Regulation of plant drought tolerance by AT-rich Interaction domain (ARID) proteins

Drought is a common adverse environmental condition that can significantly decrease crop productivity. Plants have evolved sophisticated mechanisms to mitigate the impact of drought stress. One such mechanism is to quickly close stomata to minimize water loss from transpiration via the stomatal pore. Stomatal pore is formed by a pair of guard cells that swell or shrink upon gaining or losing water, leading to opening or closing of the pore, respectively. Previous studies demonstrate that plants regulate stomatal movement mainly via posttranslational modifications of ion and solute transporters on guard cell membranes. The guard cell signal transduction that culminates at these modifications and the resulting stomatal movement represents one of the best-studied signaling processes in plants. Given the complexity of plant drought responses, however, additional mechanisms to regulate transpiration may also exist. To uncover these mechanisms, we conducted large-scale genetic screens using infrared thermo-imaging methods to isolate mutants defective in transpiration regulation in the model plant Arabidopsis. A mutant in an AT-rich interaction domain (ARID)-containing protein was isolated in the screen because of its lower leaf temperatures and higher transpiration rates. ARID proteins are nuclear DNA-binding proteins found in all eukaryotes and are involved in chromatin modifications and gene transcription. The discovery of this ARID protein as essential for transpiration regulation suggests that indeed there are hidden mechanisms in addition to protein posttranslational modifications that also regulate stomatal movement. In this study, we will investigate the underlying mechanisms for this ARID protein’s regulation of transpiration and drought stress tolerance. The specific objectives of this study are: 1) to determine the physiological processes regulated by the ARID protein; 2) to identify direct molecular targets of this ARID protein during drought stress responses; and 3) to reveal the modes of action for this protein’s regulation of transpiration. The current study will uncover novel mechanisms of transpiration regulation and the results have direct implications for improving drought stress tolerance in crop plants.