NBR1-mediated antiviral xenophagy in plant immunity.

Macroautophagy/autophagy intersects with metazoan virus infections in highly complex and multifaceted ways. Autophagy mechanisms are part of antiviral immunity, but can be manipulated by several viruses to the benefit of infection. In plants, however, the roles of autophagy in virus infections have only recently started to emerge. Here, we present and discuss our recent study that identified 2 prominent functions of autophagy upon cauliflower mosaic virus (CaMV) infection in Arabidopsis. We found that "bulk" autophagy significantly extended the life span of infected plants and increased total virus production. In addition to this proviral role, we discovered that the selective autophagy receptor protein AT4G24690/NBR1 binds viral particles to mediate their xenophagic degradation. Intriguingly, CaMV inclusion bodies protect viral particles from xenophagy and thus represent a sophisticated strategy to counter the antiviral capacity while maintaining the proviral activity of autophagy. Together, our study gives a seminal description of how autophagy is integrated into host immunity and viral pathogenesis in plants, and provides a primary example for removal of a plant pathogen by xenophagy.