Required for cold tolerance, via the activation of MAP kinases activity (PubMed:20026608, PubMed:20724845). Phosphorylates and activates MEKK1 in response to cold in a calcium-dependent manner (PubMed:23857079). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Kinase activity is stimulated by calcium/calmodulin, but blocked by chlorpromazine. Interacts with calmodulin (CaM) in a calcium- (Ca(2+)-) dependent manner (PubMed:20026608). Binds to MEKK1 (PubMed:20724845). Similar transcript expression levels in seedlings, roots, leaves, stems and flowers, and lower levels in siliques, but protein accumulates mostly in 7-day-old seedlings, old roots and young leaves and, to a lower extent, in young roots, old leaves, flowers and siliques (at protein level). Differential expression between transcripts and proteins. Induced transiently by cold and hydrogen peroxide H(2)O(2) treatments despite stable transcript level (at protein level). Increased sensitivity to chilling and freezing temperatures, associated with a delayed induction of cold-responsive genes (PubMed:20026608, PubMed:20724845). Impaired MAP kinases activation in response to cold (PubMed:20724845). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.