PxDorsal Regulates the Expression of Antimicrobial Peptides and Affects the Bt Susceptibility of Plutella xylostella

The insect NF-κB pathway is primarily constituted by nuclear factor κB (NF-κB) and the inhibitor of κB (IκB), which plays a crucial role in the innate immune response. Dorsal and Cactus, as NF-κB and IκB factors, are important downstream regulators of the Toll pathway in <i>Plutella xylostella</i>. In this study, the <i>PxDorsal</i> and <i>PxCactus</i> genes of <i>P. xylostella</i> were cloned, and the molecular docking demonstrated that PxDorsal and PxCactus can interact with each other. RT-qPCR results indicated that <i>PxDorsal</i> and <i>PxCactus</i> were expressed in all stages, and the expression of <i>PxDorsal</i>, <i>PxCactus</i>, and antimicrobial peptides <i>PxGloverin</i>2, <i>PxMoricin</i>3, and <i>PxLysozyme</i>2 were significantly down-regulated under <i>Bacillus thuringiensis</i> (Bt8010) infection. Interestingly, silencing the <i>PxDorsal</i> gene by RNA interference (RNAi) significantly down-regulated the expression of <i>PxGloverin</i>2 and <i>PxMoricin</i>3 and increased the epidermis melanization of <i>P. xylostella</i> larvae fed with Bt8010. Our findings indicate that PxDorsal and PxCactus may interact with each other, and silencing <i>PxDorsal</i> inhibits the expression of downstream antimicrobial peptides, thereby enhance the susceptibility of <i>P. xylostella</i> to Bt8010. This study contributes a theoretical basis for further research on the Toll pathway of <i>P. xylostella</i> to pathogens and offers insights for screening effective biological control targets from the perspective of the immune system.