Characterization of the wound-inducible protein ipomoelin from sweet potato

The ipomoelin (IPO) gene, a wound- and methyl jasmonate-inducible gene, was isolated from sweet potato (Ipomoea batatas cv. Tainung 57), and previously demonstrated to be regulated by dephosphorylated proteins and calcium ion (Chen Y.-C. et al. Plant Cell and Environment 26, 1373-1383, 2003). In this report, the function of the IPO protein was further studied. The IPO gene was characterized as having one intron and presenting two copies within the genome of sweet potato. The IPO protein appeared 1 d after the leaves of sweet potato were wounded. Surprisingly, the accumulation of the IPO protein remained for 7 d after wounding. Additionally, after the IPO protein was fused to a HISTIDINE TAG, the His-IPO fusion protein produced from Escherichia coli BL21DE3 was then used to perform the haemagglutination test, which demonstrated that His-IPO fusion protein agglutinated human blood cells. Furthermore, several carbohydrates, including methyl alpha-D-glucopyranoside, methyl alpha-D-mannopyranoside, maltose, mannose, glucose, galactose, and lactose, reduced the efficiency of the His-IPO fusion protein in agglutinating human blood cells. These experimental results may indicate that the IPO protein is a LECTIN, a carbohydrate-binding protein. Notably, the IPO protein retarded the growth and development of silkworm, and thus reduced silkworm survival rates. Therefore, these findings indicate that the function of the IPO protein is to protect plants from insect attack.