BdNub Is Essential for Maintaining gut Immunity and Microbiome Homeostasis in Bactrocera dorsalis .

Insects face immune challenges posed by invading and indigenous bacteria. They rely on the immune system to clear these microorganisms. However, the immune response can be harmful to the host. Therefore, fine-tuning the immune response to maintain tissue homeostasis is of great importance to the survival of insects. The gene of the OCT/POU family regulates the intestinal IMD pathway. However, the role of the gene in regulating host microbiota remains unstudied. Here, a combination of bioinformatic tools, RNA interference, and qPCR methods were adopted to study gene function in gut immune system. It's found that , , and antimicrobial peptides (AMPs), including (), (), (), () and () are significantly up-regulated in Tephritidae fruit fly after gut infection. Silencing leads to down-regulated AMPs expression, while RNAi leads to increased expression of AMPs. These results indicate that is a positive regulatory gene of the IMD pathway, while negatively regulates IMD pathway activity. Further studies also revealed that and are associated with gut microbiota composition, possibly through regulation of IMD pathway activity. Our results prove that the gene is evolutionarily conserved and participates in maintaining gut microbiota homeostasis.