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

植物是在其生命周期中经常暴露于不断变化的环境条件下的无根生物。因此，植物细胞已经进化出复杂的调节机制，使细胞外信号的转导和促进对环境信号的特定适应性反应成为可能。植物细胞通过质膜（PM）与环境分离。这种外部脂质膜包裹着细胞的内容物，促进了离子和有机化合物与周围环境的可控交换。PM也是一个重要的信号中枢，PM上的脂质是激活细胞对生物（如细菌、真菌）和非生物（如盐度、干旱、寒冷）胁迫反应的主要传感器。虽然表面上看起来是一致的，但PM脂质分布的微小变化严重影响下游细胞对应激的反应。在大多数情况下，这些变化的生物学意义尚不清楚，但许多研究将植物胁迫超敏性与PM脂质失衡联系起来，强调需要稳态调节机制来控制PM脂质在空间和时间上的组成。在哺乳动物细胞中，内质网(ER)-PM接触位点（EPCS）网络调节PM脂质稳态，该网络促进内质网合成位点和PM作用位点之间的脂质非囊性交换。在植物中，我们最近的研究提高了我们对植物EPCS结构和分子组织的理解，并确定了EPCS成分在调节脂质介导的应激反应中的关键作用；然而，植物EPCS作为非囊泡性脂质交换平台的作用仅得到间接证据的支持。在这里，我将使用模式植物拟南芥来了解植物EPCS是否，如何以及为什么在响应环境胁迫时调节非囊泡性脂质转移。该研究将使用生物信息学和细胞生物学方法来获得调节EPCS组织和脂质转移的蛋白质清单，使用生化方法来确定其分子功能，使用遗传学方法来揭示将EPCS功能转化为生物体水平应激反应的调节网络。对胁迫下EPCS功能控制机制的解剖是理解细胞过程的重要一步，包括脂质转移、离子运输和细胞内信号传导，这些过程被认为是由植物EPCS调节的。从长远来看，我们的研究计划致力于为未来开发耐胁迫作物提供坚实的理论基础和遗传靶点集合。由于与气候变化相关的严重环境压力，我们设想这些作物将在市场上具有竞争优势，并将在加拿大和国外实现更可持续的农业实践。

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.