Expression of a Vacuolar Na+/H+ Antiporter Gene of Alfalfa Enhances Salinity Tolerance in Transgenic Arabidopsis

An alfalfa (Medicago sativa) full length cDNA, designated MsNHX1, was isolated by RT-PCR according to the homologous region of plant Na+/H+ antiporter genes. Southern blot analysis revealed that there was a small antiporter gene family in alfalfa genome. Sequence analysis indicated that MsNHX1 shared high homologies with other vacuolar Na+/H+ antiporters. Transient transfection of MsNHX1-GFP fusion gene indicated that MsNHX1 was targeted to vacuolar membrane. The transcription of MsNHX1 was up-regulated after high salinity treatment. The expression of MsNHX1 in yeast partly suppressed the salt-sensitive phenotype of yeast Na+/H+ antiporter mutant, indicating that MsNHX1 is a functional Na+/H+ antiporter of alfalfa. The physiological analysis demonstrated that the expression of MsNHX1 in Arabidopsis enhanced the resistance of transgenic plants to salt stress. These results suggest that MsNHX1 is a vacuolar Na+/H+ antiporter and functions in salt tolerance of plants.