A phloem-limited unculturable bacterium induces mild xenophagy in insect vectors for persistent infection.

Xenophagy is an important antibacterial defense mechanism that many organisms use to engulf intracellular pathogens. However, the mechanisms of xenophagy triggered by insect-borne plant bacteria are not well understood. Candidatus Liberibacter asiaticus (CLas) causes Huanglongbing, which poses a serious threat to citrus production. CLas is a phloem-limited unculturable bacterium that is transmitted by the Asian citrus psyllid in a persistent and propagative manner in nature. Here, we found that CLas infection in the gut of psyllids triggered a mild and anti-bacterial xenophagy. Xenophagy limited excessive propagation of CLas to maintain psyllid survival, because overload of CLas was detrimental to psyllid life. Furthermore, the outer membrane β-barrel protein (OMBB) of CLas is the key secreted protein that induces xenophagy in psyllids by interacting with ATG8 and ATG14. OMBB can independently induce autophagy in psyllid and non-host cells. Together, these results revealed that an insect-borne plant bacterium activates mild xenophagy to control its propagation, thereby achieving persistent infection in insect vectors.