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] Expressed in flowers and roots, and at lower levels in cauline leaves. Barely detectable in rosette leaves and stems. Up-regulated by light, cycloheximide, phosphate starvation, carbon availability and high pH. Down-regulated by phosphate and phosphite. Very high sensitivity to phosphate at low pH. Not under circadian control and not affected by nitrogen supply. Lacks the autoinhibitory region and EF hands found in calcium-dependent protein kinases. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.