Abstract:In order to study the role of salicylic acid carboxyl methyltransferase (SAMT) in plant defense system, a full-length cDNA of Mikania micrantha SAMT was cloned from the SMART cDNA library by RACE, then the exogenous expression and induction pattern by SA were studied. The results showed that the full-length cDNA was 1299 bp, with a 1089 bp-length coding sequence (CDS) encoding a protein of 362 amino acids. Blast result showed 74% similarity with the amino acids of Clarkia breweri CbSAMT, confirming that Mikania micrantha SAMT may play a role in methylating SA into MeSA. Therefore this gene was named as MmSAMT and its GenBank accession number was FJ869889. Subsequently the CDS of MmSAMT was integrated into pET-32a(+), then the recombinant plasmid was transformed into Rosetta-gami (DE3) for exogenous expression. A specific monomer about 40 kD could be detected by SDS-PAGE, which was consistent with prediction. Western blot showed that the efficient solubility could be obtained cultured under 20℃,0.05 mmol/L IPTG、180 r min-1 for 6 hours. The transcription profile of MmSAMT in M. micrantha leaves sprayed 100µmol/L SA revealed that it could be activated by SA and reached a peak after 48 hours. It implied that MmSAMT may participate in the SA signaling pathway via MeSA, and induce the systemic acquired resistance (SAR) as a key signal and enhance the plant defense system.
