External-calcium Signal Transduction in Arabidopsis Guard Cells

环境信号的感知对植物的各种生理和发育过程都是至关重要的。在植物细胞中，外界信号触发细胞内游离钙离子的增加是公认的。然而，控制这些胞浆钙变化的分子成分却知之甚少。拟南芥细胞外钙敏感受体(CAS)可能是迄今为止克隆的唯一一种细胞表面受体，它能将外界刺激转化为植物细胞内钙的升高。CaS在Ca~(2+)诱导的气孔关闭中起重要作用，气孔是由叶表面的一对保卫细胞形成的。这个项目的长期目标是了解保卫细胞中钙离子o信号转导的分子机制。在本项目中，将进行以下实验：(1)通过定点突变和缺失突变来鉴定CAS N-末端的钙结合位点；(2)利用异源表达系统确认CAS激活的钙离子引发的钙释放，并启动拟南芥1，4，5-三磷酸(IP3)受体的筛选；以及(3)通过复合纯化来鉴定CAS下游的分子成分。这个项目不仅将进一步了解保卫细胞的钙信号，而且还将阐明植物中控制外部信号感知的钙机制。该项目的更广泛影响将包括教授和培训下一代博士后、研究生和本科生级别的科学家。

The perception of environmental signals is crucial for various physiological and developmental processes in plants. It is well established that external signals trigger cytosolic free Ca2+ increases in plant cells. However, the molecular components governing these cytosolic Ca2+ changes are poorly understood. The Arabidopsis extracellular Ca2+ (Ca2+o)-sensing receptor (CAS) may represent the only cell-surface receptor cloned so far that has been shown to convert an external stimulus into cytosolic Ca2+ increases in plants. CAS plays an essential role in Ca2+o-induced closing of stomatal pores, which are formed by pairs of guard cells in leaf surface. The long-term goal of this project is to understand the molecular mechanisms of Ca2+o signal transduction in guard cells. In this project, experiments will be carried out to (1) identify Ca2+-binding sites in the CAS N-terminus by site-directed and deletion mutation; (2) confirm Ca2+o activation of CAS triggering Ca2+ release using heterologous expression systems and initiate a screen for Arabidopsis inositol 1,4,5-trisphosphate (IP3) receptor; and (3) identify the molecular components downstream of CAS through complex purification. This project will not only further understanding of guard cell Ca2+o signaling but also shed light on the Ca2+ machineries governing external-signal perception in plants. The broader impacts of this project will include teaching and training of the next generation of scientists at the postdoctoral, graduate, and undergraduate levels.