Evidence of a shared binding site for Bacillus thuringiensisCry1Ac and Cry2Aa toxins in Cnaphalocrocis medinalis cadherin

Abstract

Insect midgut cadherins function as receptors and play critical roles as protein receptors of insecticidal Bacillus thuringiensis (Bt) toxins used as biopesticides and in Bt transgenic crops worldwide. Here, we cloned and characterized the full-length midgut cadherin (CmCad) cDNA from the rice leaffolder (Cnaphalocrocis medinalis), a destructive pest of rice in many Asian countries. Expression of recombinant proteins corresponding to the extracellular domain of CmCad allowed testing binding of Cry proteins. Results from in vitro ligand blotting and enzyme-linked immunosorbent assays supported that the extracellular domain of CmCad contains regions recognized by both Cry1Ac and Cry2Aa. Molecular modelling and docking simulations indicated that binding to both Cry1Ac and Cry2Aa is localized primarily within a CmCad motif corresponding to residues T1417-D1435. A recombinant CmCad protein produced without residues T1417-D1435 lacked binding to Cry1Ac and Cry2Aa, confirmed our modelling predictions that CmCad has a shared Cry1Ac and Cry2Aa binding site. The potential existence of a shared binding region in CmCad suggests that caution should be taken when using combinations of Cry1Ac and Cry2Aa in pyramided transgenic rice, as their combined use could speed the evolution of resistance to both toxins.

The Potential Role of the Methionine Aminopeptidase Gene PxMetAP1 in a Cosmopolitan Pest for Bacillus thuringiensis Toxin Tolerance

“…Brévault et al (2013) also reported that eight main lepidopteran pests commonly developed cross-resistance to Cry1A and Cry2A toxins from transgenic cotton [ 95 ]. An unusual but interesting result was presented recently by Zhong et al (2022) that the midgut cadherin (CmCad) of Cnaphalocrocis medinalis shared Cry1Ac and Cry2Aa binding sites; the knockout strain of CmCad1 simultaneously showed resistance to both Cry1A and Cry2A toxins [ 96 ].…”