Project

Discipline

insect; egg elicitors; innate immunity; pathway crosstalk; oviposition; defense gene expression; Arabidopsis thaliana

Lead
Le but de ce projet est de comprendre comment les oeufs d'insectes manipulent les défenses de la plante
Lay summary
Les plantes sont attaquées par une multitude d'insectes et ont mis en place des stratégies contre ces agressions. A l'inverse, les insectes ont évolué des mécanismes pour bloquer les défenses de la plante en détournant les voies de transmission de signaux à leur avantage. Les oeufs d'insectes représentent une menace car les larves qui éclosent vont se nourrir de feuilles. Nos recherches ont montré que la plante Arabidopsis thaliana détecte la présence de molécules d'oeufs de Pieris brassicae et qu'elle active une réponse immunitaire qui est modulée par le signal acide salicylique (SA) et se manifeste par l'expression de centaines de gènes de défense. Cette découverte est surprenante car il est connu que le SA est engagé pour résister aux attaques bactériennes et fongiques alors que le signal acide jasmonique (JA) est responsable de la défense contre les insectes. Cependant, nous avons montré que l'accumulation de SA sous les oeufs protège la plante contre la bactérie pathogène Pseudomonas syringae et permet un meilleur développement des larves. Ceci suggère que ce phénomène a évolué pour empêcher un effet néfaste d'une infection sur les jeunes larves. De plus, l'accumulation de SA bloque détruit des facteurs de transcription MYCs essentiels pour activer des gènes de défenses qui dépendent du JA, permettant également un meilleur développement des larves. Le but de ce projet est 1) d'identifier la structure des molécules de l'oeuf responsables des effets observés, 2) de comprendre l'importance biologique de la protection induite contre des pathogènes, 3) de caractériser les étapes moléculaires qui régulent la destruction des facteurs MYCs. Nous espérons découvrir de nouvelles stratégies de lutte contre les insectes nuisibles en se basant sur des processus biologiques.

Direct link to Lay Summary

Last update: 26.09.2016

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

Plants are challenged by numerous herbivorous insects and have developed sophisticated strategies to fend off these attackers. In turn, insects have evolved mechanisms to suppress plant defenses or to hijack signaling pathways for their own advantage. Eggs deposited on plants by insects represent a threat as they develop into feeding larvae. Earlier studies established that plants detect egg-associated elicitors and activate direct and indirect defenses. Recent years have seen progress in the molecular understanding of egg-induced responses in Arabidopsis thaliana. Genetic and biochemical analyses have revealed that egg perception triggers an innate immunity response that is regulated by the salicylic acid (SA) pathway. This finding was unexpected since the SA pathway is normally engaged to fight fungal and bacterial pathogens, whereas plants resist insect attack by activating jasmonic acid (JA)-dependent defenses. However, egg-induced SA accumulation was shown to protect plants against infection by the biotroph pathogen Pseudomonas syringae by activating a systemic acquired resistance (SAR). This SAR benefited the development of young hatching larvae and suggests that this phenomenon may have evolved as a strategy to prevent the detrimental effect of bacterial pathogens on feeding larvae. In addition, egg-induced SA accumulation suppressed JA-dependent gene expression by targeting key MYC transcription factors that are crucial for defense against feeding larvae. Again, this SA/JA cross talk enhanced larval performance. These intriguing findings constitute two independent examples of manipulation of a plant signaling pathway by the attacker. A major challenge is to identify egg-associated elicitors and plant receptors that lead to activation of the SA pathway. It is also necessary to better understand the biological relevance of egg-induced SAR and the precise regulation of SA/JA cross talk.The proposed research project has three objectives. The first objective is to identify a novel egg elicitor and how it is perceived by Arabidopsis. Preliminary work has identified a candidate molecule and a potential receptor that would represent the first known elicitor/receptor pair from a plant-insect interaction and would open the way for interesting structure/function analyses. The second objective is to characterize the importance of egg-induced SAR and its role against a range of biotic factors that interact with Arabidopsis. Results from this part may lead to interesting applied aspects. The third objective is to investigate how egg-induced SA/JA cross talk is modulated and the role of independent regulation steps. We also hope to identify new genes that participate in this process.This project aims at a better knowledge of plant-insect interactions. One emerging theme is that insect eggs have evolved distinct ways to highjack the SA pathway for the benefit of larvae. We hope to unveil interesting mechanisms that may apply to diverse interactions between plants and biotic factors.