Involved in cell differentiation. Required for the specification of stamen and carpel identities and for the proper termination of stem cells in the floral meristem. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] [DNA-directed RNA polymerase] + ATP = ADP + H(+) + phospho-[DNA-directed RNA polymerase] Interacts with MED14, HDA19 and LUG. Interacts with KIN10 (PubMed:23229550). Expressed in roots, leaves and stems. Expressed in young dividing tissue, such as shoot and root tips, lateral root primordia, young leaves and flowers. Expressed in the inflorescence meristem, inflorescence stem and young flowers. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. CDC2/CDKX subfamily.