Cadherin CsCad plays differential functional roles in Cry1Ab and Cry1C intoxication in Chilo suppressalis

Transgenic rice lines expressing Bacillus thuringiensis (Bt) toxins have been successfully developed for the control of Chilo suppressalis. However, the evolution of insect resistance is a major threat to Bt rice durability. Bt toxins function by binding specific receptors in the midgut of target insects; specifically, cadherin proteins have been identified as Cry toxin receptors in diverse lepidopteran species. Here, we report the functional roles of cadherin CsCad in the midgut of C. suppressalis in Cry1Ab and Cry1C toxicity. We expressed a recombinant truncated CsCad peptide (CsCad-CR11-MPED) in Escherichia coli that included the eleventh cadherin repeat and MPED region. Based on ligand blotting and ELISA binding assays, the CsCad-CR11-MPED peptide specifically bound Cry1Ab with high affinity but weakly bound Cry1C. The CsCad-CR11-MPED peptide significantly enhanced the susceptibility of C. suppressalis larvae to Cry1Ab but not Cry1C. Furthermore, the knockdown of endogenous CsCad with Stealth siRNA reduced C. suppressalis larval susceptibility to Cry1Ab but not Cry1C, suggesting that CsCad plays differential functional roles in Cry1Ab and Cry1C intoxication in C. suppressalis. This information directly enhances our understanding of the potential resistance mechanisms of C. suppressalis against Bt toxins and may assist in the development of effective strategies for delaying insect resistance.