Bacterial-tyramine-induced renal-gut countercurrent flow regulates gut immune response by promoting ROS accumulation and gut peristalsis in the fly Bactrocera dorsalis

Insects increase gut peristalsis to purge ingested pathogens. They also rely on the Duox-ROS system to mount an efficient gut response. However, how these two host defense mechanisms are coordinated to clear pathogens remained unclear. We found that gut peristalsis is the major force for bacteria elimination, while Duox is necessary as a signaling molecule to activate gut peristalsis in a Tephritidae fruit fly Bactrocera dorsalis . We found an insect-conserved renal-gut countercurrent flow formed upon recognizing bacteria-derived tyramine counteracts the gut peristalsis forced defecation and drives the accumulation of ROS. Furthermore, we demonstrated that the renal-gut countercurrent flow maintains proper microbiota composition. Our work provided a novel renal-gut interaction that ensures an efficient gut-immune response.