Overexpression of StNHX1, a Novel Vacuolar Na+/H+ antiporter gene from Solanum torvum, enhances salt tolerance in transgenic vegetable soybean

Soil salinity is the primary limiting factor affecting the growth and production of vegetable soybean [Glycine max (L.) Merrill] worldwide. Plants can survive in salinity conditions through the mechanism of sodium ion (Na+) compartmentalization, during which the vacuolar Na+/H+ antiporter (NHX) genes play a critical role. In the present study, a novel vacuolar NHX gene from Solanum torvum Swartz 'Torvum Vigor' (StNHX1; GenBank accession number: JN606860.1) was isolated and transferred into the vegetable soybean 'Xinliaoxian' through an Agrobacterium-mediated protocol. The PCR and southern blot analyses confirmed the successful integration of the exogenous genes. The GUS assay and semi-quantitative RT-PCR analysis showed that the alien genes were inherited by the progenies and that the StNHX1 gene was overexpressed in the T-3 generation. The overexpression of this gene conferred high tolerance to salt stress. Under 100 mM NaCl conditions, the scorch scores and the Na+ and malondialdehyde (MDA) contents of the leaves of the transgenic lines were significantly lower as compared with the wild-type (WT) plants, while the K+/Na+ ratio, the contents of K+, relative chlorophyll and relative water, and some morphological traits of the transgenic plants were significantly higher than those of the WT. These results indicate that the overexpression of StNHX1 enhances the salt tolerance of vegetable soybean and that StNHX1 is one of the promising target genes that can be manipulated to improve the salinity tolerance of crops.