RIPOSTE

Crop loss due to pests and diseases creates a major constraint on achieving food security. The growing global demand for sustainable food supplies and the need to reduce reliance on pesticides drive the search for complementary alternatives to plant disease control. The importance and complexity of pathogen perception and signaling pathways in the regulation and execution of plant immune responses have become apparent during the last years. Notably, R gene-mediated immunity has been shown to be the most efficient form of resistance in plants, but it is also not durable. Additional forms of resistance have gained increasing attention for breeding purposes, such as quantitative resistance, but they are still poorly understood. In addition, resistance management in the context of evolving plant diseases must take into account that investment into immunity has a trade-off with plant fitness in complex ways. Thus, to enhance plant stress tolerance and maintain productivity in terms of yield and biomass, there is a need to (i) understand the molecular diversity of resistances, (ii) identify hubs for pathogen ingress and rejection, (iii) establish the cost/benefit trade-off associated with defense genes, (iv) propose new management strategies to maintain durable resistance in an agro-ecological context, and (v) translate all this knowledge to crop species. By combining the expertise of three public teams and an industrial partner with a common interest in identifying novel resistance mechanisms and promoting their sustainability in an agro-ecological context, this proposal will exploit genetic diversity of Quantitative Disease Resistance mechanisms to identify possible sources of disease tolerance in the model plant (Arabidopsis thaliana) and in crops (Brassica, pepper and tomato). The project is based on the recent identification by partners 1 and 2 of the RKS1 gene by map-based cloning and Genome Wide Association (GWA) mapping of a major QTL in A. thaliana to Xanthomonas campestris pv. campestris (Xcc), a bacterial pathogen infecting the vascular system of plants and causing black rot disease, possibly the most important disease of crucifers. In WP1, knowledge will be provided on the integration of RKS1 with the existing defense pathways known in plants, and on the characterization of the regulatory pathway(s) controlling and controlled by RKS1. Elucidation of the forces promoting the maintenance of the RKS1 polymorphism in natural populations by (i) estimating the cost/benefit trade-offs along a range of infection intensities (WP2), and (ii) developing realistic models to understand and predict the adaptive dynamics of quantitative resistance alleles in natural populations (WP3), will allow to evaluate the suitability of the RKS1 gene (and other genes identified in WP1) for applications in crops. Finally, RKS1 and other candidate genes will then be directly tested in a high throughput manner, and through a non-GMO approach, for their potential value (alleles or orthologs) to control pathogens in tomato, pepper and Brassica in breeding programs (WP4). Through coordinated actions in fundamental and applied research, this project will contribute (i) to the dissection of a QDR resistance pathway, (ii) to one of the first comprehensive investigations of the link between ecological genetics and dynamics, and long-term evolutionary processes, and (iii) to predict the most robust plant protection systems in which increased pathogen tolerance has no (or low) impacts on other traits such as plant productivity.