May play a role in signal transduction of hyperosmotic response (Probable). Can phosphorylate BZIP46 in vitro (PubMed:22301130). Together with ABI5, PP2C30 and PYL5, is part of an abscisic acid (ABA) signaling unit that modulates seed germination and early seedling growth (PubMed:22071266). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by phosphorylation in response to hyperosmotic stress within 5 minutes. Interacts with BZIP46 (PubMed:22301130). Interacts with ABI5 and PP2C30 (PubMed:22071266). Interacts with PP2C51 (PubMed:28000033). Expressed in leaf blades, leaf sheaths and roots. Expressed in shoots and roots of young seedlings. By hyperosmotic stress in leaf blades and leaf sheaths, but not in roots (PubMed:15084714). Induced by abscisic acid (ABA) (PubMed:22071266). The C-terminal region is necessary for the kinase activation in response to hyperosmotic stress. Phosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.