Light-dependent serine/threonine protein kinase that specifically phosphorylates N-terminal threonine residues in psbA/D1, psbD/D2, psbC/CP43 and psbH, which are components of the core antenna complex of photosystem II. Phosphorylation of PSII core components facilitates the exchange of chlorophyll proteins between the grana and the stroma lamellae. Also involved in the phosphorylation of the calcium-sensing receptor (CaS). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Not significantly affected in state transitions. Enhanced thylakoid folding and reduced mobility of thylakoid proteins under low-light conditions. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. Extended N-terminus.