Identification of Cry1Ie toxin receptors in Ostrinia nubilalis

Insecticidal crystalline (Cry) proteins are produced by the bacterium Bacillus thuringiensis (Bt) during sporulation.  These toxins have been widely used in the control of insect pests either as part of spray products or expressed in transgenic crops.  The mode of action of Cry toxins includes solubilization and activation in the larval midgut fluids and binding to protein receptors on the midgut epithelium, leading to toxin insertion in the membrane and formation of a pore that results in enterocyte death by osmotic shock. The cry1Ie gene cloned from B. thuringiensis strain BTC007 is highly active against European corn borer (Ostrinia nubilalis) and diamondback moth (Plutella xylostella) larvae.  Moreover, Cry1Ie is effective against insects that are resistant to Cry1A toxins, which are commonly used in Bt pesticides and transgenic Bt crops. These observations have sparked interest in Cry1Ie as a candidate for use in Bt pesticides and transgenic crops.  However, the specific Cry1Ie receptors in target insects are unknown.  In this work we used chromatographic fractionation of midgut brush border membrane proteins combined with binding assays under native and denaturing conditions to identify putative Cry1Ie receptors in O. nubilalis larvae.  Since Cry1Ab toxin is currently expressed in Bt corn to control O. nubilalis, we tested sharing of binding sites for Cry1Ie and Cry1Ab toxins in these larvae. Our data identify unique Cry1Ie binding sites and support this toxin as an alternative to Cry1Ab for control of O. nubilalis.