Functional characterization of Arabidopsis ER-PM contact sites as non-vesicular lipid transfer platforms

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Plants are sessile organisms frequently exposed to changing environmental conditions during their life cycle. Consequently, plant cells have evolved complex regulatory mechanisms that enable the transduction of extracellular signals and promote specific adaptive responses to environmental cues. Plant cells are separated from the environment by the plasma membrane (PM). This external lipid membrane encloses the cells' content and facilitates the controlled exchange of ions and organic compounds with their surroundings. The PM is also a crucial signaling hub and lipids at the PM act as a primary sensor for the activation of cellular responses to biotic (e.g. bacteria, fungi) and abiotic (e.g. salinity, drought, cold) stresses. Although seemingly uniform in appearance, minor changes on the PM lipid distribution heavily affect downstream cellular responses to stresses. In most cases, the biological significance of these changes remains unclear, but numerous studies linking plant stress hypersensitivity and PM lipid disequilibrium underscores the need for homeostatic regulatory mechanisms to control the PM lipid composition in space and time.*** In mammalian cells, PM lipid homeostasis is regulated by a network of endoplasmic reticulum (ER)-PM Contact Sites (EPCS) that facilitate the non-vesicular exchange of lipids between their synthesis site at the ER and their action site at the PM. In plants, our recent research has advanced our understanding of the structure and molecular organization of the plant EPCS, and has established critical roles for EPCS components in the regulation of lipid-mediated responses to stress; however, the role of plant EPCS as platforms for non-vesicular lipid exchange is only supported by indirect evidence. Here, I will use the model plant Arabidopsis thaliana to understand whether, how, and why plant EPCS regulate non-vesicular lipid transfer in response to environmental stresses. The proposed research will use bioinformatics and cell biology approaches to obtain an inventory of proteins regulating EPCS organization and lipid transfer, biochemical approaches to establish their molecular function, and genetic approaches to uncover the regulatory networks that translate the EPCS function into stress responses at the organism level.*** The dissection of mechanisms controlling EPCS function during stress represents an important step towards understanding cellular processes, including lipid transfer, ionic transport, and intracellular signaling, believed to be regulated at plant EPCS. In the long-term, our research program strives to provide a solid theoretical foundation and a collection of genetic targets for the future development of stress tolerant crops. Due to the severe environmental stresses associated with climate change, we envision that these crops will have a competitive edge in the market, and will enable more sustainable agricultural practices in Canada and abroad.**