Genomic Overview of Ion Transporters in Plant Salt Tolerance

Salinity is one of the most severe environmental stresses affecting plant productivity worldwide. In many plant species, salt sensitivity is associated with the accumulation of sodium (Na+) in photosynthetic tissues. Adaptation of plants to salt stress (i.e. resumption of growth after exposure to high soil salinity) requires cellular ion homeostasis. To prevent the accumulation of Na+ in the cytoplasm, plants have developed three mechanisms that function in a cooperative manner, i.e restriction of Na+ influx, active Na+ extrusion at the root-soil interface, and subsequent vacuolar compartmentalization without toxic ion accumulation in the cytosol. Sodium ions can enter the cell through several low- and high-affinity K+ carriers. Voltage-independent, non selective cation channels (NSCC) provide a pathway for the entry of Na+ into plant cells. Some members of the HKT family (High Affinity K+ transporter) function as sodium transporter and contribute to Na+ removal from the ascending xylem sap and recirculation from the leaves to the roots via the phloem vasculature. Sodium extrusion is presumed to be of critical importance for ion homeostasis and salt tolerance of glycophytes. Na+ sequestration into the vacuole depends on expression and activity of Na+/H+ antiporter that is driven by electrochemical gradient of protons generated by the vacuolar H+-ATPase and the H+-PPase. However, we have a limited molecular understanding of the overall control of Na+ accumulation, the role of each transporter and salt stress tolerance at the whole plant level. Genomics and functional genomics provide a new opportunity in addressing the multigenicity of the plant abiotic stress response through genome sequences, stress-specific transcript collections, protein and metabolite profiles, their dynamic changes and protein interactions. In this review, we analyze available data related to omics and plant abiotic stress responses in order to enhance our understanding about how salinity and other abiotic stresses affect the most fundamental processes of cellular function which have a substantial impact on plant growth development.