Calcium-dependent protein Kinases: Bridging growth and stress responses in plants

Plants have evolved complex signal transduction networks to regulate metabolism and adapt to their environment. Calcium ions serve as key messengers in these pathways, playing central roles in a wide range of signal transduction processes. In plants, multiple classes of calcium-binding proteins can detect transient calcium signal fluctuations triggered by various stimuli, and initiate downstream responses. Calcium-dependent protein kinases (CDPKs), single-molecule Ca²⁺ sensor and effector proteins in plants, detect calcium signals and convert them into phosphorylation events, making them ideal tools for signal transduction. In this review, we provide a comprehensive review of the structural characteristics and functional features of CDPKs. We present a systematic analysis of the modular architecture of CDPKs, which determines their biological functions in plants. To elucidate how CDPKs localization to specific organelles shapes their regulatory roles in development and stress signaling, we discuss the regulatory roles of CDPKs in plant developmental processes through environmental signal transduction and hormonal signaling cascades. We further delineate the functional specialization of CDPKs in responses to abiotic stress (e.g., drought, salinity, cold, and heat) and biotic stress (e.g., pathogen defense). Three priority directions for future CDPK research are also proposed: elucidation of the molecular mechanisms underlying growth plasticity; determination of multi-signal homeostasis maintenance mechanisms; and exploring allele-specific variations for crop adaptability improvement. This review establishes a foundation for the relation between CDPK-mediated signaling networks and plant phenotypic plasticity in fluctuating environments.