The Cyclophilin ROC3 Regulates ABA-Induced Stomatal Closure and the Drought Stress Response of Arabidopsis thaliana

Abstract

Drought causes a major constraint on plant growth, development, and crop productivity. Drought stress enhances the synthesis and mobilization of the phytohormone abscisic acid (ABA). Enhanced cellular levels of ABA promote the production of reactive oxygen species (ROS), which in turn induce anion channel activity in guard cells that consequently leads to stomatal closure. Although Cyclophilins (CYPs) are known to participate in the biotic stress response, their involvement in guard cell ABA signaling and the drought response remains to be established. The <i>Arabidopsis thaliana</i> gene <i>ROC3</i> encodes a CYP. Arabidopsis <i>roc3</i> T-DNA mutants showed a reduced level of ABA-activated S-type anion currents, and stomatal closure than wild type (WT). Also, <i>roc3</i> mutants exhibited rapid loss of water in leaf than wild type. Two complementation lines of <i>roc3</i> mutants showed similar stomatal response to ABA as observed for WT. Both complementation lines also showed similar water loss as WT by leaf detached assay. Biochemical assay suggested that <i>ROC3</i> positively regulates ROS accumulation by inhibiting catalase activity. In response to ABA treatment or drought stress, <i>roc3</i> mutant show down regulation of a number of stress responsive genes. All findings indicate that <i>ROC3</i> positively regulates ABA-induced stomatal closure and the drought response by regulating ROS homeostasis and the expression of various stress-activated genes.