The Novel Na + /H + Antiporter Gene SpNHX1 from Sesuvium Portulacastrum Confers Enhanced Salt Tolerance to Transgenic Yeast

The plant Na+/H+ antiporter (NHX) plays a significant role in cellular ion homeostasis. Herein, an Na+/H+ antiporter gene, SpNHX1 from the Sesuvium portulacastrum plant, was obtained by homology-cloning method. The SpNHX1 gene contains 2113 bp with an open-reading frame encoding a polypeptide of 554 amino acid residues with an estimated molecular mass of 61.27 kDa and an isoelectric point of 7.24. The amino acid sequences of SpNHX1 shared a high similarity with Arabidopsis thaliana AtNHX1 (75.81%), AtNHX2 (77.12%) and Oryza sativa OsNHX1 (73.10%). SpNHX1 contains an amiloride-binding region (FFIYLLPPI), which is a highly-conserved domain in plant Na+/H+ antiporters. RT-PCR (reverse transcriptional PCR) analysis showed that the SpNHX1 gene had a high expression level in roots compared to other tissues under normal conditions. The qRT-PCR (quantitative real-time PCR) results indicated that NaCl treatment induced the expression of SpNHX1 gene in the roots, but its transcriptional levels were not influenced by the ABA, PEG, H2O2, heat (42 °C) or cold (4 °C) stresses. The growth of yeast cells expressing SpNHX1 was better than the non-transgenic control cells in the presence of 30 mM NaCl, 0.4 M KCl, or 0.5 mM LiCl. Furthermore, transgenic yeast cells with SpNHX1 accumulated more Na+ relative to control cells under salinity stress. These results suggested that SpNHX1 was a key determinant in the salt-stress response in Sesuvium portulacastrum.