Viral RNA polymerase as a SUMOylation decoy inhibits RNA quality control to promote potyvirus infection.

Potyvirids are the largest group of plant RNA viruses. Pelota, a core component of RNA quality controls (RQC), promotes the degradation of potyvirids' genomic RNA by recognizing a specific GA motif. Here we demonstrate that the viral RNA-dependent RNA polymerase, NIb, acts as a SUMOylation decoy to effectively reduce Pelota SUMOylation by competing with SCE1 to inhibit Pelota-mediated RQC. TuMV NIb is comprised of two functional SUMO interacting motif (SIM): SIM2 and SIM3. The former is identified as the key site for NIb's SUMOylation by SUMO3, whereas the latter is responsible for the interaction with SCE1. These two SIMs are conserved among the majority of potyvirids-encoded NIbs. Thus, virus protein-mediated SUMOylation decoy strategy to suppress host defense may be a common feature in plant virus pathosystems. These findings highlight a dynamic interplay between plant defense mechanism and viral counter-strategy by orchestrating the post-translational modifications of virus and host defense components.