FIGURE 1.

Cold stress signaling in a plant cell. The plasma membrane is considered as one of the primary target for cold sensing and eventual transmission of Ca²⁺ signals into the plant cell nuclei. Cyclic nucleotide-gated channels (CNGCs), glutamate receptor-like channels (GLRs), and the MID1-complementing activity (MCA) channels are the main plasma membrane Ca²⁺ channels that allow the entry of Ca²⁺ ions into the cytoplasm. Once the Ca²⁺ ion enters the plant cell, they are sensed by Calmodulins (CaMs) and Calmodulin-like proteins (CMLs), Calcineurin B-like proteins (CBLs), and Ca²⁺-dependent protein kinases (CDPKs). Upon cold exposure, plasma membrane associated cold sensor chilling-tolerance divergence 1 (COLD1) interacts with G protein a subunit (RGA). Ca²⁺/CaM regulated receptor-like kinase (CRLK) positively regulate cold triggered gene expression by inducing the MEKK1–MKK2–MPK4 pathway. CRLK suppress cold-induced activation of MPK3/6 and is necessary for inducer of CBF expression (ICE) accumulation. ICE proteins are stabilized by either phosphorylation (P) or sumolyation (S). Calmodulin binding transcription activators (CAMTAs) activate C-repeat binding factor (CBF) expression through the CM2 (CCGCGT) promoter motif. CBF proteins eventually activate the expression of various cold-responsive (COR) genes which confers cold tolerance in plants.