Involved in epidermal-cell morphogenesis in hypocotyls and roots. May act on the microtubule function. May have a secondary role in trichome branching. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with ARK1, ARK2 and ARK3 (via C-terminus). Belongs to the protein kinase superfamily. NEK Ser/Thr protein kinase family. NIMA subfamily.