Molecular characterization of GmNHX2, a Na⁺/H⁺ antiporter gene homolog from soybean, and its heterologous expression to improve salt tolerance in arabidopsis

Na⁺/H⁺ antiporters have been well documented to enhance plant salt tolerance by regulating cellular ion homeostasis. Here, a putative Na⁺/H⁺ antiporter gene homolog GmNHX2 from soybean was cloned and predicted to encode a protein of 534 amino acids with 10 putative transmembrane domains. GmNHX2 was expressed in all soybean plant tissues but enriched in roots and its expression was induced by NaCl and polyethylene glycol (PEG) treatments. GmNHX2 exhibits greater sequence similarity with LeNHX2 and AtNHX6 than that of AtNHX1 and AtSOS1. Although phylogenetic analysis clustered GmNHX2 with organellar (tonoplast and vesicles) antiporters, the GmNHX2-EGFP (enhanced green fluorescent protein) fusion protein was possibly localized in the plasma membrane or organelle membrane of transgenic plant cells. Furthermore, transgenic Arabidopsis plants expressing GmNHX2 were more tolerant to high NaCl concentrations during germination and seedling stages when compared with wild-type plants. These results suggest that GmNHX2 is a membrane Na⁺/H⁺ antiporter and may function to regulate ion homeostasis under salt stress.