Barley stripe mosaic virus gamma b Protein Subverts Autophagy to Promote Viral Infection by Disrupting the ATG7-ATG8 Interaction

Autophagy is a conserved defense strategy against viral infection. However, little is known about the counterdefense strategies of plant viruses involving interference with autophagy. Here, we show that gamma b protein from Barley stripe mosaic virus (BSMV), a positive single-stranded RNA virus, directly interacts with AUTOPHAGY PROTEIN7 (ATG7). BSMV infection suppresses autophagy, and overexpression of gamma b protein is sufficient to inhibit autophagy. Furthermore, silencing of autophagy-related gene ATG5 and ATG7 in Nicotiana benthamiana plants enhanced BSMV accumulation and viral symptoms, indicating that autophagy plays an antiviral role in BSMV infection. Molecular analyses indicated that gamma b interferes with the interaction of ATG7 with ATG8 in a competitive manner, whereas a single point mutation in gamma b, Tyr29Ala (Y29A), made this protein deficient in the interaction with ATG7, which was correlated with the abolishment of autophagy inhibition. Consistently, the mutant BSMV Y29A virus showed reduced symptom severity and viral accumulation. Taken together, our findings reveal that BSMV gamma b protein subverts autophagy-mediated antiviral defense by disrupting the ATG7-ATG8 interaction to promote plant RNA virus infection, and they provide evidence that ATG7 is a target of pathogen effectors that functions in the ongoing arms race of plant defense and viral counterdefense.