Required during the differentiation of the protoderm into shoots epidermis and cuticle. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Autophosphorylated and phosphorylated by ACR4. Various epidermal defects, including disorganization of epidermis-related tissues, defects in the leaf cuticle and the fusion of organs. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.