Transgenic Expression of a Viral Cystatin Gene CpBV-CST1in Tobacco Confers Insect Resistance

A viral gene, CpBV-CST1, was identified from a polydnavirus Cotesia plutellae bracovirus (CpBV). Its protein product was significantly toxic to lepidopteran insects. This study generated a transgenic tobacco plant expressing CpBV-CST1. Expression of transgene CpBV-CST1 was confirmed in T1 generation (second generation after transgenesis) in both mRNA and protein levels. Young larvae of Spodoptera exigua (Hubner) suffered high mortalities after feeding on transgenic tobacco. All 10 T1 transgenic tobacco plants had no significant variation in speed-to-kill. In order to further explore insect resistance of these transgenic tobaccos, bioassays were performed by assessing antixenosis and antibiosis. S. exigua larvae significantly avoided T1 plants in a choice test. Larvae fed with T1 plant exhibited significant decrease in protease activity in the midgut due to consuming CpBV-CST1 protein produced by the transgenic plant. Furthermore, the transgenic tobacco exhibited similar insect resistance to other tobacco-infesting insects, including a leaf-feeding insect, Helicoverpa assulta, and a sap-feeding insect, Myzus persicae. These results demonstrate that a viral cystatin gene can be used to develop insect-resistant transgenic plant, suggesting a prospective possibility of expanding the current transgenic approach to high-valued crops.