LAUSR

Heterotrimeric GTP-binding proteins (G proteins) are a group of regulators essential for signal transmission into cells. Regulator of G-protein signaling 1 (AtRGS1) possesses intrinsic GTPase-accelerating protein (GAP) activity and could suppress G-protein and glucose signal transduction in Arabidopsis (Arabidopsis thaliana). However, how AtRGS1 activity is regulated is poorly understood. Here we identified a knockout mutant of OXYSTEROL BINDING PROTEIN-RELATED PROTEIN 2A, orp2a-1, which exhibits similar phenotypes to the arabidopsis g-protein beta 1-2 (agb1-2) mutant. Transgenic lines overexpressing ORP2A displayed short hypocotyls, a hypersensitive response to sugar and lower intracellular AtRGS1 levels than the control. Consistently, ORP2A interacted with AtRGS1 in vitro and in vivo. Tissue-specific expression of two ORP2A alternative splicing isoforms implied functions in controlling organ size and shape. Bioinformatic data and phenotypes of orp2a-1, agb1-2 and the orp2a-1 agb1-2 double mutant revealed the genetic interactions between ORP2A and Gβ in the regulation of G-protein signaling and sugar response. Both alternative protein isoforms of ORP2A localized in the ER, plasma membrane (PM) and ER-PM Contact Sites and interacted with vesicle-associated membrane protein-associated protein 27-1 (VAP27-1) in vivo and in vitro through their FFAT-like motif. ORP2A also displayed differential phosphatidyl phosphoinositide binding activity mediated by the PH domain in vitro. Taken together, the Arabidopsis membrane protein ORP2A interacts with AtRGS1 and VAP27-1 to positively regulate G-protein and sugar signaling by facilitating AtRGS1 degradation.