Figure 1.

Calcium signaling-mediated plant response to cold stress in Arabidopsis. The perception of cold stimulus is the first step in the activation of cold tolerance in plants. Plants sense cold signals through the recognition of the changes in cellular membrane by cold stress, or cold signals sensor, COLD1. The perception of cold stimulus activates cold responsive Ca²⁺ channels (MCA1 and MCA2) or other unknown Ca²⁺ channels and/or pumps to induce Ca²⁺ transients, also knowns as Ca²⁺ signals or signatures. The cold stress-induced Ca²⁺ transient changes in plant cell and the expression of AtSRC2 subsequently facilitate the production of ROS, through the activation of Ca²⁺-mediated NADPH oxidase activity of AtRBOHF. Enhanced ROS further activates Ca²⁺ channels and/or pumps for inducing Ca²⁺ transients to form a positive feedback. CPKs also relay cold-triggered Ca²⁺ signals into phosphorylation and activation of the MAPK cascade. In addition, the MAPK cascade is activated by CRLK1 or CRLK2 through the interaction with calmodulin (CaM) in response to cold stress. The MAPK signaling pathway triggered by cold stress suppresses the degradation of ICE1 to establish cold tolerance in plants. CaM also relays cold stress-triggered changes into transcriptional reprogramming via AtSR1/CAMTA3. Solid arrows represent physical interaction and/or positive regulation (induction). Dashed arrows represent mechanism that is unclear.