Abstract:In order to understand the function of SMT2 gene in sterol metabolism of Dendrobium officinale, DoSMT2 gene was cloned by RACE. The results showed that the full length of DoSMT2 gene was 1 446 bp with an ORF of 1 089 bp, encoding a protein of 362 amino acids. The DoSMT2 had relative molecular weight of 40.345 kD, and the theoretical isoelectric of 8.13, showing a stable hydrophilic protein. Retrieved by BLAST P, the DoSMT2 protein belonged to the AdoMet-MTases superfamily, containing four S-adenosylmethionine binding sites, one methyltransferase domain and one sterol methyltransferase C-terminal domain. The DoSMT2 was closely homologous to the SMT2 of Apostasia shenzhenica (PKA61629.1) by phylogenetic analysis, belonging to SMT2 family. The DoSMT2 gene was expressed in both stems and leaves by using qRT-PCR. The expression of DoSMT2 gene in October was the highest, and that in leaf was significantly higher than that in stem, it was suggested that sterol metabolism in leaves was more active than that in stems. The prokaryotic expression vector pet-29a-DoSMT2 was constructed and transformed into Escherichia coli BL21 (DE3). The recombinant protein was expressed after IPTG induction. Therefore, these would provide the foundation for studies on the methylation mechanism of DoSMT2 and sterol metabolism of D. officinale.