Cloning and characterization of SucNHX1, a novel vacular Na+/H+ antiporter from the halophyte Suaeda corniculata that enhances the saline-alkali tolerance in Arabidopsis by its overexpression

Abstract

Vacuolar Na+/H+ antiporters play central roles in plant saline (NaCl) stress response. However, the functional characterizations of antiporters involved in plant saline-alkali (Na2CO3/NaHCO3) tolerance are limited. In this study, SucNHX1, a Na+/H+ antiporter gene was isolated from Suaeda corniculata, a halophyte native to the saline-alkali soil, and further studied in transgenic Arabidopsis thaliana. The SucNHX1 gene contains 2123 nucleotides with an open reading frame of 1665 nucleotides (GenBank accession number: DQ512716), encoding a polypeptide of 554 amino acids with a predicted molecular mass of 61.2 kDa. A northern blot analysis indicated that the enhanced mRNA accumulation of SucNHX1 was induced by sodium carbonate (Na2CO3) rather than by NaCl, polyethylene glycol or abscisic acid in S. corniculata seedlings. SucNHX1 was localized in membrane, nucleus and cytoplasm when it was transiently expressed in tobacco mesophyll cells. The expression of SucNHX1 in salt sensitive yeast mutant ΔenaΔnhx1 which lost of yeast vacuolar Na+/H+ antiporter ScNHX1 showed functional complementation. The transgenic Arabidopsis overexpressing SucNHX1 had higher Na2CO3 and NaCl tolerance levels than the wild-type plants. The expression patern of SucNHX1 under Na2CO3 and high NaCl stress in transgenic plants showed that SucNHX1 higher expressed under stress condition than normal control. The analysis of ion contents indicated that under Na2CO3 and NaCl conditions, there were more Na+ in the roots and higher K+/Na+ ratio in the leaves in the transgenic plants than in the wild-type plants. Thus, SucNHX1 may play a significant role in plant saline-alkali tolerance.