Binding of Bacillus thuringiensis Cry1A toxins with brush border membrane vesicles of maize stem borer (Chilo partellus Swinhoe)

Maize stem borer (Chilo partellus) is a major insect pest of maize and sorghum in Asia and Africa. Bacillus thuringiensis (Bt) δ-endotoxins have been found effective against C. partellus, both in diet-overlay assay and in transgenic plants. Gene stacking as one of the resistance management strategies in Bt maize requires an understanding of receptor sharing and binding affinity of δ-endotoxins. In the present study, binding affinity of three fluorescein isothiocyanate labeled Cry1A toxins showed high correlation with the toxicity of respective δ-endotoxins. Competitive binding studies showed that Cry1Ab toxins share some of the binding sites with Cry1Aa and Cry1Ac with low affinity and that Cry1Ab may have additional binding sites that are unavailable to the other two toxins tested.