Abstract
The processes of plant nutrition, stress tolerance, plant growth, and development are strongly dependent on transport of mineral nutrients across cellular membranes. Plant membrane transporters are key components of these processes. Among various membrane transport proteins, the monovalent cation proton antiporter (CPA) superfamily mediates a broad range of physiological and developmental processes such as ion and pH homeostasis, development of reproductive organs, chloroplast operation, and plant adaptation to drought and salt stresses. CPA family includes plasma membrane-bound Na+/H+ exchanger (NhaP) and intracellular Na+/H+ exchanger NHE (NHX), K+ efflux antiporter (KEA), and cation/H+ exchanger (CHX) family proteins. In this review, we have completed the phylogenetic inventory of CPA transporters and undertaken a comprehensive evolutionary analysis of their development. Compared with previous studies, we have significantly extended the range of plant species, including green and red algae and Acrogymnospermae into phylogenetic analysis. Our data suggest that the multiplication and complexation of CPA isoforms during evolution is related to land colonisation by higher plants and associated with an increase of different tissue types and development of reproductive organs. The new data extended the number of clades for all groups of CPAs, including those for NhaP/SOS, NHE/NHX, KEA, and CHX. We also critically evaluate the latest findings on the biological role, physiological functions and regulation of CPA transporters in relation to their structure and phylogenetic position. In addition, the role of CPA members in plant tolerance to various abiotic stresses is summarized, and the future priority directions for CPA studies in plants are discussed.
Highlights
During the process of evolution plants have evolved specific strategies and mechanisms to maintain ion homeostasis, regulate pH and adapt to continuously changing environmental conditions
cation proton antiporter (CPA) gene superfamily encompasses a wide range of plant membrane transporter involved in monovalent ion transport across cellular membranes
It is believed that members of CPA1 proteins are critical in mediating plant salt tolerance and have been evolved to maintain cellular cation and pH homeostasis
Summary
During the process of evolution plants have evolved specific strategies and mechanisms to maintain ion homeostasis, regulate pH and adapt to continuously changing environmental conditions. Plants growth and development require uptake of essential minerals, and intracellular compartmentation and tissuespecific distribution of particular ions. Development of plant reproductive organs requires coordinated work of membrane ion transport system (Sze et al, 2004). Another example is plant adaptive responses to salinity. Plant salt stress tolerance is strongly dependent on osmotic adjustment, exclusion of toxic ions from uptake, and their efficient intracellular compartmentation. All these three components of salt tolerance require involvement of various membrane transporters mediating water and ion transport across cellular membranes (Zhao et al, 2020)
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