Analyse génétique, physiologique et moléculaire de la modification de sensibilité par le voisinage végétal intra-spécifique

Since the last decade, varietal mixtures have been gaining interest in agriculture. Mixing genotypes of the same species is at the origin of an increase in production, a reduction of chemical inputs and an improvement of the sustainability of our agricultural system. Moreover, varietal mixtures allow a better management of diseases by reducing the dispersion of pathogens. In addition to these epidemiological effects, we hypothesized that intraspecific plant-plant interactions may also modify the susceptibility of plants to pathogens in varietal mixtures. To test this hypothesis, mixtures of rice or durum wheat genotypes were manually inoculated under controlled conditions, in the absence of pathogen propagation. First, by inoculating more than 400 binary mixtures of rice or wheat with major foliar pathogens, we were able to quantify the frequency and level of susceptibility modification triggered in a focal plant in the presence of a different neighbor, but of the same species. These changes due to plant-plant interactions are sometimes of the same order of magnitude as the differences that can exist between varieties. The mechanisms underlying these modifications were then analyzed more precisely in each species by focusing on a pair of genotypes. We have shown that an interaction in the soil between neighbouring plants of the same species can constitutively modify the susceptibility of the plants to different pathogens as well as their immunity. This modulation of the susceptibility of the focal plant does not require that the neighbor was previously inoculated. These analyses were complemented by transcriptomic analyses showing that different neighbors produce characteristic pattern of mofication in the focal plant. Finally, we studied the genetic determinants of the neighbor's triggering of susceptibility modulation in the focal plant by conducting an association genetics experiment. This analysis revealed a locus in the neighboring genotype that conditions this triggering. Together, our results show that disease reduction in varietal mixtures could also result from direct interactions betweenplants, in addition to mechanisms affecting pathogen spread at the field level. The identification of this phenomenon, called 'Neighbour-Modulated Susceptibility' (NMS), could provide new ways to design and especially to optimize varietal mixtures.Depuis les années 2000, les mélanges variétaux connaissent un regain d'intérêt en agriculture. Mélanger des génotypes d’une même espèce est à l’origine d’une augmentation de la production, d’une réduction des intrants chimiques et d’une amélioration de la durabilité de nos systèmes agricoles. De plus, ces mélanges de variétés permettent une meilleure gestion des maladies en permettant notamment de réduire la dispersion des agents pathogènes. Outre ces effets d’ordre épidémiologiques, nous avons fait l’hypothèse que des interactions plante plante intra-spécifiques peuvent aussi modifier la sensibilité des plantes aux agents pathogènes dans les mélanges variétaux. Pour tester cette hypothèse, des mélanges de génotypes de riz ou de blé dur ont été inoculés manuellement dans des conditions contrôlées, en l’absence de propagation des agents pathogènes. Dans un premier temps, en inoculant plus de 400 mélanges binaires de riz ou de blé avec des agents pathogènes foliaires majeurs, nous avons pu quantifier la fréquence et le niveau des modifications de sensibilité déclenchées dans une plante focale en présence d’un voisin différent, mais de la même espèce. Ces modifications dues aux interactions plante plante sont parfois du même ordre de grandeur que les différences pouvant exister entre variétés. Par la suite et ce dans chaque espèce, les mécanismes sous-jacents à ces modifications ont été analysées plus précisément en se focalisant sur un couple de génotypes. Nous avons ainsi montré qu’une interaction dans le sol entre des plantes voisines de la même espèce peut modifier la sensibilité des plantes à différents agents pathogènes ainsi que leur immunité, et ce de manière constitutive. Cette modulation de la sensibilité de la plante focale ne nécessite pas que le voisin soit lui-même malade. Ces analyses ont été complétées par des analyses transcriptomiques montrant que différents voisinages produisent des modifications caractéristiques dans la plante focale. Enfin, nous avons étudié les déterminants génétiques du déclenchement par la plante voisine de la modulation de la sensibilité dans la plante focale en menant une expérience de génétique d’association. Cette analyse a permis de mettre en évidence un locus, dans le génotype voisin, qui conditionne ce déclenchement. Ensemble, nos résultats montrent donc que la réduction des maladies dans les mélanges variétaux pourrait également résulter d'interactions directes entre plantes, en plus des mécanismes affectant la propagation des agents pathogènes à l'échelle du champ. La mise en évidence de ce phénomène, appelé 'Neighbour-Modulated Susceptibility' (NMS), pourrait permettre de fournir de nouvelles façons de concevoir et surtout d’optimiser les mélanges variétaux

Plant immunity: Good fences make good neighbors?

International audiencePlant immunity is modulated by several abiotic factors, and microbiome has emerged as a major biotic driver of plant resistance. Recently, a few studies showed that plants also modify resistance to pests and pathogens in their neighborhood. Several types of neighborhood could be identified depending on the biological processes at play: intraspecific and interspecific competition, kin and stranger recognition, plant-soil feedbacks, and danger signaling. This review highlights that molecules exchanged aboveground and belowground between plants can modulate plant immunity, either constitutively or after damage or attack. An intriguing relationship between allelopathy and immunity has been evidenced and should merit further investigation. Interestingly, most reported cases of modulation of immunity by the neighbors are positive, opening new perspectives for the understanding of natural plant communities as well as for the design of more diverse cultivated systems

Analyse des processus d'entraide dans le cadre d’un laboratoire virtuel et distant pour l'apprentissage de l'informatique

International audienceThis transdisciplinary research seeks to analyze student behaviour in mutual aid situations, in the context of a virtual and remote laboratory for computer education. This study allows to identify different configurations of mutual aid, and reveals that students contribute homogeneously to chat sessions supported by a peer terminal consultation tool. It also shows that the task difficulty would impact the quality of the mutual aid sessions.Cette recherche transdisciplinaire vise à analyser les comportements des étudiants en situation d'entraide dans le cadre d’un laboratoire virtuel et distant pour l'apprentissage de l'informatique. Cette étude permet d’identifier différentes configurations d'entraide, et révèle que les étudiants contribuent de façon homogène aux sessions de chat supportées par un outil de consultation de terminal d'un pair. Elle montre également que la difficulté et le calibrage de la tâche impacteraient la qualité des sessions d'entraide

Analyse des processus d'entraide dans le cadre d’un laboratoire virtuel et distant pour l'apprentissage de l'informatique

International audienceThis transdisciplinary research seeks to analyze student behaviour in mutual aid situations, in the context of a virtual and remote laboratory for computer education. This study allows to identify different configurations of mutual aid, and reveals that students contribute homogeneously to chat sessions supported by a peer terminal consultation tool. It also shows that the task difficulty would impact the quality of the mutual aid sessions.Cette recherche transdisciplinaire vise à analyser les comportements des étudiants en situation d'entraide dans le cadre d’un laboratoire virtuel et distant pour l'apprentissage de l'informatique. Cette étude permet d’identifier différentes configurations d'entraide, et révèle que les étudiants contribuent de façon homogène aux sessions de chat supportées par un outil de consultation de terminal d'un pair. Elle montre également que la difficulté et le calibrage de la tâche impacteraient la qualité des sessions d'entraide

Strategies for selective functionalization of amorphous chalcogenide rib waveguides

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Towards an ecological view of plant immunity

International audienceAmong the major scientific questions that remain to be solved in plant pathology is how plant-pathogen interactions hold up in an ecological context? Indeed, for most interactions, we have very little idea of how interactions between plants and microbes are affected by the ecological environment in which they live. At the same time, the concept of eco-immunity has been described. Broadly speaking, this concept aims to understand and explain variation in immune response, in other words, to determine why and how biotic and abiotic factors contribute to variation in the immunity of a living organism. An ecological context that seems interesting to study for its positive impact on the control of epidemics is varietal mixtures. However, this general benefit is not systematic and can be suppressed by specific allele combinations. This highlights the need to know the genetic basis of neighbor-regulated immunity in order to make better use of mixtures. According to our first results, the plant immunity regulated by the neighborhood relies on inter-root communication events. One of our hypotheses is that this inter-root communication would be ensured by specialized metabolites exuded into the rhizosphere that has been described in the context of allelopathic mechanisms. Other phenomena that could be involved include nutrient competition in the root compartment, but the molecular mechanisms by which immunity is regulated under mixed conditions have yet to be described

A major genetic locus in neighbours controls changes of gene expression and susceptibility in intraspecific rice mixtures

International audienceReports indicate that intraspecific neighbours alter the physiology of focal plants, and with a few exceptions, their molecular responses to neighbours are unknown. Recently, changes in susceptibility to pathogen resulting from such interactions were demonstrated, a phenomenon called neighbour-modulated susceptibility (NMS). However, the genetics of NMS and the associated molecular responses are largely unexplored. Here, we analysed in rice the modification of biomass and susceptibility to the blast fungus pathogen in the Kitaake focal genotype in the presence of 280 different neighbours. Using genome-wide association studies, we identified the loci in the neighbour that determine the response in Kitaake. Using a targeted transcriptomic approach, we characterized the molecular responses in focal plants co-cultivated with various neighbours inducing a reduction in susceptibility. Our study demonstrates that NMS is controlled by one major locus in the rice genome of its neighbour. Furthermore, we show that this locus can be associated with characteristic patterns of gene expression in focal plant. Finally, we propose an hypothesis where Pi could play a role in explaining this case of NMS. Our study sheds light on how plants affect the physiology in their neighbourhood and opens perspectives for understanding plant-plant interactions

Plant neighbour-modulated susceptibility to pathogens in intraspecific mixtures

International audienceAs part of a trend towards diversifying cultivated areas, varietal mixtures are subject to renewed interest as a means to manage diseases. Besides the epidemiological effects of varietal mixtures on pathogen propagation, little is known about the effect of intraspecific plant–plant interactions and their impact on responses to disease. In this study, genotypes of rice (Oryza sativa) or durum wheat (Triticum turgidum) were grown with different conspecific neighbours and manually inoculated under conditions preventing pathogen propagation. Disease susceptibility was measured together with the expression of basal immunity genes as part of the response to intra-specific neighbours. The results showed that in many cases for both rice and wheat susceptibility to pathogens and immunity was modified by the presence of intraspecific neighbours. This phenomenon, which we term ‘neighbour-modulated susceptibility’ (NMS), could be caused by the production of below-ground signals and does not require the neighbours to be infected. Our results suggest that the mechanisms responsible for reducing disease in varietal mixtures in the field need to be re-examined