Antimicrobial activity of γ-thionin-like soybean SE60 in E. coli and tobacco plants

The SE60, a low molecular weight, sulfur-rich protein in soybean, is known to be homologous to wheat γ-purothionin. To elucidate the functional role of SE60, we expressed SE60 cDNA in Escherichia coli and in tobacco plants. A single protein band was detected by SDS–polyacrylamide gel electrophoresis (SDS–PAGE) after anti-FLAG affinity purification of the protein from transformed E. coli. While the control E. coli cells harboring pFLAG-1 showed standard growth with Isopropyl β-d-1-thiogalactopyranoside (IPTG) induction, E. coli cells expressing the SE60 fusion protein did not grow at all, suggesting that SE60 has toxic effects on E. coli growth. Genomic integration and the expression of transgene in the transgenic tobacco plants were confirmed by Southern and Northern blot analysis, respectively. The transgenic plants demonstrated enhanced resistance against the pathogen Pseudomonas syringae. Taken together, these results strongly suggest that SE60 has antimicrobial activity and play a role in the defense mechanism in soybean plants.