Collaborative Research: Regulation of exocytic membrane trafficking required for cytokinesis and polarized cell expansion

质膜是所有细胞的外膜，它调节细胞内部和环境之间物质的进出。在植物中，质膜被细胞壁包围，细胞壁提供额外的机械强度和保护。大量新的质膜和细胞壁材料的产生是植物细胞分裂和扩张所必需的。此外，调节位于质膜上的蛋白质的活性、分布和丰度对于植物的生长和健康所必需的许多细胞过程是非常关键的，包括营养吸收、激素信号、病原体感知、胁迫反应和细胞壁的构建。本项目将侧重于了解质膜形成和维持所需材料的输送在细胞分裂和扩张过程中是如何控制的。更广泛的影响活动包括研究的内在价值，因为预计从这些研究中获得的信息将导致开发新的工具和战略，通过改进生物燃料和其他重要农学产品的生产，提高粮食安全和能源独立所需的作物的产量和质量。除了经济效益和科研效益外，该项目还将为本科生和研究生阶段的青年科学家提供重要的研究培训。参与这个项目的学生将接受现代细胞生物学研究的生物化学、遗传学和显微镜基础领域的高级培训。在植物中，多亚单位SCD复合体是通过一种称为胞吐作用的过程将膜、蛋白质和细胞壁材料输送到质膜上所必需的。SCD复合体的主要亚基包括含Denn结构域的蛋白SCD1(气孔胞质分裂缺陷1)和螺旋卷曲蛋白SCD2，它们是拟南芥细胞质分裂和细胞生长所必需的膜运输所必需的。此外，生化研究还发现了SCD复合体的另一个亚基MyTH1，它与后生动物I类肌球蛋白的膜结合区域有关。SCD复合体亚基的同源物存在于陆地植物和绿藻以及其他真核生物中，但在酵母和后生动物中丢失，这表明SCD复合体具有古老的进化起源。这个项目的具体目标是：1)确定SCD复合体的生化活性和调控；2)描述控制SCD复合体组装和胞外膜运输所需的膜结合的蛋白质-蛋白质和蛋白质-脂相互作用网络；3)在拟南芥和植酸菌(Physcomitrium(Physcomitrella)Patens)模型系统中进行SCD1、SCD2和MyTH1同源物的比较研究。这些结合的方法将提供对SCD复合体亚单位关键的保守和分化功能的洞察，这是胞外运输所必需的，跨越被子植物和苔藓植物之间的进化距离。此外，由于到目前为止，胞吐作用的机制主要是在缺乏SCD复合体的酵母和后生动物模型系统中研究的，该项目将产生对海洋、淡水和陆地生态系统的多样性和健康至关重要的其他植物和真核生物的胞吐分子机制的基本知识。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The plasma membrane is the outer membrane of all cells that regulates the entry and exit of material between the inside of the cell and its environment. In plants, the plasma membrane is surrounded by a cell wall that provides additional mechanical strength and protection. Production of large amounts of new plasma membrane and cell wall material is essential for plant cell division and expansion. In addition, regulation of the activity, distribution, and abundance of proteins located at the plasma membrane is highly critical for numerous cellular processes essential for growth and health of plants, including nutrient uptake, hormone signaling, pathogen perception, stress responses, and construction of the cell wall. This project will focus on understanding how the delivery of material required for plasma membrane formation and maintenance is controlled in dividing and expanding cells. Broader Impact activities include the intrinsic merit of the research as it is expected that the information gained in these studies will lead to the development of new tools and strategies for enhancing yield and quality of crop plants necessary for food security and energy independence through the improved production of biofuels and other agronomically important products. In addition to its economic and scientific benefits, this project will also provide important research training for young scientists at the undergraduate and graduate level. Students involved in this project will receive advanced training in the areas of biochemistry, genetics, and microscopy fundamental to modern cell biology research.In plants, the multisubunit SCD complex is essential for the delivery of membrane, proteins, and cell wall material to the plasma membrane by a process known as exocytosis. Major subunits of the SCD complex include the DENN domain-containing protein, SCD1 (stomatal cytokinesis defective1) and the coiled-coil protein, SCD2, which have previously been shown to be necessary for membrane trafficking required for cytokinesis and cell growth in Arabidopsis thaliana. Additionally, biochemical studies have identified another subunit of the SCD complex, MyTH1, which is related to the membrane-binding domain of metazoan class I myosins. Homologs of SCD complex subunits are present in land plants and green algae as well as other eukaryotes but were lost in yeast and metazoans, suggesting that the SCD complex is of ancient evolutionary origin. The specific aims of this project are to 1) define the biochemical activity and regulation of the SCD complex, 2) delineate the network of protein-protein and protein-lipid interactions that govern SCD complex assembly and membrane association required for exocytic membrane trafficking and 3) perform comparative studies of SCD1, SCD2, and MyTH1 homologs in the model systems Arabidopsis and Physcomitrium (Physcomitrella) patens. These combined approaches will provide insights into critical conserved and divergent functions of SCD complex subunits, necessary for exocytic trafficking, extending across the evolutionary distance between angiosperms and bryophytes. In addition, as the mechanisms of exocytosis have to date been primarily studied in yeast and metazoan model systems lacking the SCD complex, this project will generate fundamental knowledge of the exocytic molecular machinery of other plants and eukaryotes, which are important for the diversity and health of marine, freshwater, and terrestrial ecosystems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.