Characterizing the early dialogue between host plants and pathogenic oomycetes: biological and physical approaches – COOL

Reducing the environmental impact of chemical treatments and controlling epidemics are two imperatives of modern agriculture. In the soil, a plant disease begins with the interaction between root cells and a pathogen. A molecular dialogue is established and leads successively to the attraction of the pathogen towards the host, adhesion and aggregation, association with telluric microorganisms, penetration and then colonization of plant tissues. In recent years, advances in knowledge have mainly concerned the stages of penetration and colonization. Concerning the upstream events, the mechanisms of regulation remain to be characterized. COOL is a project that explores the early communication established between host plants, pathogens of the oomycetes class and soil bacteria. It focuses on the stages of attraction and aggregation. Oomycetes of the Phytophthora genus are a major class of plant eukaryotic pathogens, with high impact in agro- and ecosystems. They disseminate as zoospores which are biflagellate cells that swim towards the root plants during the attraction phase. Previous analyses have shown that during the Arabidopsis thaliana -Phytophthora parasitica interaction, the zoospores move and preferentially aggregate on the surface of the root elongation zone whose physiological activity generates cationic gradients. They also showed that the in vitro application of ion gradients in microfluidic devices is sufficient to control zoospore swimming and cause their aggregation. Using the tripartite interaction Arabidopsis thaliana-Phytophthora parasitica-bacteria as a model, the COOL project explores the hypothesis that the ionic gradients generated by the host root in the rhizosphere have a critical effect on the attraction and aggregation of zoospores to the infection site, as on disease. COOL is focused on the characterization of the role of proton gradients in the regulation of attraction signal(s). The objectives are, firstly to characterize the proton pumps of the host plant that regulate the behavior of zoospores and bacteria around the root elongation zone, and on the other hand, to understand their mode of action. Cool is an interdisciplinary project that brings together expertise in the fields of biology and genetics of plant-oomycete interactions, biophysics of biofilms, microfluidics and physics of spore movement, pH homeostasis and ion membrane electrophysiology. COOL will contribute to understand the adaptation of oomycetes to the root environment for moving towards a host. It will provide new tools and methods for analyzing biotic interactions in the rhizosphere. Ultimately, this research could help develop solutions for managing soil diseases.