CDPKs as Ca2+ signaling decoders in guard cell signaling

Stomatal movements are essential for balancing photosynthetic carbon dioxide uptake with water conservation and defense against pathogens. These processes are controlled by complex signaling networks in guard cells, in which calcium ions (Ca2+) act as a ubiquitous second messenger. Although stimulus-specific Ca2+ signatures have been well documented, how these signals are decoded into distinct physiological responses remains a central question in plant biology. Increasing evidence highlights calcium-dependent protein kinases (CDPKs) as key signal decoders in guard cell signaling. This mini-review summarizes recent advances in our understanding of how CDPKs perceive and translate Ca2+ fluctuations into stomatal responses. We focus on the roles of CDPKs in signaling pathways triggered by diverse stimuli, including phytohormones such as abscisic acid ABA, jasmonates, and salicylic acid, as well as biotic cues such as microbe- or pathogen-associated molecular patterns (MAMPs/PAMPs) and pathogen infection. We also discuss how gaseous signals and metabolic cues are integrated into CDPK-mediated pathways. In addition to their established role as downstream decoders of Ca2+ signals, emerging studies suggest that CDPKs can act upstream of Ca2+ oscillations and may also function through Ca2+-independent mechanisms. Together, these findings highlight the context-dependent and integrative roles of CDPKs in regulating stomatal behavior, contributing to plant fitness under fluctuating environmental conditions.