The potassium homeostasis-stress adaptation continuum: An integrative signaling platform for plant survival

Potassium (K⁺) is the predominant cation in plants and has traditionally been viewed as essential for nutrition and osmotic regulation. Studies over the past decade have demonstrated that it is also key to plant response coordination under conditions such as drought, salinity, temperature extremes, and pathogen attack. This review discusses the literature on K⁺ homeostasis-stress adaptation that highlights K⁺ transmembrane flux as an integrative signaling platform connecting Ca²⁺ signaling, reactive oxygen species (ROS) production, hormonal regulation, and immune responses. The K⁺ pathway from rhizosphere perception to shoot function is assessed, and the CBL (calcineurin B-like protein)-CIPK (CBL-interacting protein kinase) signaling module is highlighted as a context-dependent regulator of K⁺ transport. We identify the absence of a dedicated K⁺ sensor as an evolutionary puzzle and propose that plants may rely on distributed sensing-membrane potential, Ca²⁺ signatures, and transporter-kinase complexes-rather than a single receptor. We define the K⁺ homeostasis-stress adaptation continuum as the temporal, spatial, and functional integration of K⁺ perception, transport and signaling during stress adaptation. The review suggests future opportunities for crop improvement, including the use of natural allelic variation in Clade IV high-affinity K⁺ transporters to engineer the CBL-CIPK-TORC (target of rapamycin complex) regulatory network that can improve potassium use efficiency and tolerance to multiple stresses. By presenting K⁺ homeostasis as an integral part of plant stress adaptation, this review provides a scientific basis for future breeding and biotechnological approaches.