Role of SCD1 in Plant Cytokinesis and Polarized Cell Expansion

细胞的生长和分裂对多细胞动植物的正常生长和发育至关重要。这项工作的长期目标是了解在植物细胞分裂(胞质分裂)和植物细胞扩张过程中发生的细胞内小泡运输所涉及的分子事件和机制。在细胞质分裂期间，一个或多个胞外分泌途径朝着分裂平面极化--即分泌小泡移动到分裂部位--导致称为细胞板的细胞动细胞器的从头形成(细胞壁的前身结构，最终将两半分裂成单独的细胞)。类似地，植物细胞的扩张是通过携带膜和细胞壁成分的分泌小泡传递和融合到质膜上的特定位置，导致新的膜和壁成分嵌入到现有的细胞表面，从而实现细胞扩张。目前，对植物胞外和胞内途径的组织、它们与细胞骨架的相互作用以及参与这些复杂过程的分子机制知之甚少。Bednarek博士最近证明，在模式植物拟南芥中，一种植物特有的蛋白SCD1对细胞板的形成和极化细胞的扩张至关重要。SCD1是一个130 kDa的外周膜蛋白，含有一个N端Denn结构域(以人类Denn蛋白的氨基酸序列命名：在正常细胞和肿瘤细胞中差异表达)和8个C端WD-40重复序列，这通常与蛋白质之间的相互作用有关。虽然Denn结构域的确切功能尚不清楚，但已在与RABS(调节分泌性囊泡运输的小GTP酶)和其他信号蛋白(包括丝裂原激活的蛋白激酶)相互作用的动物蛋白中被鉴定。Bednarek博士假设，在细胞分裂和扩张过程中，SCD1可能调节囊泡运输和/或细胞骨架动力学。这个项目的目的是：1)研究SCD1在植物内膜系统中的定位和靶向；2)了解与SCD1相关的内膜的身份；以及3)识别植物极化膜运输所需的SCD1相互作用蛋白。该项目将使用实验方法，整合互补的正向和反向分子遗传学、细胞学和生化方法。该项目的成果将有助于理解植物分泌途径的功能和组织，以及它在细胞板生物发生和极化细胞扩张中的作用。该项目完成后，预计将了解SCD1在植物形态发生中的功能。这些研究也将有助于对含Denn结构域的蛋白在其他真核细胞膜转运和信号转导中的功能有一个全面的了解。更广泛的影响：该项目将为本科生、研究生和研究生水平的年轻科学家提供有价值的现代细胞生物学研究培训。研究生和博士后研究助理也将通过帮助本科生课堂教学和监督与资助项目相关的本科生自主学习项目来学习宝贵的教学和指导技能。该项目产生的所有试剂和研究工具将分发给其他实验室，以协助进一步确定膜运输和细胞骨架对植物生长和发育的调节。

Cell growth and division are crucial for normal growth and development of multicellular plants and animals. The long-term objective of this work is to understand the molecular events and mechanisms involved in intracellular vesicle trafficking that take place during plant cell division (cytokinesis) and plant cell expansion. During cytokinesis, one or more exocytic secretory pathways are polarized toward the plane of division - i.e., secretory vesicles move to the division site -- resulting in the de novo formation of the cytokinetic organelle known as the cell plate (a structure that is the precursor to the cell wall that will eventually divide the two halves into separate cells). Similarly, plant cell expansion is mediated through the delivery and fusion of secretory vesicles carrying membrane and cell wall components to specific sites on the plasma membrane, resulting in intercalation of new membrane and wall components to the existing cell surface and thereby cell expansion. At the present time, relatively little is known about the organization of the exocytic and endocytic pathways, their interaction with the cytoskeleton, and the molecular machinery involved in these complex processes in plants. Dr. Bednarek has recently demonstrated that, in the model plant Arabidopsis thaliana, a plant-specific protein, SCD1, is critical for cell plate formation and polarized cell expansion. SCD1 is a 130 kDa peripheral membrane protein containing an N-terminal DENN domain (named for the human DENN protein which it resembles in terms of amino acid sequence: Differentially Expressed in Normal and Neoplastic cells) and eight C-terminal WD-40 repeats, which are commonly associated with protein-protein interactions. Although the precise function of DENN domains is not known, they have been identified in animal proteins that interact with Rabs (small GTPases that regulate secretory vesicle trafficking) and other signaling proteins including mitogen-activated protein kinases. Dr. Bednarek hypothesizes that SCD1 may regulate vesicle trafficking and/or cytoskeletal dynamics during cell division and expansion. This project has been designed to: 1) study the localization and targeting of SCD1 within the plant endomembrane system; 2) learn the identity of SCD1-associated endomembranes; and 3) identify SCD1-interacting proteins required for polarized membrane trafficking in plants. The project will use experimental approaches that integrate complementary forward and reverse molecular genetic, cytological, and biochemical approaches. The outcome of this project is expected to contribute significantly to both an understanding of the function and organization of the plant secretory pathway and its role in cell plate biogenesis and polarized cell expansion. Upon completion of the project, it is expected that the function of SCD1 in plant morphogenesis will be understood. These studies will also contribute to a general understanding of the function of DENN-domain containing proteins in membrane trafficking and signaling in other eukaryotic cells. Broader Impact: This project will provide valuable research training in modern cell biology for young scientists at the undergraduate, graduate and postgraduate level. Graduate students and postdoctoral research associates will also learn valuable teaching and mentoring skills by assisting undergraduate classroom instruction and by supervising undergraduate independent study projects related to the funded project. All reagents and research tools generated by this project will be distributed to other laboratories to assist in the further characterization of membrane trafficking and cytoskeletal regulation of plant growth and development.