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Staff Publications

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    '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.

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    Data from: Combinations of Spok genes create multiple meiotic drivers in Podospora
    Vogan, Aaron A. ; Ament-Velásquez, S.L. ; Granger-Farbos, Alexandra ; Svedberg, Jesper ; Bastiaans, Eric ; Debets, Fons ; Coustou, Virginie ; Yvanne, Hélène ; Clavé, Corinne ; Saupe, Sven J. ; Johannesson, Hanna - \ 2019
    Dryad
    podospora anserina - meiotic drive - genomics - gene drive - Podospora pauciseta - Spore-killing - Spok - genomic conflict
    Meiotic drive is the preferential transmission of a particular allele during sexual reproduction. The phenomenon is observed as spore killing in multiple fungi. In natural populations of Podospora anserina, seven spore killer types (Psks) have been identified through classical genetic analyses. Here we show that the Spok gene-family underlies the Psks. The combination of Spok genes at different chromosomal locations defines the spore killer types and creates a killing hierarchy within the same population. We identify two novel Spok homologs located within a large (74-167 kbp) region (the Spok block) that resides in different chromosomal locations in given strains. We confirm that the SPOK protein performs both killing and resistance functions and show that these activities are dependent on distinct domains, a predicted nuclease and kinase domain. Genomic and phylogenetic analyses across ascomycetes suggest that the Spok genes disperse via cross-species transfer, and evolve by duplication and diversification within lineages.
    Combinations of Spok genes create multiple meiotic drivers in Podospora
    Vogan, Aaron A. ; Ament-Velásquez, S.L. ; Granger-Farbos, Alexandra ; Svedberg, Jesper ; Bastiaans, Eric ; Debets, Alfons J.M. ; Coustou, Virginie ; Yvanne, Hélène ; Clavé, Corinne ; Saupe, Sven J. ; Johannesson, Hanna - \ 2019
    eLife 8 (2019). - ISSN 2050-084X
    evolutionary biology - fungi - gene drive - genetics - genomic conflict - genomics - Podospora - selfish genetic element - spore killer

    Meiotic drive is the preferential transmission of a particular allele during sexual reproduction. The phenomenon is observed as spore killing in multiple fungi. In natural populations of Podospora anserina, seven spore killer types (Psks) have been identified through classical genetic analyses. Here we show that the Spok gene family underlies the Psks. The combination of Spok genes at different chromosomal locations defines the spore killer types and creates a killing hierarchy within a population. We identify two novel Spok homologs located within a large (74-167 kbp) region (the Spok block) that resides in different chromosomal locations in different strains. We confirm that the SPOK protein performs both killing and resistance functions and show that these activities are dependent on distinct domains, a predicted nuclease and kinase domain. Genomic and phylogenetic analyses across ascomycetes suggest that the Spok genes disperse through cross-species transfer, and evolve by duplication and diversification within lineages.

    Experimental evolution reveals that high relatedness protects multicellular cooperation from cheaters
    Bastiaans, Eric ; Debets, Alfons J.M. ; Aanen, Duur K. - \ 2016
    Nature Communications 7 (2016). - ISSN 2041-1723

    In multicellular organisms, there is a potential risk that cheating mutants gain access to the germline. Development from a single-celled zygote resets relatedness among cells to its maximum value each generation, which should accomplish segregation of cheating mutants from non-cheaters and thereby protect multicellular cooperation. Here we provide the crucial direct comparison between high- and low-relatedness conditions to test this hypothesis. We allow two variants of the fungus Neurospora crassa to evolve, one with and one without the ability to form chimeras with other individuals, thus generating two relatedness levels. While multicellular cooperation remains high in the high-relatedness lines, it significantly decreases in all replicate low-relatedness lines, resulting in an average threefold decrease in spore yield. This reduction is caused by cheating mutants with reduced investment in somatic functions, but increased competitive success when fusing with non-cheaters. Our experiments demonstrate that high genetic relatedness is crucial to sustain multicellular cooperation.

    Experimental demonstration of the benefits of somatic fusion and the consequences for allorecognition
    Bastiaans, E. ; Debets, A.J.M. ; Aanen, D.K. - \ 2015
    multicellularity - social evolution - kin selection - ascomycete fungi - heterokaryon incompatibility
    Allorecognition, the ability to distinguish ‘self’ from ‘non-self’ based on allelic differences at allorecognition loci, is common in all domains of life. Allorecognition restricts the opportunities for social parasitism, and is therefore crucial for the evolution of cooperation. However, the maintenance of allorecognition diversity provides a paradox. If allorecognition is costly relative to cooperation, common alleles will be favored. Thus, the cost of allorecognition may reduce the genetic variation upon which allorecognition crucially relies, a prediction now known as ‘Crozier's paradox’. We establish the relative costs of allorecognition, and their consequences for the short-term evolution of recognition labels theoretically predicted by Crozier. We use fusion among colonies of the fungus Neurospora crassa, regulated by highly variable allorecognition genes, as an experimental model system. We demonstrate that fusion among colonies is mutually beneficial, relative to absence of fusion upon allorecognition. This benefit is due not only to absence of mutual antagonism, which occurs upon allorecognition, but also to an increase in colony size per se. We then experimentally demonstrate that the benefit of fusion selects against allorecognition diversity, as predicted by Crozier. We discuss what maintains allorecognition diversity.
    Experimental demonstration of the benefits of somatic fusion and the consequences for allorecognition
    Bastiaans, E. ; Debets, A.J.M. ; Aanen, D.K. - \ 2015
    Evolution 69 (2015)4. - ISSN 0014-3820 - p. 1091 - 1099.
    vegetative incompatibility - neurospora-crassa - heterokaryon incompatibility - natural-populations - filamentous fungi - recognition - evolution - selection - genetics - cooperation
    Allorecognition, the ability to distinguish “self” from “nonself” based on allelic differences at allorecognition loci, is common in all domains of life. Allorecognition restricts the opportunities for social parasitism, and is therefore crucial for the evolution of cooperation. However, the maintenance of allorecognition diversity provides a paradox. If allorecognition is costly relative to cooperation, common alleles will be favored. Thus, the cost of allorecognition may reduce the genetic variation upon which allorecognition crucially relies, a prediction now known as “Crozier's paradox.” We establish the relative costs of allorecognition, and their consequences for the short-term evolution of recognition labels theoretically predicted by Crozier. We use fusion among colonies of the fungus Neurospora crassa, regulated by highly variable allorecognition genes, as an experimental model system. We demonstrate that fusion among colonies is mutually beneficial, relative to absence of fusion upon allorecognition. This benefit is due not only to absence of mutual antagonism, which occurs upon allorecognition, but also to an increase in colony size per se. We then experimentally demonstrate that the benefit of fusion selects against allorecognition diversity, as predicted by Crozier. We discuss what maintains allorecognition diversity
    On the evolution of allorecognition and somatic fusion in ascomycete filamentous fungi
    Bastiaans, E. - \ 2015
    Wageningen University. Promotor(en): Bas Zwaan, co-promotor(en): Duur Aanen; Fons Debets. - Wageningen : Wageningen University - ISBN 9789462572973 - 128
    ascomycota - schimmels - genetica - moleculaire herkenning - celgroei - evolutie - ascomycota - fungi - genetics - molecular recognition - cell growth - evolution

    Cooperation -behaviour that benefits other individuals- can be beneficial at the level of the group. For example, a large group is better protected against predators than a small group, and a group of individuals dividing certain tasks may be more efficient than a group of individuals that perform all tasks separately. A cooperating group can thus reach a higher reproduction than a group of non-cooperating individuals. However, even though cooperation increases fitness at the level of the group, it is difficult to explain the evolution of cooperation: within a cooperative group, non-cooperative individuals, which still do profit from other, cooperating, individuals will have more resources to spend on reproduction, and thus are predicted to have a higher fitness. Natural selection will thus select these cheaters until there are no cooperating individuals left.

    Hamilton’s kin-selection theory predicts that stable cooperation can evolve when cooperation is directed with a higher probability towards genetically related individuals (kin) than towards unrelated individuals. In his formulized condition (rB - C > 0), cooperation is stable when the cost of helping (expressed as the number of offspring not produced because of the cooperative allele) is lower than the benefit (the number of additional offspring as a consequence of the cooperative allele), multiplied by the average relatedness of the individuals that receive the help. Kin-selection theory is not the only theory that can explain cooperation, but is generally accepted as an important factor in many forms of cooperation. One mechanism to direct help preferentially towards kin is population viscosity. Little dispersal results in progeny and ancestors staying close together in a group. If individuals are more motile, active kin discrimination becomes important. In order to direct cooperation preferentially towards kin, many organisms have developed specialized genetic kin recognition mechanisms, based on one or more polymorphic recognition loci. These organisms only cooperate with individuals that partially or fully match their own recognition genes. Crozier made a model based on marine invertebrates that form colonies. When colonies are close to each other they cooperatively fuse with neighbouring colonies when they are clonally related, or actively compete when they are less related. The decision to cooperate is based on genetic allorecognition. Crozier’s model predicted that if fusion increases fitness, common alleles will be favoured since individuals with common recognition alleles will fuse more often. This will lead to selection of the most frequent recognition alleles until recognition polymorphism disappears completely. Thus, there is a cost of allorecognition that may reduce the genetic variation upon which allorecognition crucially relies, a prediction now known as ‘Crozier’s paradox’. An important hypothesis that can solve this paradox is to incorporate the effect of cheating. Cheating will lead to a cost to the group of cooperating individuals and therefore can impose selection pressure to maintain allorecognition. Another hypothesis is that allorecognition diversity may be selected for another function.

    Multicellularity is an extreme example of cooperation: the cells of an individual usually show division of labour, and altruism is strong because only a fraction of the cells reach the germline. A multicellular individual thus essentially is a cooperating group of cells, and evolution acts at different levels. The multicellular individual gets selected based on its fitness compared to the multicellular individuals it competes with, while at the same time the cells within the multicellular individual are under natural selection. This can lead to a potential conflict, where cheating cells evolve that have a higher fitness relative to other cells within the individual, but at the same time reduce the fitness of the multicellular individual. Theory predicts that a high relatedness among the cells of an individual reduces the opportunities for such cheating cells. Consistent with this hypothesis, there are some important mechanisms, which maintain high relatedness observed in multicellular organisms. One mechanism is regular single-celled bottlenecks in the lifecycle such as spores or seeds or zygotes from which multicellular individuals develop by mitotic division. Another important mechanism to maintain the high relatedness after the single-celled bottleneck is allorecognition to prevent fusion with non-self cells. Allorecognition is found in most multicellular organisms, but seems most relevant for organisms in which fusion between individuals or aggregation of cells is a notable part of their lifecycle.

    In this thesis, I have used filamentous ascomycete fungi as a model for the evolution of stable multicellularity and allorecognition. The fungi have regular single-celled bottlenecks in the form of spore formation, from which they develop by clonal division of the nuclei to form a tubular network known as the fungal mycelium or colony. An interesting aspect of fungal growth is that the mycelium is not clearly divided into cell compartments, with the result that cytoplasm and nuclei can freely move through parts of the colony. This implies that organelles (nuclei, mitochondria), and not cells, are the main potential selective unit below the individual. Another important feature of fungi is that fungal colonies can fuse. Whether neighbouring colonies fuse or reject each other is determined by a highly polymorphic genetic allorecognition mechanism.

    In this thesis, I have used these fungi to address the theoretical problem identified by Crozier, the evolutionary stability of genetic kin recognition. We first tested whether fusion between colonies indeed is beneficial compared to allorecognition, and whether this can lead to erosion of allorecognition diversity (chapter 2). We used the ascomycete fungus Neurospora crassa, a well-established model species for genetic research, of which numerous strains are available of different allotype. We found that cultures grown from a single allotype have a higher spore production than cultures grown from a mixture of different allotypes. This shows that fusion is beneficial relative to allorecognition. We determined the precise causes of this relative cost of allorecognition, by using a fusion mutant that partially mimics the effect of allorecognition. Colonies remain separated from each other, similar to colonies separated due to allorecognition. However, in contrast to confrontations between colonies with a different allotype, in which part of the mycelium is sacrificed in a cell death reaction, in confrontations between different colonies of the fusion mutant, there is no active rejection. This comparison showed that the benefit of fusion is due not only to absence of mutual antagonism, which occurs upon allorecognition, but also to an increase in colony size per se. We then experimentally demonstrated that the benefit of fusion selects against allorecognition diversity, as predicted by Crozier. We show that there is a positive correlation between the frequency of an allotype and its competitive fitness, thus showing that positive frequency dependent selection acts on allotype diversity, thus leading to erosion of allotype diversity.

    In the remaining part of the thesis, I have used different ascomycete fungus models to test various hypotheses to explain the evolutionary stability of allorecognition. One hypothesis considers allorecognition as a means to protect against cheating genotypes, genotypes that have a competitive advantage in combination with a wildtype genotype, but that reduce total reproductive output (chapter 3). According to recent theoretical models that simulate the evolution of allorecognition in combination with the possibility of somatic cheating, high allorecognition diversity can evolve in combination with low frequencies of cheating. The main condition is that cheating can evolve from cooperative genotypes. In order to test the hypothesis that cheating is a realistic threat to multicellular growth in fungi, we used an experimental evolution approach with N. crassa that maximised the potential for cheating genotypes by selecting under low relatedness, conditions: a high inoculation density, complete mixing at each transfer and in the absence of allorecognition. Within less than 300 generations, all eight replicate lines we evolved under these conditions significantly decreased their average asexual spore production. This yield reduction was caused by genotypes that matched the criteria for cheating: they had increased competitive fitness relative to a cooperative ancestral type, but spore production was significantly decreased when grown in mono culture or together with a cooperative type. A parallel control experiment, in which relatedness was kept high within the colony by using a fusion mutant, did not result in a reduction in asexual spore yield, showing that maintaining high relatedness provides efficient protection against cheating. From these results we can conclude that cheating can evolve quickly from cooperative genotypes, but that cheating only is selected when relatedness is low. This explains that cheating genotypes are generally not picked up from nature, since relatedness will usually be higher under natural conditions. First, the extremely high density used in our experiments is unlikely to occur in nature, so that there is more clonal outgrowth relative to fusion. Second, the high diversity of allorecognition alleles observed in nature will increase the average relatedness among the nuclei of a single individual. At the same time, the threat of cheating creates selection pressure to maintain allorecognition.

    A different hypothesis, specific to fungi, is the possibility that allorecognition provides protection against cytoplasmic cheaters (chapter 4). Usually, mitochondria are restricted in their movement by cell compartments, so that there is selection at the level below that of the cells. In fungi, mitochondria can move through the mycelium similar to the nuclei. For this reason, mitochondria can be selected within a fungal colony similar to the way nuclei can be selected within a fungal colony. We studied the evolutionary dynamics of mutant mitochondria that cause senescence in Neurospora intermedia, a species closely related to N. crassa. The mitochondria mutate under the influence of a natural occurring mitochondrial plasmid that acts as a mutagen. The mutated mitochondria have a selective advantage within the fungal colony, which allows them to increase in frequency at the cost of colony fitness. Once the mutated mitochondria reach a high frequency, the colony dies. Therefore, these mitochondrial mutants are typical cheaters, which increase their own relative fitness at the cost of the colony. We performed evolution experiments where we varied relatedness by varying fusion and bottleneck size. We show that reduction of the bottleneck size reduces the predictability of selection of mutant mitochondria. Then, we show that evolution with a fusion mutant effectively selects against mutant mitochondria and prevents senescence of the cultures. In a following experiment we then show that allorecognition can prevent or delay senescence in a similar way as what happens in cultures with a fusion mutant. These experiments confirmed that cheating mitochondrial genotypes provide a realistic threat to fungal multicellularity and that allorecognition can help keeping these mutants at a low frequency.

    Although the selective pressure by cheating appears to be sufficient to maintain the allorecognition diversity observed in fungi, it does not exclude the hypothesis that allorecognition diversity can also be the result of selection for another function. In chapter 5, I describe the highly polymorphic ­het-c locus in Podospora anserina. The het-c locus determines allorecognition together with two unlinked loci termed het-d and het-e. Each het-c allele is incompatible with a specific subset of the het-d and het-e alleles. We found that the het-c allorecognition gene is under diversifying selection and more polymorphic than most other fungal allorecognition genes. Several aspects hint to a possible function in pathogen recognition for the het-c, het-d and het-e allorecognition system, such as its high variability and structural and sequence homologies to plant defence genes. Therefore, we argue that diversity in these genes may be selected for both maintaining allorecognition and pathogen recognition. The characteristics of these genes seem an exception and have not been found for other fungal allorecognition genes. The functioning of these genes in pathogen recognition and defence remains to be demonstrated. So although these results are interesting, cheating remains the most probable solution to explain the evolution of allorecognition diversity.

    The results described in this thesis emphasize the influence of somatic cheating on the evolution of allorecognition in fungi. Fungi are economically and medically very important for society. Therefore, the results described in this thesis are very useful since they give new insight in how high relatedness can keep fungal growth stable if this is desired and how cheating might be useful to use against undesired fungal growth. Finally, I discuss that cheating is a risk in most multicellular organisms and that allorecognition is very important to prevent such cheating genotypes from spreading between individuals.

    Natural Variation of Heterokaryon Incompatibility Gene het-c in Podospora anserina Reveals Diversifying Selection
    Bastiaans, E. ; Debets, A.J.M. ; Aanen, D.K. ; Diepeningen, A.D. van; Saupe, S.J. ; Paoletti, M. - \ 2014
    Molecular Biology and Evolution 31 (2014)4. - ISSN 0737-4038 - p. 962 - 974.
    plant immune-system - glycolipid transfer protein - chestnut blight fungus - amino-acid sites - vegetative incompatibility - neurospora-crassa - cell-death - cryphonectria-parasitica - membrane interaction - filamentous fungi
    In filamentous fungi, allorecognition takes the form of heterokaryon incompatibility, a cell death reaction triggered when genetically distinct hyphae fuse. Heterokaryon incompatibility is controlled by specific loci termed het-loci. In this article, we analyzed the natural variation in one such fungal allorecognition determinant, the het-c heterokaryon incompatibility locus of the filamentous ascomycete Podospora anserina. The het-c locus determines an allogenic incompatibility reaction together with two unlinked loci termed het-d and het-e. Each het-c allele is incompatible with a specific subset of the het-d and het-e alleles. We analyzed variability at the het-c locus in a population of 110 individuals, and in additional isolates from various localities. We identified a total of 11 het-c alleles, which define 7 distinct incompatibility specificity classes in combination with the known het-d and het-e alleles. We found that the het-c allorecognition gene of P. anserina is under diversifying selection. We find a highly unequal allele distribution of het-c in the population, which contrasts with the more balanced distribution of functional groups of het-c based on their allorecognition function. One explanation for the observed het-c diversity in the population is its function in allorecognition. However, alleles that are most efficient in allorecognition are rare. An alternative and not exclusive explanation for the observed diversity is that het-c is involved in pathogen recognition. In Arabidopsis thaliana, a homolog of het-c is a pathogen effector target, supporting this hypothesis. We hypothesize that the het-c diversity in P. anserina results from both its functions in pathogen-defense, and allorecognition
    Regular bottlenecks and restrictions to somatic fusion prevent the accumulation of mitochondrial defects in Neurospora
    Bastiaans, E. ; Aanen, D.K. ; Debets, A.J.M. ; Hoekstra, R.F. ; Lestrada, B. ; Maas, M.F.P.M. - \ 2014
    Philosophical Transactions of the Royal Society B. Biological sciences 369 (2014)1646. - ISSN 0962-8436
    vegetative incompatibility - filamentous fungi - dna mutations - hyphal fusion - evolution - populations - senescence - intermedia - selection - crassa
    The replication and segregation of multi-copy mitochondrial DNA (mtDNA) are not under strict control of the nuclear DNA. Within-cell selection may thus favour variants with an intracellular selective advantage but a detrimental effect on cell fitness. High relatedness among the mtDNA variants of an individual is predicted to disfavour such deleterious selfish genetic elements, but experimental evidence for this hypothesis is scarce. We studied the effect of mtDNA relatedness on the opportunities for suppressive mtDNA variants in the fungus Neurospora carrying the mitochondrial mutator plasmid pKALILO. During growth, this plasmid integrates into the mitochondrial genome, generating suppressive mtDNA variants. These mtDNA variants gradually replace the wild-type mtDNA, ultimately culminating in growth arrest and death. We show that regular sequestration of mtDNA variation is required for effective selection against suppressive mtDNA variants. First, bottlenecks in the number of mtDNA copies from which a 'Kalilo' culture started significantly increased the maximum lifespan and variation in lifespan among cultures. Second, restrictions to somatic fusion among fungal individuals, either by using anastomosis-deficient mutants or by generating allotype diversity, prevented the accumulation of suppressive mtDNA variants. We discuss the implications of these results for the somatic accumulation of mitochondrial defects during ageing
    Sex-linked transcriptional divergence in the hermaphrodite fungus Neurospora tetrasperma
    Samils, N. ; Gioti, A. ; Karlsson, M. ; Sun, Y.Y. ; Kasuga, T. ; Bastiaans, E. ; Wang, Z. ; Li, N. ; Townsend, J.P. ; Johannesson, H. - \ 2013
    Proceedings of the Royal Society. B: Biological Sciences 280 (2013)1764. - ISSN 0962-8452
    biased gene-expression - mating-type chromosomes - false discovery rates - x-chromosome - evolution - crassa - recombination - drosophila - microarrays - selection
    In the filamentous ascomycete Neurospora tetrasperma, a large (approx. 7 Mbp) region of suppressed recombination surrounds the mating-type (mat) locus. While the remainder of the genome is largely homoallelic, this region of recombinational suppression, extending over 1500 genes, is associated with sequence divergence. Here, we used microarrays to examine how the molecular phenotype of gene expression level is linked to this divergent region, and thus to the mating type. Culturing N. tetrasperma on agar media that induce sexual/female or vegetative/male tissue, we found 196 genes significantly differentially expressed between mat A and mat a mating types. Our data show that the genes exhibiting mat-linked expression are enriched in the region genetically linked to mating type, and sequence and expression divergence are positively correlated. Our results indicate that the phenotype of mat A strains is optimized for traits promoting sexual/female development and the phenotype of mat a strains for vegetative/male development. This discovery of differentially expressed genes associated with mating type provides a link between genotypic and phenotypic divergence in this taxon and illustrates a fungal analogue to sexual dimorphism found among animals and plants.
    Phylogenetic and biological species diversity within the Neurospora tetrasperma complex
    Menkis, A. ; Bastiaans, E. ; Jacobson, D.J. ; Johannesson, H. - \ 2009
    Journal of Evolutionary Biology 22 (2009)9. - ISSN 1010-061X - p. 1923 - 1936.
    mating-type chromosome - het-c locus - natural-populations - sexual dysfunction - model eukaryote - fungi - recognition - evolution - strains - heterothallism
    The objective of this study was to explore the evolutionary history of the morphologically recognized filamentous ascomycete Neurospora tetrasperma, and to reveal the genetic and reproductive relationships among its individuals and populations. We applied both phylogenetic and biological species recognition to a collection of strains representing the geographic and genetic diversity of N. tetrasperma. First, we were able to confirm a monophyletic origin of N. tetrasperma. Furthermore, we found nine phylogenetic species within the morphospecies. When using the traditional broad biological species recognition all investigated strains of N. tetrasperma constituted a single biological species. In contrast, when using a quantitative measurement of the reproductive success, incorporating characters such as viability and fertility of offspring, we found a high congruence between the phylogenetic and biological species recognition. Taken together, phylogenetically and biologically defined groups of individuals exist in N. tetrasperma, and these should be taken into account in future studies of its life history traits.
    Identification of the het-r vegetative incompatibility gene of Podospora anserina as a member of the fast evolving HNWD gene family
    Chevanne, D. ; Bastiaans, E. ; Debets, A.J.M. ; Saupe, S.J. ; Clave, C. ; Paoletti, M. - \ 2009
    Current Genetics 55 (2009)1. - ISSN 0172-8083 - p. 93 - 102.
    programmed cell-death - chestnut blight fungus - non-self recognition - heterokaryon incompatibility - neurospora-crassa - filamentous fungi - virus transmission - protein - locus - domain
    In fungi, vegetative incompatibility is a conspecific non-self recognition mechanism that restricts formation of viable heterokaryons when incompatible alleles of specific het loci interact. In Podospora anserina, three non-allelic incompatibility systems have been genetically defined involving interactions between het-c and het-d, het-c and het-e, het-r and het-v. het-d and het-e are paralogues belonging to the HNWD gene family that encode proteins of the STAND class. HET-D and HET-E proteins comprise an N-terminal HET effector domain, a central GTP binding site and a C-terminal WD repeat domain constituted of tandem repeats of highly conserved WD40 repeat units that define the specificity of alleles during incompatibility. The WD40 repeat units of the members of this HNWD family are undergoing concerted evolution. By combining genetic analysis and gain of function experiments, we demonstrate that an additional member of this family, HNWD2, corresponds to the het-r non-allelic incompatibility gene. As for het-d and het-e, allele specificity at the het-r locus is determined by the WD repeat domain. Natural isolates show allelic variation for het-r
    Two high-density AFLP linkage maps of Zea mays L. : analysis of distribution of AFLP markers
    Vuylsteke, M. ; Mank, R. ; Antonise, R. ; Bastiaans, E. ; Senior, M.L. ; Stuber, C.W. ; Melchinger, A.E. ; Lubberstedt, T. ; Xia, X.C. ; Stam, P. ; Zabeau, M. - \ 1999
    Theoretical and Applied Genetics 99 (1999). - ISSN 0040-5752 - p. 921 - 935.
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