Regulates the auxin-related MAX (More Axillary Growth) pathway during the shoot branching. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Mostly expressed in apical parts, including flower buds, and particularly in anthers. Also present in root hairs. Repressed by auxin (IAA) treatment. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.