Two Different Bacillus thuringiensis Delta-Endotoxin Receptors in the Midgut Brush Border Membrane of the European Corn Borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae)

Abstract

Binding of three Bacillus thuringiensis insecticidal crystal proteins (ICPs) to the midgut epithelium of Ostrinia nubilalis larvae was characterized by performing binding experiments with both isolated brush border membrane vesicles and gut tissue sections. Our results demonstrate that two independent ICP receptors are present in the brush border of 0. nubilalis gut epithelium. From competition binding experiments performed with 1251-labeled and native ICPs it was concluded that CryIA(b) and CryIA(c) are recognized by the same receptor. An 11-fold-higher binding affinity of CryIA(b) for this receptor correlated with a 10-fold-higher toxicity of this ICP compared with CryIA(c). The CryIB toxin did not compete for the binding site of CryIA(b) and CryLA(c). Immunological detection of ingested B. thuringiensis ICPs on gut sections of 0. nubilalis larvae revealed binding only along the epithelial brush border membrane. CryID and CryIE, two ICPs that are not toxic to 0. nubilalis, were not bound to the apical microvilli of gut epithelial cells. In vitro binding experiments performed with native and biotinylated ICPs on tissue sections confirmed the correlation between ICP binding and toxicity. Moreover, by performing heterologous competition experiments with biotinylated and native ICPs, it was confirmed that the CryIB receptor is different from the receptor for CryIA(b) and CryIA(c). Retention of activated crystal proteins by the peritrophic membrane was not correlated with toxicity. Furthermore, it was demonstrated that CryIA(b), CryIA(c), and CryIB toxins interact in vitro with the

Cross‐resistance of Cry1Ab‐selected Asian corn borer to other Cry toxins

“…Similarly, in the present study, selection for Cry1Ab resistance in O. furnacalis resulted in cross-resistance to Cry1Ac. These data are consistent with previous studies that suggest Cry1Ab and Cry1Ac share a common binding site (Wolfersberger 1990;Gould et al 1992;Denolf et al 1993), and resistance to one would imply cross-resistance to the other, if resistance in the ACB-AbR strain was because of an alteration in the receptor.…”

Binding of Cry delta-endotoxins to brush border membrane vesicles of Helicoverpa armigera and Helicoverpa punctigera (Lepidoptera: Noctuidae)

“…The peritrophic membrane of H. armigera larvae also retained Cry1Ac toxin. Similar results were reported for Cry1Ac and Cry1B binding to Ostrinia nubilalis (Denolf et al, 1993) and for Cry1Ab and Cry1B toxin binding to M. sexta (Bravo et al, 1992b). The basis for binding of peritrophic membrane by Cry proteins has not been established and may differ from that for binding to the brush border (Bravo al., 1992a;Denolf et al, 1993).…”

“…However, for both Cry1Ab and Cry1Ac the K com values for the second binding site were considerably in excess of 15 nmol/L (Tables 2 & 3), indicating that the second site is unlikely to be physiologically relevant. In general, toxicity seems to be associated with the presence of high affinity (K com 5 nmol/L) binding sites ( Denolf et al, 1993;Ferré et al, 1991;Hofmann et al, 1988b;Van Rie et al, 1990a).…”

Evaluation of stress‐ and immune‐response biomarkers in Atlantic salmon, Salmo salar L., fed different levels of genetically modified maize (Bt maize), compared with its near‐isogenic parental line and a commercial suprex maize

“…The Cry proteins are endotoxins produced from the soil bacterium Bacillus thuringiensis (Bt) which exhibit insecticidal properties. These proteins act by binding to receptors of the mid-gut brush border membrane (Gill, Cowles & Pietrantonio 1992;Denolf, Jansens, Peferoen, Degheele & Van Rie 1993) and cause lethal damage to the intestinal tract of the ECB (Knowles 1994).…”