Calcineurin-dependent 20E signaling pathway enhances attacin expression to prime the immunity of Helicoverpa armigera against Bacillus thuringiensis Cry1Ac toxin.

Enhancing the insecticidal efficacy of Bacillus thuringiensis (Bt) toxins by suppressing the immune responses of target insects can simultaneously augment the effectiveness of Bt-based products and address the growing issue of resistance. Our previous studies found that the inhibition of calcineurin (CaN) activity can enhance the toxicity of Cry1Ac, a Bt toxin, against Helicoverpa armigera, and that CaN regulates the expression of antimicrobial peptides (AMPs) in response to external pathogen invasion through the transcription factor Relish in H. armigera. Our objective was to investigate the regulatory relationship between AMPs expression and susceptibility to Cry1Ac. Our findings demonstrated that the transcription factors Relish and Dorsal mediate the CaN-induced upregulation of attacin expression, while attacin itself interacts with Cry1Ac to reduce its toxicity against H. armigera. Furthermore, Cry1Ac treatment results in elevated levels of 20E in H. armigera, partly triggering an increase in intracellular Ca2+ concentration, which in turn activates CaN. These findings contribute to the robust body of evidence that insects can elicit immune defenses as an adaptive mechanism against Bt toxins, and also offer a potential strategy for improving pest control effectiveness in agricultural settings.