Protein kinase required for hyphal elongation. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Produced preferentially in dark grown mycelia. Produced preferentially in illuminated mycelia. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. COT1 subfamily.