External-calcium Signal Transduction in Arabidopsis Guard Cells

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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.