Role of Calcium in Plant Stress Signalling: Molecular Mechanisms and Gene Expression Modulation

Calcium (Ca 2+ ) is a versatile signaling molecule crucial for mediating diverse physiological and defense responses under biotic and abiotic stress conditions. Specific Ca 2+ “signatures” are generated in different cellular compartments and decoded by sensor proteins such as calmodulins, calcium‐dependent protein kinases (CDPKs/CPKs), and calcineurin B‐like proteins (CBLs) with their CIPK partners. These sensors coordinate early defense events, including stomatal regulation, hypersensitive cell death, and systemic acquired resistance. Ca 2+ signaling also regulates the production of reactive oxygen species, activation of phytohormone pathways, and expression of stress‐responsive genes. At the molecular level, Ca 2+ influences chromatin remodelling and controls enzymes that mediate post‐translational modifications (PTMs), including phosphorylation and S‐nitrosylation. These modifications fine‐tune protein function and reprogram transcriptional responses. Understanding the molecular basis of Ca 2+ signaling is critical for unraveling the complex regulatory networks that govern plant defense. This review highlights its links with PTMs and adaptive gene expression. It also outlines how these mechanisms contribute to plant immunity and abiotic stress adaptation.