Chloride Channels and Transporters of the CLC Family in Plants
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Chloride Channels and Transporters of the CLC Family in Plants O. I. Nedelyaevaa, *, A. V. Shuvalova, and Yu. V. Balnokina aTimiryazev
Institute of Plant Physiology, Russian Academy of Sciences, Moscow, 127276 Russia *e-mail: [email protected]
Received February 6, 2020; revised March 16, 2020; accepted March 17, 2020
Abstract—Proteins of the chloride channel family CLC (ChLoride Channel) 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 from Arabidopsis 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. Keywords: chloride channel family (CLC), Arabidopsis thaliana, Nicotiana tabacum, Oryza sativa, Glycine max, Glycine soja, Zea mays, Poncirus trifoliate, Thellungiella halophila, Suaeda altissima, anion channels, anion/proton antiporters, anion homeostasis DOI: 10.1134/S1021443720050106
INTRODUCTION The name chloride channel family (CLC, ChLoride Channel) derived from the first protein of this family, CLC-0, that was found in electric organs of the electric ray Torpedo californica and recognized as a voltage-gated chloride channel [1]. The proteins of this family were long believed to only participate in passive chloride transport, i.e., represent chloride channels like CLC-0. The cloning of similar genes from other organisms and studying the functions of the encoded proteins by means of gene expression in Xenopus oocytes [2] has led to the discovery of many related genes [3]. The CLC family was found to contain not only anion channels but also anion/proton antiporters. The antiporters carry out secondary active transport of anions in exchange for protons using energy of the electrochemical proton gradient. Proteins of the chloride channel family are integral membrane proteins that contain 10–12 transmembrane domains [4]. All eukaryotic CLCs comprise two hydrophilic regulatory CBS domains (cystathionineβ-synthetase domains) [
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