Submitted to: Book Chapter
Publication Type: Book / chapter
Publication Acceptance Date: 11/5/2009
Publication Date: 8/25/2010
Citation: Zhu, Y., Chen, M., Abel, C.A. 2010. Potential Use of Proteinase Inhibitors, Avidin, and Other Bio-reagents for Synergizing Bt Performance and Delaying Resistance Development to Bt. In: Liu, T.X., Kang, L., editors. Recent Advances in Entomological Research. Molecular Biology to Pest Management. Springer. High Education Press. p. 200-208. Interpretive Summary: Grower adoption of transgenic Bt cotton has resulted in a substantial reduction in the number of chemical insecticide applications. Because these applications controlled non-target pests of cotton, there has been a resurgence of sucking insects as a serious problem in the crop. Transgenic cotton with genes that target a wider range of pests may be useful. In addition to its efficacy against lepidopteran insects, avidin is highly insecticidal against many coleopteran pests. If avidin is shown to also be effective against sucking insects, its introduction into transgenic cotton, along with its synergistic action with Bt toxins, could be a major advance in cotton insect control and Bt resistance management. Besides avidin, another alternative for increasing control range and for delaying Bt resistance development is proteinase inhibitors. Serine proteinases are common luminal enzymes in midguts of many Lepidoptera species. Serine proteinases in the midgut also activate protoxins, thereby mediating Bt toxicity. In this study, the addition of avidin and proteinase inhibitors with Bt-toxins enhanced the control of cotton bollworm over Bt-toxins along. The introduction of proteinase inhibitors into host plants may substantially suppress protein digestion, and subsequently achieve insect control in a broad range through nutrient deficiency. In addition, introduction of proteinase inhibitors into the gut will certainly modify biochemical balance within target insects feeding on Bt cotton, making the Bt-toxins more stable and more effective against target insects.
Technical Abstract: After being ingested by target insects, the insecticidal proteins from Bacillus thuringiensis (Bt) need to go through a proteolytic process by insect midgut proteinases to become activated. At the same time, Bt can be hydrolyzed and degraded by midgut proteinases to become non-toxic to target insects. Once activated, the Bt proteins need to bind to midgut brush border membrane vesicle (BBMV) to cause gut lining lesions and eventually death in the target insect. A few bio-reagents may interact with the Bt binding to the receptors. By applying proteinase inhibitors to Bt-containing (sublethal dose) diet, the growth and development of Helicoverpa zea were significantly decreased when compared with the Bt only control. Midgut samples tested against the substrates for major midgut enzymes showed significant decreases in the protease activity of larvae fed Bt plus inhibitor versus control. Avidin, causing sequestration of biotin and vitamin deficiency, potentially interacts with Bt by binding to biotin-containing proteins. Besides possessing insecticidal toxicity itself, avidin at a sublethal dose could significantly synergize Bt toxicity against H. zea larvae. Because of different modes of action from that of Bt, proteinase inhibitors, avidin, and other bio-reagents could be used to enhance Bt performance, delay resistance development to Bt, and expand control range beyond lepidopterans.