Research Progress on Chloride Channel- and Transporter- Related Gene Families in Plants

Chloride (Cl^-) is an essential micronutrient for plants that supports multiple physiological functions throughout plant growth and development. Its effects are strongly concentration-dependent: low Cl^- availability promotes beneficial physiological processes, whereas excessive accumulation can induce cytotoxicity. In plants, the movement of Cl^- across plasma and organellar membranes is primarily mediated by three principal channel and transporter families: chloride channels (CLC), aluminum-activated malate transporters (ALMT), and slow anion channel-associated homologs (SLAC/SLAH). These families differ in gating mechanisms, ion selectivity, transport properties, and subcellular localization. This review synthesizes current knowledge of plant chloride transport proteins, with emphasis on their phylogenetic distribution, structural organization, and functional diversification. We summarize their core physiological roles in stomatal regulation, water-use efficiency, nutrient uptake, ion homeostasis, growth modulation, and abiotic stress tolerance. We also discuss how their activities are regulated by post-translational modifications, notably phosphorylation and dephosphorylation, as well as by ion concentrations, pH shifts, and phytohormone signaling. Unlike earlier reviews that primarily focused on individual transporter families or specific stress responses, this work provides an integrated framework linking structure-function relationships with regulatory networks. It also evaluates recent advances in high-resolution structural biology, electrophysiological approaches, and in vivo imaging techniques. Furthermore, we delineate current technical bottlenecks and unresolved questions, such as the molecular determinants of substrate specificity and potential cross-talk among transporter families, and propose future directions for crop improvement. By integrating structural, physiological, and regulatory perspectives, this review aims to serve as a valuable reference and stimulate interdisciplinary research on plant chloride biology.