Negative regulator of freezing tolerance that phosphorylates 14-3-3 proteins (e.g. GRF6) thus triggering their translocation from the cytosol to the nucleus in response to cold stress. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by cold. Interacts with and phosphorylates 14-3-3 proteins. Binds to GRF6 at the plasma membrane. Accumulates upon P.brassicae oviposition and in response to bacterial elicitors (e.g. flg22 and elf26). Autophosphorylated. Enhanced freezing tolerance due to impaired phosphorylation and subsequent translocation of 14-3-3 proteins in cold conditions. Altered cold induction of cold-responsive C-repeat-binding factor (CBF) target genes. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.