Expression of a Cholera Toxin B Subunit-Neutralizing Epitope of the Porcine Epidemic Diarrhea Virus Fusion Gene in Transgenic Lettuce (Lactuca sativa L.)

Transgenic plants have been used as a safe and economic expression system for the production of edible vaccines. A synthetic cholera toxin B subunit gene (CTB) was fused with a synthetic neutralizing epitope gene of the porcine epidemic diarrhea virus (sCTB-sCOE), and the sCTB-sCOE fusion gene was introduced into a plant expression vector under the control of the ubiquitin promoter. This plant expression vector was transformed into lettuce (Lactuca sativa L.) using the Agrobacterium-mediated transformation method. Stable integration and transcriptional expression of the sCTB-sCOE fusion gene was confirmed using genomic DNA PCR analysis and northern blot analysis, respectively. The results of western blot analysis with anti-cholera toxin and anti-COE antibody showed the synthesis and assembly of CTB-COE fusion protein into oligomeric structures with pentameric sizing. The biological activity of CTB-COE fusion protein to its receptor, G(M1)-ganglioside, in transgenic plants was confirmed via G(M1)-ELISA with anti-cholera toxin and anti-COE antibody. Based on G(M1)-ELISA, the expression level of CTB-COE fusion proteins reached 0.0065% of the total soluble protein in transgenic lettuce leaf tissues. Transgenic lettuce successfully expressing CTB-COE fusion protein will be tested to induce efficient immune responses against porcine epidemic diarrhea virus infection by administration with raw material.