Acts as negative regulator of salt tolerance (PubMed:18299802). Mediates sugar response during early seedling development (PubMed:24320620). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with UGT72E1. Colocalizes with UGT72E1 in the nucleus. Expressed roots, rosette and cauline leaves, and at lower levels in flowers and siliques. Down-regulated by salt treatment. No visible phenotype under normal growth conditions, but mutant plants exhibit increased tolerance to salt stress during germination (PubMed:18299802). No visible phenotype under normal growth conditions, but mutant plants display a sugar-resistant seedling development phenotype (PubMed:24320620). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.