Overexpression of the Halophytic Vacuolar Na+/H+ Antiporter Enhances Salt Tolerance in Arabidopsis thaliana

The use of genes derived from halophytes represents a promising strategy for enhancing salt tolerance. Among salt tolerance mechanisms, vacuolar Na+/H+ exchangers (NHXs) play a central role in cellular Na+ sequestration in both halophytes and glycophytes. In this study, we identified the SvNHX2 gene from the halophyte Sporobolus virginicus and characterized its role in salinity tolerance. SvNHX2 expression was strongly induced by salt stress, particularly in shoots in S. virginicus. Arabidopsis thaliana plants overexpressing SvNHX2 exhibited significantly improved growth at the vegetative growth stage under 100 and 125 mM NaCl on agar plates and at the reproductive growth stage under 100 mM NaCl in hydroponic systems, although no clear correlation was observed between transgene expression levels and tolerance. Ion analysis showed that SvNHX2 overexpression increased Na+ accumulation in roots under NaCl stress, suggesting enhanced vacuolar Na+ sequestration, while K+ levels remained comparable to the wild type. These findings indicated that SvNHX2 contributes to salt tolerance primarily by promoting Na+ compartmentalization, and that its capacity is comparable to those of NHX proteins in glycophytes. In this study, we provide additional insights into the function of halophytic NHX and demonstrated that SvNHX2 is a valuable gene for engineering salt-tolerant crops.