Calcium-independent kinase involved in light-dependent phosphoenolpyruvate carboxylase phosphorylation. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Constitutively active and not activated by phosphorylation. A number of isoforms are produced. According to EST sequences. Expressed in rosette leaves, and to lower levels in flowers and roots. Barely detectable in siliques, cauline leaves and stems. Up-regulated by light, cycloheximide, phosphate starvation, carbon availability and high pH. Down-regulated by phosphate and phosphite. Not under circadian control and not affected by nitrogen supply. Retarded growth and loss of light-induced phosphoenolpyruvate carboxylase phosphorylation, but little or no effect on the metabolic flux through the anaplerotic pathway. Lacks the autoinhibitory region and EF hands found in calcium-dependent protein kinases. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.