|Zhu, Kun Yan|
Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2004
Publication Date: 9/1/2004
Citation: Li, H., Gonzalez-Cabrera, J., Oppert, B.S., Ferre, J., Higgins, R.A., Buschman, L.L., Radke, G.A., Zhu, K., Huang, F. 2004. Binding analyses of Cry1Ab and Cry1Ac with membrane vesicles from Bacillus thuringiensis-resistant and -susceptible Ostrinia nubilalis (lepidoptera: crambidae). Biochemical and Biophysical Research Communications 323: 52-57. Interpretive Summary: Transgenic crops have been developed which contain insecticidal toxins from the bacterium Bacillus thuringiensis (Bt) to control insect pests. If insects become resistant to the toxins, transgenic crops with Bt toxins will not control the target pest. Therefore, we have studied the changes in insects that have been selected for resistance to Bt in the laboratory. Because Bt toxins bind to the gut lining of insects, we compared the binding of two different Bt toxins in Bt-susceptible and -resistant European corn borer larvae. Using three different methods to compare Bt toxin binding, we found no differences in the binding of Bt toxins in Bt-susceptible and -resistant insects. These data combined with data from a previous paper suggest that Bt-resistance in the European corn borer is not associated with a loss of toxin binding, but instead is due to reduced protoxin activation by gut proteinases in resistant insects. Therefore, it is important that transgenic crops express a fully-activated toxin to avoid this type of resistance.
Technical Abstract: The binding properties of Bacillus thuringiensis toxins to brush border membrane vesicles of Dipel-resistant and -susceptible Ostrinia nubilalis larvae were compared using ligand blot analysis, surface plasmon resonance, and radiolabeled toxin binding assays. In ligand blot analysis, the number of Cry1Ab or Cry1Ac toxin binding proteins and the relative toxin binding intensity were similar in vesicles from resistant and susceptible larvae. Surface plasmon resonance with immobilized Cry1Ab activated toxin and fluid-phase brush border membrane vesicles from resistant and susceptible larvae indicated that there were no significant differences in binding. Homologous competition assays with radiolabeled Cry1Ab and Cry1Ac toxin and vesicles from resistant and susceptible larvae resulted in similar toxin dissociation constants and binding site concentrations. Heterologous competition binding assays indicated that Cry1Ab and Cry1Ac completely competed for binding, thus they share binding sites in the epithelium of the larval midguts of O. nubilalis. Overall, the binding analyses indicate that resistance to Cry1Ab and Cry1Ac in this Bt-resistant strain of O. nubilalis is not associated with a loss of toxin binding.