Molecular Cloning and Functional Analysis of a Na+/H+ Antiporter Gene ThNHX1 from a Halophytic Plant Thellungiella halophila

Na+/H+ exchanger catalyzes the countertransport of Na+ and H+ across membranes. Using the rapid amplification of cDNA ends method, a Na+/H+ antiporter gene (ThNHX1) was isolated from a halophytic plant, salt cress (Thellungiella halophila). The deduced amino acid sequence contained 545 amino acid residues with a conserved amiloride-binding domain ((LFFIYLLPPI96)-L-87) and shared more than 94% identity with that of AtNHX1 from Arabidopsis thaliana. The ThNHX1 mRNA level was upregulated by salt and other stresses (abscisic acid, polyethylene glycol, and high temperature). This gene partially complemented the Na+/Li+-sensitive phenotype of a yeast mutant that was deficient in the endosomal-vacuolar Na+/H+ antiporter ScNHX1. Overexpression of ThNHX1 in Arabidopsis increased salt tolerance of transgenic plants compared with the wild-type plants. In addition, the silencing of ThNHX1 gene in T. halophila caused the transgenic plants to be more salt and osmotic sensitive than wild-type plant. Together, these results suggest that ThNHX1 may function as a tonoplast Na+/H+ antiporter and play an important role in salt tolerance of T. halophila.