Characterization of a mannose-binding lectin gene from Typhonium divaricatum (L.) Decne

Monocot mannose-binding lectins ( MMBLs) or agglutinins are an extended superfamily of structurally and evolutionarily related proteins and they play important roles in plant defenses. Here the full-length cDNA of monocot mannose-binding agglutinin ( designated as TDA, GenBank accession no.: AY347940) was isolated from Typhonium divaricatum, a traditional Chinese medicinal herb. Sequence analysis revealed that the full-length cDNA of TDA was 870 bp, and had a 594 bp open reading frame ( ORF) encoding a putative 197-aa agglutinin precursor with a C-terminal domain. Multiple alignments of TDA amino acids with those of seven other MMBLs revealed three highly conserved domains among them, indicating TDA belongs to a member of the MMBL superfamily. Predicted tertiary structure analysis showed that TDA had three potential equal mannose-binding sites. Phylogenetic analysis indicated that 20 MMBLs including TDA belonged to an extended superfamily. Northern blot analysis showed that TDA expressed in T. divaricatum in a tissue-specific manner, with highest expression in tuber and almost no expression in petiole and leaf. The cloning and characterization of TDA will enable us to study its potential insect resistance function in the future.