Chloride Channels and Transporters of the CLC Family in Plants

Proteins of the chloride channel family CLC (ChLorideChannel) are found in prokaryotes and eukaryotes. The family includes anion channels and anion/proton antiporters. In plants, the CLC proteins are found in various tissues and diverse intracellular membranes. They perform multiple functions and play important physiological roles, such as nitrate and chloride homeostasis at the cellular and whole plant levels, the regulation of transmembrane electrical potential and lumenal pH in organelles, the distribution of newly synthesized proteins among intracellular compartments, and the formation of plant resistance to biotic and abiotic stress factors. This review describes the currently known CLC proteins of plant origin whose genes are identified at the molecular-genetic and functional levels; the properties of CLC proteins fromArabidopsis thaliana(L.) Heynh. and other plant species are discussed with emphasis on the results obtained in the last decade. The functional and structural aspects of plant CLC proteins, as well as their physiological roles under normal and stressful conditions, are considered. A hypothesis is put forward that the endosomes and the proteins of the CLC family localized in endosomal membranes are involved in maintaining the anionic balance in the cytoplasm. The prospects of further studies on plant CLC proteins are briefly considered.