Serine/threonine-protein kinase that could be involved in the negative regulation of root growth. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with KCBP, PERK8, PERK9, PERK10 AND PERK13. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.