Invader

The epidermis is the first cellular barrier in direct contact with the environment in both animal and plant organisms. In plants, the epidermis consists of a monolayer of cells that can take different shapes and thickness depending on the type of organ they cover. During pollination or infection with pathogens, epidermal cells promptly react to the new comer in order to adjust the most relevant responses. The success of fertilization is tightly linked to the result of the early communication event occurring at the female organ surface between the pollen grain and the stigma epidermis. Similarly, following infection by filamentous pathogens, hypha grows on the epidermal surface before penetrating the inner tissues of the host and early response of the first cell layers including epidermal cells is decisive for the result of this cell-cell interaction. At the molecular level, extensive work has led to identification of components of the plant immune response with the discovery of the key role played by receptor-like kinases (RLK) in recognizing the pathogen-derived stimuli. Remarkably, the RLK FERONIA was initially found to be involved in pollen tube guidance during fertilization and later to play a negative role in resistance to the powdery mildew fungus, suggesting a similarity between the two processes. Besides, self-pollen recognition that occurs in self-incompatible (SI) species of the Brassicaceae family also involves a plasma membrane RLK. The rationale of this proposal relies on the assumption that further similarities may exist between these two mechanisms that control the growth of an invading organism (pollen tube/oomycete hypha). This project aims at characterizing the early cellular and molecular responses of plant epidermal cells following interaction with two types of cell, the pollen grain during the process of pollination when pollen lands on the stigma papilla surface, and the hyphae of filamentous pathogens during root infection. As mentioned earlier, while similarities between these two cell communications exist, a thorough comparative analysis of how epidermal cells respond to these two types of invasive organism has never been carried out. Using high-resolution live-cell imaging confocal microscopy, comparative translatomic/transcriptomic profiling and functional analysis, our study will provide invaluable information to better our understanding of the way epidermal cells sense and react to the growth of pollen tubes and hyphae. Our data will uncover common as well as specific features of these cell-cell interactions and will reveal the evolutionary relationships that exist between these processes. Altogether, the expected results of this research work should allow us to establish the first gene network linking plant reproduction and plant-pathogen response. Another originality of this project relies on the complementary expertise of developmental biologists (partner 1, SiCE team, ENS Lyon) and plant pathologists (partner 2, IPO team, INRA Sophia Antipolis), who will share their models and concepts to dissect the fundamental processes of plant reproduction and pathogen defense. Such collaborative research programs between these two communities are not so common, and we expect from these exchanges the discovery of novel and unanticipated concepts. Lastly, it is worth noting the biological and economical importance of these cellular communication mechanisms. Indeed, on one hand, successful pollen-stigma interaction is an indispensable prerequisite to fertilization and seed production in flowering plants. On the other hand, oomycetes represent some of the most devastating plant and animal pathogens. Sharing knowledge obtained from the study of these two processes will be greatly beneficial for a better understanding of cell-cell communication in plants during biotic interactions and will provide novel and unanticipated clues to develop innovative strategies for controlling these agronomical traits.