Cloning and expression of a novel cDNA encoding a mannose-specific jacalin-related lectin from Oryza sativa

Lectin plays an important role in defense signaling in plants. A few genes of this family have been cloned. Here we report on a mannose-specific jacalin-related lectin in rice. Using sequence information of wheat gene VER2, which we had previously cloned, we were able to amplify a cDNA of OsJAC1 from Oryza sativa by RT-PCR. The cDNA of OsJAC1 was 1172 bp and contained a 921-bp open reading frame (ORF) encoding dirigent (amino acids 26-139) and jacalin (amino acids 175-305) domains of 306 amino acids. Comparison of the OsJAC1 sequence with those of other lectins (jacalin) from rice, wheat and other species revealed that OsJAC1 had the 12 amino acid positions conserved in all mannose-binding lectins. Semi-quantitative RT-PCR revealed that OsJAC1 expression was present in stems, leaves and young spikes but not young roots; the expression was high in leaves and low in stems and spikes. And methyl jasmonate could induce the expression of OsJAC1. To test the activity of OsJAC1, the jacalin domain at the C-terminal was expressed in E. coli. BL21 (DE3). The purified recombinant protein could agglutinate red blood cells of rabbit, and the agglutination activity was strongly inhibited by mannose compared with other carbohydrates. These results indicate that lectin with dirigent and jacalin domains exists in rice as well as wheat. This is the first report of cDNA cloning of mannose-binding jacalin-related lectin with a dirigent domain in N-terminal region from O. sativa.