Water is crucial to all aspects of plant growth, development and ecological distribution, as well as agricultural production. Drought triggers osmotic-stress signaling events in plants, which regulate the gene expression network and subsequent physiological and developmental processes, reducing water loss. Among these signaling events, the initial perception for osmotic stress is poorly understood at the gene level. The project is designed to identify and study the genes encoding sensors for drought/water as well as their regulatory components in plants. In this project, the identification and examination of the gene family of water sensors will not only further our understanding of how plants sense water, but also provide potential genetic targets for engineering drought resistant plants, such as crops, grasses and trees.
It is well established for over the last 20 years that osmotic stress evokes a transient increase in cytosolic Ca2+ concentration ([Ca2+]i), which is thought to be involved in osmosensing. However, the molecular nature of the corresponding osmosensing components remains largely unknown. Using aequorin Ca2+ imaging-based unbiased forward genetic screens, Arabidopsis mutants defective in osmotic stress-induced [Ca2+]i increases (oici) were previously isolated, and one gene, OSCA1, was identified as the founding member of a functionally novel and evolutionarily conserved family of channel proteins. OSCA1 forms hyperosmolality-gated, non-selective cation channels with Ca2+ permeability in the plasma membrane. Suppression of OSCA1 results in attenuated osmotic signaling in stomatal movements and root growth, suggesting that OSCA1 functions as an osmosensor in plants. In this project, the detailed biophysical properties of OSCA1 channels will be determined (Aim 1). Then, 14 other OSCA1 homologs will be screened for their osmosensing activities (Aim 2), and their physiological functions in drought stress and root hydrotropism will be assessed (Aim 3). Finally, novel osmosensing-related components will be isolated via fine-mapping of additional oici mutants (Aim 4). This project will establish the Ca2+-mediated sensory machinery by which plants perceive water availability in both external environments and internal tissues.
