Turlings, Ted

2020, Grandi, Luca, Turlings, Ted

Le coton (Gossypium spp.) est la plante modèle la plus étudiée à cause de son énorme importance économique. En effet, ce genre est cultivé partout dans le monde, principalement pour ses fibres, mais aussi comme fourrage et huile de cuisson. Comme toutes les plantes, le coton interagit de manière bénéfique ou antagoniste avec plusieurs organismes grâce à différents traits développés au cours de l’évolution. Pour protéger et augmenter la performance des cultures de coton, plusieurs stratégies de lutte contre les ravageurs sont aujourd’hui appliquées. Par exemples, des pesticides, herbicides et fertilisants sont utilisés intensivement sur le coton. De plus, des variétés énétiquement modifiées ont été créées afin de les rendre résistantes contre les ravageurs ou tolérantes aux herbicides. Bien que ces techniques donnent un retour rapide en termes économiques, le développement des traits de résistances des ravageurs, l’affaiblissement des défenses naturelles des plantes, la pollution environnementale due aux produits agrochimiques et les effets imprévisibles liés à l’utilisation de cultures génétiquement modifiées, ont mis en exergue l’urgent besoin de stratégies alternatives plus respectueuses de la nature. Cette nécessité prend tout son sens à la lumière de l’activité humaine, qui aujourd’hui facilite extrêmement l’introduction et la dispersion d’organismes invasifs. Des plans de contrôle biologique et des stratégies de lutte intégrée contre les ravageurs (IPM) ont été lancés dans cette voie, mais il y a encore une grande marge de progression à réaliser avant de connaître et rejoindre le potentiel total de ces stratégies. Par exemple, une compréhension plus complète des défenses naturelles, directes, indirectes et inductibles des plantes contre les insectes et les pathogènes est essentielle. Des études sur les défenses indirectes des plantes ont montré que les composés organiques volatiles (COVs) émis par une plante attaquée par des herbivores sont capables d’attirer les ennemis naturels des ravageurs et de repousser ces derniers. De plus, les COVs peuvent être utilisés comme signaux d’alerte par des parties intactes de la plante elle-même ou d’une plante voisine, résultant en un effet de « priming » pour des défenses améliorées en cas d’attaque future.Des études récentes suggèrent que ce « priming » des individus voisins a un grand potentiel d’application dans le renforcement de la résistance aux ravageurs du coton. Cependant, les mécanismes à la base de ce phénomène sont encore mal connus. Le but de cette thèse est de contribuer à une meilleure compréhension des rôles des COVs dans l’interaction entre les plantes de coton, en mettant en lumière les mécanismes biochimiques et moléculaires sous-jacent des phénomènes de “priming” et d’induction des défenses. Via différentes expériences, en exposant des plantes aux COVs, il a pu être prouvé que ces derniers peuvent changer la physiologie de la plante, en activant l’expression des gènes de défense et en altérant les niveaux des phytohormones et des métabolites secondaires de défense. Ces changements ont mené à une augmentation des émissions des COVs par les plantes exposées et ont réduit l’attraction des chenilles envers ces mêmes plantes. Ces changements sont spécifiques au génotype de la plante et semblent être dus aux COVs émis par le coton après une infestation prolongée des chenilles (COVs inductibles). Cette dernière hypothèse est basée sur les résultats d’une expérience ou nous avons exposé des plantes à des COVs émis par des plantes avec des dégâts frais ou avec des dégâts plus vieux. L’importance des différentes classes d’odeurs a également été testés en exposant des planes à plusieurs combinaisons de versions de synthèse et authentiques de certains COVs. Malheureusement, à cause de la grande variance et les difficultés dans le contrôle du taux d’émission des distributeurs d’odeur, il n’a pas été possible d’identifier le simple ou groupes de COVs responsable(s) pour l’activation des défenses dans les plantes voisines L’hypothèse qu’une plante intacte nécessite soit un bouquet d’odeurs complet et naturel, soit un ratio spécifique entre certains composés ou bien d’autres composés non-testés pour activer une réponse de défense a donc été émises. De plus, lors de l’analyse de feuilles de coton collectées dans des champs de culture avec des plantes endommagées mécaniquement (i.e. écimage) ou intactes, nous avons observé comme les composés organiques volatiles émis par les plantes endommagées peuvent induire la production de certains composés de défense dans la plante elle-même et parfois dans la plante voisine également. Cette thèse met en lumière le potentiel d’utilisation de certaines composés organiques volatiles pour le développement d’une nouvelle stratégie IPM visée à augmenter la résistance du coton aux ravageurs. Toutefois, de plus amples investigations sont nécessaires pour identifier des composés spécifiques puissants qui pourraient être in fine appliqué et protéger activement le coton. ABSTRACT Cotton (Gossypium spp) is one of the most studied plants in the world due to its great economic importance. This highly valuable crop is cultivated worldwide primarily to produce textile fibers and, to a lesser extent, for animal forage and cooking oil production. As for all plants, cotton is involved in several beneficial and antagonistic interactions and in nature it has evolved several direct and indirect defenses to ward off antagonists and to facilitate beneficial interactions. To protect and enhance the performance of cultivated cotton, various pest-management strategies are currently applied. For instance, pesticides, herbicides and fertilizers are intensively used in cotton cultivation. In addition, genetically modified varieties have been created in order to tolerate herbicides or enhance resistance to pest insects. Although these techniques result in short term economic returns, development of resistance in pests, weakening of natural plant defenses, environment pollution with agrochemicals, and unpredictable effects of introducing genetic modified crops, have increased the need for alternative, more environmentally friendly pest control strategies. This need is further enhanced by human activities that facilitate the introduction and dispersal of non-native invasive organisms. To fight these pests, bio-control and integrated pest management (IPM) strategies have been proposed, but much knowledge is lacking to achieve the full potential of these strategies. For instance, a comprehensive understanding of the plant’s direct and indirect inducible defenses against insects and pathogens under natural conditions is essential. Studies on indirect plants defenses have shown that volatile organic compounds (VOCs) emitted by herbivore-attacked plants, are able to attract the natural enemies of pests and may repel pests. Moreover, these herbivore-induced plant volatiles (HIPVs) may also serve as signals that alert undamaged leaves and neighboring plants to incoming attack and may prime them for enhanced defense induction. Recent studies suggest that this priming of neighbors has potential for application, by enhancing pest resistance in cotton, but the underlying mechanisms are still poorly understood. The aim of my thesis was to contribute to a better understanding of VOC-mediated signaling among cotton plants by elucidating the biochemical and molecular mechanisms that are involved in priming and/or induction. With a number of controlled plant exposure experiments I could show that cotton HIPVs change the physiology of receiver plants by means of defense-related gene activation, changes in plant hormones levels, as well as increases in levels of secondary metabolites. These changes resulted in increased VOC emissions by receiver plants and reduced palatability of the plants to caterpillar pests. These changes were found to be plant genotype-specific and seem to be mainly driven by VOCs that are emitted in the later stage of the caterpillar infestations (inducible volatiles). This notion was based on an experiment where plants were exposed to the volatiles of relatively freshly damaged plants or of plants with older damage. We further tested the importance of the different classes of volatiles by exposing plants to different sets of authentic, pure versions of VOCs. Unfortunately, due to high variation and difficulties in controlling dispenser emission rates, we could not determine single or group of compounds responsible for defense induction in neighboring plants. We hypothesized that intact plants may require a full natural blend, a specific ratio or other non-tested compounds in order to activate defense responses. Furthermore, we also analyzed field-collected leaves from plots with and without mechanically damaged (i.e. topped) plants and we could confirm that damage-induced volatiles can enhance the production of defense compounds in the plant itself and in neighboring plants. This thesis highlights the potential using volatile-mediated interactions among cotton plants for the development of a novel IPM strategy that enhances cotton resistance to pests. Still, further studies are required in order to identify potent volatiles compounds that may eventually be applied for cotton protection.

2007, Ton, Jurriaan, D'Alessandro, Marco, Jourdie, Violaine, Jakab, Gabor, Karlen, Danielle, Held, Matthias, Mauch-Mani, Brigitte, Turlings, Ted

Plants counteract attack by herbivorous insects using a variety of inducible defence mechanisms. The production of toxic proteins and metabolites that instantly affect the herbivore's development are examples of direct induced defence. In addition, plants may release mixtures of volatile organic compounds (VOCs) that indirectly protect the plant by attracting natural enemies of the herbivore. Recent studies suggest that these VOCs can also prime nearby plants for enhanced induction of defence upon future insect attack. However, evidence that this defence priming causes reduced vulnerability to insects is sparse. Here we present molecular, chemical and behavioural evidence that VOC-induced priming leads to improved direct and indirect resistance in maize. A differential hybridization screen for inducible genes upon attack by Spodoptera littoralis caterpillars identified 10 defence-related genes that are responsive to wounding, jasmonic acid (JA), or caterpillar regurgitant. Exposure to VOCs from caterpillar-infested plants did not activate these genes directly, but primed a subset of them for earlier and/or stronger induction upon subsequent defence elicitation. This priming for defence-related gene expression correlated with reduced caterpillar feeding and development. Furthermore, exposure to caterpillar-induced VOCs primed for enhanced emissions of aromatic and terpenoid compounds. At the peak of this VOC emission, primed plants were significantly more attractive to parasitic Cotesia marginiventris wasps. This study shows that VOC-induced priming targets a specific subset of JA-inducible genes, and links these responses at the molecular level to enhanced levels of direct and indirect resistance against insect attack.

2014, D'Alessandro, Marco, Erb, Matthias, Ton, Jurriaan, Brandenburg, Anna, Karlen, Danielle, Zopfi, Jakob, Turlings, Ted

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.

2013, D'Alessandro, Marco, Erb, Matthias, Ton, Jurriaan, Brandenburg, Anna, Karlen, Danielle, Zopfi, Jakob, Turlings, Ted

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.