The autophagy pathway participates in resistance to Candidatus Liberibacter asiaticus infection in Diaphorina citri

BACKGROUND: Autophagy is a conserved mechanism by which eukaryotic organisms defend against pathogen infection. However, the molecular mechanisms underlying the role of autophagy in the interactions of insect vectors with the phloem-limited bacterial pathogen remain unclear. The citrus Huanglongbing (HLB)-associated pathogen 'Candidatus Liberibacter asiaticus' (CLas) seriously endangers development of the citrus industry. It spreads via Diaphorina citri in a persistent and propagative manner. RESULTS: In this study, a total of 30 autophagy-related genes (ATG) were identified in the D. citri genome, among which multiple genes were significantly regulated after CLas infection. Concurrently, CLas infection also leads to an increased number of autophagosomes and enhanced accumulation of ATG8-II. Ultrastructural observations revealed the presence of bacterial-like structures within autophagosomes in the midgut of CLas-infected D. citri. Furthermore, both activation and inhibition of autophagy significantly influenced CLas titers. However, autophagy cannot completely eliminate CLas in D. citri. We identified a CLas effector, SDE4040 (CLIBASIA_04040), that interacts with DcATG8 and co-localizes on autophagosomes in D. citri. Co-expression of SDE4040 and DcATG8 induces autophagy in Spodoptera frugiperda (Sf9) cells. CONCLUSION: Taken together, these results indicate that CLas infection activates the autophagy pathway in D. citri, contributing to a reduction in bacterial titer. Our data also revealed that CLas may trigger complex interactions with the insect. © 2025 Society of Chemical Industry.