Arabidopsis ORP2A positively regulates glucose signaling by interacting with AtRGS1 and promoting AtRGS1 degradation

Heterotrimeric GTP-binding proteins (G proteins) are a group of regulators essential for signal transmission into cells. AtRGS1 (Regulator of G protein Signaling 1) with intrinsic GTPase-accelerating protein (GAP) activity could suppress G protein and glucose signal transduction in Arabidopsis. However, how AtRGS1 activity is regulated is currently poor understood. Here we identified a knockout mutant orp2a-1 (oxysterol-binding protein (OSBP)-related protein 2A) which shows phenotypes similar to agb1-2 (arabidopsis g-protein beta 1). With overexpression of ORP2A, transgenic lines display short hypocotyl, hypersensitivity to sugar and lower intracellular AtRGS1 level than control. Consistently, ORP2A shows interaction with AtRGS1 in vitro and vivo. Tissue specificity of ORP2A with two alternative protein forms imply its functions in organ size and shape controlling. Bioinformatic data and phenotypes of orp2a-1, agb1-2 and double mutant reveal genetic interactions in the regulation of G protein signaling and sugar response between ORP2A and G{beta}. Both alternative splicing forms of ORP2A locate in the ER, PM (Plasma Membrane) and EPCS (ER-PM Contact Sites), and interact with VAP27-1 mediated by a FFAT-like motif in vivo and vitro. ORP2A also displays differential phosphatidyl phosphoinositide binding activity mediated by its PH domain in vitro. Taken together, it is suggested that Arabidopsis membrane protein ORP2A interacts with AtRGS1 and VAP27-1 to positively regulate G protein and sugar signaling by facilitating AtRGS1 degradation.