Pleiotropic immunoregulation by growth‐blocking peptide in Ostrinia furnacalis

Insects rely on their innate immune system to eliminate pathogenic microbes. As a system component, cytokines transmit intercellular signals to control immune responses. Growth‐blocking peptide (GBP) is a member of the stress‐responsive peptide family of cytokines found in several orders of insects, including Drosophila . However, the physiological role of GBP in defence against pathogens is not thoroughly understood. In this study, we explored the functions of GBP in a lepidopteran pest, Ostrinia furnacalis . Injection of recombinant O. furnacalis GBP ( Of GBP) precursor (proGBP) and chemically synthesised GBP significantly induced the transcription of antimicrobial peptides (AMPs) and other immunity‐related genes including immune deficiency ( IMD ) and Dorsal . The level of Of GBP mRNA was upregulated after bacterial infection. Knockdown of Of GBP expression led to a decrease in IMD , Relish , MyD88 and Dorsal mRNA levels. Of GBP induced phenoloxidase activity and affected hemocyte behaviours in O. furnacalis larvae. In summary, GBP is a potent cytokine, effectively regulating AMP synthesis, melanization response and cellular immunity to eliminate invading pathogens.