Résumé
RNA silencing is a major antiviral defense mechanism in plants andinvertebrates. Plant ARGONAUTE1 (AGO1) is pivotal in RNA silencing, and hence is a major target for counteracting viral suppressorsof RNA-silencing proteins (VSRs). P0 from Turnip yellows virus(TuYV) is a VSR that was previously shown to trigger AGO1 degradation via an autophagy-like process. However, the identity ofhost proteins involved and the cellular site at which AGO1 and P0interact were unknown. Here we report that P0 and AGO1 associate on the endoplasmic reticulum (ER), resulting in their loadinginto ER-associated vesicles that are mobilized to the vacuole in anATG5- and ATG7-dependent manner. We further identified ATG8-Interacting proteins 1 and 2 (ATI1 and ATI2) as proteins that associate with P0 and interact with AGO1 on the ER up to the vacuole.Notably, ATI1 and ATI2 belong to an endogenous degradationpathway of ER-associated AGO1 that is significantly induced following P0 expression. Accordingly, ATI1 and ATI2 deficiency causesa significant increase in posttranscriptional gene silencing (PTGS)activity. Collectively, we identify ATI1 and ATI2 as components ofan ER-associated AGO1 turnover and proper PTGS maintenance andfurther show how the VSR P0 manipulates this pathway.