Acts with CLE41p and CLE44p peptides as a ligand-receptor pair in a signal transduction pathway involved in the regulation of procambium maintenance and polarity during vascular-tissue development (PubMed:17570668, PubMed:18812507, PubMed:27055373). Mediates repression of tracheary element differentiation and the promotion of procambial cells formation and polar division adjacent to phloem cells in the veins (PubMed:17570668, PubMed:18812507, PubMed:27055373). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts specifically with the mature peptides CLE41p and CLE44p, especially in the presence of SERK2 (PubMed:18812507, PubMed:27055373, PubMed:27449136, PubMed:27498761). Interacts with LURE1.2 (PubMed:26863186). Widely expressed along the vascular strands. In roots and hypocotyls, confined to procambial cells. Reduced procambial cells number, and adjacent or interspersed xylem and phloem formation. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.