20-Hydroxyecdysone regulates the expression of antimicrobial peptides through dorsal and relish in Helicoverpa armigera

Abstract

20-hydroxyecdysone (20E) plays a key role in insect development, not only regulating molting and metamorphosis but also participating in the innate immune responses. The regulation of immunity by 20E varies among different insect species. The pathway and mechanism of 20E regulates immunity in the cotton bollworm (Helicoverpa armigera) remain unclear. In this study, we confirmed that the enhanced immunity is regulated by 20E in H. armigera. 20E upregulates the expression of antimicrobial peptides (AMPs). Knockdown of Dorsal suppressed the 20E-induced expression of AMPs, while knockdown of Relish similarly inhibited the expression of AMPs except Moricin. Overexpression of Dorsal promotes its nuclear translocation and activates the expression of AMPs. However, overexpression of Cactus (IκB-like protein, the inhibitor of NFκB) isoform A binds to Dorsal and inhibits its nuclear translocation. 20E upregulates Dorsal expression via direct EcR mediation and facilitates Dorsal release through phosphorylation of Cactus A. We also report spontaneous activation of HaRelish through auto-proteolytic cleavage, liberating its N-terminal domain (Rel-N). Nuclear Rel-N interacts with Dorsal to co-regulate AMP transcription. These data indicate that 20E induces the expression of AMPs in H. armigera through activation of Dorsal and Relish, thereby enhancing immunity during the metamorphosis stage.