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

植物是固着生物，在其生命周期中经常暴露在不断变化的环境条件下。因此，植物细胞进化出了复杂的调控机制，使细胞外信号的转导成为可能，并促进对环境提示的特定适应性反应。植物细胞由质膜(PM)与环境隔离。这种外部类脂膜包裹着细胞的内容物，并促进离子和有机化合物与其周围环境的受控交换。质膜也是一个重要的信号中枢，质膜上的脂质是细胞对生物(如细菌、真菌)和非生物(如盐分、干旱、寒冷)胁迫反应的主要感受器。虽然外观上看起来是一致的，但PM脂质分布上的微小变化会严重影响下游细胞对压力的反应。在大多数情况下，这些变化的生物学意义尚不清楚，但许多将植物应激过敏性与PM脂质失衡联系在一起的研究强调了需要动态平衡调节机制来控制PM脂质组成的空间和时间。在哺乳动物细胞中，质膜脂质动态平衡由内质网(ER)-质膜接触位点(EPCS)网络调节，EPCS促进内质网合成部位和PM作用部位之间的脂类非囊泡性交换在植物中，我们最近的研究提高了我们对植物EPCS的结构和分子组织的理解，并确立了EPCS组分在调节脂质介导的逆境反应中的关键作用；然而，植物EPCS作为非囊泡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、如何以及为什么调控非囊泡脂肪转移来响应环境胁迫。这项拟议的研究将使用生物信息学和细胞生物学的方法来获得调控EPCS组织和脂质转移的蛋白质的清单，使用生化方法来确定它们的分子功能，以及使用遗传方法来揭示在生物体水平上将EPCS功能转化为应激反应的调控网络。因此，对胁迫过程中控制EPCS功能的机制的剖析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递，据信这些过程在植物EPCS中受到调节。从长远来看，我们的研究计划努力为未来耐逆作物的发展提供坚实的理论基础和一系列遗传靶点。由于与气候变化相关的严重环境压力，我们预计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.