Premier Presentation: Resistance to Bacillus thuringiensis Cry2Ab toxin in Helicoverpa spp. is conferred by mutations in a novel ABC transporter

Transgenic crops expressing the insecticidal protein Cry2Ab from Bacillus thuringiensis (Bt) are used worldwide to suppress damage by lepidopteran pests, pyramided with Cry1Ac toxin to delay resistance evolution. Previous studies have shown that Cry2Ab toxin-binding sites in the midgut are different from Cry1Ac-binding sites, but little additional information on Cry2Ab mode of action is available. Resistance to Cry1Ac can be caused by alterations in its binding targets, including a membrane-bound alkaline phosphatase, a 12-cadherin-domain protein, and the ABC transporter ABCC2, but resistance mechanisms to Cry2Ab have not been identified. In Australia, Cry2Ab-resistant strains of Helicoverpa armigera and H. punctigera have been isolated from the field using F₁ and F₂ screens, and these strains show no cross-resistance to Cry1Ac. Using a positional cloning approach, we identified mutations in a novel ABC protein in both species that truncate the protein and confer high levels of resistance to Cry2Ab. This resistance is genetically independent from Cry1Ac resistance caused by mutations or downregulation of a different ABC protein, ABCC2. We discuss the implications of this finding for Bt toxin modes of action and resistance management.