Voici les éléments 1 - 10 sur 98
  • Publication
    Métadonnées seulement
    Herbivore-induced plant volatiles mediate host selection by a root herbivore
    (2012)
    Robert, Christelle Aurélie Maud
    ;
    ;
    Duployer, M.
    ;
    ;
    Doyen, G. R.
    ;
    In response to herbivore attack, plants mobilize chemical defenses and release distinct bouquets of volatiles. Aboveground herbivores are known to use changes in leaf volatile patterns to make foraging decisions, but it remains unclear whether belowground herbivores also use volatiles to select suitable host plants. We therefore investigated how above- and belowground infestation affects the performance of the root feeder Diabrotica virgifera virgifera, and whether the larvae of this specialized beetle are able to use volatile cues to assess from a distance whether a potential host plant is already under herbivore attack. Diabrotica virgifera larvae showed stronger growth on roots previously attacked by conspecific larvae, but performed more poorly on roots of plants whose leaves had been attacked by larvae of the moth Spodoptera littoralis. Fittingly, D similar to virgifera larvae were attracted to plants that were infested with conspecifics, whereas they avoided plants that were attacked by S similar to littoralis. We identified (E)-beta-caryophyllene, which is induced by D similar to virgifera, and ethylene, which is suppressed by S similar to littoralis, as two signals used by D similar to virgifera larvae to locate plants that are most suitable for their development. Our study demonstrates that soil-dwelling insects can use herbivore-induced changes in root volatile emissions to identify suitable host plants.
  • Publication
    Métadonnées seulement
    Volatiles produced by soil-borne endophytic bacteria increase plant pathogen resistance and affect tritrophic interactions
    (2013)
    D'Alessandro, Marco
    ;
    ;
    Ton, Jurriaan
    ;
    Brandenburg, Anna
    ;
    Karlen, Danielle
    ;
    ;
    Volatile organic compounds (VOCs) released by soil microorganisms influence plant growth and pathogen resistance. Yet, very little is known about their influence on herbivores and higher trophic levels. We studied the origin and role of a major bacterial VOC, 2,3-butanediol (2,3-BD), on plant growth, pathogen and herbivore resistance, and the attraction of natural enemies in maize. One of the major contributors to 2,3-BD in the headspace of soil-grown maize seedlings was identified as Enterobacter aerogenes, an endophytic bacterium that colonizes the plants. The production of 2,3-BD by E.?aerogenes rendered maize plants more resistant against the Northern corn leaf blight fungus Setosphaeria turcica. On the contrary, E.?aerogenes-inoculated plants were less resistant against the caterpillar Spodoptera littoralis. The effect of 2,3-BD on the attraction of the parasitoid Cotesia marginiventris was more variable: 2,3-BD application to the headspace of the plants had no effect on the parasitoids, but application to the soil increased parasitoid attraction. Furthermore, inoculation of seeds with E.?aerogenes decreased plant attractiveness, whereas inoculation of soil with a total extract of soil microbes increased parasitoid attraction, suggesting that the effect of 2,3-BD on the parasitoid is indirect and depends on the composition of the microbial community.
  • Publication
    Métadonnées seulement
    Plant elicitor peptides are conserved signals regulating direct and indirect antiherbivore defense
    (2013)
    Huffaker, Alisa
    ;
    Pearce, Gregory
    ;
    ; ; ;
    Sartor, Ryan
    ;
    Shen, Zhouxin
    ;
    Briggs, Steven P.
    ;
    Vaughan, Martha M.
    ;
    Alborn, Hans T.
    ;
    Teal, Peter E. A.
    ;
    Schmelz, Eric A.
    Insect-induced defenses occur in nearly all plants and are regulated by conserved signaling pathways. As the first described plant peptide signal, systemin regulates antiherbivore defenses in the Solanaceae, but in other plant families, peptides with analogous activity have remained elusive. In the current study, we demonstrate that a member of the maize (Zea mays) plant elicitor peptide (Pep) family, ZmPep3, regulates responses against herbivores. Consistent with being a signal, expression of the ZmPROPEP3 precursor gene is rapidly induced by Spodoptera exigua oral secretions. At concentrations starting at 5 pmol per leaf, ZmPep3 stimulates production of jasmonic acid, ethylene, and increased expression of genes encoding proteins associated with herbivory defense. These include proteinase inhibitors and biosynthetic enzymes for production of volatile terpenes and benzoxazinoids. In accordance with gene expression data, plants treated with ZmPep3 emit volatiles similar to those from plants subjected to herbivory. ZmPep3-treated plants also exhibit induced accumulation of the benzoxazinoid phytoalexin 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside. Direct and indirect defenses induced by ZmPep3 contribute to resistance against S. exigua through significant reduction of larval growth and attraction of Cotesia marginiventris parasitoids. ZmPep3 activity is specific to Poaceous species; however, peptides derived from PROPEP orthologs identified in Solanaceous and Fabaceous plants also induce herbivory-associated volatiles in their respective species. These studies demonstrate that Peps are conserved signals across diverse plant families regulating antiherbivore defenses and are likely to be the missing functional homologs of systemin outside of the Solanaceae.
  • Publication
    Accès libre
    Climate Change in the Underworld: Impacts for Soil-Dwelling Invertebrates
    (New York: Wiley Online library, 2016) ;
    Johnson, Scott N.
    ;
    ;
    Nielsen, Uffe N.
    This chapter reviews and discusses the impact of elevated atmospheric CO2 and climatic changes on three of the functionally most important invertebrate taxa in soil ecosystems: nematodes, insects, and earthworms. The effects of climate and atmospheric CO2 change on soil abiotic conditions vary and numerous biotic feedbacks occur. Many soil‐dwelling insects are herbivores and devastate crops, which impact human societies through yield decreases; therefore an understanding of how climate change will affect their pest status is essential. The chapter discusses potential broader impacts of soil nematode community responses to climate change on ecosystems. Soil‐dwelling insects that feed on roots are usually the juvenile stages of insects that live aboveground as adults. These soil invertebrates can reach astonishing densities, with root‐feeding cicadas of deciduous forests of North America having the largest collective biomass per unit area of any terrestrial animal.
  • Publication
    Métadonnées seulement
  • Publication
    Accès libre
    Modification of plant resistance and metabolism by above- and belowground herbivores
    (2009) ;
    Turlings, Théodor
    Plants are often attacked by above- and belowground herbivores. As a result, they have evolved defense mechanisms to protect both their roots and shoot. However, physiological processes in roots and shoots are tightly connected, and attack of one of these plant parts can dramatically alter primary and secondary metabolism of the other (chapter 1). It is therefore important to understand how the plant reacts aboveground upon belowground insect attack and vice versa. This thesis investigates how shoots of maize plants respond to root attack by lavae of the beetle Diabrotica virgifera and vice versa, how roots react to shoot attack by Spodoptera littoralis caterpillars. This is one of the first studies highlighting the physiology and potential evolutionary significance of plant-mediated above-belowground interactions. The results obtained show that root infestation by D. virgifera broadly increases defenses in maize leaves, mostly after prolonged infestation (chapters 2-4). Many of these processes were found to be inducible by absisic acid (ABA), a well-known stress-hormone that increased in concentration aboveground after prolonged belowground attack by D. virgifera. The increase of ABA coincided with a decrease of leaf-water content, and our experiments suggest that the observed ABA-dependent defense reaction is the consequence of a physiological stress induced by the root herbivore. The changes in shoot physiology boosted the plant’s resistance against the necrotrophic pathogen Setosphaeria turcica and the herbivore S. littoralis in the laboratory, as well as against lepidopteran pests in the field, demonstrating that D. virgifera has an ecologically important impact on aboveground interactions. While the observed ABA response can explain the reduction of S. turcica growth in the leaves (chapter 2), S. littoralis was negatively affected by the reduction of leaf-water contents (chapter 3). Shoot herbivory by S. littoralis profoundly altered root gene expression, even early after infestation (chapter 4). The reaction in the roots was entirely different from the changes in shoot transcriptional profiles, suggesting that the root-shoot signal(s) are dissimilar to the known systemic shoot defense signals. S. littoralis had a strong impact on root protein biosynthesis, a novel finding that demands further attention. The strong effect of S. littoralis infestation on root physiology was reflected in a dramatically increased resistance of attacked maize plants against D. virgifera. In conclusion, both root- and shoot herbivores change the physiology of plants not only locally, but also in the unattacked parts. These changes increase the resistance of the plant against herbivores and pathogens. Root-herbivore induced shoot resistance seems to be caused by physiological constraints rather than plant adaptive behaviour, while shoot-herbivore induced root resistance is likely to be the result of the plant’s integrated, systemic defensive system.
  • Publication
    Métadonnées seulement
    Volatiles produced by soil-borne endophytic bacteria increase plant pathogen resistance and affect tritrophic interactions
    (2014)
    D'Alessandro, Marco
    ;
    ;
    Ton, Jurriaan
    ;
    Brandenburg, Anna
    ;
    Karlen, Danielle
    ;
    ;
    Volatile organic compounds (VOCs) released by soil microorganisms influence plant growth and pathogen resistance. Yet, very little is known about their influence on herbivores and higher trophic levels. We studied the origin and role of a major bacterial VOC, 2,3-butanediol (2,3-BD), on plant growth, pathogen and herbivore resistance, and the attraction of natural enemies in maize. One of the major contributors to 2,3-BD in the headspace of soil-grown maize seedlings was identified as Enterobacter aerogenes, an endophytic bacterium that colonizes the plants. The production of 2,3-BD by E.?aerogenes rendered maize plants more resistant against the Northern corn leaf blight fungus Setosphaeria turcica. On the contrary, E.?aerogenes-inoculated plants were less resistant against the caterpillar Spodoptera littoralis. The effect of 2,3-BD on the attraction of the parasitoid Cotesia marginiventris was more variable: 2,3-BD application to the headspace of the plants had no effect on the parasitoids, but application to the soil increased parasitoid attraction. Furthermore, inoculation of seeds with E.?aerogenes decreased plant attractiveness, whereas inoculation of soil with a total extract of soil microbes increased parasitoid attraction, suggesting that the effect of 2,3-BD on the parasitoid is indirect and depends on the composition of the microbial community.
  • Publication
    Accès libre
    Direct and indirect effect of the rhizobacteria 'Pseudomonas putida' KT2440 on maize plants
    To protect themselves against biotic and abiotic stresses, plants have developed a broad range of defense mechanisms that are constitutively present or that can be induced in response to a stress. Such induced defense can be the result of a resistance elicitation by non-pathogenic organisms that are present in soil and is then called induced systemic resistance (ISR). ISR confers plant resistance against a large variety of attackers such as pathogens and herbivores. In monocotyledonous plants this phenomenon has been less studied than in dicots such as Arabidopsis. Hence, the aim of this thesis was to enhance our knowledge on ISR in monocots and more specifically in maize plants.
    To facilitate plant root manipulation for our experiments, we established a soil-free system for growing maize plants. Based on an existing system for root observation, we adapted a system that is convenient for working with beneficial as well as pathogenic microbes.
    ISR establishment necessitates the local recognition of the beneficial microbe by the plant. Thus, we studied the reaction of maize after inoculation with a well-known maize colonizer rhizobacterium Pseudomonas putida KT2440. The presence of these bacteria activated plant immunity early in the interaction. We hypothesized that KT2440 manipulates root defense to be able to colonize roots. We observed that KT2440 had a beneficial effect on plant growth, showing their capacity to be a plant growth promoting rhizobacteria.
    After analyzing the local plant response to KT2440 inoculation we tested the efficiency of KT2440 to induce a systemic defense against various types of attacks. We demonstrated that ISR triggered by KT2440 was efficient against an hemibiotrophic fungus, Colletotrichum graminicola, and a generalist herbivore, Spodoptera littoralis. However, the efficacy of ISR induced by KT2440 was dependent of the host-plant specialization of the leaf herbivores as ISR triggered by KT2440 did not affect the specialist S. frugiperda. Our transcript and metabolite analyses revealed the involvement of phenolic compounds as well as ethylene-dependent signaling in maize ISR. However, mechanisms involved in ISR induced by KT2440 in maize remain to be further investigated.
  • Publication
    Accès libre
    Systemic root signalling in a belowground, volatile-mediated tritrophic interaction
    (2011) ; ;
    Robert, Christelle Aurélie Maud
    ;
    Plants attacked by leaf herbivores release volatile organic compounds (VOCs) both locally from the wounded site and systemically from non-attacked tissues. These volatiles serve as attractants for predators and parasitoids. This phenomenon is well described for plant leaves, but systemic induction of VOCs in the roots has remained unstudied. We assessed the spatial and temporal activation of the synthesis and release of (E)-β-caryophyllene (EβC) in maize roots upon feeding by larvae of Diabrotica virgifera virgifera, as well as the importance of systemically produced EβC for the attraction of the entomopathogenic nematode Heterorhabditis megidis. The production of EβC was found to be significantly stronger at the site of attack than in non-attacked tissues. A weak, but significant, increase in transcriptional activity of the EβC synthase gene tps23 and a corresponding increase in EβC content were observed in the roots above the feeding site and in adjacent roots, demonstrating for the first time that herbivory triggers systemic production of a volatile within root systems. In belowground olfactometers, the nematodes were significantly more attracted towards local feeding sites than systemically induced roots. The possible advantages and disadvantages of systemic volatile signalling in roots are discussed.
  • Publication
    Accès libre
    The products of a single maize sesquiterpene synthase form a volatile defense signal that attracts natural enemies of maize herbivores
    (2006)
    Schnee, Christiane
    ;
    Köllner, Tobias G.
    ;
    ; ;
    Gershenzon, Jonathan
    ;
    Degenhardt, Jörg
    Plants can defend themselves against herbivores by attracting natural enemies of the herbivores. The cues for attraction are often complex mixtures of herbivore-induced plant volatiles, making it difficult to demonstrate the role of specific compounds. After herbivory by lepidopteran larvae, maize releases a mixture of volatiles that is highly attractive to females of various parasitic wasp species. We identified the terpene synthase TPS10 that forms (E)-β-farnesene, (E)-α-bergamotene, and other herbivory-induced sesquiterpene hydrocarbons from the substrate farnesyl diphosphate. The corresponding gene is expressed in response to herbivore attack and is regulated at the transcript level. Overexpression of tps10 in Arabidopsis thaliana resulted in plants emitting high quantities of TPS10 sesquiterpene products identical to those released by maize. Using these transgenic Arabidopsis plants as odor sources in olfactometer assays showed that females of the parasitoid Cotesia marginiventris learn to exploit the TPS10 sesquiterpenes to locate their lepidopteran hosts after prior exposure to these volatiles in association with hosts. This dissection of the herbivore-induced volatile blend demonstrates that a single gene such as tps10 can be sufficient to mediate the indirect defense of maize against herbivore attack.