In addition, the phosphorylation of MEKK1 via Ca2+ signaling has been detected during the cold response. Moreover, the Ca2+/calmodulin (CaM)-regulated receptor-like kinase, CRLK1, a positive regulator of the response to freezing temperatures that is activated in the presence of Ca2 CaM, can phosphorylate MEKK1. These reports suggest that the