Abstract
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.
Highlights
The bacterium Bacillus thuringiensis (Bt) produces crystalline (Cry) proteins that exhibit specific insecticidal activity; these proteins have been used worldwide in insecticidal spray formulations or produced in transgenic Bt crops[1]
Cadherin has been studied in insects extensively as putative Bt toxin receptors
Coleopterans and dipterans, many cadherins have been identified as receptors of Bt toxins, facilitating a post-binding specific proteolytic cleavage step that induces toxin oligomerization and pore formation and further mediates toxin susceptibility[5]
Summary
The bacterium Bacillus thuringiensis (Bt) produces crystalline (Cry) proteins that exhibit specific insecticidal activity; these proteins have been used worldwide in insecticidal spray formulations or produced in transgenic Bt crops[1]. The binding of the Cry1A toxin to C. suppressalis aminopeptidase (CsAPN) and cadherin (CsCad) expressed in insect cell cultures suggests that these proteins play a role in Cry intoxication[30,31]. The exposure to the heterologous CsCad-CR11-MPED peptide significantly enhanced the susceptibility of C. suppressalis larvae to Cry1Ab but not to Cry1C.
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