May play a role in signal transduction of hyperosmotic response (Probable). Can phosphorylate ABI5 in vitro (PubMed:21055780). Can phosphorylate BZIP46 in vitro (PubMed:22301130). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by hyperosmotic stress. Interacts with BZIP46. Expressed in leaf blades and leaf sheaths. Expressed in shoots and roots of young seedlings. Weakly induced by hyperosmotic stress in leaf blades, leaf sheaths and roots. Weakly induced by abscisic acid (ABA) in leaf blades and roots. May be phosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.