Involved in the regulation of cellular expansion and differentiation. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with PUB9, PUB13, PUB14 and PUB38. Expressed in the root-hypocotyl transition zone, at the base of lateral roots, axillary buds and pedicels. By wounding and Xanthomonas campestris pv. campestris. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.