Alteration of a Cry1A Shared Binding Site in a Cry1Ab-Selected Colony of Ostrinia furnacalis.

Daniel Pinos,Juan Ferré,Yueqin Wang,Kanglai He,Patricia Hernández-Martínez

doi:10.3390/toxins14010032

Abstract

The Asian corn borer, Ostrinia furnacalis (Guenée, 1854), is a highly damaging pest in Asia and the Pacific islands, and larvae feed mainly from corn crops. To determine the suitability of Bt-corn technology for the future control of this pest, understanding the potential to develop resistance to Cry1Ab and the basis of cross-resistance to other Cry1 proteins is of great interest. Here, we have explored the binding of Cry1A proteins to brush border membrane vesicles from two O. furnacalis colonies, one susceptible (ACB-BtS) and one laboratory-selected with Cry1Ab (ACB-AbR). The insects developed resistance to Cry1Ab and showed cross-resistance to Cry1Aa, Cry1Ac, and Cry1F. Binding assays with radiolabeled Cry1Ab and brush border membrane vesicles from susceptible insects showed that Cry1A proteins shared binding sites, though the results were not conclusive for Cry1F. The results were confirmed using radiolabeled Cry1Aa. The resistant insects showed a reduction of the specific binding of both Cry1Ab and Cry1Aa, suggesting that part of the binding sites were lost or altered. Competition binding assays showed full competition between Cry1Ab and Cry1Aa proteins in the susceptible colony but only partial competition in resistant insects, confirming the alteration of some, but not all, binding sites for these two proteins. The binding site model for Cry1A proteins in O. furnacalis is in agreement with the occurrence of multiple membrane receptors for these proteins.

Highlights

Bacillus thuringiensis (Bt) is known to produce many insecticidal proteins that, either as Bt-based pesticides or expressed in genetically modified crops, can effectively control different insect pests [1]
Competition binding studies, in which the inhibition of binding of a labeled protein by different proteins is determined, have provided models showing whether Bt proteins bind to more than one site and whether different proteins share binding sites
The results have shown that Cry1A proteins share binding sites in this insect species and that at least one of these sites has been altered in the resistant insects

Summary

Introduction

Bacillus thuringiensis (Bt) is known to produce many insecticidal proteins that, either as Bt-based pesticides or expressed in genetically modified crops, can effectively control different insect pests [1]. Bt corn is considered a promising technology to control the Asian corn borer, Ostrinia furnacalis, a highly damaging insect that affects mainly this crop [4,5]. The mode of action of Bt insecticidal proteins involves, among other steps, binding to membrane molecules in the midgut (referred to as “receptors”) This step is responsible for the specificity of the toxic action, but it is the main step responsible for developing high levels of resistance by alteration of the membrane receptor [6]. These binding site models have been useful to predict and understand the basis of cross-resistance to Bt proteins since the alteration of a shared binding site can confer resistance to more than one Bt protein [7,8]

Methods

Results

Conclusion