Insights on Calcium-Dependent Protein Kinases (CPKs) Signaling for Abiotic Stress Tolerance in Plants

Abstract

Abiotic stresses are the major limiting factors influencing the growth and productivity of plants species. To combat these stresses, plants can modify numerous physiological, biochemical, and molecular processes through cellular and subcellular signaling pathways. Calcium-dependent protein kinases (CDPKs or CPKs) are the unique and key calcium-binding proteins, which act as a sensor for the increase and decrease in the calcium (Ca) concentrations. These Ca flux signals are decrypted and interpreted into the phosphorylation events, which are crucial for signal transduction processes. Several functional and expression studies of different CPKs and their encoding genes validated their versatile role for abiotic stress tolerance in plants. CPKs are indispensable for modulating abiotic stress tolerance through activation and regulation of several genes, transcription factors, enzymes, and ion channels. CPKs have been involved in supporting plant adaptation under drought, salinity, and heat and cold stress environments. Diverse functions of plant CPKs have been reported against various abiotic stresses in numerous research studies. In this review, we have described the evaluated functions of plant CPKs against various abiotic stresses and their role in stress response signaling pathways.

Keywords: ABA; calcium signaling; calcium-dependent protein kinases; drought; salinity.

Figure 1

Structure and activation process of plant CPKs. (A) CPK domain structure under the inactive state, (B) activation of CPKs after the binding of Ca²⁺ to the active site of the protein kinase domain (PKD), the autoinhibitory junction (AJ), and calmodulin-like domain (CaM-like domain, CaM-LD).

Figure 2

Role of different CPKs under various abiotic stresses; (A) Ca²⁺-dependent ABA-mediated drought and salt stress signal recognition by CPKs; (B) Ca²⁺ binding at the active site of protein kinase domain (PKD); (C) some drought-responsive genes involved in metabolite regulation and signal transduction pathways; (D) some salt-responsive genes and their role in antioxidant production (i.e., H₂O₂), as well as ROS detoxification; (E) some cold stress-responsive genes and their interaction genes activation; and (F) phosphorylation events controlling the anion channel regulation, K⁺-inward channel regulation, Ca²⁺-concentration, and channel regulation in the cell, and ABA-mediated CATALASE 3 regulation in plant cells.