The Vacuolar Na+/H+ Antiporter Gene SsNHX1 from the Halophyte Salsola soda Confers Salt Tolerance in Transgenic Alfalfa (Medicago sativa L.)

摘要

A putative vacuolar Na+/H+ antiporter gene (SsNHX1) was isolated from the halophyte Salsola soda using the rapid amplification of cDNA ends method. Highly conserved regions of plant vacuolar Na+/H+ antiporter, including amiloride-binding domain, NHE (Na+/H+ exchange) domain, and 12 transmembrane segments, were found in the deduced amino acid sequence of SsNHX1. Multiple alignments of vacuolar Na+/H+ antiporters showed that SsNHX1 shared high identity with other plant vacuolar Na+/H+ antiporters. Phylogenetic relationship analysis indicated that SsNHX1 was clustered into the vacuolar Na+/H+ antiporter group. Taken together, these results suggest that SsNHX1 is a new member of the vacuolar Na+/H+ antiporter family. The effective expression of SsNHX1 in alfalfa (Medicago sativa L.) enhanced the salt tolerance of transgenic alfalfa which could grow in high concentrations of NaCl (up to 400 mM) over 50 days. This was the highest level of salt tolerance reported in transgenic plants. A further analysis of the physiological characteristics of transgenic and wild-type plants, including the Na+ and K+ contents, superoxide dismutase activity, the rate of electrolyte leakage, and the proline content, showed that large amounts of Na+ in the cytoplasm of leaves were transported into vacuoles by the exogenous Na+/H+ antiporter, which averted the toxic effects of Na+ to the cell of transgenic alfalfa.