ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with ARAC5. Mostly expressed in leaf primordia, root and shoot apical meristems, lateral root primordia, and stele of older roots and hypocotyls. In leaves and cotyledons, highest levels observed in trichomes, vasculatures, and hydathode endothem. Phosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.