Cloning and expression analysis of a vacuolar Na+/H+ antiporter gene from Alfalfa

A full-length cDNA, named MsNHX1, encoding a vacuolar Na+/H+ antiporter was cloned from alfalfa (Medicago sativa), using degenerate primers, followed by 3' and 5' RACE. The cDNA sequence was 2225 bp long and included an open reading frame encoding a deduced protein of 541-amino-acid polypeptide. The deduced amino acid sequence showed high similarity (more than 73%) to those of the previously cloned Na+/H+ antiporters; form Arabidopsis thaliana, Qryza sativa, Atriplex gemlinin, Beta vulgaris and Hordeum vulgare. Southern hybridization showed that MsNHX1 has only one copy in alfalfa genome. Semiquantitative RT-PCR analysis indicated that the mRNA level of MsNHX1 was moderate without stress and markedly up-regulated after treatment by NaCl and ABA (abscisic acid). Those results suggest that the MsNHX1 product play an important role in salt tolerance of the alfalfa, and its transcript expression is possibly partially regulated through ABA-dependent signaling pathway.