Molecular Cloning and Characterization of a Mannose-binding Lectin Gene from Dendrobium officinale

Using RNA extracted from Dendrobium officinale young leaves and primers designed according to the conservative regions of Orchidaceae lectins, the full-length cDNA of Dendrobium officinale agglutinin (DOA) was cloned by rapid amplification of cDNA ends (RACE). The full-length cDNA of doa was 768 bp and contained a 498 bp open reading frame (ORF) encoding a lectin precursor of 165 amino acids. Through comparative analysis of doa gene and its deduced amino acid sequence with those of other Orchidaceae species, it was found that doa encoded a precursor lectin with signal peptide. DOA was a mannose-binding lectin with three mannose-binding sites. Semi-quantitative RT-PCR analysis revealed that doa mRNA expression was detected in all tested tissues including root, stem and leaf, however, the expression was higher in stem, lower in leaf. As the doa mRNA was detected in all the tested plant tissues, the doa was considered to be a constitutively expressed gene.