Tea plant (Camellia sinensis) is an important traditional horticultural plant known for the tea products processed from its leaves, which often faces many different adverse conditions, including saline environments. Na+/H+ antiporters (NHXs) are extensively involved in the process of plant response to salt stress and resistance acquisition, but studies in tea plant are less common. In this study, a novel NHX gene named CsNHX6 was cloned from tea plant, which encodes 528 amino acids with 12 typical transmembrane domains. Our results showed that CsNHX6 had both Na+ and K+ dual transport function, and the transport activity depended on an appropriate H+ concentration. In addition, three conserved acidic residues, D164, E188 and D193 in CsNHX6, are essential for Na+ and K+ transport. Further, we found that CsNHX6 was significantly induced by salt stress, and its overexpression enhanced the tolerance of yeast and Arabidopsis to salt stress, this was closely related to the improvement of Na+ storage capacity of cells. Furthermore, subcellular localization assay revealed that CsNHX6 was localized in a Golgi-to-vacuole transport system, including Golgi, TGN, PVC and vacuole, and this localized distribution could be enhanced by salt stress. Taken together, these findings suggest that a potential Na+ transport network is dominated by CsNHX6 under salt stress, which directly or indirectly achieves the regionalization of excessive Na+, thus endowing organisms with salt tolerance.
