Plants interact with microbes (bacteria and fungi), in both friendly and hostile ways – this is the essence of plant symbiosis. My studies focus on the molecular recognition events that take place in such plant-microbe encounters, and on the plants' means to distinguish between friend and foe.

Plants have an extremely acute chemical sense, “a nose”, so to speak, for molecules that are characteristic of microbes. One of our preferred examples is the plant's ability to “smell” bacterial flagellin, the main component of the flagellum, which allows bacteria to move. Flagellin triggers massive changes in gene expression in the model plant Arabidopsis, and the response is reminiscent of the “innate immunity” response, thought to be a first line of defense in animals and humans. Plants respond very differently to “friendly” microbes, such as nitrogen-fixing rhizobia and mycorrhizal fungi. Using Medicago truncatula as a model plant, we study the recognition of such symbionts and the molecular events lea- ding to a mutually beneficial symbiosis.