of plant performance in diverse environments
    Molenaar, J.A. - \ 2015
    Wageningen University. Promotor(en): Harro Bouwmeester; Joost Keurentjes, co-promotor(en): Dick Vreugdenhil. - Wageningen : Wageningen University - ISBN 9789462573444 - 186
    planten - genomen - loci voor kwantitatief kenmerk - warmtestress - genetische kartering - groei - droogte - plantengenetica - plantenfysiologie - plants - genomes - quantitative trait loci - heat stress - genetic mapping - growth - drought - plant genetics - plant physiology


    All plants are able to respond to changes in their environment by adjusting their morphology and metabolism, but large differences are observed in the effectiveness of these responses in the light of plant fitness. Between and within species large differences are observed in plant responses to drought, heat and other abiotic stresses. This natural variation is partly due to variation in the genetic composition of individuals. Within-species variation can be used to identify and study genes involved in the genetic regulation of plant performance.

    Growth of the world population will, in the coming years, lead to an increased demand for food, feed and other natural products. In addition, extreme weather conditions with, amongst others, more and prolonged periods of drought and heat are expected to occur due to climate change. Therefore breeders are challenged to produce stress tolerant cultivars with improved yield under sub-optimal conditions. Knowledge about the mechanisms and genes that underlie tolerance to drought, heat and other abiotic stresses will ease this challenge.

    The aim of this thesis was to identify and study the role of genes that are underlying natural variation in plant performance under drought, salt and heat stress. To reach this goal a genome wide association (GWA) mapping approach was taken in the model species Arabidopsis thaliana. A population of 350 natural accessions of Arabidopsis, genotyped with 215k SNPs, was grown under control and several stress conditions and plant performance was evaluated by phenotyping one or several plant traits per environment. Genes located in the genomic regions that were significantly associated with plant performance, were studied in more detail.

    Plant performance was first evaluated upon osmotic stress (Chapter 2). This treatment resulted not only in a reduced plant size, but also caused the colour of the rosette leaves to change from green to purple-red due to anthocyanin accumulation. The latter was visually quantified and subsequent GWA mapping revealed that a large part of the variation in anthocyanin accumulation could be explained by a small genomic region on chromosome 1. The analysis of re-sequence data allowed us to associate the second most frequent allele of MYB90 with higher anthocyanin accumulation and to identify the causal SNP. Interestingly MYB75, a close relative of MYB90, was not identified by GWA mapping, although causal sequence variation of this gene for anthocyanin accumulation was identified in the Cvi x Ler and Ler x Eri-1 RIL populations. Re-sequence data revealed that one allele of MYB75 was dominating the population and that the MYB75 alleles of Cvi and Ler were both rare, explaining the lack of association at this locus in GWA mapping. For MYB90, two alleles were present in a substantial part of the population, suggesting balancing selection between them.

    Next, the natural population was exposed to short-term heat stress during flowering (Chapter 3). This short-term stress has a large impact on seed set, while it hardly affects the vegetative tissues. Natural variation for tolerance against the effect of heat on seed set was evaluated by measuring the length of all siliques along the inflorescence in both heat-treated and control plants. Because the flower that opened during the treatment was tagged, we could analyse the heat response for several developmental stages separately. GWA mapping revealed that the heat response before and after anthesis involved different genes. For the heat response before anthesis strong evidence was gained that FLC, a flowering time regulator and QUL2, a gene suggested to play a role in vascular tissue development, were causal for two strong associations.

    Furthermore, the impact of moderate drought on plant performance was evaluated in the plant phenotyping platform PHENOPSIS. Homogeneous drought was assured by tight regulation of climate cell conditions and the robotic weighing and watering of the pots twice a day. Because plant growth is a dynamic trait it was monitored over time by top-view imaging under both moderate drought and control conditions (Chapter 4 and 5). To characterise growth it was modelled with an exponential function. GWA mapping of temporal growth data resulted in the detection of time-dependent QTLs whereas mapping of model parameters resulted in another set of QTLs related to the entire growth period. Most of these QTLs would not have been identified if plant size had only been determined on a single day. For the QTLs detected under control conditions eight candidate genes with a growth-related mutant or overexpression phenotype were identified (Chapter 4). Genes in the support window of the drought-QTLs were prioritized based on previously reported gene expression data (Chapter 5). Additional validation experiments are needed to confirm causality of the candidate genes.

    Next, to search for genes that determine plant size across many environments, biomass accumulation in the natural population was determined in 25 different environments (Chapter 6). Joint analysis of these data by multi-environment GWA mapping resulted in the detection of 106 strongly associated SNPs with significant effects in 7 to 16 environments. Several genes involved in starch metabolism, leaf size control and flowering time determination were located in close proximity of the associated SNPs. Two genes, RPM1 and ACD6, were located in close proximity of SNPs with significant GxE effects. For both genes, alleles have been identified that increase resistance to bacterial infection, but that reduce biomass accumulation. The sign of the allelic effect is therefore dependent on the environmental conditions. Whole genome predictions revealed that most of the GxE interactions observed at the phenotypic level were not the consequence of strong associations with strong QxE effects, but of moderate and weak associations with weak QxE effects.

    Finally, in Chapter 7 I discuss the usefulness of GWA mapping in the identification of genes underlying natural variation in plant performance under drought, heat stress and a number of other environments. Strong associations were observed for both environment-specific as well as common plant performance regulators. Some choices in phenotyping and experimental design were crucial for our success, like evaluation of plant performance over time and simplification of the quantification of the phenotype. It is suggested that follow-up work should focus on the functional characterization of the causal genes, because such analyses would be helpful to identify pathways in which the causal genes are involved and to understand why sequence variation results in changes at the phenotype level. Although translation of the findings to applications in crops is challenging, this thesis contributes to the understanding of the genetic regulation of stress response and therefore will likely contribute to the development of stress tolerant and stable yielding crops.

    Breeding program for indigenous chicken in Kenya
    Ngeno, K. - \ 2015
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Liesbeth van der Waaij; A.K. Kahi. - Wageningen : Wageningen University - ISBN 9789462572775 - 154
    kippen - pluimvee - inheems vee - dierveredeling - veredelingsprogramma's - genetische diversiteit - ecotypen - genomen - genetische verbetering - kenya - fowls - poultry - native livestock - animal breeding - breeding programmes - genetic diversity - ecotypes - genomes - genetic improvement - kenya


    Ngeno, K. (2015). Breeding program for indigenous chicken in Kenya. Analysis of diversity in indigenous chicken populations. PhD thesis, Wageningen University, the Netherlands

    The objective of this research was to generate knowledge required for the development of an indigenous chicken (IC) breeding program for enhanced productivity and improved human livelihood in Kenya. The initial step was to review five questions; what, why and how should we conserve IC in an effective and sustainable way, who are the stakeholders and what are their roles in the IC breeding program. The next step of the research focused on detecting distinctive IC ecotypes through morphological and genomic characterization. Indigenous chicken ecotypes were found to be populations with huge variability in the morphological features. Molecular characterization was carried out using microsatellite markers and whole genome re-sequenced data. The studied IC ecotypes are genetically distinct groups. The MHC-linked microsatellite markers divided the eight IC ecotypes studied into three mixed clusters, composing of individuals from the different ecotypes whereas non-MHC markers grouped ICs into two groups. Analysis revealed high genetic variation within the ecotype with highly diverse MHC-linked alleles which are known to be involved in disease resistance. Whole genome re-sequencing revealed genomic variability, regions affected by selection, candidate genes and mutations that can explain partially the phenotypic divergence between IC and commercial layers. Unlike commercial chickens, IC preserved a high genomic variability that may be important in addressing present and future challenges associated with environmental adaptation and farmers’ breeding goals. Lastly, this study showed that there is an opportunity to improve IC through selection within the population. Genetic improvement utilizing within IC selection requires setting up a breeding program. The study described the systematic and logical steps in designing a breeding program by focusing on farmers’ need, how to improve IC to fit the farming conditions, and management regimes.

    The hybrid nature of pig genomes : unraveling the mosaic haplotype structure in wild and commercial Sus scrofa populations
    Bosse, M. - \ 2015
    Wageningen University. Promotor(en): Martien Groenen, co-promotor(en): Hendrik-Jan Megens; Ole Madsen. - Wageningen : Wageningen University - ISBN 9789462573000 - 253
    dieren - varkens - dierveredeling - genomen - hybridisatie - sus scrofa - haplotypen - genomica - populaties - genetische variatie - animals - pigs - animal breeding - genomes - hybridization - sus scrofa - haplotypes - genomics - populations - genetic variation - cum laude
    cum laude graduation
    Genomics 4.0 : syntenic gene and genome duplication drives diversification of plant secondary metabolism and innate immunity in flowering plants : advanced pattern analytics in duplicate genomes
    Hofberger, J.A. - \ 2015
    Wageningen University. Promotor(en): Eric Schranz. - Wageningen : Wageningen University - ISBN 9789462573147 - 142
    genomica - planten - metabolisme - bloeiende planten - genomen - genen - next generation sequencing - genomics - plants - metabolism - flowering plants - genomes - genes - next generation sequencing

    Genomics 4.0 - Syntenic Gene and Genome Duplication Drives Diversification of Plant Secondary Metabolism and Innate Immunity in Flowering Plants

    Johannes A. Hofberger1, 2, 3

    1 Biosystematics Group, Wageningen University & Research Center, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands (August 2012 – December 2013)

    2 Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands (December 2010 – July 2012)

    3 Chinese Academy of Sciences/Max Planck Partner Institute for Computational Biology, 320 Yueyang Road,

    Shanghai 200031, PR China (January 2014 – December 2014)


    Large-scale comparative analysis of Big Data from next generation sequencing provides powerful means to exploit the potential of nature in context of plant breeding and biotechnology. In this thesis, we combine various computational methods for genome-wide identification of gene families involved in (a) plant innate immunity and (a) biosynthesis of defense-related plant secondary metabolites across 21 species, assess dynamics that affected evolution of underlying traits during 250 Million Years of flowering plant radiation and provide data on more than 4500 loci that can underpin crop improvement for future food and live quality.


    As sessile organisms, plants are permanently exposed to a plethora of potentially harmful microbes and other pests. The surprising resilience to infections observed in successful lineages is due to a complex defense network fighting off invading pathogens. Within this network, a sophisticated plant innate immune system is accompanied by a multitude of specialized biosynthetic pathways that generate more than 200,000 secondary metabolites with ecological, agricultural, energy and medicinal importance. The rapid diversification of associated genes was accompanied by a series of duplication events in virtually all plant species, including local duplication of short sequences as well as multiplication of all chromosomes due to meiotic errors (plant polyploidy). In a comparative genomics approach, we combined several bioinformatics techniques for large-scale identification of multi-domain and multi-gene families that are involved in plant innate immunity or defense-related secondary metabolite pathways across 21 representative flowering plant genomes. We introduced a framework to trace back duplicate gene copies to distinct ancient duplication events, thereby unravelling a differential impact of gene and genome duplication to molecular evolution of target genes. Comparing the genomic context among homologs within and between species in a phylogenomics perspective, we discovered orthologs conserved within genomic regions that remained structurally immobile during flowering plant radiation. In summary, we described a complex interplay of gene and genome duplication that increased genetic versatility of disease resistance and secondary metabolite pathways, thereby expanding the playground for functional diversification and thus plant trait innovation and success. Our findings give fascinating insights to evolution across lineages and can underpin crop improvement for food, fiber and biofuels production

    Structural variations in pig genomes
    Paudel, Y. - \ 2015
    Wageningen University. Promotor(en): Martien Groenen, co-promotor(en): Ole Madsen; Hendrik-Jan Megens. - Wageningen : Wageningen University - ISBN 9789462572171 - 204
    varkens - dierveredeling - genomen - genomica - single nucleotide polymorphism - dna-sequencing - fenotypische variatie - chromosoomafwijkingen - evolutie - soortvorming - pigs - animal breeding - genomes - genomics - single nucleotide polymorphism - dna sequencing - phenotypic variation - chromosome aberrations - evolution - speciation


    Paudel, Y. (2015). Structural variations in pig genomes. PhD thesis, Wageningen University, the Netherlands

    Structural variations are chromosomal rearrangements such as insertions-deletions (INDELs), duplications, inversions, translocations, and copy number variations (CNVs). It has been shown that structural variations are as important as single nucleotide polymorphisms (SNPs) in regards to phenotypic variations. The general aim of this thesis was to use next generation sequencing data to improve our understanding of the evolution of structural variations such as CNVs, and INDELs in pigs. We found that: 1) the frequency of copy number variable regions did not change during pig domestications but rather reflected the demographic history of pigs. 2) CNV of olfactory receptor genes seems to play a role in the on-going speciation of the genus Sus. 3) Variation in copy number of olfactory receptor genes in pigs (Sus scrofa) seems to be shaped by a combination of selection and genetic drift, where the clustering of ORs in the genome is the major source of variation in copy number. 4) Analysis on short INDELs in the pig genome shows that the level of purifying selection of INDELs positively correlates with the functional importance of a genomic region, i.e. strongest purifying selection was observed in gene coding regions. This thesis provides a highly valuable resource for copy number variable regions, INDELs, and SNPs, for future pig genetics and breeding research. Furthermore, this thesis discusses the limitations and improvements of the available tools to conduct structural variation analysis and insights into the future trends in the detection of structural variations.

    Sociable swine: prospects of indirect genetic effects for the improvement of productivity, welfare and quality
    Duijvesteijn, N. - \ 2014
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Piter Bijma; E.F. Knol. - Wageningen : Wageningen University - ISBN 9789462571525 - 202
    varkens - sociaal gedrag - groepsinteractie - genetische effecten - prestatieniveau - dierenwelzijn - androsteron - genomen - genetische correlatie - varkensfokkerij - stakeholders - beoordeling - dierlijke productie - pigs - social behaviour - group interaction - genetic effects - performance - animal welfare - androsterone - genomes - genetic correlation - pig breeding - stakeholders - assessment - animal production

    Towards Healthy Diets for parents: efectiveness of a counselling intervention

    Eveline J.C. Hooft van Huysduynen


    Introduction and Objective: As parents’ modelling of dietary behaviour is one of the factors influencing children’s diets, improving parents’ diets is expected to result in improved dietary intake of their children. This thesis describes research that was conducted to develop and evaluate a counselling intervention to improve parental adherence to the Dutch dietary guidelines.

    Methods: A counselling intervention was developed, which was underpinned with the theory of planned behaviour and the transtheoretical model. In 20 weeks, five face-to-face counselling sessions were provided by a registered dietician who used motivational interviewing to improve parental adherence to the Dutch dietary guidelines. In addition, parents received three individually tailored email messages. During the counselling, the dietary guidelines and additional eating behaviours, that were hypothesized to affect diet quality, were addressed. The intervention was evaluated in a randomised controlled trial with 92 parents receiving the counselling and 94 parents as controls. Effects on dietary intake, biomarkers, intermediate markers of health and children’s dietary intake were evaluated. With mediation analyses, it was investigated if changes in dietary intake were established via changes in behavioural determinants. Thereby, it was also examined if spot urine samples could be used to replace 24 h urine samples for evaluating changes in sodium and potassium intake.

    Results: The intervention group increased their adherence to the dietary guidelines, as assessed with the Dutch Healthy Diet-index (ranging from 0 to 100 points), by 6.7 points more than the control group did. This improvement was achieved by small increases in the scores of seven out of ten index components. The most substantial changes were shown in fruit and fish intakes of which increases in fish intake were reflected in changes in fatty acid profiles derived from blood plasma. Also a small decrease in waist circumference was observed. Based on parental reports, the children in the intervention group increased their intakes of fruit, vegetables and fish more than the children in the control group. Improvements in parental fruit intake were mediated by changes in the behavioural determinants attitude and habit strength. Decreases in snack intake were mediated by changes in self-identity as a healthy eater. Although the results of a study in young Caucasian women showed that spot urine can be used to rank individuals for their ratios of sodium to potassium, no intervention effects on these ratios were observed.

    Conclusion: This thesis provides empirical knowledge on potential effective elements for counselling interventions aiming at improving the dietary pattern as a whole of parents and provides knowledge on methods to evaluate changes in dietary intake.

    Filling the gap between sequence and function: a bioinformatics approach
    Bargsten, J.W. - \ 2014
    Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Jan-Peter (Jp) Nap. - Wageningen : Wageningen University - ISBN 9789462570764 - 170
    bio-informatica - planten - genomica - nucleotidenvolgordes - functionele genomica - vergelijkende genomica - vergelijkende genetische kartering - genomen - genetische kartering - plantenveredeling - methodologie - bioinformatics - plants - genomics - nucleotide sequences - functional genomics - comparative genomics - comparative mapping - genomes - genetic mapping - plant breeding - methodology

    The research presented in this thesis focuses on deriving function from sequence information, with the emphasis on plant sequence data. Unravelling the impact of genomic elements, in most cases genes, on the phenotype of an organism is a major challenge in biological research and modern plant breeding. An important part of this challenge is the (functional) annotation of such genomic elements. Currently, wet lab experiments may provide high quality, but they are laborious and costly. With the advent of next generation sequencing platforms, vast amounts of sequence data are generated. This data are used in connection with the available experimental data to derive function from a bioinformatics perspective.

    The connection between sequence information and function was approached on the level of chromosome structure (chapter 2) and of gene families (chapter 3) using combinations of existing bioinformatics tools. The applicability of using interaction networks for function prediction was demonstrated by first markedly improving an existing method (chapter 4) and by exploring the role of network topology in function prediction (chapter 5). Taken together, the combination of methods and results presented indicate the potential as well as the current state-of-the-art of function prediction in (plant) bioinformatics.

    Chapter 1 introduces the basis for the approaches used and developed in this thesis. This includes the concepts of genome annotation, comparative genomics, gene function prediction and the analysis of network topology for gene function prediction. A requirement for the study of any new organism is the sequencing and annotation of its genome. Current genome annotation is divided into structural identification and functional categorization of genomic elements. The de facto standard for categorizing functional annotation is provided by the Gene Ontology. The Gene Ontology is divided into three domains, molecular function, biological process and cellular component. Approaches to predict molecular function and biological process are outlined. Accurate function prediction generally relies on existing input data, often of experimental origin, that can be transferred to unannotated genomic elements. Plants often lack such input data, which poses a big challenge for current function prediction algorithms. In unravelling the function of genomic elements, comparative genomics is an important approach. Via the comparison of multiple genomes it gives insights into evolution, function as well as genomic structure and variation. Comparative genomics has become an essential toolkit for the analysis of newly sequenced organisms. Often bioinformatics methods need to be adapted to the specific needs of plant genome research. With a focus on the commercially important crop plants tomato and potato, specific requirements of plant bioinformatics, such as the high amount of repetitive elements and the lack of experimental data, are outlined.

    In chapter 2, the structural homology of the long arm of chromosome 2 (2L) of tomato, potato and pepper is analyzed. Molecular organization and collinear junctions are delineated using multi-color BAC FISH analysis and comparative sequence alignment. We identify several large-scale rearrangements including inversions and segmental translocations that were not reported in previous comparative studies. Some of the structural rearrangements are specific for the tomato clade, and differentiate tomato from potato, pepper and other solanaceous species. There are many small-scale synteny perturbations, but local gene vicinity is largely preserved. The data suggests that long distance intra-chromosomal rearrangements and local gene rearrangements have evolved frequently during speciation in the Solanum genus, and that small changes are more prevalent than large-scale differences. The occurrence of transposable elements and other repeats near or at junction breaks may indicate repeat-mediated rearrangements. The ancestral 2L topology is reconstructed and the evolutionary events leading to the current topology are discussed.

    In chapter 3, we analyze the Snf2 gene family. As part of large protein complexes, Snf2 family ATPases are responsible for energy supply during chromatin remodeling, but the precise mechanism of action of many of these proteins is largely unknown. They influence many processes in plants, such as the response to environmental stress. The analysis is the first comprehensive study of Snf2 family ATPases in plants. Some subfamilies of the Snf2 gene family are remarkably stable in number of genes per genome, whereas others show expansion and contraction in several plants. One of these subfamilies, the plant-specific DRD1 subfamily, is non-existent in lower eukaryote genomes, yet it developed into the largest Snf2 subfamily in plant genomes. It shows the occurrence of a complex series of evolutionary events. Its expansion, notably in tomato, suggests novel functionality in processes connected to chromatin remodeling. The results underpin and extend the Snf2 subfamily classification, which could help to determine the various functional roles of Snf2 ATPases and to target environmental stress tolerance and yield in future breeding with these genes.

    In chapter 4, a new approach to improve the prediction of protein function in terms of biological processes is developed that is particularly attractive for sparsely annotated plant genomes. The combination of the network-based prediction method Bayesian Markov Random Field (BMRF) with the sequence-based prediction method Argot2 shows significantly improved performance compared to each of the methods separately, as well as compared to Blast2GO. The approach was applied to predict biological processes for the proteomes of rice, barrel clover, poplar, soybean and tomato. Analysis of the relationships between sequence similarity and predicted function similarity identifies numerous cases of divergence of biological processes in which proteins are involved, in spite of sequence similarity. Examples of potential divergence are identified for various biological processes, notably for processes related to cell development, regulation, and response to chemical stimulus. Such divergence in biological process annotation for proteins with similar sequences should be taken into account when analyzing plant gene and genome evolution. This way, the integration of network-based and sequence-based function prediction will strengthen the analysis of evolutionary relationships of plant genomes.

    In chapter 5 the influence of network topology on network-based function prediction algorithms is investigated. The analysis of biological networks using algorithms such as Bayesian Markov Random Field (BMRF) is a valuable predictor of the biological processes that proteins are involved in. The topological properties and constraints that determine prediction performance in such networks are however largely unknown. This chapter presents analyses based on network centrality measures, such as node degree, to evaluate the performance of BMRF upon progressive removal of highly connected hub nodes (pruning). Three different protein-protein interaction networks with data from Arabidopsis, human and yeast were analyzed. All three show that the average prediction performance can improve significantly. The chapter paves the way for further improvement of network-based function prediction methods based on node pruning.

    Chapter 6 discusses the results and methods developed in this thesis in the context of the vast amount of generated sequencing data. Sequencing or re-sequencing a (plant) genome has become fairly straightforward and affordable, but the interpretation for subsequent use of this sequence data is far from trivial. The topics addressed in this thesis, annotation of function, analysis of genome structure and identifying genomic variation, focus on this main bottleneck of biological research. Issues discussed in connection with this work and its future are data accuracy, error propagation, possible improvements and future implications for biological research in crop plants. In particular the shift of costs from sequencing to downstream analyses, with functional genome annotation as essential step, is covered. One of the biggest challenges biology and bioinformatics will face is the integration of results from such downstream analyses and other sources into a complete picture. Only this will allow understanding of complex biological systems.

    Natural variation in memory formation among Nasonia parasitic wasps : from genes to behaviour
    Hoedjes, K.M. - \ 2014
    Wageningen University. Promotor(en): Louise Vet; Marcel Dicke, co-promotor(en): Hans Smid. - Wageningen : Wageningen University - ISBN 9789461739483 - 191
    nasonia - hymenoptera - geheugen - leervermogen - genetische factoren - dierecologie - diergedrag - genomen - nasonia - hymenoptera - memory - learning ability - genetic factors - animal ecology - animal behaviour - genomes

    The ability to learn and form memory has been demonstrated in various animal species, ranging from relatively simple invertebrates, such as snails and insects, to more complex vertebrate species, including birds and mammals. The opportunity to acquire new skills or to adapt behaviour through learning is an obvious benefit. However, memory formation is also costly: it can be maladaptive when unreliable associations are formed and the process of memory formation can be energetically costly. The balance between costs and benefits determines if learning and memory formation are beneficial to an animal or not. Variation in learning abilities and memory formation between species is thought to reflect species-specific differences in ecology.

    This thesis focused on variation in the number of trials required to form long-term memory (LTM). LTM is considered the most stable and durable type of memory, but also the most costly, because it requires protein synthesis. Many animal species require multiple learning experiences, which are spaced in time, to form LTM. This allows re-evaluation of information before an animal invests in costly LTM. There is, however, variation in the number of trials that animal species require to induce LTM formation. A number of insect species, including a number of parasitic wasp species, form LTM after only a single learning experience. Parasitic wasps can learn odours that guide them towards suitable hosts for their offspring, so-called oviposition learning. Substantial differences in LTM formation are observed among closely related species of parasitic wasps, which provides excellent opportunities for comparative studies. Both ecological and genetic factors involved in variation in LTM formation have been studied in this project. A multidisciplinary approach is essential to understand the evolution of variation in LTM formation, because the interaction between genes and environment shapes learning and memory formation.

    LTM formation was studied in closely related species of the genus Nasonia. These small parasitic wasps (~2 mm in length) lay their eggs in various species of fly pupae and differences in the ecology of the four known species of this genus have been described. A high-throughput method for olfactory conditioning was developed in which the wasps associated an odour, either chocolate or vanilla, with the reward of a host. A T-maze olfactometer was designed for high-throughput testing of memory retention. Using these methods, variation in memory retention was observed between three Nasonia species. Both N. vitripennis and N. longicornis form a long-lasting memory after a single conditioning trial, which lasts at least 5 days. Nasonia giraulti, on the other hand, lost its memory after 1 to 2 days after a single conditioning trial. Further studies focused on the difference between N. vitripennis and N. giraulti, which was most pronounced. By inhibiting LTM with transcription and translation inhibitors, it was confirmed that N. vitripennis forms this type of memory after a single conditioning trial. LTM is visible 4 days after conditioning in N. vitripennis. Nasonia giraulti does not form LTM after a single conditioning trial. Long-lasting memory is only formed after two trials, with a 4-hour interval between them. This difference in LTM formation makes N. vitripennis and N. giraulti excellent model species to study both ecological and genetic factors involved in this difference.

    Ecological factors such as the value of the reward and the reliability of the learned association have been shown to affect memory formation in a number of animal species. A recent study on oviposition learning in two parasitic wasp species demonstrated that LTM formation depends on the host species, i.e. the reward offered during conditioning. LTM was formed when a host with a higher quality was offered, but not when a host of lower quality was offered. The effect of host quality on memory retention of N. vitripennis and N. giraulti was tested. Either a large host, Calliphora vomitoria, a medium-sized host, Lucilia sericata, or a small host, Musca domestica, was offered during conditioning. These hosts were observed to differ significantly in their quality, i.e. in the number of parasitoid offspring that emerged and the size of the offspring. There was, however, no effect of host species on memory retention in either Nasonia species. These results suggest that host quality is not important for LTM formation in N. vitripennis and N. giraulti. This observation shows that ecological factors that are important for memory formation in one species may not be important for another species.

    The genetic basis of memory formation is highly conserved among distant animal phyla. A large number of genes involved in LTM formation have been identified in genetic model organisms, including fruit flies, honeybees, the California sea hare, mice and rats, and the zebra finch.Genetic factors responsible for natural variation in LTM formation between species are currently unknown, however. Two approaches were used to study genetic factors responsible for the difference in LTM formation between N. vitripennis and N. giraulti. The first approach took advantage of the unique possibility to interbreed Nasonia species. Hybrid offspring of N. vitripennis and N. giraulti did not form LTM after a single conditioning trial, similar to N. giraulti. The dominant LTM phenotype of N. giraulti was then backcrossed into the genetic background of N. vitripennis for up to 5 generations. Using a genotyping microarray analysis and subsequent confirmation experiments, we detected two genomic regions (quantitative trait loci – QTLs) that both reduce long-lasting memory, but not completely remove this memory. These results indicate that multiple QTLs regulate the difference in LTM formation between the two Nasonia species. Concluding, our approach has provided insights in the genomic basis of a naturally occurring difference in LTM formation between two species. Excellent opportunities for fine-scale QTL mapping are available for the genus Nasonia. This will allow identification of decisive regulatory mechanisms involved in LTM formation that are located in the two genomic regions detected in this study.

    The second approach took advantage of next-generation sequencing techniques that allow transcriptome-wide studies of gene expression levels. RNA from heads of N. vitripennis and N. giraulti was collected before conditioning and immediately, 4 hours, or 24 hours after conditioning. This RNA was sequenced strand-specifically using HiSeq technology, which allows detection of sense and antisense transcripts. Various genes, from a number of different signalling pathways known to be involved in LTM formation, were uniquely differentially expressed after conditioning in N. vitripennis. These genes are likely involved in the ongoing process of LTM formation in this species. A number of other genes with a known role in LTM formation,including genes involved in dopamine synthesis and in the Ras-MAPK and PI3K signalling pathways, were uniquely differentially expressed in N. giraulti. These genes may have a role in a LTM inhibitory mechanism in this species. Antisense transcripts were detected for a number of known memory genes, which may indicate a role inregulation of transcription, alternative splicing, or translation. This study is the first to compare gene expression patterns after conditioning between two species that differ in LTM formation. The results provide promising candidate genes for future studies in which the regulation of these genes, the function of specific splice variants, and spatial expression patterns in the brain should be studied to understand how these genes are involved in the regulation of LTM formation.

    Learning and memory formation have an important role in animal and human behaviour.Novel and valuable insights on both ecological and genetic factors responsible for variation in LTM formation have been revealed by the research presented in this thesis. Integrating ecological factors and genetic factors is essential, as genes are the level on which ecological factors can drive the evolution of variation in learning and memory formation. The genus Nasonia has offered excellent opportunities for ecological research as well as unique opportunities for studies on genomic and genetic factors, which were addressed by comparing closely related species that differ in memory formation. This thesis provides the basis for the identification of genomic differences responsible for the difference in memory formation between Nasonia species, but it also characterized the consequences of these genomic differences on gene expression. The genetic basis of learning and memory formation are highly conserved among distant animal species and insights from this thesis are likely applicable to other animal species and humans, as well.Altogether, these small parasitic wasps allow us to understand and value differences in memory formation.

    Comparative genomics of Dothideomycete fungi
    Burgt, A. van der - \ 2014
    Wageningen University. Promotor(en): Pierre de Wit, co-promotor(en): Jerome Collemare. - Wageningen : Wageningen University - ISBN 9789461739056 - 176
    dothideomycetes - plantenziekteverwekkende schimmels - passalora fulva - dothistroma - genomen - vergelijkende genomica - dothideomycetes - plant pathogenic fungi - passalora fulva - dothistroma - genomes - comparative genomics

    Fungi are a diverse group of eukaryotic micro-organisms particularly suited for comparative genomics analyses. Fungi are important to industry, fundamental science and many of them are notorious pathogens of crops, thereby endangering global food supply. Dozens of fungi have been sequenced in the last decade and with the advances of the next generation sequencing, thousands of new genome sequences will become available in coming years. In this thesis I have used bioinformatics tools to study different biological and evolutionary processes in various genomes with a focus on the genomes of the Dothideomycetefungi Cladosporium fulvum, Dothistroma septosporumand Zymoseptoria tritici.

    Chapter 1introduces the scientific disciplines of mycology and bioinformatics from a historical perspective. It exemplifies a typical whole-genome sequence analysis of a fungal genome, and focusses in particular on structural gene annotation and detection of transposable elements. In addition it shortly reviews the microRNA pathway as known in animal and plants in the context of the putative existence of similar yet subtle different small RNA pathways in other branches of the eukaryotic tree of life.

    Chapter 2addresses the novel sequenced genomes of the closely related Dothideomyceteplant pathogenic fungi Cladosporium fulvumand Dothistroma septosporum. Remarkably, it revealed occurrence of a surprisingly high similarity at the protein level combined with striking differences at the DNA level, gene repertoire and gene expression. Most noticeably, the genome of C. fulvumappears to be at least twice as large, which is solely attributable to a much larger content in repetitive sequences.

    Chapter 3describes a novel alignment-based fungal gene prediction method (ABFGP) that is particularly suitable for plastic genomes like those of fungi. It shows excellent performance benchmarked on a dataset of 7,000 unigene-supported gene models from ten different fungi. Applicability of the method was shown by revisiting the annotations of C. fulvumand D. septosporumand of various other fungal genomes from the first-generation sequencing era. Thousands of gene models were revised in each of the gene catalogues, indeed revealing a correlation to the quality of the genome assembly, and to sequencing strategies used in the sequencing centres, highlighting different types of errors in different annotation pipelines.

    Chapter 4focusses on the unexpected high number of gene models that were identified by ABFGP that align nicely to informant genes, but only upon toleration of frame shifts and in-frame stop-codons. These discordances could represent sequence errors (SEs) and/or disruptive mutations (DMs) that caused these truncated and erroneous gene models. We revisited the same fungal gene catalogues as in chapter 3, confirmed SEs by resequencing and successively removed those, yielding a high-confidence and large dataset of nearly 1,000 pseudogenes caused by DMs. This dataset of fungal pseudogenes, containing genes listed as bona fide genes in current gene catalogues, does not correspond to various observations previously done on fungal pseudogenes. Moreover, the degree of pseudogenization showing up to a ten-fold variation for the lowest versus the highest affected species, is generally higher in species that reproduce asexually compared to those that in addition reproduce sexually.

    Chapter 5describes explorative genomics and comparative genomics analyses revealing the presence of introner-like elements (ILEs) in various Dothideomycetefungi including Zymoseptoria triticiin which they had not identified yet, although its genome sequence is already publicly available for several years. ILEs combine hallmark intron properties with the apparent capability of multiplying themselves as repetitive sequence. ILEs strongly associate with events of intron gain, thereby delivering in silico proof of their mobility. Phylogenetic analyses at the intra- and inter-species level showed that most ILEs are related and likely share common ancestry.

    Chapter 6provides additional evidence that ILE multiplication strongly dominates over other types of intron duplication in fungi. The observed high rate of ILE multiplication followed by rapid sequence degeneration led us to hypothesize that multiplication of ILEs has been the major cause and mechanism of intron gain in fungi, and we speculate that this could be generalized to all eukaryotes.

    Chapter 7describes a new strategy for miRNA hairpin prediction using statistical distributions of observed biological variation of properties (descriptors) of known miRNA hairpins. We show that the method outperforms miRNA prediction by previous, conventional methods that usually apply threshold filtering. Using this method, several novel candidate miRNAs were assigned in the genomes of Caenorhabditis elegansand two human viruses. Although this chapter is not applied on fungi, the study does provide a flexible method to find evidence for existence of a putative miRNA-like pathway in fungi.

    Chapter 8provides a general discussion on the advent of bioinformatics in mycological research and its implications. It highlights the necessity of a prioriplanning and integration of functional analysis and bioinformatics in order to achieve scientific excellence, and describes possible scenarios for the near future of fungal (comparative) genomics research. Moreover, it discusses the intrinsic error rate in large-scale, automatically inferred datasets and the implications of using and comparing those.

    ‘Speciale technieken alleen voor topfokkerij': Gary Hennip voorspelt het einde van KI als geavanceerde technieken worden gecombineerd
    Hogenkamp, W. ; Veerkamp, R.F. - \ 2014
    Boerderij 99 (2014)27. - ISSN 0006-5617 - p. 38 - 38.
    veehouderij - dierveredeling - fokwaarde - kunstmatige inseminatie - genetica - genomen - technieken - nieuwe combinatie - toekomst - livestock farming - animal breeding - breeding value - artificial insemination - genetics - genomes - techniques - new combination - future
    Gary Hennip, onderzoeker bij Penn State University (VS), denkt dat ki overbodig is bij slim combineren van technieken als ovum pick-up, ivf, genomics en sperma seksen op het bedrijf. Boerderij legt de stelling voor aan professor generieke genetcia Roel Veerkamp.
    Physiology and biochemistry of aromatic hydrocarbon-degrading bacteria that use chlorate and/or nitrate as electron acceptor
    Oosterkamp, M.J. - \ 2013
    Wageningen University. Promotor(en): Fons Stams, co-promotor(en): Caroline Plugge; Peter Schaap. - Wageningen : Wageningen University - ISBN 9789461737779 - 191
    bacteriën - aromatische koolwaterstoffen - fysiologie - biochemie - elektronen - genomen - nitraten - chloraten - microbiologie - bacteria - aromatic hydrocarbons - physiology - biochemistry - electrons - genomes - nitrates - chlorates - microbiology
    Optimizing genomic selection for scarcely recorded traits
    Pszczola, M.J. - \ 2013
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Mario Calus; T. Strabel. - Wageningen : Wageningen UR - ISBN 9789461737663 - 158
    melkvee - genomen - selectief fokken - genetische verbetering - fokwaarde - fenotypen - genotypen - kenmerken - voeropname - dierveredeling - dairy cattle - genomes - selective breeding - genetic improvement - breeding value - phenotypes - genotypes - traits - feed intake - animal breeding

    Animal breeding aims to genetically improve animal populations by selecting the best individuals as parents of the next generation. New traits are being introduced to breeding goals to satisfy new demands faced by livestock production. Selecting for novel traits is especially challenging when recording is laborious and expensive and large scale recording is not possible. Genetic improvement of novel traits may be thus limited due to the small number of observations. New breeding tools, such as genomic selection, are therefore needed to enable the genetic improvement of novel traits. Using the limited available data optimally may, however, require alternative approaches and methodologies than currently used for conventional breeding goal traits. The overall objective of this thesis was to investigate different options for optimizing genomic selection for scarcely recorded novel traits. The investigated options were: (1) genotype imputation for ungenotyped but phenotyped animals to be used to enlarge the reference population; (2) optimization of the design of the reference population with respect to the relationships among the animals included in it; (3) prioritizing genotyping of the reference population or the selection candidates; and (4) using easily recordable predictor traits to improve the accuracy of breeding values for scarcely recorded traits. Results showed that: (1) including ungenotyped animals to the reference population can lead to a limited increase in the breeding values accuracy; (2) the reference population is designed optimally when the relationship within the reference are minimized and between reference population and potential selection candidates maximized; (3) the main gain in accuracy when moving from traditional to genomic selection is due to genotyping the selection candidates, but preferably both reference population and selection candidates should be genotyped; and (4) including the predictor traits in the analysis when it is recorded on both reference population and selection candidates can lead to a significant increase in the selection accuracy. The key factors for successful implementation of selection for a novel trait in a breeding scheme are: (1) maximizing accuracy of genotype prediction for ungenotyped animals to be used for updating the reference population; (2) optimizing the design of the reference population; (3) determining easy to record indicator traits that are also available on the selection candidates (4) developing large scale phenotyping techniques; and (5) establishing strategies and policies for increasing the engagement of farmers in the recording of novel traits.

    De tomatenkaart is klaar, wat nu?
    Finkers, H.J. ; Visser, R.G.F. - \ 2013
    Kennis Online 10 (2013)mei. - p. 3 - 5.
    moleculaire genetica - plantengenetica - dna-sequencing - tomaten - rassen (planten) - plantenveredeling - genetische bronnen van plantensoorten - genomen - molecular genetics - plant genetics - dna sequencing - tomatoes - varieties - plant breeding - plant genetic resources - genomes
    In 2012 publiceerde Nature de genomische sequentie van de tomaat. Maar daarmee is het werk niet af, zegt Richard Finkers. Hij bepaalde de basenvolgorde van nog eens 150 verwanten van de modeltomaat, om plantenveredelaars in staat te stellen op zoek te gaan naar nieuwe genen in oude rassen.
    Genomics in de fokkerij: in tien jaar van topwetenschap naar big business
    Arendonk, J.A.M. van; Groenen, M. - \ 2013
    Kennis Online 10 (2013)mei. - p. 7 - 8.
    dierveredeling - genomica - fokkerijmethoden - moleculaire technieken - single nucleotide polymorphism - selectiemethoden - melkvee - varkens - genomen - animal breeding - genomics - animal breeding methods - molecular techniques - single nucleotide polymorphism - selection methods - dairy cattle - pigs - genomes
    Genomics was tien jaar geleden topwetenschap die alleen bedreven werd in dure laboratoria van universiteiten en onderzoeksinstituten. Nu gebruiken fokbedrijven DNA-chips om al op jonge leeftijd te kunnen voorspellen welke stier het beste sperma levert, en om te zien of berengeur bij varkens door een slim fokprogramma kan worden voorkomen.
    'Ui is een puzzel met 150 duizend stukjes'
    Smulders, M.J.M. - \ 2013
    Kennis Online 10 (2013)mei. - p. 12 - 12.
    moleculaire genetica - dna-sequencing - genomen - plantenveredeling - onderzoek - molecular genetics - dna sequencing - genomes - plant breeding - research
    Om zeer grote genomen in kaart te kunnen brengen, moeten eerst fundamentele vragen worden opgelost. Zonder hulp van de overheid komen die antwoord er niet, zegt René Smulders. Terwijl grondige sequencing veredeling aantoonbaar versnelt.
    Use of SNP markers to conserve genome-wide genetic diversity in livestock
    Engelsma, K.A. - \ 2012
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Jack Windig. - S.l. : s.n. - ISBN 9789461733863 - 178
    dierveredeling - rundvee - single nucleotide polymorphism - genetische diversiteit - genomen - genomica - conservering - animal breeding - cattle - single nucleotide polymorphism - genetic diversity - genomes - genomics - conservation

    Conservation of genetic diversity in livestock breeds is important since it is, both within and between breeds, under threat. The availability of large numbers of SNP markers has resulted in new opportunities to estimate genetic diversity in more detail, and to improve prioritization of animals for conservation of genetic diversity. The aim of this thesis was to further explore the potential of SNP markers for estimation and conservation of genetic diversity within livestock breeds. This was evaluated analyzing Holstein cattle populations, genotyped with a commonly used 50k SNP chip. Genetic diversity was estimated with SNP markers and compared to genetic diversity estimated with pedigree information. Both methods could detect differences in overall genetic diversity, even between two closely related populations. With SNP markers, differences in genetic diversity at the chromosomal level could be identified as well. Subsequently, SNP markers and pedigree information were used to prioritize animals for conservation in a gene bank using optimal contributions. SNP based prioritization was slightly more effective than pedigree based information, both over the whole genome and at specific regions of the genome. We extended the optimal contribution method to simultaneously conserve a single allele at a specific frequency and maximize the overall genetic diversity conserved in a gene bank. The loss of overall genetic diversity was larger when the target frequency for animals conserved in the gene bank differed more from the original frequency in the population. It can be concluded that dense SNP data form a powerful tool for estimation and conservation of genetic diversity in livestock breeds. Although pedigree information gives a good representation of the overall genetic diversity, SNP markers can provide more detailed information about the genetic diversity over the genome. Especially for small populations, SNP markers can play an important role in conservation of unique alleles, while simultaneously minimizing the loss of genetic diversity at the rest of the genome.

    The role and evolution of fungal effectors in plant pathogenesis
    Jonge, R. de - \ 2012
    Wageningen University. Promotor(en): Pierre de Wit, co-promotor(en): Bart Thomma. - S.l. : s.n. - ISBN 9789461733917 - 148
    plantenziekteverwekkende schimmels - moleculaire plantenziektekunde - evolutie - gastheer parasiet relaties - pathogenese - genomica - immuniteit - genomen - plant pathogenic fungi - molecular plant pathology - evolution - host parasite relationships - pathogenesis - genomics - immunity - genomes - cum laude
    cum laude graduation (with distinction)
    Co-option of pre-existing pathways during Rhizobium-legume symbiosis evolution
    Lillo, A. - \ 2012
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Rene Geurts. - S.l. : s.n. - ISBN 9789461733443 - 151
    rhizobium - fabaceae - symbiose - evolutie - stikstoffixatie - wortels - fylogenetica - genomen - medicago - eerste wortels - rhizobium - fabaceae - symbiosis - evolution - nitrogen fixation - roots - phylogenetics - genomes - medicago - root primordia

    Fixed nitrogen is one of the most limiting factors for plant growth. One of the most important nitrogen-fixing systems is the rhizobium root nodule symbiosis. In this Thesis I have studied the legume-rhizobium symbiosis, starting from the idea that part of pre-existing signalling pathways have been co-opted during evolution of this mutualistic interaction. Gene duplications -of which a whole genome duplication (WGD) is the most dramatic variant- are known as important driving forces in evolution of new traits. 56 to 65 million years ago an ancestral legume species within the Papilionoidae subfamily (Papilionoids) experienced a WGD event and subsequently gave rise to several major phylogenetic crowns. I hypothesize that among the orthologous gene pairs maintained are genes that are essential for nodulation. I adopted a phylogenetic strategy to identify new candidate genes involved in the legume-Rhizobium symbiosis
    In a targeted approach, we focussed on the cytokinin phosphorelay pathway. This resulted in the identification of one gene pair encoding type-A Response Regulators (RRs) with a positive regulatory role for these proteins in root nodule formation. Yet the illustrated role for MtRR9 and MtRR11 in rhizobial symbiosis provides a proof of principle of this method to identify gene pairs involved in legume specific characters. An unbiased search for paralogous gene pairs revealed two conserved gene duplications in the NADPH oxidases gene family. NADPH oxidases are reactive oxygen species (ROS) producing enzymes. We identified two sets of duplicated genes that have been maintained after the Papilionoid specific WGD and we show that MtRBOHA and MtRBOHG are redundant, yet essential during symbiosis.
    Moreover, although it is commonly believed that exclusively pericycle cells give rise to the lateral root primordium, similar as seen in Arabidopsis thaliana, we provide morphological evidence that in the studied legume species this is not the case. In both, Lotus and Medicago, also root cortical cell divisions occur during lateral root formation. Furthermore, we found a striking correlation in the cell layers that are recruited during lateral root and nodule primordium formation. This supports the hypothesis that at least parts of the lateral root developmental program have been recruited during evolution of symbiotic root nodules.

    Waarom maakt aardappelplant knollen?
    Bachem, C.W.B. - \ 2012
    Kennis Online 9 (2012)mei. - p. 8 - 8.
    aardappelen - genomica - moleculaire genetica - genomen - genen - genexpressie - potatoes - genomics - molecular genetics - genomes - genes - gene expression
    Nu het aardappelgenoom in kaart is gebracht, kan het werk eigenlijk pas goed beginnen. ‘We kunnen doelgerichter zoeken naar genen die betrokken zijn bij resistenties en kwaliteit.’ En naar waarom de aardappel knollen vormt en zijn zusje de tomaat niet.
    Een kaart van het gigantische leliegenoom en de genetische hutspot van prei
    Arens, P. ; Scholten, O.E. - \ 2012
    Kennis Online 9 (2012)april. - p. 10 - 11.
    moleculaire genetica - dna-sequencing - genomen - lilium - allium porrum - chromosoomkaarten - molecular genetics - dna sequencing - genomes - lilium - allium porrum - chromosome maps
    Van allerlei organismen is de complete DNA-volgorde bekend. Lelieveredelaars moeten het echter nog doen met een kaart van niks. Dat komt door de onwaarschijnlijke omvang van het genoom van de bloem. Een lelie heeft tien keer meer DNA dan een mens. Niet alleen de lelie, ook prei laat zich lastig in kaart brengen. Dat komt niet alleen door de omvang van het DNA, maar vooral door de organisatie ervan. Waar mensen en veel planten van elk chromosoom twee kopieën hebben, heeft prei er vier.
    Evolution of rhizobium symbiosis
    Camp, R.H.M. Op den - \ 2012
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Rene Geurts. - S.l. : s.n. - ISBN 9789461731982 - 136
    papilionoideae - rhizobium - symbiose - genomen - parasponia - mycorrhizae - evolutie - moleculaire biologie - papilionoideae - rhizobium - symbiosis - genomes - parasponia - mycorrhizas - evolution - molecular biology

    The evolution of rhizobium symbiosis is studied from several points of view in this thesis. The ultimate goal of the combined approaches is to unravel the genetic constrains of the symbiotic interaction. To this end the legume rhizobium symbiosis is studied in model plant species from the Papilionoideae subfamily such as Medicago truncatula and Lotus japonicus. In these model plants the genetic signaling cascade used for rhizobium symbiosis has been largely unraveled. The cascade is triggered by lipo-chitooligosaccharade-based signal molecules excreted by rhizobia, called Nod factors.

    In chapter 2 we make use of a whole genome duplication that has occurred at the root of the legume Papilionoideae subfamily to identify maintained paralogous gene pairs. We hypothesized that a substantial fraction of gene pairs which are maintained in distinct Papilionoideae lineages that split roughly 54 million years ago fulfill legume specific functions, among which is rhizobium symbiosis. Furthermore we argue that such approach could identify novel genes as it can also identify genes pairs that are (partially) redundant in function. With applying this approach specifically to the cytokinin phosphorelay pathway we identified a pair of type-A cytokinin Response Regulators that are involved in rhizobium symbiosis. This study provides a proof-of-principle for this strategy.

    It is known for over fifty years that cytokinin plays an important role in the symbiotic interaction between rhizobia and legume hosts. External application of cytokinin can even result in nodule formation. Only, never had cytokinin levels been quantified in legume root extracts upon symbiotic interaction. In chapter 3 we describe a method for extraction of both cytokinins and auxin from Medicago truncatula roots. We show that cytokinins accumulate in the root zone susceptible to symbiotic interaction upon Nod factor exposure and that this response is dependent on CCaMK; a key gene of the Nod factor signaling cascade. Furthermore, it was found that ethylene signaling has a negative effect on Nod factor induced cytokinin accumulation. The method set up to measure cytokinin as well as auxin provides a tool to further study hormone interactions in rhizobium symbiosis.

    Parasponia,the only non-legume that can engage the rhizobium symbiosis is also subject of study in this thesis. The genetics of the Parasponia-rhizobium symbiosis had not been studied before. It was therefore unknown whether this independently evolved rhizobium symbiosis makes use of the same symbiotic signaling cascade as legumes. In chapter 4 we provide first evidence that Parasponia indeed makes use of the same signaling cascade as found in legumes. Furthermore, we show that in Parasponia a single Nod factor-like receptor is indispensable for two symbiotic interactions; rhizobium and mycorrhiza, respectively. Therefore we conclude that the rhizobium Nod factor perception mechanism is recruited from the widespread endomycorrhizal symbiosis.

    Parallel to our studies in Parasponia (Chapter 4), the research team of Jean Dénarié of the French National Institute for Agricultural Research (INRA) published the structure of the signal molecule of the arbuscular endomycorrhizae; theMyc factor (Maillet et al., 2011, Fungal lipochitooligosaccharide symbiotic signals in arbuscular mycorrhiza. Nature, 469, 58-63). It appeared that Myc factors and Nod factors are structurally very similar. In chapter 5 we discuss these findings and present a more thorough phylogenetic analysis of the NFP-like LysM-type receptor kinases. Together, these results suggest that non-legumes that can engage an arbuscular endomycorrhizaesymbiosis can recognize Nod factor-like molecules as well.

    The last chapter is about a study on the promiscuity and effectiveness of the Parasponia-rhizobium symbiosis. Parasponia uses a single receptor to control entry of rhizobium as well as arbuscular endomycorrhizal fungi and has evolved the rhizobium symbiosis only recently. This made us to hypothesize that Parasponia Nod factor receptors did not coevolve yet with rhizobia and therefore did not diverge from mycorrhizal recognition to develop specificity for the Nod factor. This implies that Parasponia could be a very promiscuous host for rhizobium species. In chapter 6 we describe that Parasponia andersonii can be nodulated by a broad range of rhizobia belonging to 4 different genera, and therefore it is concluded that Parasponia is highly promiscuous for rhizobial engagement. There is a drawback to this high symbiotic promiscuity. Among the strains identified to nodulate Parasponia, a very inefficient rhizobium species, Rhizobium tropici WUR1, was characterized. As this species is able to make effective nodules on two different legume species it suggests that the ineffectiveness of Parasponia andersonii nodules is the result of the incompatibility between both partners. In Parasponia andersonii nodules rhizobia of the ineffective strain become embedded in a dense matrix, but remain vital. This suggests that sanctions or genetic control against underperforming microsymbionts may not be effective in Parasponia. Therefore we argue that the Parasponia-Rhizobium symbiosis is a delicate balance between mutual benefits and parasitic colonization.

    Parasponiahas been given little attention in the rhizobium symbiosis field over the past two decades but with our efforts renewed interest has been established. We believe that in the end, the comparison of Parasponia to its closest related non-symbiotic sister species Trema, will result in the determination of the genetic constrains of rhizobium symbiosis.

    Genome bioinformatics of tomato and potato
    Datema, E. - \ 2011
    Wageningen University. Promotor(en): W. Stiekema, co-promotor(en): Roeland van Ham. - [S.l.] : S.n. - ISBN 9789461730473 - 139
    gewassen - solanum lycopersicum - solanum tuberosum - genomica - bio-informatica - nucleotidenvolgordes - genomen - genen - crops - solanum lycopersicum - solanum tuberosum - genomics - bioinformatics - nucleotide sequences - genomes - genes

    In the past two decades genome sequencing has developed from a laborious and costly technology employed by large international consortia to a widely used, automated and affordable tool used worldwide by many individual research groups. Genome sequences of many food animals and crop plants have been deciphered and are being exploited for fundamental research and applied to improve their breeding programs. The developments in sequencing technologies have also impacted the associated bioinformatics strategies and tools, both those that are required for data processing, management, and quality control, and those used for interpretation of the data.

    This thesis focuses on the application of genome sequencing, assembly and annotation to two members of the Solanaceae family, tomato and potato. Potato is the economically most important species within the Solanaceae, and its tubers contribute to dietary intake of starch, protein, antioxidants, and vitamins. Tomato fruits are the second most consumed vegetable after potato, and are a globally important dietary source of lycopene, beta-carotene, vitamin C, and fiber. The chapters in this thesis document the generation, exploitation and interpretation of genomic sequence resources for these two species and shed light on the contents, structure and evolution of their genomes.

    Chapter 1introduces the concepts of genome sequencing, assembly and annotation, and explains the novel genome sequencing technologies that have been developed in the past decade. These so-called Next Generation Sequencing platforms display considerable variation in chemistry and workflow, and as a consequence the throughput and data quality differs by orders of magnitude between the platforms. The currently available sequencing platforms produce a vast variety of read lengths and facilitate the generation of paired sequences with an approximately fixed distance between them. The choice of sequencing chemistry and platform combined with the type of sequencing template demands specifically adapted bioinformatics for data processing and interpretation. Irrespective of the sequencing and assembly strategy that is chosen, the resulting genome sequence, often represented by a collection of long linear strings of nucleotides, is of limited interest by itself. Interpretation of the genome can only be achieved through sequence annotation – that is, identification and classification of all functional elements in a genome sequence. Once these elements have been annotated, sequence alignments between multiple genomes of related accessions or species can be utilized to reveal the genetic variation on both the nucleotide and the structural level that underlies the difference between these species or accessions.

    Chapter 2describes BlastIf, a novel software tool that exploits sequence similarity searches with BLAST to provide a straightforward annotation of long nucleotide sequences. Generally, two problems are associated with the alignment of a long nucleotide sequence to a database of short gene or protein sequences: (i) the large number of similar hits that can be generated due to database redundancy; and (ii) the relationships implied between aligned segments within a hit that in fact correspond to distinct elements on the sequence such as genes. BlastIf generates a comprehensible BLAST output for long nucleotide sequences by reducing the number of similar hits while revealing most of the variation present between hits. It is a valuable tool for molecular biologists who wish to get a quick overview of the genetic elements present in a newly sequenced segment of DNA, prior to more elaborate efforts of gene structure prediction and annotation.

    In Chapter 3 a first genome-wide comparison between the emerging genomic sequence resources of tomato and potato is presented. Large collections of BAC end sequences from both species were annotated through repeat searches, transcript alignments and protein domain identification. In-depth comparisons of the annotated sequences revealed remarkable differences in both gene and repeat content between these closely related genomes. The tomato genome was found to be more repetitive than the potato genome, and substantial differences in the distribution of Gypsy and Copia retrotransposable elements as well as microsatellites were observed between the two genomes. A higher gene content was identified in the potato sequences, and in particular several large gene families including cytochrome P450 mono-oxygenases and serine-threonine protein kinases were significantly overrepresented in potato compared to tomato. Moreover, the cytochrome P450 gene family was found to be expanded in both tomato and potato when compared to Arabidopsis thaliana, suggesting an expanded network of secondary metabolic pathways in the Solanaceae. Together these findings present a first glimpse into the evolution of Solanaceous genomes, both within the family and relative to other plant species.

    Chapter 4explores the physical and genetic organization of tomato chromosome 6 through integration of BAC sequence analysis, High Information Content Fingerprinting, genetic analysis, and BAC-FISH mapping data. A collection of BACs spanning substantial parts of the short and long arm euchromatin and several dispersed regions of the pericentrometric heterochromatin were sequenced and assembled into several tiling paths spanning approximately 11 Mb. Overall, the cytogenetic order of BACs was in agreement with the order of BACs anchored to the Tomato EXPEN 2000 genetic map, although a few striking discrepancies were observed. The integration of BAC-FISH, sequence and genetic mapping data furthermore provided a clear picture of the borders between eu- and heterochromatin on chromosome 6. Annotation of the BAC sequences revealed that, although the majority of protein-coding genes were located in the euchromatin, the highly repetitive pericentromeric heterochromatin displayed an unexpectedly high gene content. Moreover, the short arm euchromatin was relatively rich in repeats, but the ratio of Gypsy and Copia retrotransposons across the different domains of the chromosome clearly distinguished euchromatin from heterochromatin. The ongoing whole-genome sequencing effort will reveal if these properties are unique for tomato chromosome 6, or a more general property of the tomato genome.

    Chapter 5presents the potato genome, the first genome sequence of an Asterid. To overcome the problems associated with genome assembly due tothe high level of heterozygosity that is observed in commercial tetraploid potato varieties, a homozygous doubled-monoploid potato clone was exploited to sequence and assemble 86% of the 844 Mb genome. This potato reference genome sequence was complemented with re-sequencing of aheterozygous diploid clone, revealing the form and extent of sequence polymorphism both between different genotypes and within a single heterozygous genotype. Gene presence/absence variants and other potentially deleterious mutations were found to occur frequently in potato and are a likely cause of inbreeding depression. Annotation of the genome was supported by deep transcriptome sequencing of both the doubled-monoploid and the heterozygous potato, resulting in the prediction of more than 39,000 protein coding genes. Transcriptome analysis provided evidence for the contribution of gene family expansion, tissue specific expression, and recruitment of genes to new pathways to the evolution of tuber development. The sequence of the potato genome has provided new insights into Eudicot genome evolution and has provided a solid basis for the elucidation of the evolution of tuberisation. Many traits of interest to plant breeders are quantitative in nature and the potato sequence will simplify both their characterization and deployment to generate novel cultivars.

    The outstanding challenges in plant genome sequencing are addressed in Chapter 6. The high concentration of repetitive elements and the heterozygosity and polyploidy of many interesting crop plant species currently pose a barrier for the efficient reconstruction of their genome sequences. Nonetheless, the completion of a large number of new genome sequences in recent years and the ongoing advances in sequencing technology provide many excitingopportunities for plant breeding and genome research. Current sequencing platforms are being continuously updated and improved, and novel technologies are being developed and implemented in third-generation sequencing platforms that sequence individual molecules without need for amplification. While these technologies create exciting opportunities for new sequencing applications, they also require robust software tools to process the data produced through them efficiently. The ever increasing amount of available genome sequences creates the need for an intuitive platform for the automated and reproducible interrogation of these data in order to formulate new biologically relevant questions on datasets spanning hundreds or thousands of genome sequences.

    Genome structure and pathogenicity of the fungal wheat pathogen Mycosphaerella graminicola
    M'Barek, S. Ben - \ 2011
    Wageningen University. Promotor(en): Pierre de Wit, co-promotor(en): Gert Kema. - [S.l.] : S.n. - ISBN 9789085859970 - 229
    triticum aestivum - triticum turgidum - tarwe - mycosphaerella graminicola - plantenziekteverwekkende schimmels - genoomstructuur - eiwitexpressieanalyse - pathogeniteit - pathogenesis-gerelateerde eiwitten - genomen - plasticiteit - plant-microbe interacties - triticum aestivum - triticum turgidum - wheat - mycosphaerella graminicola - plant pathogenic fungi - genomic structure - proteomics - pathogenicity - pathogenesis-related proteins - genomes - plasticity - plant-microbe interactions

    The phytopathogenic fungus Mycosphaerella graminicola (Fuckel) J. Schröt. in Cohn (asexual stage: Zymoseptoria tritici (Desm.) Quaedvlieg & Crous) causes septoria tritici leaf blotch (STB) in wheat and is one of the most important diseases of this crop worldwide. However, STB control, mainly based on the use of resistant cultivars and fungicides, is significantly hampered by the limited understanding of the genetic and biochemical bases of pathogenicity, and mechanisms of infection and resistance in the host. M. graminicola has a very active sexual cycle under field conditions, which is an important driver of STB epidemics. Moreover, it results in high genetic diversity of field populations that causes a major challenge for the development and sustainable management of resistant cultivars and the discovery of new antifungal compounds. Understanding the role of the sexual and asexual life cycles on genome composition of this versatile pathogen and its infection strategy is crucial in order to develop novel control methods.

    Chapter 1 is an introduction to the biology and pathogenicity of M. graminicola. In addition, it shortly describes the impact of improved and novel technologies on the speed, scope and scale of comparative genomics research.

    Chapter 2 provides detailed genetic analyses of two M. graminicola mapping populations, using mainly DArT markers, and the analysis of the meiotic transmission of unequal chromosome numbers. Polymorphisms in chromosome length and number were frequently observed in progeny isolates, of which 15–20% lacked one or more chromosomes despite their presence in one or both parents, but these had no apparent effect on sexual and pathogenic fitness. M. graminicola has up to eight so called dispensable chromosomes that can be easily lost - collectively called the dispensome - which is, so far, the highest number of dispensable chromosomes reported in filamentous fungi. They represent small-sized chromosomes and make up 38% of the chromosome complement of this pathogen. Much of the observed genome plasticity is generated during meiosis and could explain the high adaptability of M. graminicola in the field. The generated linkage map was crucial for finishing the M. graminicola genome sequence.

    Chapter 3 describes the M. graminicola genome sequence with highlights on genome structure and organization including the eight dispensable chromosomes. The genome comprises a core set of 13 chromosomes and a dispensome, consisting of eight chromosomes that are distinct from the core chromosomes in structure, gene and repeat content. The dispensome contains a higher frequency of transposons and the genes have a different codon use. Most of the genes present one the dispensome are also present on the core chromosomes but little synteny is observed neither between the M. graminicola dispensome and the core chromosomes nor with the chromosomes of other related Dothideomycetes. The dispensome likely originates from ancient horizontal transfer(s) from (an) unknown donor(s).

    Chapter 4 shows a global analysis of proteins secreted by M. graminicola in apoplastic fluids during infection. It focuses mainly on fungal proteins secreted in a compatible interaction. The study showed that many of the annotated secreted proteins have putative functions in fungal pathogenicity, such as cell wall degrading enzymes and proteases, but the function of a substantial number of the identified proteins is unknown. During compatible interactions proteins are primarily secreted during the later stages. However, many pathogenesis-related host proteins, such as PR-2, PR-3 and PR-9, accumulated earlier and at higher concentrations during incompatible interactions, indicating that fungal effectors are recognized by resistant plants and trigger resistant gene-mediated defence responses, though without a visible hypersensitive response.

    Chapter 5 further details the initial identification and characterization of necrosis-inducing proteins that are produced in culture filtrates (CFs) of M. graminicola. The necrosis-inducing activity of CFs is light dependent and inactivated by proteinase K and heat treatment (100C). This is reminiscent of the necrosis-inducing properties of host selective toxins of other Dothideomycete pathogens such as Stagonospora nodorum and Pyrenophora tritici-repentis. Subsequent purifications of CFs and mass spectrometry identified several candidate proteins with necrosis-inducing activity. Heterologous expression of the two most prominent proteins in Pichia pastoris produced sufficient quantities for infiltration assays in a panel of wheat cultivars that showed differential responses, suggesting specific recognition.

    Chapter 6 provides a general discussion of the thesis and puts the results obtained in a broader perspective with a focus on the genome structure of M. graminicola and its function. In addition, aspects of the hemi-biotrophic lifestyle, the relevance of secreted proteins for the wheat-M. graminicola pathosystem in relation to gene-for-gene models and the potential implications for resistance breeding strategies are discussed.

    Genome transcription/translation of segmented, negative-strand RNA viruses
    Geerts-Dimitriadou, C. - \ 2011
    Wageningen University. Promotor(en): Just Vlak, co-promotor(en): Richard Kormelink. - [s.l.] : S.n. - ISBN 9789085859314 - 151
    rna-virussen - tomatenbronsvlekkenvirus - genomen - transcriptie - translatie - luzernemozaïekvirus - nucleotidenvolgordes - genexpressie - genexpressieanalyse - rna viruses - tomato spotted wilt virus - genomes - transcription - translation - alfalfa mosaic virus - nucleotide sequences - gene expression - genomics

    The requirements for alignment of capped RNA leader sequences along the viral genome during influenza transcription initiation (“cap-snatching”) have long been an enigma. Previous work on Tomato spotted wilt virus (TSWV) transcription initiation has revealed that this virus displays a preference for leaders with increasing base complementarity to the 3'-ultimate residues of the viral RNA template. Assuming that cap-snatching is a highly conserved mechanism, it is tempting to speculate that the findings for TSWV apply to all segmented negative RNA viruses. The research in this thesis aimed to analyze whether similar cap donor requirements applied for Influenza A virus transcription initiation as compared to what has been found for TSWV. Indeed, in vitro studies demonstrated that influenza transcriptase prefers multiple base-pairing capped leaders. Additionally, the occurrence of “prime-and-realign” during influenza transcription initiation was observed, as well as internal priming at the 3'-penultimate viral residue. The in vitro findings were confirmed by similar studies performed during influenza infection of cell cultures. Whereas transcription initiation of TSWV has been relatively well studied, transcription termination has not. It is postulated that transcription termination/translation is triggered by the formation of a hairpin structure. In cell experiments support a role of the TSWV hairpin structure in translation.

    Genetic variation in the chicken genome: insights in selection
    Elferink, M.G. - \ 2011
    Wageningen University. Promotor(en): Martien Groenen, co-promotor(en): Richard Crooijmans. - [S.l.] : S.n. - ISBN 9789085859208 - 162
    pluimvee - dierveredeling - genomen - populatiegenetica - genen - rassen (dieren) - genetische kartering - genetische variatie - selectie - poultry - animal breeding - genomes - population genetics - genes - breeds - genetic mapping - genetic variation - selection

    The chicken currently provides more than a quarter of the meat and nearly all eggs produced worldwide. For future improvements in production traits and animal welfare as well as to address future consumer demands it is necessary to understand the etiology and biology underlying production traits and diseases. The primary aim of the research described in this thesis was to investigate the utility of several molecular approaches to identify causative variants underlying a variety of traits in the chicken.
    The general introduction in chapter 1 provides an overview of the domestication history of the chicken - with a particular focus on commercial chicken breeds - and describes the importance to identify causative variants underlying production traits and diseases. Furthermore, several different molecular techniques and methods are introduced that are being used to detect causative variants underlying monogenic and polygenic traits.
    Linkage maps are essential for linkage analysis, important to study recombination rates and recombination hotspots within the genome and can assist in the sequence assembly of genomes. In chapter 2 we describe the construction of a new high-resolution linkage map of the chicken genome based on two chicken populations with a total of 1619 individuals. The two populations used are a purebred broiler line and a broiler x broiler cross. This high resolution allowed accurate identification of recombination hotspots in the chicken genome, including sex specific recombination. Furthermore, to improve the current reference genome (WASHUC2), 613 unmapped markers were included in the genome-wide assay that included a total of 17,790 SNPs. The resulting linkage map comprises 13,340 SNPs, of which 360 had not been assigned to a known chromosome on chicken genome build WASHUC2. The resulting linkage map is composed of 31 linkage groups, with a total length of 3,054 cM for the sex-average map of the combined population. Regional differences in recombination hotspots between the two mapping populations were observed for several chromosomes near the telomere of the p arm. The sex-specific analysis revealed that these regional differences were mainly caused by female-specific recombination hotspots in the broiler × broiler cross.
    In chapter 3 we describe the molecular characterization of the locus causing the late feathering phenotype; a monogenic trait in chicken that results in a delayed emergence of flight feathers at hatch. The late feathering phenotype is beneficial to breeders as it can be used for sex typing at hatch. The locus has, therefore, been extensively used in diverse commercial chicken breeds. However, a retrovirus closely linked to the late feathering allele causes a negative pleiotropic effect on egg production and causes viral infections. Within this chapter we describe the identification of a 180 kb tandem duplication in the late feathering allele using a quantitative PCR approach. The tandem duplication results in the partial duplication of two genes; the prolactin receptor and the gene encoding sperm flagellar protein 2. Sequence analysis revealed that the duplication is identical in broiler, white egg-layer, and brown egg-layer lines. This information was also used to design a molecular test to detect this duplication, particularly in heterozygous individuals.
    The recent advances in massive parallel sequencing technologies have enabled rapid and cost-effective detection of all genetic variants within genomes. The detection of all genetic variants within a genome has further increased our ability to identify causative variants underlying quantitative trait loci (QTL). In chapter 4, we combined a genome-wide association study with whole-genome resequencing to identify causative variants underlying the pulmonary hypertension syndrome (PHS), a polygenic trait in chicken. PHS is a metabolic disease that has been linked to intense selection on growth rate and feed conversion ratio of modern broilers (meat-type chicken). PHS has become one of the most frequent causes of mortality within the broiler industry and leads to substantial economic losses and reduced animal welfare. In total, 18 QTL regions were identified in the genome-wide association study. In order to detect causative variants underlying these QTL regions, we sequenced the genomes of twelve individuals. To maximize the detection of causative variants we selected the individuals based on extreme phenotypes for PHS. Within 8 QTL regions we identified a total of 10 genes that contain at least one variant that is predicted to affect protein function. Moreover, 7.62 million SNPs were detected within the twelve animals compared to the reference genome. These markers can be used in the development of future genome-wide assays.
    Genomic regions that have undergone selection should contain loci that influence important phenotypic traits and will, therefore, include causative variant(s) that could aid in further future improvement of production traits and disease resistance. In chapter 5, we applied hitch-hiking mapping to make a broad assessment of the effects of selection histories in domesticated chicken. Towards this end, we sampled commercial chickens representing all major breeding goals from multiple breeding companies. In addition, we sampled non-commercial chicken diversity by sampling almost all recognized traditional Dutch breeds and a representative sample of breeds from China. The broad sample of 67 commercial and non-commercial breeds were assessed for signatures of selection in the genome using information of 57,636 SNPs that were genotyped on pooled DNA samples. Our approach demonstrates the strength of including many different populations with similar, and breed groups with different selection histories to reduce stochastic effects based on single populations. The detection of regions of putative selection resulted in the identification of several candidate genes that could aid in further improvement of production traits and disease resistance.
    Finally, the general discussion in chapter 6 describes the main findings of this thesis. In this chapter recommendations are given for the best strategies to detect causative variants underlying monogenic or polygenic traits. All strategies can benefit substantially from the recent developments in massive parallel sequencing, although the high costs of this method currently prevent large scale studies. In order to perform powerful and cost-effective studies, several strategies are discussed that combine massive parallel sequencing with other existing methods and techniques. Furthermore, the limitations of the different strategies are addressed, as well as the improvements needed in the near future to identify causative variants underlying a variety of traits in, but not limited to, the chicken.

    Efficiënte koe stoot minder methaan uit : fokken op voerefficiëntie in mogelijk
    Haas, Y. de; Haan, M.H.A. de - \ 2011
    V-focus 8 (2011)2. - ISSN 1574-1575 - p. 22 - 23.
    melkveehouderij - rundveevoeding - efficiëntie - dierveredeling - genomen - selectie - fokkerijmethoden - dairy farming - cattle feeding - efficiency - animal breeding - genomes - selection - animal breeding methods
    Fokken op een hoge voerefficiëntie zal de voerkosten drukken en het milieu sparen. Dat er nog geen fokprogramma is om op voerefficiëntie van melkkoeien te fokken, komt doordat de dataverzameling van voeropname erg lastig en kostbaar is. Met genomic selection lijken er nieuwe mogelijkheden te komen.
    The role of non-specific interactions in nuclear organization
    Nooijer, S. de - \ 2010
    Wageningen University. Promotor(en): Ton Bisseling; Bela Mulder, co-promotor(en): Joan Wellink. - [S.l. : S.n. - ISBN 9789085857921 - 117
    arabidopsis - celkernen - chromosomen - genomen - chromatine - interacties - cytogenetica - moleculaire biologie - arabidopsis - nuclei - chromosomes - genomes - chromatin - interactions - cytogenetics - molecular biology
    The most important organelle in eukaryotic cells is the nucleus. Many processes occurring within the nucleus depend on spatial organization of the nucleus. The spatial organization of the eukaryotic nucleus derives from interactions between its constituents. Both specific interactions, for instance the interactions between a DNA binding protein and its target DNA sequence, and non-specific interactions occur. Non-specific interactions stem from physical encounters between molecules or particles, which can favour particular organizations, i.e. the ones that have the lowest entropy. The role of non-specific interactions in nuclear organization is so far not extensively studied. Here, we investigate the effects of non-specific interactions on nuclear organization, using molecular dynamics simulation techniques. Chromatin folding models can be implemented in these simulations as chains of monomers, which can form loops, branches or networks. Through a comparison of simulation results with experimental data, these models can be verified or falsified.

    We used MD simulations of models for Arabidopsis chromatin organisation to show that non-specific interactions can explain the in vivo localisation of nucleoli and chromocenters. Also, we quantitatively demonstrate that chromatin looping contributes to the formation of chromosome territories. Focussing on the forces driving nuclear organization in the rosette model, we derive effective interaction potentials for rosette-loop interactions. These potentials are weak, but nevertheless drive chromocenters and nucleoli to the nuclear periphery and away from each other.

    We also study the folding of a single human chromosome within its territory. The results of our simulations are analysed using a virtual confocal microscope algorithm which has the same limitations as a real confocal microscope. Thus we show that chromatin looping increases the volume occupied by a 10Mbp chromosomal sub-domain, but decreases the overlap between two neighbouring sub-domains. Our results furthermore show that the measured amount of overlap is highly dependent on both spatial resolution and signal detection threshold of the confocal microscope, and that in typical fluorescence in situ hybridisation experiments these two factors contribute to a gross underestimation of the real overlap. Zooming out to whole nucleus organization, we show that an interplay between interactions between heterochromatin and nuclear lamina generates a wide variety of nuclear organizations, with those occurring in nature requiring a fine balance between both interactions.

    The differences between chromosome folding in human and Arabidopsis can be explained through differences in genomic structure and chromosome loop formation, but the underlying mechanisms and forces that organize the nucleus are very similar. The insight how specific and non-specific forces cooperate to shape nuclear organization, is therefore the most important contribution of this thesis to scientific progress.

    Bioinformatics' approaches to detect genetic variation in whole genome sequencing data
    Kerstens, H.H.D. - \ 2010
    Wageningen University. Promotor(en): Martien Groenen; Mari Smits. - [S.l. : S.n. - ISBN 9789085857808 - 182
    bio-informatica - genomen - nucleotidenvolgordes - genetische variatie - varkens - kalkoenen - kippen - anas platyrhynchos - dierveredeling - genexpressieanalyse - single nucleotide polymorphism - marker assisted breeding - bioinformatics - genomes - nucleotide sequences - genetic variation - pigs - turkeys - fowls - anas platyrhynchos - animal breeding - genomics - single nucleotide polymorphism - marker assisted breeding
    Current genetic marker repositories are not sufficient or even are completely lacking for most farm animals. However, genetic markers are essential for the development of a research tool facilitating discovery of genetic factors that contribute to resistance to disease and the overall welfare and performance in farm animals.
    By large scale identification of Single Nucleotide Polymorphisms (SNPs) and Structural Variants (SVs) we aimed to contribute to the development of a repository of genetic variants for farm animals. For this purpose bioinformatics data pipelines were designed and validated to address the challenge of the cost effective identification of genetic markers in DNA sequencing data even in absence of a fully sequenced reference genome.
    To find SNPs in pig, we analysed publicly available whole genome shotgun sequencing datasets by sequence alignment and clustering. Sequence clusters were assigned to genomic locations using publicly available BAC sequencing and BAC mapping data. Within the sequence clusters thousands of SNPs were detected of which the genomic location is roughly known.
    For turkey and duck, species that both were lacking a sufficient sequence data repository for variant discovery, we applied next-generation sequencing (NGS) on a reduced genome representation of a pooled DNA sample. For turkey a genome reference was reconstructed from our sequencing data and available public sequencing data whereas in duck the reference genome constructed by a (NGS) project was used. SNPs obtained by our cost-effective SNP detection procedure still turned out to cover, at intervals, the whole turkey and duck genomes and are of sufficient quality to be used in genotyping studies. Allele frequencies, obtained by genotyping animal panels with a subset our SNPs, correlated well with those observed during SNP detection. The availability of two external duck SNP datasets allowed for the construction of a subset of SNPs which we had in common with these sets. Genotyping turned out that this subset was of outstanding quality and can be used for benchmarking other SNPs that we identified within duck.
    Ongoing developments in (NGS) allowed for paired end sequencing which is an extension on sequencing analysis that provides information about which pair of reads are coming from the outer ends of one sequenced DNA fragment. We applied this technique on a reduced genome representation of four chicken breeds to detect SVs. Paired end reads were mapped to the chicken reference genome and SVs were identified as abnormally aligned read pairs that have orientation or span sizes discordant from the reference genome. SV detection parameters, to distinguish true structural variants from false positives, were designed and optimized by validation of a small representative sample of SVs using PCR and traditional capillary sequencing.
    To conclude: we developed SNP repositories which fulfils a requirement for SNPs to perform linkage analysis, comparative genomics QTL studies and ultimately GWA studies in a range of farm animals. We also set the first step in developing a repository for SVs in chicken, a relatively new genetic marker in animal sciences.
    The interplay between a Phytophthora RXLR effector and an Arabidopsis lectin receptor kinase
    Bouwmeester, K. - \ 2010
    Wageningen University. Promotor(en): Francine Govers; Pierre de Wit. - [S.l. : S.n. - ISBN 9789085856474 - 223
    phytophthora infestans - arabidopsis - solanum tuberosum - genen - genomen - virulentie - kinasen - lectinen - receptoren - genexpressie - plant-microbe interacties - phytophthora infestans - arabidopsis - solanum tuberosum - genes - genomes - virulence - kinases - lectins - receptors - gene expression - plant-microbe interactions
    Phytophthora infestans – the causal agent of potato late blight – secretes a plethora of effector proteins to facilitate plant infection. The central subject of this thesis is ipiO, one of the first cloned Phytophthora genes with a putative function in pathogenicity as was anticipated based on its in planta induced (ipi) expression, in particular during early stages of host infection. IPI-O contains two striking motifs: RXLR-dEER and RGD. RGD is a cell adhesion motif and was shown to be involved in binding to the extracellular lectin domain of LecRK-I.9, a lectin receptor kinase of Arabidopsis. The RXLR-dEER motif plays a role in effector trafficking into host cells and is shared by several secreted oomycete effector proteins which are known to function as race-specific avirulence (Avr) factors. In a previous study, that was aimed at identifying novel pairs of P. infestans Avr and host plant resistance (R) genes, a high-throughput effector genomics screen identified ipiO as Avr-blb1, the counterpart of the late blight R gene Rpi-blb1 which originates from the nightshade Solanum bulbocastanum. Often R genes exploited in late blight resistance breeding become rapidly ineffective as a result of adaptation of P. infestans. However, unlike most late blight R genes that interact in a gene-for-gene manner with Avr genes, Rpi-blb1 seemed to have the potential to remain its effectiveness. In section 2 we monitored the genetic variation and distribution of the ipiO family in an extensive isolate collection of P. infestans and closely related species. This resulted in the identification of 16 IPI-O variants that could be sub-divided in three distinct classes. Variants from class I and class II were shown to induce cell death when co-infiltrated with Rpi-blb1 in Nicotiana benthamiana. Class III consists solely of the highly divergent variant IPI-O4, that is not able to trigger Rpi-blb1-mediated cell death. Class I is highly diverse and represented in all P. infestans isolates analyzed so far, except in two Mexican P. infestans isolates. The latter two are capable to infect Rpi-blb1 plants, suggesting that the lack of class I variants in the genome of these strains allows them to escape recognition by Rpi-blb1 plants. We propose that profiling of the ipiO variants within P. infestans populations can predict the effectiveness of Rpi-blb1-mediated resistance in potato and, as such, can facilitate integrated disease management.
    Section 3 of this thesis deals with legume-like lectin receptor kinases (LecRKs), membrane-spanning proteins with potential roles in adaptive responses and cell wall integrity. We present an inventory and a phylogenetic analysis of the Arabidopsis LecRK gene family. The rationale behind this study was to gain better insight into the diversity of LecRKs and their potential roles in plant defense. A comprehensive expression analysis based on exploration of existing databases revealed that several LecRK genes are induced upon treatment with elicitors or during pathogen infection. Based on the phylogenetic analysis we have reclassified the LecRK genes and proposed a new nomenclature.
    LecRK-I.9, one of the clade I Arabidopsis LecRKs which binds the RGD cell adhesion motif of IPI-O, was shown to mediate adhesion between the cell wall (CW) and plasma membrane (PM). In contrast, IPI-O disrupts these adhesions by virtue of its RGD motif. We analyzed Arabidopsis LecRK-I.9 knock-out lines (lecrk-I.9) for their response to pathogen infection, in particular to Phytophthora brassicae. We also analyzed transgenic Arabidopsis lines expressing ipiO, and observed that both the ipiO-expressing lines and lecrk-I.9 lines are impaired in their resistance to oomycete pathogens. To unravel the mechanisms underlying this phenomenon we analysed callose deposition upon MAMP (i.e. flg22) treatment and investigated the strength of CW-PM adhesions under plasmolysis-inducing conditions. The results indicated that LecRK-I.9 is not only important for the maintenance of the CW-PM continuum, but also in MAMP-triggered immunity. Also here, both the ipiO-expressing lines and the lecrk-I.9 knock-outs displayed a destabilized CW-PM continuum and impaired callose deposition, and hence, they can be regarded as phenocopies. Arabidopsis plants that constitutively express LecRK-I.9 were smaller in size, and displayed increased levels of anthocyanin and lignin. Additionally, these lines were shown to exhibit enhanced resistance to P. brassicae. Furthermore, we studied transgenic potatoes that constitutively Arabidopsis LecRK-I.9. In comparison to the parental control potato line the transgenic lines were less susceptible to mild and moderately aggressive P. infestans isolates, but the increased tolerance was not sufficient to provide resistance to aggressive isolates. These results strongly suggest that LecRK-I.9 is a novel resistance component that plays a role in defense against Phytophthora.
    In Section 4 we describe a novel method for propagating P. brassicae zoospores on an intermediate host plant. This resulted in the production of high numbers of zoospores thereby facilitating highly reproducible small and large scale inoculation experiments.
    This thesis is completed with a general discussion (Section 5) addressing the current understanding of effector uptake by host cells, the subsequent recognition by cognate R proteins mediating effector-triggered immunity, and RXLR-dEER effector diversity. We also discuss the role of the RGD motif in effectors of both animal and plant pathogens, and the potential functions of LecRKs. Finally, we high-light the advantages of Arabidopsis-Phytophthora pathosystems as research object.
    Nucleotide variation and footprints of selection in the porcine and chicken genomes
    Amaral, A.J. - \ 2010
    Wageningen University. Promotor(en): Martien Groenen, co-promotor(en): Hendrik-Jan Megens; Henri Heuven. - [S.l. : S.n. - ISBN 9789085856559 - 160
    varkens - kippen - genomen - nucleotiden - genetische diversiteit - kunstmatige selectie - selectief fokken - rassen (dieren) - genetica - pigs - fowls - genomes - nucleotides - genetic diversity - artificial selection - selective breeding - breeds - genetics
    Jubileum voor de zandraket
    Sikkema, A. - \ 2010
    Resource: weekblad voor Wageningen UR 4 (2010)8. - ISSN 1874-3625 - p. 18 - 20.
    arabidopsis thaliana - mutanten - genomen - genetische bronnen - genetische modellen - plantenfysiologie - wetenschappelijk onderzoek - arabidopsis thaliana - mutants - genomes - genetic resources - genetic models - plant physiology - scientific research
    Je kunt ’m in Nederland op elke straathoek tegenkomen tussen de trottoirtegels: de zandraket of Arabidopsis thaliana. Dit jaar viert dit ‘onkruid’ zijn zilveren jubileum als modelplant van de plantenwetenschappers. Onderzoek aan dit plantje heeft geleid tot detailkennis van vrijwel alle moleculaire processen in planten.
    Genome-wide gene expression surveys and a transcriptome map in chicken
    Nie, H. - \ 2010
    Wageningen University. Promotor(en): Martien Groenen; Mari Smits, co-promotor(en): Richard Crooijmans. - [S.l.] : S.n. - ISBN 9789085856221 - 164
    kippen - pluimvee - dierveredeling - genomen - genexpressie - transcriptie - genetische kartering - genexpressieanalyse - microarrays - dna microarrays - transcriptomics - marker assisted breeding - moleculaire veredeling - fowls - poultry - animal breeding - genomes - gene expression - transcription - genetic mapping - genomics - microarrays - dna microarrays - transcriptomics - marker assisted breeding - molecular breeding
    The chicken (Gallus gallus) is an important model organism in genetics, developmental biology, immunology, evolutionary research, and agricultural science. The completeness of the draft chicken genome sequence provided new possibilities to study genomic changes during evolution by comparing the chicken genome to that of other species. The development of long oligonucleotide microarrays based on the genome sequence made it possible to survey genome-wide gene expression in chicken. This thesis describes two gene expression surveys across a range of healthy chicken tissues in both adult and embryonic stages. Specifically, we focus on the mechanisms of regulation of gene transcription and their evolution in the vertebrate genome.

    Chapter 1 provides a brief history of the chicken as a model organism in biological and genomics research. In particular a brief overview is presented about expression profiling experiments, followed by an introduction to gene transcription regulation in general. Finally, the aim and outline of this thesis is presented.

    An important aim of this thesis is to generate surveys of genome-wide gene expression data in chicken using microarrays. In chapter 2, we introduce microarray data normalization including background correction, within-array normalization and between-array normalization. Based on these results an analysis approach is recommended for the analysis of two-color microarray data as performed in the experiments described in this thesis. We also briefly explain the relevant methodology for the identification of differentially expressed genes and how to translate resulting gene lists into biological knowledge. Finally, specific issues related to updating microarray probe annotation in farm animals, is discussed. For the analysis of the microarray data in this thesis re-annotation of the probes on the chicken 20K oligoarray was done using the oligoRAP, analysis pipeline.

    The vast amount of data generated from a single transcriptomics study makes it impossible to extract meaningful biological knowledge by manually going through individual genes from a list with hundreds and thousands of differentially expressed genes. In chapter 3, we present a practical approach using a collection of R/Bioconductor packages to extract biological knowledge from a microarray experiment in farm animals. Furthermore, a locally adaptive statistical procedure (LAP) analysis approach is used to identify differentially expressed chromosomal regions in a microarray experiment.

    Chapter 4 presents a genome-wide gene expression survey across eight different tissues (brain, bursa of Fabricius, kidney, liver, lung, small intestine, spleen, and thymus from 10-week old chickens) in adult birds using a chicken 20K microarray. To a certain extent, most genes show some tissue-specific pattern of expression. Housekeeping and tissue-specific genes are identified based on gene expression patterns across the eight different tissues. The results show that housekeeping genes are more compact, i.e. are smaller, with shorter, coding sequence length, intron length, and smaller length of the intergenic regions. This observed compactness of housekeeping genes may be a result of selection on economy of transcription during evolution. Furthermore, a comparative analysis of gene expression among mouse, chicken, and frog showed that the expression patterns of orthologous genes are conserved during evolution between mammals, birds, and amphibians.

    The chicken embryo has been a very popular model for developmental biology. To study the overall gene expression pattern in whole chicken embryos at different developmental stages and/or embryonic tissues, a genome-wide gene expression survey across different developmental and embryonic stages was performed (chapter 5). The study included four different developmental stages (HH stage 3, 10, 15, 22) and eight different embryonic tissues (brain, bursa of Fabricius, heart, kidney, liver, lung, small intestine, and spleen from HH stage 36). We were able to identify several embryonic stage- and tissue-specific genes in our analysis. Genomic features of genes widely expressed under these 12 conditions suggest that widely expressed genes are more compact than tissue-specific genes, confirming the findings described in chapter 4. The analysis of the differentially expressed genes during the different developmental stages of whole embryo indicates a gradual change in gene expression during embryo development. A comparison of the gene expression profiles between the same organs, of adults and embryos reveals both striking similarities as well as differences.

    The overall goal of this thesis was to improve our understanding of the mechanisms of transcriptional regulation in the chicken. In chapter 6, a transcriptome map for all chicken chromosomes is presented based on the expression data described in chapter 4. The results reveal the presence of two distinct types of chromosomal regions characterized by clusters of highly or lowly expressed genes respectively. Furthermore, these regions show a high correlation with a number of genome characteristics, like gene density, gene length, intron length, and GC content. A comparative analysis between the chicken and human transcriptome maps suggests that the regions with clusters of highly expressed genes are relatively conserved between the two genomes. Our results revealed the presence of a higher order organization of the chicken genome that affects gene expression, confirming similar observations in other species.

    Finally, in chapter 7 I summarize the main findings and discuss some of the limitations of the analyses described in this thesis. I also discuss the different merits and shortcomings of studying gene expression using either microarrays or next-generation sequencing technology and propose directions for future research. The rapid developments in new-generation sequencing technology will facilitate better coverage and depth of the chicken genome. This will provide a better genome assembly and an improved genome annotation. The sequence-based approaches for studying gene expression will reduce noise levels compared to hybridization-based approaches. Overall, next-generation sequencing is already providing greatly enhance tools to further improve our understanding of the chicken transcriptome and its regulation.

    On some surprising statistical properties of a DNA fingerprinting technique called AFLP
    Gort, G. - \ 2010
    Wageningen University. Promotor(en): A. Stein; Fred van Eeuwijk. - [S.l. : S.n. - ISBN 9789085855378 - 154
    planten - statistische analyse - dna-fingerprinting - genomen - biometrie - moleculaire genetica - dna - aflp - biostatistiek - toegepaste statistiek - plants - statistical analysis - dna fingerprinting - genomes - biometry - molecular genetics - dna - amplified fragment length polymorphism - biostatistics - applied statistics
    AFLP is a widely used DNA fingerprinting technique, resulting in band absence - presence profiles, like a bar code. Bands represent DNA fragments, sampled from the genome of an individual plant or other organism. The DNA fragments travel through a lane of an electrophoretic gel or microcapillary system, and are separated by length, with shorter fragments traveling further. Multiple individuals are simultaneously fingerprinted on a gel. One of the applications of AFLP is the estimation of genetic similarity between individuals, e.g. in diversity and phylogenetic studies. In that case, profiles of two individuals are compared, and the fraction of shared (comigrating) bands is calculated, e.g. using the Dice similarity coefficient. Two comigrating bands may share the same fragment, but band sharing could also be due to chance, if two equally sized, but different fragments are amplified. This is called homoplasy. Homoplasy biases similarity coefficients. Homoplasy could also occur within a lane, if two different fragments of equal length are amplified, resulting in a single band. We call this collision. The main objective of this thesis is the study of collision and homoplasy in AFLP. The length distribution of AFLP fragments plays an important role. This distribution is highly skewed with more abundant short fragments. By simulation the expected similarity for unrelated genotypes is calculated. As much as 40% of the bands may be shared by chance in case of profiles with 120 bands. The collision problem is analogous to the birthday problem, which has a surprising solution. The collision problem is even more extreme, making it even more surprising. Profiles with only 19 bands contain collision(s) with probability 1/2. These findings have consequences for practice. In some cases it is better to prevent the occurrence of collisions by decreasing the number of bands, in other cases a correction for homoplasy and collision is preferred. Modified similarity coefficients are proposed, that estimate the fraction of homologous fragments, correcting for homoplasy and collision. Partially related to homoplasy and collision, we study the codominant scoring of AFLP in association panels. Examples of AFLP in lettuce and tomato serve as illustrations.
    DNA helpt bij management : met een melkmonster op 21 dagen dracht controleren dankzij gensignalen? Interview met M. Smits
    Booij, A. ; Smits, M.A. - \ 2009
    Veeteelt 26 (2009)14. - ISSN 0168-7565 - p. 38 - 39.
    melkveehouderij - melkkoeien - drachtigheidsperiode - melkmonsters - dierveredeling - genomen - selectie - signalen - functionele genomica - dairy farming - dairy cows - gestation period - milking portions - animal breeding - genomes - selection - signals - functional genomics
    History and structure of the closed pedigreed population of Icelandic Sheepdogs
    Oliehoek, P.A. ; Bijma, P. ; Meijden, A. van der - \ 2009
    Genetics, Selection, Evolution 41 (2009). - ISSN 0999-193X - 12
    hondenrassen - genetische diversiteit - genomen - bedrijfsvoering - dierziekten - honden - schaapherdershonden - dog breeds - genetic diversity - genomes - management - animal diseases - dogs - sheep dogs - genome - netherlands - disease
    Background - Dog breeds lose genetic diversity because of high selection pressure. Breeding policies aim to minimize kinship and therefore maintain genetic diversity. However, policies like mean kinship and optimal contributions, might be impractical. Cluster analysis of kinship can elucidate the population structure, since this method divides the population in clusters of related individuals. Kinship-based analyses have been carried out on the entire Icelandic Sheepdog population, a sheep-herding breed. Results - Analyses showed that despite increasing population size and deliberately transferring dogs, considerable genetic diversity has been lost. When cluster analysis was based on kinships calculated seven generation backwards, as performed in previous studies, results differ markedly from those based on calculations going back to the founder-population, and thus invalidate recommendations based on previous research. When calculated back to the founder-population, kinship-based clustering reveals the distribution of genetic diversity, similarly to strategies using mean kinship. Conclusion - Although the base population consisted of 36 Icelandic Sheepdog founders, the current diversity is equivalent to that of only 2.2 equally contributing founders with no loss of founder alleles in descendants. The maximum attainable diversity is 4.7, unlikely achievable in a non-supervised breeding population like the Icelandic Sheepdog. Cluster analysis of kinship coefficients can provide a supporting tool to assess the distribution of available genetic diversity for captive population management
    Genome-wide evaluation of populations
    Daetwyler, H.D. - \ 2009
    Wageningen University. Promotor(en): Johan van Arendonk; J.A. Woolliams, co-promotor(en): B. Villanueva. - [S.l. : S.n. - ISBN 9789085855286 - 187
    dierveredeling - loci voor kwantitatief kenmerk - genomen - rundvee - inteelt - dierziekten - stamboom - genomica - diergenetica - genotyping - animal breeding - quantitative trait loci - genomes - cattle - inbreeding - animal diseases - pedigree - genomics - animal genetics - genotyping
    Dit proefschrift onderzoekt het gebruik van moleculaire merkers voor genetische evaluatie van populaties. Moleculaire merkers kunnen worden gebruikt om de nauwkeurigheid van geschatte fokwaardes te verhogen. In het verleden was men gericht op het opsporen van een beperkt aantal zogenaamde QTL, delen van het genoom, die direct in verband staan met een kenmerk. Het doel was om deze QTL te benutten in fokprogramma’s met behulp van merker-ondersteunde selectie. Met het beschikbaar komen van grote hoeveelheden SNP-merkers kan gebruik worden gemaakt van een methode die gericht is op het gehele genoom, en bekend staat als “genome-wide evaluation” (GWE). Dit proefschrift presenteert resultaten van zowel QTL-detectie als GWE. Deterministische voorspellingen van nauwkeurigheid worden gepresenteerd en getest, en de invloed van de genetische structuur op nauwkeurigheid wordt onderzocht. Een methode wordt gepresenteerd voor het berekenen van missende genotypes, met als doel merkerdichtheid en nauwkeurigheid van GWE te verhogen. Daarnaast worden praktische toepassing van GWE en manieren om ontbrekende genetische variatie te kwantificeren bediscussieerd.
    Genomic selection: een revolutie in fokkerij : selecteren op basis van DNA-merkers
    Calus, M.P.L. ; Veerkamp, R.F. - \ 2009
    V-focus 6 (2009)5. - ISSN 1574-1575 - p. 12 - 14.
    rundveehouderij - dierveredeling - selectief fokken - genetische merkers - fokwaarde - dna - genomen - cattle husbandry - animal breeding - selective breeding - genetic markers - breeding value - dna - genomes
    Genomic selection is in de fokkerijwereld het gesprek van de dag. Maar wat houdt het nu precies in? En wat voor gevolgen heeft het voor fokprogramma’s?
    Selection at DNA level: Genomic selection brings about a revolution in animal breeding
    Calus, M.P.L. ; Bastiaansen, J.W.M. ; Meuwissen, T.H.E. ; Veerkamp, R.F. - \ 2009
    Cow Management 2009 (2009)jan/feb. - p. 6 - 9.
    melkveehouderij - dierveredeling - selectief fokken - genomen - dna - genetische merkers - dairy farming - animal breeding - selective breeding - genomes - dna - genetic markers
    10 years ago it was still a futuristic dream. Today, genomic selection is the hot topic in the world of animal breeding. But what precisely does it involve? Dutch researchers outline the background to this new technology.
    A molecular cytogenetic study of intergenomic recombination and introgression of chromosomal segments in lilies (Lilium)
    Nadeem Khan, M. - \ 2009
    Wageningen University. Promotor(en): Richard Visser; Jaap van Tuyl. - [S.l. : S.n. - ISBN 9789085853800 - 121
    lilium - cytogenetica - recombinatie - genomen - introgressie - hybridisatie - hybriden - genetische kartering - polyploïdie - koppelingskartering - lilium - cytogenetics - recombination - genomes - introgression - hybridization - hybrids - genetic mapping - polyploidy - linkage mapping
    Lilies (Lilium L.) are one of the most important ornamental bulbous crops for cut flower industry
    grown extensively in The Netherlands for last few decades. The genus Lilium consists of seven
    different sections with about 80 species. The species within genus Lilium (2n = 2x = 24)
    comprise a range of desirable and complementary characters. Besides being an important
    horticultural crop, lily (Lilium) also serves as an interesting model plant for molecular
    cytogenetic research and introgression breeding for several reasons like, i). Lily is a model crop
    for interspecific hybridization and it includes plants of different taxonomic species each of which
    possess valuable horticultural traits that need to be combined in the new cultivars. ii) Through
    careful selection n and 2n gametes can be obtained in interspecific hybrids. iii) The genomes of
    different species are so well differentiated genetically that the parental chromosomes can be
    clearly identified in the F1 hybrids as well as in the progenies through DNA in situ hybridization
    techniques. iv) The chromosomes are large enough and the number and position of
    homoeologous recombination sites can be clearly detected. v) The large and easily identified
    chromosomes in different lily species could be a potential source for the cytological mapping of
    the Lilium genomes. Taking advantage of these favourable attributes of lily, a molecular
    cytogenetic investigation was conducted to evaluate the amount of recombination and
    introgression of characters between Longiflorum - Asiatic (LA) and Oriental - Asiatic (OA)
    hybrids through the use of n and 2n gametes.
    For this purpose different F1 Longiflorum × Asiatic (LA) and Oriental × Asiatic (OA)
    hybrids were backcrossed with different Asiatic cultivars. Ovule and embryo rescue techniques
    were employed to get backcross (BC) progenies. Most of the F1 LA appeared to be sterile but
    some hybrids were able to produce only 2n gametes in considerable frequencies. However, in
    rare occasions it was also found that normal meiosis took place in few of the LA hybrids which
    resulted into the formation of normal n gametes. Ploidy level and intergenomic recombination
    was studied in LA interspecific hybrids in order to assess the possibility of functional n gametes
    and their potential use in introgression at diploid level in lily. A total of 104 BC1 LA
    interspecific lily hybrids were obtained, 27 diploids (2n = 2x = 24), 73 triploids (2n = 2x = 36)
    and 4 aneuploids (2x – 1, 2x + 2 or 2x + 3). Similarly, triploid BC1 (LAA) plants were
    backcrossed to diploid Asiatic parents. As a result 14 diploid BC2 progenies were produced. The
    intergenomic recombination and amount of introgression of respective genome (L and A) was
    assessed in these diploid genotypes through GISH (Genomic in situ Hybridization). Extensive
    intergenomic recombination was found among the chromosomes in LA hybrids. A large of
    amount of L- genome was transmitted from F1 LA hybrids to their subsequent BC1 progenies.
    However, very few segments of L- genome were introgressed from the BC1 diploid and triploid
    (LAA) plants to the BC2 progenies (Chapter 2). GISH identifies a considerable amount of
    recombination events amongst different interspecific lily hybrids (LA and OA) obtained from
    functional 2n gametes. Based on recombination sites on different chromosomes identified by
    GISH, cytological maps of three genomes of Lilium were constructed. For this purpose, BC
    progenies of two diploid interspecific hybrids of lily, viz., Longiflorum × Asiatic (LA) and
    Oriental × Asiatic (OA) were used. The BC progenies of LA hybrids consisted of both triploid
    (2n = 3x = 36) and diploid (2n = 2x = 24) with some aneuploid genotypes and those of OA
    hybrids mostly consisted of triploid (2n = 3x = 36) and some aneuploid genotypes. In LA
    hybrids 248 recombination sites were cytologically localized on 12 different chromosomes of
    each genomes (i.e., L and A). Similarly, 116 recombinant sites were marked on 12 chromosomes
    each from the BC progenies of OA hybrids (O and A genomes). The distances of the
    recombination sites from the centromeres are measured (in micrometres). Based on these
    recombination sites four cytological maps were constructed. Since an Asiatic parent was
    involved in both hybrids, viz., LA and OA, two maps were constructed for A genome which
    were indicated as Asiatic (L) and Asiatic (O) and one each for Longiflorum (A) and Oriental (A)
    genomes (Chapter 3).
    With a view to generate genetic variation via homoeologous recombination in BC
    progenies of LA and OA hybrids the most logical approach was the use of 2n gametes. 63 BC1
    LA (LA × AA or AA × LA) and 53 OA (AA × OA) progeny plants were obtained after unilateral
    sexual polyploidization. 16 genotypes from F2 LA populations were obtained after bilateral
    sexual polyploidization through sib-mating of F1 LA hybrids. GISH was employed for the
    identification of the parental genomes, mode of origin of these progenies and measurement of the
    introgression in different interspecific lily hybrids. Most of the BC1 progeny plants (LA and OA)
    had originated through 2n gametes by First Division Restitution (FDR) mechanism. However,
    there were 12 genotypes in LA hybrids and four genotypes in OA hybrids that originated through
    2n gametes formation as the result of Indeterminate Meiotic Restitution (IMR). A higher amount
    of recombination was found in LA hybrids as compared to OA hybrids. Intergenomic
    recombination was also determined in the sib-mated F2 LA population. In this case both parents
    had contributed gametes with the somatic number of chromosomes (i.e., 2n-2n) thus confirming
    the event of bilateral sexual polyploidization in interspecific LA hybrids. Based on these results,
    the relevance of interspecific lily hybrids obtained from uni- and bilateral sexual
    polyploidization leading to allotriploid and allotetraploid formation in interspecific lily hybrids is
    discussed in the context of introgression and mapping (Chapter 4). Molecular markers are an important tool for the construction of genetic linkage maps, as the first step in the genetic
    dissection of the required traits leading to crop improvement followed by the marker assisted
    breeding in different plants. Lilium has one of the largest genome in plant kingdom and genetic
    mapping in lilies is constrained by its large genome. DArT (Diversity Array Technology), a
    molecular marker technique can detect and type DNA variation at several hundred genomic loci
    in parallel without relying on genome sequence information. The DArT technique was developed
    for Longiflorum × Asiatic (LA) lily hybrids to enable an efficient and effective genetic mapping
    with the production of a large numbers of markers in microarrays-based assay. The restriction
    enzyme PstI + TaqI combination generated the largest frequency of polymorphic genomic
    representations for a genotyping array. Genomic representations from 88 F1 LA plants were used
    to assemble a DArT genotyping microarray. A total of 687 DArT markers were developed and
    382 polymorphic markers were mapped on 14 main linkage groups which is two more then the
    haploid chromosome number (i.e. n = 12). The resulting linkage map with 382 DArT markers
    spanned 1329 cM (3.5 cM/marker on average). The results highlighted the potential of DArT as
    a genetic technique for genome profiling in the context of molecular breeding and genomics,
    especially in crops with large genome sizes where other techniques proved to be less useful
    (Chapter 5).
    The results of the present investigation are of practical implication. These results show
    the advantages of the n gametes and their subsequent progenies which opened a new approach of
    lily breeding ‘the analytic breeding’ in the allopolyploids. It also shows the possibility of using
    certain triploid hybrids for further breeding. A comparison has been made between different
    types of interspecific crosses, the amount of intergenomic recombination and introgressions of
    chromosomal segments obtained after unilateral sexual polyploidization. Furthermore, bilateral
    sexually polyploidization via sib-mated F1 hybrids producing 2n gametes has been proven. The
    use of allotetraploids obtained from bilateral sexual polyploidization could be a novel approach
    in the breeding of LA-hybrids. These allotetraploid with recombinant chromosomal segment
    may be a potential source to generate genetic variation in subsequent progenies. The molecular
    cytogenetic GISH and FISH techniques proved to be a powerful tool useful for the construction
    of cytogenetic maps in interspecific crosses in crops with large genomes sizes like lily. These
    techniques are also used for the identification and integration of genetic maps with chromosome
    maps. FISH also helps to monitor the introgressed chromosome segment or marker of interest in
    the subsequent progenies. Application of the DArT technique proved to be an effective method
    to construct genetic linkage maps especially crops (like Lilium) with large genome sizes where
    other techniques might be less useful.

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