Cry toxin binding site models and their use in strategies to delay resistance evolution.

Abstract

Abstract The binding of Cry toxins to receptors on the midgut brush border membrane is a necessary step in the Cry intoxication process. Alterations in this binding step are commonly associated with high levels of resistance to Cry toxins in laboratory and field pest populations. When alterations affect binding to a site shared by distinct Cry toxins, cross-resistance is observed. Consequently, pyramiding of Cry toxins recognizing distinct sites has been used to delay the evolution of resistance against transgenic crops expressing cry toxin genes for pest control. The availability of accurate binding site models describing binding sites for diverse Cry toxins in targeted pests is critical to identifying genes that are amenable to pyramiding. Many of these models have been proposed and refined in the past 25 years from quantitative binding competition data. In this chapter, we review and revise Cry toxin binding site models for the most relevant pest species targeted by Bt crops and for Plutella xylostella as the insect pest with the most binding data available. Our motivation is to provide binding site models as a tool to allow predictions of resistance and cross-resistance risks in order to optimize combinations of diverse Cry toxins for delaying resistance evolution to Bt crops.