Abstract

G-protein and calcium signaling have both been shown to play a role in the response to environmental abiotic stress in plants; however, the interaction between calcium-binding proteins and G-protein signaling molecules remains elusive. This study examines the interactions between RD20/CLO3 and Gα (the alpha subunit of the G-protein complex) from Arabidopsis, and their closest homologs, Ta-CLO3 and Ta-GA3 in wheat (Triticum aestivum). Using in vitro GTPase assays, it is demonstrated that RD20/CLO3 and Ta-CLO3 have GTPase-activating protein (GAP) activity toward GPA1 and Ta-GA3, respectively, and this activity is potentiated by high calcium levels indicative of stress conditions. Phenotypic examination of mutant plants reveals a pattern of phenotypes congruent with the hypothesis of RD20/CLO3 acting as a downregulator of GPA1 activity. These findings reveal a novel role for RD20/CLO3 in regulating plant stress response. Furthermore, this work sheds light on the molecular mechanisms involved in controlling stomatal density under abiotic stress. In vivo interactions were tested through bimolecular fluorescence complementation (BiFC) with other caleosin proteins to further characterize the caleosin gene family. The work contributes to the understanding of G-protein signaling in response to environmental stress conditions.