Abstract

We isolated a vacuolar Na⁺/H⁺ antiporter gene (CmNHX1) from melon using the rapid amplification of cDNA ends approach. Sequence analysis indicated that the full-length cDNA of CmNHX1 was 2534 bp, including an open reading frame (ORF) of 1659 bp, which encoded a deduced polypeptide of 553 amino acids. The deduced protein contained conserved structural domains and shared a high degree of homology with putative vacuolar Na⁺/H⁺ antiporters from other higher plants. Subcellular localization revealed that this protein located to the vacuolar membrane. These results indicated that, CmNHX1 is a vacuolar Na⁺/H⁺ antiporter. As shown by RT-PCR, expression of CmNHX1 was detected in roots, stems and leaves. In addition, the expression increased in the root but decreased in the leaves with increasing NaCl concentration. Similarly, expression increased with increasing time in plants treated with 100 mM NaCl. Expression of CmNHX1 in ATX3 yeast Na⁺/H⁺antiporter mutants showed functional complementation. No differences in yeast cell growth were detected in the presence or absence of CmNHX1 on a NaCl-free medium. However, control yeast growth was noticeably suppressed on medium containing NaCl, whereas, yeasts overexpressing CmNHX1 showed increased population growth rates. These results indicate that the CmNHX1 protein enhanced AXT3 salt tolerance.

Keywords: Melon (Cucumis melo L.), Na⁺/H⁺ antiporter, salt tolerance, vacuolar membrane, yeast.

Abbreviation

CFP, Cyan fluorescent protein; NHX, vacuolar Na⁺/H⁺ antiporter;ORF, open-reading frame; RACE, rapid amplification of cDNA ends; UPM,universal primer mixture; YPG, yeast extract/peptone/galactose.