Glucose-regulated GTPase-accelerating protein (GAP) for the GTP-bound self-activating heterotrimeric G alpha protein GPA1. Cooperates with G beta-gamma dimers to maintain an unactivated but fully functional pool of GPA1. Phosphorylation-dependent endocytosis of RGS1 physically uncouples the two proteins, resulting in signal activation. Free AGB1 is essential, but not sufficient, for RGS1 endocytosis. Modulates cell proliferation, abscisic acid (ABA) and drought stress signal transduction by acting in a hexokinase-independent glucose-signaling pathway (PubMed:26528314). Involved in the shapes of leaves, the development of floral buds, the elongation of stems, siliques, and hypocotyls, the time of flowering and the regulation of guard-cell K(+) and anion channels. Important for the kinetics of voltage activation of inward K(+) current but not for the current amplitude. Interacts (via C-ter) with GPA1 (PubMed:14500984, PubMed:17951432, PubMed:18817773, PubMed:21952135). Interacts with WNK1, WNK8, WNK10, SYP23. The association with WNK8 at the plasma membrane is triggered by induction of glucose and continues with trafficking into endocytic compartments (PubMed:21952135). Interacts with NDL1, NDL2 and NDL3 (PubMed:19948787). Interacts with RHIP1 (PubMed:26528314). accumulates at the nascent cell plate during cytokinesis. Expressed in hypocotyls, cotyledons, guard cells and root and shoot apical meristems. Up-regulated by ozone. The C-terminal domain (249-459) is able to bind to and to accelerate the GTPase activity of GPA1. Phosphorylated by WNK8 and WNK10, and in vitro by WNK1. Also phosphorylated at Ser-435 or Ser-436. Increased cell elongation and longer hypocotyls when grown in the dark. Longer primary roots when grown in light due to increased cell production in root meristem. Loss of stratification requirement for seed germination. Decreased sensitivity to glucose and abscisic acid (ABA) in seed germination process (PubMed:26528314). No effect on ABA inhibition of stomatal opening.