May be involved in brassenosteroid (BR) perception in roots. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Highly expressed in roots. Expressed at low levels in shoots. Contains two pairs of conservatively spaced Cys (Cys pair 1 and 2) possibly involved in forming some heterodimers. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.