Expression and Functional Analysis of Peptidoglycan Recognition Protein OfPGRP-B in Ostrinia furnacalis

To elucidate the role of the peptidoglycan recognition protein OfPGRP-B in the innate immunity of Ostrinia furnacalis, a recombinant expression system was established using a prokaryotic expression strategy. The recombinant plasmid encoding OfPGRP-B was constructed and expressed in Escherichia coli, and the target protein was successfully obtained after induction. Purification and Western blot analysis confirmed that the molecular weight of the recombinant protein was consistent with the predicted value. The immune functions of OfPGRP-B were further investigated through antibacterial activity assays, bacterial agglutination tests, amidase activity assays, phenoloxidase (PO) cascade activation, and in vivo melanization assays. The results showed that OfPGRP-B alone exhibited weak direct antibacterial activity against the tested bacteria but significantly promoted bacterial agglutination and was capable of degrading peptidoglycan derived from E. coli and Staphylococcus aureus. In the presence of bacterial peptidoglycan, OfPGRP-B enhanced the activation of the PO cascade, but had no significant effect on in vivo melanization. These findings suggest that OfPGRP-B may function as an immunomodulatory factor involved in the humoral immune response of O. furnacalis, providing a theoretical basis for the development of biological control strategies based on host immune mechanisms.