Molecular characterization and functional analysis of a vacuolar Na+/H+ antiporter gene (HcNHX1) from Halostachys caspica

According to sequences of several vacuolar Na+/H+ antiporter genes from Xinjiang halophytic plants, a new vacuolar Na+/H+ antiporter gene (HcNHX1) from the halophyte Halostachys caspica was obtained by RACE and RT-PCR using primers corresponding to conserved regions of the coding sequences. The obtained HcNHX1 cDNA was 1,983 bp and contained a 1,656 bp open reading frame encoding a deduced protein of 551 amino acid residues. The deduced amino acid sequence showed high identity with other NHX1 we have cloned previously from halophyte in Xinjiang desert area. The phylogenetic analysis showed that HcNHX1 formed a clade with NHX homologs of Chenopodiaceae. Expression profiles under salt treatment and ABA induction were investigated, and the results revealed that expression of HcNHX1 was induced by NaCl and ABA. To compare the degree of salt tolerance, we over-expressed HcNHX1 in Arabidopsis. Two transgenic lines grew more vigorously than the wild type (WT) under salt stress. The analysis of ion contents indicated that under salt stress, the transgenic plants compartmentalized more Na+ in the leaves compared with wild-type plants. Together, these results suggest that the products of the novel gene HcNHX1 from halophyte Halostachys caspica is a functional tonoplast Na+/H+ antiporter.