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.

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Unraveling molecular mechanisms underlying plant defense in response to dual insect attack : studying density-dependent effects
Kroes, A. - \ 2016
University. Promotor(en): Marcel Dicke; Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462577756 - 265 p.
016-3953 - arabidopsis thaliana - insect pests - herbivory - pest resistance - defence mechanisms - insect plant relations - molecular plant pathology - density - insectenplagen - herbivorie - plaagresistentie - verdedigingsmechanismen - insect-plant relaties - moleculaire plantenziektekunde - dichtheid

In the field, plants suffer from attack by herbivorous insects. Plants have numerous adaptations to defend against herbivory. Not only do these defense responses reduce performance of the feeding herbivore, they also result in the attraction of natural enemies of herbivores.

The majority of studies investigating plant-insect interactions addressed mainly the effects of attack by a single herbivore species on induced plant defenses. However, because plants are members of complex communities, plants are exposed to different insect attackers at the same time. Moreover, attacks by different herbivores interact at different levels of biological organization, ranging from the level of gene expression, phytohormone production and biochemical changes up to the individual level. Effects of plant responses to feeding by two or more herbivore species simultaneously might cascade through the community and thereby affect insect community composition.

The induction of plant defense responses is regulated by a network of signaling pathways that mainly involve the phytohormones jasmonic acid (JA), salicylic acid (SA) and ethylene (ET). The signaling pathways of the two phytohormones SA and JA interact antagonistically, whereas JA and ET signaling pathways can interact both synergistically and antagonistically in regulating plant defense responses. In general, JA-mediated signaling underlies defense responses against leaf-chewing herbivores, such as caterpillars, whereas phloem-feeding insects, such as aphids, mainly induce SA-regulated defenses.

When caterpillars and aphids simultaneously feed on the same host plant, crosstalk between phytohormonal signaling pathways may affect the regulation of plant defenses. Consequently, multiple insect herbivores feeding on plants interact indirectly through plant-mediated effects. Studies investigating molecular mechanisms underlying interference by multiple attacking insects with induced plant defenses will benefit studies on the ecological consequences of induced plant responses.

The aim of this thesis was to elucidate molecular mechanisms that underlie plant-mediated interactions between attacking herbivores from different feeding guilds, namely Brevicoryne brassicae aphids and Plutella xylostella caterpillars.

Because herbivore density affects the regulation of plant defense responses, it may also influence the outcome of multiple insect-plant interactions. To study if modulation of induced plant defenses in response to dual insect attack depends on insect density, plants were infested with two densities of aphids.

Responses of Arabidopsis thaliana plants to simultaneous feeding by aphids and caterpillars were investigated by combining analyses of phytohormone levels, defense gene expression, volatile emission, insect performance and behavioral responses of parasitoids. To better predict consequences of interactions between plants and multiple insect attackers for herbivore communities, the regulation of defense responses against aphids and caterpillars was also studied in the ecological model plant wild Brassica oleracea.

Transcriptomic changes of plants during multiple insect attack and their consequences for the plant’s interactions with members of the associated insect community take place at different time scales. Direct correlation of transcriptomic responses with community development is, therefore, challenging. However, detailed knowledge of subcellular mechanisms can provide tools to address this challenge.

One of the objectives of this thesis, therefore, was to investigate the involvement of phytohormonal signaling pathways and their interactions during defense responses against caterpillars or aphids at different densities, when feeding alone or simultaneously on the model plant A. thaliana. The studies show that aphids at different densities interfere in contrasting ways with caterpillar-induced defenses, which required both SA- and JA-signal-transduction pathways. Transcriptional analysis revealed that expression of the SA transcription factor gene WRKY70 was differentially affected upon infestation by aphids at low or high densities. Interestingly, the expression data indicated that a lower expression level of WRKY70 led to significantly higher MYC2 expression through SA-JA crosstalk. Based on these findings, it is proposed that by down-regulating WRKY70 expression, the plant activates JA-dependent defenses which could lead to a higher resistance against aphids and caterpillars.

Plutella xylostella caterpillars also influenced plant defense responses when feeding simultaneously with aphids. Caterpillar feeding affected aphid-induced defenses which had negative consequences for aphid performance. Induction of both ET- and JA-mediated defense responses is required for this interference. Moreover, aphid density also played an important role in the modulation by P. xylostella of aphid-induced defenses: P. xylostella caterpillars induced changes in levels of JA and its biologically active from, JA-Ile, only when feeding simultaneously with aphids at a high density.

To study the overall effect of dual herbivory on induced plant defenses, not only interference with induced direct defense, but also with induced indirect defenses was addressed in A. thaliana. We found a significant preference of the aphid parasitoid Diaeretiella rapae for volatiles from aphid-infested A. thaliana wild-type plants and ein2-1 (ET-insensitive) mutants. Interestingly, simultaneous feeding by P. xylostella caterpillars on wild-type plants increased D. rapae’s preference for odors from aphid-infested plants. However, upon disruption of the ET-signaling pathway, D. rapae did not distinguish between ein2-1 mutants infested by aphids or by both aphids and caterpillars. This showed that intact ET signaling is needed for caterpillar modulation of the attraction of D. rapae parasitoids.

On the other hand, attraction of the caterpillar parasitoid Diadegma semiclausum to volatiles emitted by A. thaliana plants simultaneously infested by caterpillars and aphids was influenced by the density of the feeding aphids. Biosynthesis and emission of the terpene (E,E)-α-farnesene could be linked to the observed preference of D. semiclausum parasitoids for the HIPV blend emitted by plants dually infested by caterpillars and aphids at a high density, compared to dually infested plants with a low aphid density.

Transcriptomic changes in the response of A. thaliana wild-type plants to simultaneous feeding by P. xylostella caterpillars and B. brassicae aphids compared to plants infested by P. xylostella caterpillars alone were assessed using a microarray analysis. I particularly addressed the question whether the transcriptomic response to simultaneously attacking aphids and caterpillars was dependent on aphid density and time since initiation of herbivory. The data show that in response to simultaneous feeding by P. xylostella caterpillars and B. brassicae aphids the number of differentially expressed genes was higher compared to plants on which caterpillars had been feeding alone. Additionally, specific genes were differentially expressed in response to aphids feeding at low or high density. Cluster analysis showed that the pattern of gene expression over the different time points in response to dual infestation was also affected by the density of the attacking aphids. These results suggest that insects attacking at a high density cause an acceleration in plant responses compared to insects attacking at low density.

As a next step in the study of multiple interacting herbivores, I studied whether plant responses to dual herbivory have consequences for the performance of a subsequently arriving herbivore, Mamestra brassicae caterpillars. The ecological consequences of plant responses to dual herbivory cascading into a chain of interactions affecting other community members have remained unstudied so far. We used wild B. oleracea plants to evaluate dual herbivore-induced plant adaptations for subsequent herbivory. We found that simultaneous feeding by P. xylostella and B. brassicae resulted in different plant defense-related gene expression and differences in plant hormone levels compared to single herbivory, and this had a negative effect on subsequently arriving M. brassicae caterpillars. Differential induction of JA-regulated transcriptional responses to dual insect attack was observed which could have mediated a decrease in M. brassicae performance. The induction of plant defense signaling also affected both P. xylostella and B. brassicae performance. This study further helps to understand herbivore community build-up in the context of plant-mediated species interactions.

Altogether, findings from this thesis reveal a molecular basis underlying plant responses against multiple herbivory and provide insight in plant-mediated interactions between aphids and caterpillars feeding on plants growing in the field or used in agriculture.

On the modulation of innate immunity by plant-parasitic cyst nematodes
Postma, W.J. - \ 2013
University. Promotor(en): Jaap Bakker, co-promotor(en): Geert Smant; Aska Goverse. - S.l. : s.n. - ISBN 9789461735560 - 154
plantenparasitaire nematoden - globodera rostochiensis - heterodera schachtii - planten - interacties - immuniteit - immuunsysteem - modulatie - receptoren - signaaltransductie - moleculaire plantenziektekunde - plant parasitic nematodes - plants - interactions - immunity - immune system - modulation - receptors - signal transduction - molecular plant pathology

Plant-parasitic cyst nematodes are major agricultural pests worldwide. These obligate endoparasites invade the roots of host plants where they transform cells near the vascular cylinder into a permanent feeding site. Plants possess a multilayered innate immune system consisting of different types of extracellular and intracellular immune receptors. These enable detection of most invading nematodes and initiate immune responses that result in resistance. Many plant pathogens use effectors to overcome resistance. Here, modulation of plant innate immunity by plant-parasitic cyst nematodes was investigated. Extracellular immune receptor signaling and hormone-mediated signaling pathways were found to contain infection of susceptible Arabidopsis thalianawith Heterodera schachtii. A large family of effectors was identified in Globodera rostochiensis. One of these so-called SPRYSECs interacted with a novel CC-NB-LRR type resistance protein of a susceptible tomato without inducing resistance responses. Instead, the effector was found to suppress defense-related programmed cell death and resistance mediated by several CC-NB-LRR type resistance proteins. In addition, a secreted antimicrobial peptide was identified in G. rostochiensis. Plant-parasitic cyst nematodes thus most likely secrete effectors that protect against plant immune responses and secondary infections. The current evidence for the existence of immune modulating effectors is reviewed and directions for further research are given.

The role and evolution of fungal effectors in plant pathogenesis
Jonge, R. de - \ 2012
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)
Verticillium wilt resistance in Arabidopsis and tomato: identification and functional characterization
Yadeta, K.A. - \ 2012
University. Promotor(en): Pierre de Wit, co-promotor(en): Bart Thomma. - S.l. : s.n. - ISBN 9789461733849 - 147
solanum lycopersicum - arabidopsis thaliana - modellen - plant-microbe interacties - ziekteresistentie - verdedigingsmechanismen - verticillium - verwelkingsziekten - moleculaire plantenziektekunde - models - plant-microbe interactions - disease resistance - defence mechanisms - wilts - molecular plant pathology

Vascular wilt pathogens, which comprise bacteria, fungi and oomycetes, are among the most destructive plant pathogens that affect annual crops as well as woody perennials, thus not only impacting world food and feed production but also natural ecosystems. Vascular wilt pathogens colonize the xylem vessels of their host plants and interfere with the normal transportation of water and nutrients from the roots to upper parts of the plant, thus causing wilting symptoms. The structure and composition of xylem vessels has a significant impact on the colonization of host plants by these pathogens. Presently, genetic resistance is the most preferred control strategy against this group of plant pathogens.

Verticillium wilt disease, which is caused by the vascular fungal pathogen Verticillium spp., is among the major diseases in various horticultural crops in tropical, subtropical, and temperate agro-ecological regions. The genus Verticilllium comprises of three major plant pathogenic species; V. dahliae, V. albo-atrum,and V. longisporum. While V. dahliae and V. albo-atrum arecharacterized with the ability to infect broad host range, V. longisporum has relatively limited host range infecting mainly crucifers family. V. dahliae and V. albo-atrum isolates are categorized into race 1 and race 2 based on their ability to infect tomato plants containing a Ve1 resistance gene. On tomato, while race 1 isolates are contained by Ve1 resistance gene, race 2 isolates overcome Ve1-mediated resistance.

Chapter 1is the introduction to the thesis that describes xylem defence responses that are directed against vascular wilt pathogens. Plants recognize xylem-invading vascular wilt pathogens by using extracellular or intracellular receptors. Pathogen recognition activates innate immune responses that include physical and chemical defense responses in the xylem vessels and the surrounding parenchyma cells. While physical defense responses often halt pathogen movement between vessels, chemical defense responses can eliminate the pathogen or inhibit its growth, thereby leading to resistance.

In order to identify novel sources of Verticillium wilt resistance, a collection of activation-tagged Arabidopsis mutants was screened for plants that displayed enhanced Verticillium wilt resistance. Chapter 2 describes four mutants (A1 to A4) that showed enhanced resistance to not only V. dahliae, but also to V. albo-atrum, and the Brassicaceae pathogen V. longisporum. Further characterization of resistance in these mutants against other vascular wilt pathogens, Ralstonia solanacearum and Fusarium oxysporum f. sp. Raphani, and the foliar pathogens such Botrytis cinerea, Plectosphaerella cucumerina, Alternaria brassicicola, and Pseudomonas syringae pv. tomato, is presented in this chapter. Except for mutant A2, that showed enhanced resistance to R. solanacearum, and mutants A1 and A3, that showed enhanced susceptibility to P. syringae, all the mutants responded similar as wild-type plants to these pathogens. In chapter 2, we furthermore describe the cloning and functional characterization of the gene encoding the AT-hook DNA-binding protein AHL19 that is responsible for the enhanced resistance of the A1 mutant to Verticillium wilt disease. The Arabidopsis genome contains 29 AHL proteins (Fujimoto et al., 2004)some of which have been implicated in various biological processes including plant development (Lim et al., 2007; Xiao et al., 2009)and defense (Kim et al., 2007Kim et al., 2007; Lu et al., 2010). AHL19 provides Verticillium wilt resistance upon over-expression, whereas knock-out enhances susceptibility, indicating that AHL19 positively regulates Verticillium wilt resistance. AHL19 not only regulates Verticillium wilt resistance, but also affects plant development, as AHL19 over-expressing plants showed larger leaf size, delayed maturity, and low seed production (Yadeta et al., 2011).

Chapter 3describes the cloning and functional characterization of EVR1 (for Enhanced Verticillium Resistance 1), the gene that is responsible for the enhanced Verticillium wilt resistance in mutant A2. Mutant A2 furthermore confers resistance to the bacterial vascular wilt pathogen R. solanacearum (Yadeta et al., 2011). While EVR1 over-expression enhances Arabidopsis resistance to three vascular wilt pathogens: V. dahliae, R. solanacearum, and F. oxysporum, knock-out enhances susceptibility to V. dahliae and R. solanacearum. Furthermore, EVR1 appears to regulate drought stress resistance. EVR1 is a single copy gene that encodes a protein of unknown function, and EVR1 homologs are only found in Brassicaceae species thus far. Interestingly, over-expression of the B. oleraceae EVR1 homolog in Arabidopsis conferred Verticillium wilt resistance. Moreover, over-expression of Arabidopsis and B. oleraceae EVR1 and BoEVR1 in the Solanaceous species N. benthamiana enhanced Verticillium wilt resistance. This suggests that the Brassicaceae-specific EVR1 gene can be used to engineer Verticillium wilt resistance in other plant families.

Whereas chapters 2 and 3 focus on the identification of novel sources of Verticillium wilt resistance by screening a collection of Arabidopsis gain-of-function mutants, Chapter 4 describes the identification of novel Verticillium wilt resistance in wild tomato accessions. Six wild accessions were identified that displayed enhanced resistance to race 2 isolates. Surprisingly, however, these accessions did not show enhanced resistance to race 1 isolates. Using virus-induced gene silencing, the resistance signalling leading to race 2 resistance in the wild accessions was investigated, showing that the resistance signalling in the wild accessions is distinct from the signalling pathway employed by the resistance protein Ve1.

Finally in chapter 5, the highlights of this thesis are discussed and placed in a broader perspective.

Plant Fungal Pathogens: Methods and Protocols
Bolton, M.D. ; Thomma, B.P.H.J. - \ 2012
New York, USA : Humana Press (Methods in Molecular Biology 835) - ISBN 9781617795008 - 648
plantenziekteverwekkende schimmels - plant-microbe interacties - genomica - moleculaire plantenziektekunde - schimmelziekten - methodologie - protocollen - plant pathogenic fungi - plant-microbe interactions - genomics - molecular plant pathology - fungal diseases - methodology - protocols
Over the course of evolution, fungi have adapted to occupy specific niches, from symbiotically inhabiting the flora of the intestinal tract of mammals to saprophytic growth on leaf litter resting on the forest floor. In Plant Fungal Pathogens: Methods and Protocols, expert researchers in the field detail many of the methods which are now commonly used to study fungal plant pathogens. These include methods and techniques for model systems such as Arabidopsis thaliana as well as crop plants, aspects of fungal biology, genome annotation, next-generation sequencing, and fungal transformation and molecular tools for disease and/or pathogen quantification that are critical for revealing the role for a fungal gene of interest in disease development. Chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and key tips on troubleshooting and avoiding known pitfalls.
DNA-extractie zonder remming
Bonants, P.J.M. ; Lee, T.A.J. van der - \ 2011
Gewasbescherming 42 (2011)2. - ISSN 0166-6495 - p. 75 - 78.
moleculaire plantenziektekunde - moleculaire detectie - plantenplagen - plantenziekten - dna - extractie - molecular plant pathology - molecular detection - plant pests - plant diseases - extraction
Moleculaire technieken voor de detectie en identificatie van plantenpathogenen maken gebruik van het DNA of RNA van de ziekteverwekker. Voor een aantal substraten, zoals grond, is de extractie van amplificeerbaar nucleïnezuur een probleem. Tijdens de DNA-extractie uit sommige moeilijke substraten worden ook andere stoffen meegezuiverd, die vervolgens de PCR remmen en daarmee vals-negatieve reacties opleveren.
Levend of dood, dat is de vraag!
Lee, T.A.J. van der; Leeuwen, G. van; Haan, E. de; Helder, J. ; Koenraadt, H. ; Bonants, P.J.M. - \ 2011
Gewasbescherming 42 (2011)2. - ISSN 0166-6495 - p. 71 - 75.
moleculaire plantenziektekunde - plantenziekten - plantenplagen - moleculaire detectie - quarantaine organismen - infectiviteit - moleculaire technieken - molecular plant pathology - plant diseases - plant pests - molecular detection - quarantine organisms - infectivity - molecular techniques
In de literatuur zijn voor de detectie van plantenpathogenen diverse methodieken beschreven. De biologische methodieken detecteren alleen levende organismen. Morfologische, serologische en moleculaire technieken maken mmestal geen onderscheid tussen dood en levend of infectieus en niet infectieus. Met name voor quarantaineorganismen is het onderscheid tussen levende en dode pathogenen van essentieel belang. Binnen het FES-programma 'Versterking infrastructuur plantgezondheid' is binnen werkpakket 3 'Ontwikkeling van methoden voor het aantonen van vitaliteit van plantenpathogenen' gewerkt aan de detectie van vitaliteit in nematoden, schimmels en bacteriën.
CSI ook in de Plantenwereld
Bonants, P.J.M. ; Lee, T.A.J. van der - \ 2011
Gewasbescherming 42 (2011)2. - ISSN 0166-6495 - p. 66 - 71.
plantenplagen - plantenziekten - moleculaire detectie - polymerase-kettingreactie - quarantaine organismen - moleculaire plantenziektekunde - moleculaire herkenning - moleculaire technieken - plant pests - plant diseases - molecular detection - polymerase chain reaction - quarantine organisms - molecular plant pathology - molecular recognition - molecular techniques
In de land- en tuinbouw heeft de ontwikkeling van (moleculaire) detectiemethoden van plantenpathogenen de laatste jaren een hoge vlucht genomen. Inmiddels worden deze methoden al grootschalig toegepast in de praktijk. Werd in het begin alleen conventionele polymerase chain reaction (PCR) ingezet voor moleculaire detectie, momenteel vindt ook real-time PCR meer en meer ingang. Binnen het FES-programma ‘Versterking infrastructuur plantgezondheid’ zijn binnen het werkpakket ‘Identificatie- en Detectiemethoden’ vele projecten uitgevoerd om de ‘daders’ van aantastingen te kunnen identificeren. De focus was hierbij gericht op quarantaineorganismen.
Plantenziektes bestrijden met genetische vingerafdruk
Bonants, P.J.M. - \ 2009
Kennis Online 6 (2009)okt. - p. 4 - 5.
plantenziektebestrijding - plantenziekteverwekkers - polymerase-kettingreactie - identificatie - quarantaine organismen - fytosanitair beleid - moleculaire plantenziektekunde - moleculaire herkenning - plant disease control - plant pathogens - polymerase chain reaction - identification - quarantine organisms - phytosanitary policies - molecular plant pathology - molecular recognition
Nederland speelt een belangrijke rol in een Europees project dat quarantaineorganismen wil voorzien van een DNA-streepjescode. Wageningen UR, de Plantenziektenkundige Dienst, en het Centraalbureau voor Schimmelcultures van de KNAW gaan samen met zeventien andere Europese onderzoeksinstituten op zoek naar de unieke streepjescode voor elke plantenplaag
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