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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    Biomarkers for grain yield stability in rice under drought stress
    Melandri, Giovanni ; AbdElgawad, Hamada ; Riewe, David ; Hageman, Jos A. ; Asard, Han ; Beemster, Gerrit T.S. ; Kadam, Niteen ; Jagadish, Krishna ; Altmann, Thomas ; Ruyter-Spira, Carolien ; Bouwmeester, Harro - \ 2020
    Journal of Experimental Botany 71 (2020)2. - ISSN 0022-0957 - p. 669 - 683.
    Oryza sativa - Drought - leaf oxidative stress status - leaf primary metabolism - PLSR - reproductive stage

    Crop yield stability requires an attenuation of the reduction of yield losses caused by environmental stresses such as drought. Using a combination of metabolomics and high-throughput colorimetric assays, we analysed central metabolism and oxidative stress status in the flag leaf of 292 indica rice (Oryza sativa) accessions. Plants were grown in the field and were, at the reproductive stage, exposed to either well-watered or drought conditions to identify the metabolic processes associated with drought-induced grain yield loss. Photorespiration, protein degradation, and nitrogen recycling were the main processes involved in the drought-induced leaf metabolic reprogramming. Molecular markers of drought tolerance and sensitivity in terms of grain yield were identified using a multivariate model based on the values of the metabolites and enzyme activities across the population. The model highlights the central role of the ascorbate-glutathione cycle, particularly dehydroascorbate reductase, in minimizing drought-induced grain yield loss. In contrast, malondialdehyde was an accurate biomarker for grain yield loss, suggesting that drought-induced lipid peroxidation is the major constraint under these conditions. These findings highlight new breeding targets for improved rice grain yield stability under drought.

    Association mapping and genetic dissection of drought-induced canopy temperature differences in rice
    Melandri, Giovanni ; Prashar, Ankush ; Mccouch, Susan R. ; Linden, Gerard Van Der; Jones, Hamlyn G. ; Kadam, Niteen ; Jagadish, Krishna ; Bouwmeester, Harro ; Ruyter-Spira, Carolien ; Dhankher, Om - \ 2020
    Journal of Experimental Botany 71 (2020)4. - ISSN 0022-0957 - p. 1614 - 1627.
    Drought-stressed plants display reduced stomatal conductance, which results in increased leaf temperature by limiting transpiration. In this study, thermal imaging was used to quantify the differences in canopy temperature under drought in a rice diversity panel consisting of 293 indica accessions. The population was grown under paddy field conditions and drought stress was imposed for 2 weeks at flowering. The canopy temperature of the accessions during stress negatively correlated with grain yield (r= –0.48) and positively with plant height (r=0.56). Temperature values were used to perform a genome-wide association (GWA) analysis using a 45K single nucleotide polynmorphism (SNP) map. A quantitative trait locus (QTL) for canopy temperature under drought was detected on chromosome 3 and fine-mapped using a high-density imputed SNP map. The candidate genes underlying the QTL point towards differences in the regulation of guard cell solute intake for stomatal opening as the possible source of temperature variation. Genetic variation for the significant markers of the QTL was present only within the tall, low-yielding landraces adapted to drought-prone environments. The absence of variation in the shorter genotypes, which showed lower leaf temperature and higher grain yield, suggests that breeding for high grain yield in rice under paddy conditions has reduced genetic variation for stomatal response under drought.
    Understanding drought tolerance in rice by the dissection and genetic analysis of leaf metabolism, oxidative stress status and stomatal behavior
    Melandri, Giovanni - \ 2019
    Wageningen University. Promotor(en): H.J. Bouwmeester, co-promotor(en): C. Ruyter-Spira. - Wageningen : Wageningen University - ISBN 9789463806022 - 181

    In Chapter 1, I explain that in the coming decades, drought episodes associated with climate change will be more frequent and erratic. Under this scenario, increasing or maintaining crop yields to meet the growing global food demand will become gradually more difficult. Rice (Oryza sativa), a staple food for more than half of the world’s population, shows the greatest sensitivity to water limitation among the cereal crops. Improving drought tolerance in rice by limiting the stress-induced yield penalties is pivotal for global food security.

    Drought stress impacts the physiology of plants and disrupts cellular homeostasis leading to metabolic alterations and increased oxidative stress. In this thesis, I investigate how drought- induced changes in rice physiology, central metabolism and oxidative stress status impact crop growth and yield. I also exploit the genetic diversity of a large panel of indica rice accessions to map genes and genomic regions associated with the quantitative variation in metabolic and physiological traits important for drought tolerance.

    In Chapter 2, I study the physiological, metabolic and antioxidative responses to drought in three indica rice varieties selected for their contrasting levels of tolerance/susceptibility to the stress. The analysis was conducted during both the vegetative and reproductive stages and different mechanisms of tolerance to drought were identified between the different tolerant varieties and between stages. This study provides a framework for the exploration of the genetic control of these mechanisms of tolerance to drought.

    In Chapter 3, I analyse the stress-induced changes in flag leaf central metabolism and oxidative stress status in ~300 indica rice accessions exposed to drought in the field at the reproductive stage. Photorespiration, protein degradation and nitrogen recycling were identified as the main flag leaf metabolic processes induced by drought. By integrating the metabolite data and the oxidative stress status of the accessions I showed that the activity of specific enzymatic antioxidants is important to limit the metabolic processes associated with drought stress which have a negative impact on grain yield. Finally, the levels of metabolites and oxidative stress markers/enzymes were also used to generate a multivariate model that accurately predicts grain yield loss across the accessions. The best predictors of this model can be used as biomarkers for grain yield stability in rice under drought.

    In Chapter 4, I quantify the differences in transpiration among the same accessions used in Chapter 3 by measuring canopy temperature, a proxy for stomatal conductance, in the field. Canopy temperature under drought at the reproductive stage was negatively correlated with the grain yield performance of the accessions, proving that leaf temperature under stress is a good predictor of drought tolerance that can be used to accelerate physiological selection in plant breeding. In addition, association mapping of canopy temperature data revealed a QTL associated with temperature differences under drought. Genetic variation for the significant markers of the QTL was present only within the tall, low-yielding landraces of rice adapted to drought-prone environments. This study confirms that these old varieties and landraces represent a strategic reservoir of genetic variation that can be tapped into for developing new varieties that are physiologically adapted to environments with unpredictable and variable water availability.

    In Chapter 5, I show that the multivariate model based on the set of metabolites and oxidative stress markers/enzymes developed in Chapter 3 also accurately predicts grain yield per se under well-watered and drought conditions in ~270 accessions of the population. The latter model predicted grain yield more accurately than a genomics-based model that I developed for the same genotypes. Finally, the best metabolic and enzymatic model predictors of grain yield were used as traits in a GWA study and the resulting associations allowed me to identify genetic markers that can be used in breeding to improve rice grain yield under optimal conditions and/or grain yield/yield stability under drought stress.

    Finally, in Chapter 6, I discuss the main findings of this thesis, connecting the results of the different experimental chapters and highlighting how they can be used to improve drought tolerance in rice.

    Plant host and drought shape the root associated fungal microbiota in rice
    Andreo-Jimenez, Beatriz ; Vandenkoornhuyse, Philippe ; Lê Van, Amandine ; Heutinck, Arvid ; Duhamel, Marie ; Kadam, Niteen ; Jagadish, Krishna ; Ruyter-Spira, Carolien ; Bouwmeester, Harro - \ 2019
    PeerJ 2019 (2019)9. - ISSN 2167-8359
    Drought - Fungi - Host - Microbiota - Oryza sativa (rice) - Yield

    Background and Aim. Water is an increasingly scarce resource while some crops, such as paddy rice, require large amounts of water to maintain grain production. A better understanding of rice drought adaptation and tolerance mechanisms could help to reduce this problem. There is evidence of a possible role of root-associated fungi in drought adaptation. Here, we analyzed the endospheric fungal microbiota composition in rice and its relation to plant genotype and drought. Methods. Fifteen rice genotypes (Oryza sativa ssp. indica) were grown in the field, under well-watered conditions or exposed to a drought period during flowering. The effect of genotype and treatment on the root fungal microbiota composition was analyzed by 18S ribosomal DNA high throughput sequencing. Grain yield was determined after plant maturation. Results. There was a host genotype effect on the fungal community composition. Drought altered the composition of the root-associated fungal community and increased fungal biodiversity. The majority of OTUs identified belonged to the Pezizomycotina subphylum and 37 of these significantly correlated with a higher plant yield under drought, one of them being assigned to Arthrinium phaeospermum. Conclusion. This study shows that both plant genotype and drought affect the rootassociated fungal community in rice and that some fungi correlate with improved drought tolerance. This work opens new opportunities for basic research on the understanding of how the host affects microbiota recruitment as well as the possible use of specific fungi to improve drought tolerance in rice.

    The mechanism underlying strigolactone diversification in sorghum and its role in resistance against the parasitic weed Striga hermonthica
    Shimels, Mahdere Z. - \ 2019
    Wageningen University. Promotor(en): H.J. Bouwmeester, co-promotor(en): C.P. Ruyter-Spira. - Wageningen : Wageningen University - ISBN 9789463950916 - 153

    Striga hermonthica (Striga) is a parasitic plant that attaches to the roots of a host plant from which it drains nutrients and water to complete its life cycle. Sorghum is one of the host plants that is greatly affected by Striga infestation which can result in up to 70-100% yield losses. In Chapter 1 of this thesis, I discuss the challenges of controlling Striga infestation, the different Striga resistance mechanisms, with the emphasis on Low Germination Stimulant activity (LGS) and factors affecting this trait, strigolactones. Strigolactones are the key player in inducing the germination of Striga seeds by serving as a signaling molecule for host presence when exuded into the rhizosphere by the host plant. The current knowledge on their evolution, biosynthesis and diversification is extensively discussed. Furthermore, their positive role in the rhizosphere, to induce a symbiotic relationship with arbuscular mycorrhizal (AM) fungi, and in regulating plant architecture is addressed.

    So far, more than 20 strigolactones have been identified from different plant species. Different blends of strigolactones can be produced by a single plant species. The amount and/or type of strigolactones produced/exuded differs from one plant species to the other. Moreover, the blend can also differ between different cultivars of the same species. In Chapter 2, we investigated the correlation of these differences with Striga resistance in sorghum. We showed that not the level but the type of strigolactone, in a stereospecific manner, determines the resistance of sorghum lines. Sorghum lines with high Striga germination stimulant activity predominantly produce 5-deoxystrigol while the low germination stimulant lines produce orobanchol. Since the purpose of sorghum to exude strigolactones into the rhizosphere is to attract AM-fungi, we looked at how the stereospecific difference of strigolactones affects this symbiotic relationship. I showed that the colonization by three AM fungi species was similar in the high- and low- germination stimulant sorghum lines. Furthermore, we provided evidence for the functional loss of an enzyme annotated as a sulfotransferase (Sobic.005G213600, SbSOT4A) and hypothesized it is responsible for the stereospecific difference of strigolactones between low- and high- germination stimulant sorghum lines.

    In Chapter 3, I further investigated the role of SbSOT4A in the total strigolactone profile of low-and high- germination stimulant lines. We provided evidence on how a sulfotransferase can possibly be involved in strigolactone biosynthesis. We showed that SbSOT4A is localized in the cytosol, suggesting it sulfates small molecules such as hormones. Using protein modeling and substrate docking, we showed the enzyme has good affinity to C18-hydroxycarlactone and proposed a new model on strigolactone biosynthesis in sorghum. In summary, this model proposes that in high germination stimulant lines, SbSOT4A is intact; after sulfation of C18-hydroxycarlactone it is further oxidized at the C19 position to form a carboxy group and upon the loss of the sulfate group ring closure occurs which results in the formation of 5-deoxystrigol. The loss of SbSOT4A function results in the lack of the sulfated intermediate; rather further oxidation of the C18 hydroxyl group results in a carbonyl; upon ring closure orobanchol will be produced which will lead to low germination stimulant activity towards Striga. We further showed that inhibition of sulfotransferases using Triclosan gave a similar phenotype which can be integrated as a tool to control Striga.

    These findings emphasize the importance of strigolactone diversification. Therefore, in Chapter 4, we further studied the production of sorgomol, a strigolactone produced by sorghum that can induce a higher level of Striga germination than 5-deoxystrigol. Using Recombinant Inbred Lines (RILs) derived from parents contrasting for the presence of sorgomol, we identified the locus that correlates with sorgomol production in sorghum. With further investigation using RNAseq and bulk segregant analysis, we narrowed down the list of candidate genes and presented evidences on the involvement of two priori candidate genes in sorgomol production in sorghum. I proposed the role of Sobic.008G106200, which encodes a cytochrome P450, in catalyzing the conversion of 5-deoxystrigol to sorgomol while Sobic.001G319900 is regulating the level of production.

    Strigolactone diversification is achieved by different modifications such as hydroxylation, acetylation, demethylation, esterification, decarboxylation, epoxidation and oxidation. The key players in catalyzing these steps are MAX1, CYP711A homologs that belong to the cytochrome P450 super family of enzymes. Sorghum has four MAX1 homologs and in Chapter 5, we characterized their response to phosphate starvation and their expression pattern in different sorghum parts such as root, lower stem, axillary buds and the flower head. Using phylogenetic tree analysis with functionally characterized MAX1 homologs from different plants, I predicted the part of the biosynthesis that are likely to be catalyzed by these MAX1 homologs from sorghum. I also showed their affinity to use carlactone as a substrate using a transient assay in Nicotiana benthamiana.

    In Chapter 6, I discuss the main highlights of the thesis, the challenges and future perspectives. Based on the fact that the success of Striga infestation is dependent on the type of strigolactones exuded by sorghum plants, I propose possible tools that can be used to eradicate Striga. I also address the concept of integrated Striga management with the emphasis on the cultural aspects of the farmers based on my personal observation during a field trip that gave me an opportunity to hear the farmer’s side of the Striga control measures.

    Essays on co-operatives’ idiosyncrasies : structure, performance, and membership
    Benos, Theo - \ 2019
    Wageningen University. Promotor(en): J.M.E. Pennings, co-promotor(en): Nikos Kalogeras; Ko de Ruyter. - Wageningen : Wageningen University - ISBN 9789463439381 - 223

    The idiosyncratic member-owned, principles-driven, and people-centered business model of co-operatives (co-ops) has persistently been adept at combining a social mission with economic goals, creating superior value for its member-users and benefiting society at large. Currently, co-ops occupy a strong socio-economic position globally (e.g., three million co-ops with a billion members and 100 million employees), and are treated by policymakers as vehicles for sustainable development. Still, while academic studies and policy reports on co-op issues abound, some co-op idiosyncrasies remain obscured or under-researched. Firstly, few studies have examined the relationship between co-op organizational attributes and features of mainstream businesses (e.g., market-oriented strategies). Secondly, extant research has neglected to accurately address the idiosyncratic nature of co-ops when investigating their performance, typically adopting a single-objective angle (e.g., profit-maximization) and omitting the social-membership standpoint (e.g., member benefits). Thirdly, the social component of membership has attracted limited attention in general. These knowledge gaps persist because co-ops have been overlooked by research in mainstream business disciplines (e.g., management, marketing). In this dissertation, we aim to illuminate such co-op idiosyncrasies and confront them with business features ingrained in conventional or other organizational forms (e.g., social enterprises). In so doing, we advocate a dual outlook, deliberating upon co-ops’ capacity and proclivity to attend to (often contradictory) business and social demands.

    In Chapter 2, we aim to examine the influence of idiomorphic co-op organizational attributes on co-op performance and on mainstream strategic attributes (market and brand orientation), as well as the influence of the latter on co-op performance. Motivated by a policy change, we develop an empirically grounded classification of traditional versus restructured co-op organizational attributes and argue that the restructured ones positively influence both market orientation and performance. We empirically test the attribute-performance relationships with agribusiness co-ops in two studies (Study 2 replicates Study 1 over time at a smaller scale). We exhibit that strategic attributes have a larger impact on performance than organizational attributes, although part of the latter (e.g., exit barriers, differentiated pricing) exert some influence on market orientation. We conclude that greater emphasis should be placed on customer-focused strategies like market and brand orientation, while reforms of organizational structure should be primarily geared toward stimulating member commitment in the long run.

    In Chapter 3, we aim to deliver a comprehensive dashboard for co-op performance assessment that reflects co-op specificities, accounting for multiple performance objectives and harmonizing business–social aspects. We concentrate on the agricultural domain, but we consider all sectors, in three phases. In phase 1, we consolidate empirical research on co-op performance metrics and create a preliminary framework, in which we detail five sub-categories. In phase 2, we employ a Delphi study with co-op experts to test the framework. As a result, we narrow it down to a workable bundle of three sub-categories. The first sub-category (i.e., BFA – Business Financial Appraisal) reflects the business aspects; the second (i.e., SMA – Subjective Membership Appraisal) conveys the social-membership viewpoint; and the third (i.e., OMA - Objective Membership Appraisal) solidifies the first two. In phase 3, we review comparable research efforts for an organizational form (i.e., social enterprises) that also blends business with social components and faces similar business–social challenges. This inquiry prompts a reinforcement of the social perspective with social value measurement elements beyond the co-op boundaries. The dashboard we eventually deliver serves as a “currency matrix” (a “medium of knowledge exchange” or common benchmark) for future empirical studies.

    In Chapter 4a, we aim to explore a core co-op threat (i.e., member-customer ostracism) relating to co-ops’ social environment, and develop a diagnostic tool. We adopt a member-customer perspective, conceptualize co-op ostracism, and argue that it elicits negative outcomes, regardless of the source (e.g., members, employees). Following a meticulous seven-step process and using different types of co-ops, we develop a reliable and valid diagnostic tool. We also find that co-op ostracism is fairly common in co-op life, hurting member-customers and the co-op alike. In Chapter 4b, we aim to delve into the toxic effects of co-op ostracism. We adopt a relationship marketing perspective and develop a conceptual model to empirically assess its’ influence on critical relational exchange and membership outcomes. Across three different co-op samples and domains (i.e., agribusiness, retail banking, consumer), we find support for our premise that co-op ostracism acts as a “relationship poison” for both member-customers and the co-op, despite the presence of other relationship-building (i.e., trust) or relationship-destroying accounts (i.e., social undermining). Still, we develop an “antidote” (a coping strategy) to buffer ostracism’s deleterious effects and empirically test it in an extra study with co-op members. Indeed, we show that coupling entitativity with cognitive capital attenuates ostracism’s impact.

    Overall, this dissertation builds on rich settings, collection procedures, data, and analysis methods, and sheds light on co-op idiosyncrasies that, together with mainstream business features, shelter unique co-op assets and condition co-ops’ sustainability. This dissertation will hopefully aid co-op leaders in making informed decisions about organizational and strategic attributes, documenting co-ops’ socio-economic impact consistently, and fending off a core social threat to the central co-op element, the membership.

    Distinct roles for strigolactones in cyst nematode parasitism of Arabidopsis roots
    Escudero Martinez, Carmen M. ; Guarneri, Nina ; Overmars, Hein ; Schaik, Casper van; Bouwmeester, Harro ; Ruyter-spira, Carolien ; Goverse, Aska - \ 2019
    European Journal of Plant Pathology 154 (2019)1. - ISSN 0929-1873 - p. 129 - 140.
    Phytohormones play an essential role in different stages of plant-nematode interactions. Strigolactones (SLs) are a novel class of plant hormones which play an important role in plant development. Furthermore, certain soil-inhabiting organisms exploit this plant molecule as allelochemical. However, whether SLs play a role in plant parasitism by nematodes is as yet unknown. This prompted us to investigate the potential role of SLs in different stages of the nematode life cycle using the beet cyst nematode Heterodera schachtii and Arabidopsis as a model system. We analyzed the effect of SLs on cyst nematode hatching, host attraction and invasion, and the establishment of a feeding relation upon infection of the SL deficient mutant max4-1 and the SL signaling mutant max2-1. In addition, infection assays were performed under phosphate shortage to enhance SL production and in the presence of the synthetic SL analog GR24. From this study, we can conclude that SLs do not contribute to cyst nematode hatching at the levels tested but that they do play a role in host attraction and subsequent invasion in a MAX2 dependent manner. Furthermore, we observed that increased levels of exogenous and endogenous SLs change the root invasion zone. Upon root infection, cyst nematode development was enhanced in both the max2-1 and max4-1 mutants due to the formation of enlarged feeding cells. These data provide evidence for distinct roles of SLs during cyst nematode parasitism of plant roots.
    The interaction of strigolactones with abscisic acid during the drought response in rice
    Haider, Imran ; Andreo-Jimenez, Beatriz ; Bruno, Mark ; Bimbo, Andrea ; Floková, Kristýna ; Abuauf, Haneen ; Ntui, Valentine Otang ; Guo, Xiujie ; Charnikhova, Tatsiana ; Al-Babili, Salim ; Bouwmeester, Harro J. ; Ruyter-Spira, Carolien - \ 2018
    Journal of Experimental Botany 69 (2018)9. - ISSN 0022-0957 - p. 2403 - 2414.
    Abscisic acid - Biosynthesis - Drought - DWARF27 - Rice - Strigolactones

    Both strigolactones (SLs) and abscisic acid (ABA) biosynthetically originate from carotenoids. Considering their common origin, the interaction of these two hormones at the biosynthetic and/or regulatory level may be anticipated. Here we show that, in rice, drought simultaneously induces SL production in the root, and ABA production and the expression of SL biosynthetic genes in the shoot. Under control conditions, the ABA concentration was higher in shoots of the SL biosynthetic rice mutants dwarf10 (d10) and d17 than in wild-type plants, while a similar trend was observed for the SL perception mutant d3. These differences were enhanced under drought. However, drought did not result in an increase in leaf ABA content in the rice mutant line d27, carrying a mutation in the gene encoding the first committed enzyme in SL biosynthesis, to the same extent as in the other SL mutants and the wild type. Accordingly, d10, d17, and d3 lines were more drought tolerant than wild-type plants, whereas d27 displayed decreased tolerance. Finally, overexpression of OsD27 in rice resulted in increased levels of ABA when compared with wild-type plants. We conclude that the SL and ABA pathways are connected with each other through D27, which plays a crucial role in determining ABA and SL content in rice.

    Harnessing a 'currency matrix' for performance measurement in cooperatives : A multi-phased study
    Benos, Theo ; Kalogeras, Nikos ; Wetzels, Martin ; Ruyter, Ko de; Pennings, Joost M.E. - \ 2018
    Sustainability 10 (2018)12. - ISSN 2071-1050
    Cooperatives - Delphi method - Extensive review - Interdisciplinary dialogue - Performance measurement - Social enterprises - Socio-economic impact

    The cooperative organizational form is by nature a sustainable one, which has proved to be resilient in the face of crises and a solid lever in addressing present-day societal challenges. Still, little is known about its socio-economic impact. Also, despite the plethora of studies on cooperative performance, research remains inconclusive about how to best measure it. In fact, scholarly work has largely favored the use of appraisal tools reflecting those of investor-owned firms (IOFs), having undermined the dual idiosyncratic nature of the cooperative organizational form, which is manifest in the business and social-membership objectives. The goal of this article is to fill these gaps by delivering a comprehensive dashboard for cooperative performance assessment that harmonizes business-social aspects and catalogs the basic components for future attempts. To reach this goal, we used an extensive review of empirical research in cooperative performance (phase 1) and a Delphi study with 14 experts (phase 2). In addition, we reviewed comparable research efforts for a business form (social enterprises) that combines business with social goals and faces similar challenges (phase 3). This inquiry was particularly insightful for the social perspective and the overlooked role of cooperatives as a socially-embedded organizational form that hardly documents its societal impact and outreach.

    Agrobacterium rhizogenes transformed calli of the holoparasitic plant Phelipanche ramosa maintain parasitic competence
    Libiaková, Dagmara ; Ruyter-Spira, Carolien ; Bouwmeester, Harro J. ; Matusova, Radoslava - \ 2018
    Plant Cell, Tissue and Organ Culture: an international journal on in vitro culture of higher plants 135 (2018)2. - ISSN 0167-6857 - p. 321 - 329.
    Genetic transformation - Holoparasitic plant - In vitro - Phelipanche ramosa - Regeneration
    Phelipanche and Orobanche spp. (broomrapes) are economically important parasitic weeds, causing severe damage to many agricultural crops. However, conventional methods to control these parasitic weeds are often not effective. Targeting molecular and biochemical processes involved in the establishment of the connection between the parasite and the host may offer a new perspective for control. However, progress in the understanding of these processes is hampered by the fact that genetic transformation and regeneration of these parasites is difficult if not impossible due to their specific lifecycle. Phelipanche and Orobanche spp. are holoparasites that need to attach to the roots of a host plant to get their assimilates, nutrients and water to develop and reproduce. The present study describes a highly efficient genetic transformation and regeneration protocol for the root holoparasitic Phelipanche ramosa. We present a new transformation system for P. ramosa using Agrobacterium rhizogenes MSU440 carrying a non-destructive selection marker gene coding for a red fluorescent protein (DsRed1). Using this protocol up to 90% transformation efficiency was obtained. We transformed 4 weeks old P. ramosa calli and transgenic calli expressing DsRed1 were then cultured on host plants. For the first time, we present shoot and flower development of the transgenic parasitic plant P. ramosa after successful connection of transgenic calli with the host plant roots. Moreover, we also present, for the first time, growth and development of P. ramosa shoots and flowers in vitro in the absence of a host plant.
    Diagnosing member-customer ostracism in co-operatives and counterpoising its relationship-poisoning effects
    Benos, Theo ; Kalogeras, Nikos ; Ruyter, Ko de; Wetzels, Martin - \ 2018
    European Journal of Marketing 52 (2018)9/10. - ISSN 0309-0566 - p. 1778 - 1801.
    Co-operatives - Coping strategy - Membership - Ostracism - Relationship marketing - Relationship poison

    Purpose: This paper aims to examine a core member-customer threat in co-operatives (co-ops) by drawing from ostracism research, assessing co-op ostracism’s impact on critical membership and relational exchange outcomes and discussing why relationship marketing research needs to pay more attention to the overlooked role of implicit mistreatment forms in customer harm-doing. Design/methodology/approach: Three studies were conducted. In Study 1, ostracism in co-ops was explored, and a measurement scale for co-op ostracism was developed. In Study 2, the core conceptual model was empirically tested with data from members of three different co-ops. In Study 3, a coping strategy was integrated into an extended model and empirically tested with a new sample of co-op members. Findings: Ostracism is present in co-ops and “poisons” crucial relational (and membership) outcomes, despite the presence of other relationship-building or relationship-destroying accounts. Coupling entitativity with cognitive capital attenuates ostracism’s impact. Research limitations/implications: Inspired by co-ops’ membership model and inherent relational advantage, this research is the first to adopt a co-op member-customer perspective and shed light on an implicit relationship-destroying factor. Practical implications: Co-op decision makers might use the diagnostic tool developed in the paper to detect ostracism and fight it. Moreover, a novel coping strategy for how co-ops (or other firms) might fend off ostracism threats is offered in the article. Originality/value: The present study illuminates a dark side of a relationally profuse customer context, painting a more complete picture of relationship marketing determinants. Little attention has been given to ostracism as a distinct and important social behaviour in marketing research and to co-ops as a research context.

    The tomato MAX1 homolog, SlMAX1, is involved in the biosynthesis of tomato strigolactones from carlactone
    Zhang, Yanxia ; Cheng, Xi ; Wang, Yanting ; Díez-Simón, Carmen ; Flokova, Kristyna ; Bimbo, Andrea ; Bouwmeester, Harro J. ; Ruyter-Spira, Carolien - \ 2018
    New Phytologist 219 (2018)1. - ISSN 0028-646X - p. 297 - 309.
    cytochrome P450 (CYP) - didehydro-orobanchol isomers - MORE AXILLARY GROWTH 1 (MAX1) - orobanchol - solanacol - tomato strigolactones
    Strigolactones (SLs) are rhizosphere signalling molecules exuded by plants that induce seed germination of root parasitic weeds and hyphal branching of arbuscular mycorrhiza. They are also phytohormones regulating plant architecture. MORE AXILLARY GROWTH 1 (MAX1) and its homologs encode cytochrome P450 (CYP) enzymes that catalyse the conversion of the strigolactone precursor carlactone to canonical strigolactones in rice (Oryza sativa), and to an SL-like compound in Arabidopsis. Here, we characterized the tomato (Solanum lycopersicum) MAX1 homolog, SlMAX1. The targeting induced local lesions in genomes method was used to obtain Slmax1 mutants that exhibit strongly reduced production of orobanchol, solanacol and didehydro-orobanchol (DDH) isomers. This results in a severe strigolactone mutant phenotype in vegetative and reproductive development. Transient expression of SlMAX1 – together with SlD27, SlCCD7 and SlCCD8 – in Nicotiana benthamiana showed that SlMAX1 catalyses the formation of carlactonoic acid from carlactone. Plant feeding assays showed that carlactone, but not 4-deoxy-orobanchol, is the precursor of orobanchol, which in turn is the precursor of solanacol and two of the three DDH isomers. Inhibitor studies suggest that a 2-oxoglutarate-dependent dioxygenase is involved in orobanchol biosynthesis from carlactone and that the formation of solanacol and DDH isomers from orobanchol is catalysed by CYPs.
    Weerbaarder, guller en attractiever : naar een nieuwe aanpak voor het veen in het Lage Midden van Fryslân
    Ruyter, P. de; Vogelzang, T.A. ; Prins, H. - \ 2018
    Bureau Peter de Ruyter Landschapsarchitectuur - 32 p.
    Zeapyranolactone − A novel strigolactone from maize
    Charnikhova, Tatsiana V. ; Gaus, Katharina ; Lumbroso, Alexandre ; Sanders, Mark ; Vincken, Jean Paul ; Mesmaeker, Alain De; Ruyter-Spira, Carolien P. ; Screpanti, Claudio ; Bouwmeester, Harro J. - \ 2018
    Phytochemistry Letters 24 (2018). - ISSN 1874-3900 - p. 172 - 178.
    Maize (Zea mays) - NMR - Prep-HPLC–MS - Strigolactones - Zeapyranolactone
    The structure of a new strigolactone present in the root exudate and root extract of maize hybrid cv NK Falkone plants was elucidated and characterized as zeapyranolactone: Methyl.(E)-3-((4-methyl-5-oxo-2,5-dihydrofuran-2-yl)oxy)-2-(4,4,5-trimethyl-2-oxo-2,3,4,6,7,7a-hexahydrocyclopenta[b]pyran-7-yl)acrylate. Unlike any other strigolactone published so far, it contains a 4,4-dimethyltetrahydropyran-2-one as A ring. The impact of the elucidation of this structure on the earlier postulated biosynthetic pathway of another maize strigolactone, zealactone, is discussed.
    Blockchain for agriculture and food : Findings from the pilot study
    Ge, Lan ; Brewster, Christopher ; Spek, Jacco ; Smeenk, Anton ; Top, Jan ; Diepen, Frans van; Klaase, Bob ; Graumans, Conny ; Ruyter de Wildt, Marieke de - \ 2017
    Wageningen : Wageningen Economic Research (Wageningen Economic Research report 2017-112) - ISBN 9789463438179 - 33
    This report documents experiences and findings from the public private partnership (PPP) project ‘Blockchain for Agrifood’ that was started in March 2017. The project aims to contribute to a better understanding of the blockchain technology (BCT) and its implications for agrifood, especially how it can impact specific aspects of supply chains and what is needed to apply BCT in agrifood chains. A second aim of this project is to conceptualise and develop a proof of concept in an application based on a use case concerning table grapes from South Africa where BCT could be applied. This has been done by building a demonstrator that keeps track of different certificates involved in the table grapes supply chain. The code of this demonstrator is published at Github. Furthermore, the project explored issues regarding the relevance, applicability and implications of BCT for the agrifood sector through literature study and stakeholder consultation.
    Exploring the resistance against root parasitic plants in Arabidopsis and tomato
    Cheng, Xi - \ 2017
    Wageningen University. Promotor(en): H.J. Bouwmeester, co-promotor(en): C.P. Ruyter-Spira. - Wageningen : Wageningen University - ISBN 9789463437004 - 305
    plants - parasitic plants - arabidopsis thaliana - solanum lycopersicum - host parasite relationships - plant growth regulators - resistance - planten - parasitaire planten - arabidopsis thaliana - solanum lycopersicum - gastheer parasiet relaties - plantengroeiregulatoren - weerstand
    Root parasitic plant species such as broomrapes (Orobanche and Phelipanche spp.) and witchweeds (Striga spp.) are notorious agricultural weeds. They cause damage to crops by depriving them of water, nutrients and assimilates via a vascular connection. The difficulty in controlling root parasitic weeds is largely due to their intricate lifecycle and partially underground lifestyle. Their life cycle includes processes such as germination of the seed, the formation of the vascular connection with the host, the growth and development of the parasite after attachment and the emergence of shoots and flowers aboveground. The germination of many parasitic plants is induced by strigolactones that were recently shown to also be signalling compounds that stimulate mycorrhizal symbiosis. In addition, in the past few years, their role in plant development and plant defense has been established revealing them as a new class of plant hormones that exert their function likely in interaction with other hormones.
    The role of strigolactones and the fungal microbiome in rice during drought adaptation
    Andreo Jimenez, Beatriz - \ 2017
    Wageningen University. Promotor(en): H.J. Bouwmeester, co-promotor(en): C. Ruyter-Spira. - Wageningen : Wageningen University - ISBN 9789463437028 - 205
    drought resistance - drought - abiotic injuries - rice - oryza sativa - plant-microbe interactions - nutrient uptake - defence mechanisms - hormones - fungi - genes - droogteresistentie - droogte - abiotische beschadigingen - rijst - oryza sativa - plant-microbe interacties - voedingsstoffenopname (planten) - verdedigingsmechanismen - hormonen - schimmels - genen

    Rice is the most important food crop in the world, feeding over half the world’s population. However, rice water use efficiency, defined by units of yield produced per unit of water used, is the lowest of all crops. The aim of this thesis was to study the effect of plant hormones and the root microbiome on drought tolerance in rice. The new plant hormone, strigolactone, was shown to be upregulated under drought and to regulate drought tolerance in interaction with the drought-hormone abscisic acid. Using a large collection of rice genotypes grown in the field, we showed that the composition of the root associated fungal microbiome is determined by the rice genotype and can contribute to drought tolerance.

    Mutation in sorghum LOW GERMINATION STIMULANT 1 alters strigolactones and causes Striga resistance
    Gobena, Daniel ; Shimels, Mahdere ; Rich, Patrick J. ; Ruyter-Spira, Carolien ; Bouwmeester, Harro ; Kanuganti, Satish ; Mengiste, Tesfaye ; Ejeta, Gebisa - \ 2017
    Proceedings of the National Academy of Sciences of the United States of America 114 (2017)17. - ISSN 0027-8424 - p. 4471 - 4476.
    Gene - Sorghum - Stereochemistry - Striga - Strigolactone

    Striga is a major biotic constraint to sorghum production in semiarid tropical Africa and Asia. Genetic resistance to this parasitic weed is the most economically feasible control measure. Mutant alleles at the LGS1 (LOW GERMINATION STIMULANT 1) locus drastically reduce Striga germination stimulant activity. We provide evidence that the responsible gene at LGS1 codes for an enzyme annotated as a sulfotransferase and show that functional loss of this gene results in a change of the dominant strigolactone (SL) in root exudates from 5-deoxystrigol, a highly active Striga germination stimulant, to orobanchol, an SL with opposite stereochemistry. Orobanchol, although not previously reported in sorghum, functions in the multiple SL roles required for normal growth and environmental responsiveness but does not stimulate germination of Striga. This work describes the identification of a gene regulating Striga resistance and the underlying protective chemistry resulting from mutation.

    The role of endogenous strigolactones and their interaction with ABA during the infection process of the parasitic weed Phelipanche ramosa in tomato plants
    Cheng, Xi ; Floková, Kristýna ; Bouwmeester, Harro ; Ruyter-Spira, Carolien - \ 2017
    Frontiers in Plant Science 8 (2017). - ISSN 1664-462X
    Abscisic acid - Plant architecture - Post-attachment resistance - Root parasitic plant - Strigolactone
    The root parasitic plant species Phelipanche ramosa, branched broomrape, causes severe damage to economically important crops such as tomato. Its seed germination is triggered by host-derived signals upon which it invades the host root. In tomato, strigolactones (SLs) are the main germination stimulants for P. ramosa. Therefore, the development of low SL-producing lines may be an approach to combat the parasitic weed problem. However, since SLs are also a plant hormone controlling many aspects of plant development, SL deficiency may also have an effect on post-germination stages of the infection process, during the parasite-host interaction. In this study, we show that SL-deficient tomato plants (Solanum lycopersicum; SlCCD8 RNAi lines), infected with pre-germinated P. ramosa seeds, display an increased infection level and faster development of the parasite, which suggests a positive role for SLs in the host defense against parasitic plant invasion. Furthermore, we show that SL-deficient tomato plants lose their characteristic SL-deficient phenotype during an infection with P. ramosa through a reduction in the number of internodes and the number and length of secondary branches. Infection with P. ramosa resulted in increased levels of abscisic acid (ABA) in the leaves and roots of both wild type and SL-deficient lines. Upon parasite infection, the level of the conjugate ABA-glucose ester (ABA-GE) also increased in leaves of both wild type and SL-deficient lines and in roots of one SL-deficient line. The uninfected SL-deficient lines had a higher leaf ABA-GE level than the wild type. Despite the high levels of ABA, stomatal aperture and water loss rate were not affected by parasite infection in the SL-deficient line, while in wild type tomato stomatal aperture and water loss increased upon infection. Future studies are needed to further underpin the role that SLs play in the interaction of hosts with parasitic plants and which other plant hormones interact with the SLs during this process.
    Vechten tegen rijstvampiers : parasitaire planten bedreigen voedselzekerheid in Afrika
    Bastiaans, Lammert ; Tippe, Dennis ; Ruyter-Spira, Carolien - \ 2017

    Verwoestende parasitaire onkruiden richten voor miljoenen schade aan in de gewassen ten zuiden van de Sahara. Ze zuigen hun waardplanten uit als vampiers. Onderzoekers proberen deze ondergrondse profiteurs te dwarsbomen.

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