Abstract: Plant salt overly sensitive 1（SOS1）gene,encoding a Na+/H+ anti-port protein,plays an important role in biological processes of plants against salt stress. Using the total RNA extracted from the young leaves of Melilotus officinalis（L.）Lam. as the template,the full-length sequence of SOS1 gene was amplified by the reverse transcription polymerase chain reaction（RT-PCR）method and rapid amplification of cDNA ends（RACE）,named MoSOS1. The bioinformatics analysis showed that MoSOS1 was in a length of 3931 bp with a complete open reading frame（ORF 2 874 bp）,encoding a 957 amino acid residues of MoSOS1 protein with an estimated molecular weight of 112.8 kD and a calculated isoelectric point（pI）of 5.31. The prediction of transmembrane region of MoSOS1 by TMHAM software indicated that MoSOS1 had 8 transmembrane regions and N-terminal and C-terminal were located outside the cell. Amino acid alignment analysis demonstrated that the protein of MoSOS1 contained a conserved Na+/H+ exchanger superfamily,a cNMP（Cyclic nucleotide-monophosphate）and a CAP_ED（Catabolite gene activator protein-effector domain）superfamily. The bioinformatics analysis showed that MoSOS1 protein belonged to unstable acidic protein with mainly secondary structure of α spiral and random coil,and in which there was no signal peptide. Quantitative real-time RT-PCR analysis showed that expression levels of MoSOS1 presented an increase trend in both shoots and roots with the increase of external NaCl concentrations,and its levels in roots were higher than those in shoots,indicating that the expression of MoSOS1 was induced and regulated by salt.

Key words: Melilotus officinalis（L.）Lam., MoSOS1 gene, homo-cloning, sequence analysis, gene expression