Hijacking a host scaffold protein, RACK 1, for replication of a plant RNA virus

Summary Receptor for activated C kinase 1 ( RACK 1) is strictly conserved across eukaryotes and acts as a versatile scaffold protein involved in various signaling pathways. Plant RACK 1 is known to exert important functions in innate immunity against fungal and bacterial pathogens. However, the role of the RACK 1 in plant–virus interactions remains unknown. Here, we addressed the role of RACK 1 of Nicotiana benthamiana during infection by red clover necrotic mosaic virus ( RCNMV ), a plant positive‐stranded RNA virus. Nb RACK 1 was shown to be recruited by the p27 viral replication protein into endoplasmic reticulum‐derived aggregated structures (possible replication sites). Downregulation of Nb RACK 1 by virus‐induced gene silencing inhibited viral cap‐independent translation and p27‐mediated reactive oxygen species ( ROS ) accumulation, which are prerequisite for RCNMV replication. We also found that Nb RACK 1 interacted with a host calcium‐dependent protein kinase (Nb CDPK iso2) that activated a ROS ‐generating enzyme. Interestingly, Nb RACK 1 was required for the interaction of p27 with Nb CDPK iso2, suggesting that Nb RACK 1 acts as a bridge between the p27 viral replication protein and Nb CDPK iso2. Collectively, our findings provide an example of a viral strategy in which a host multifaceted scaffold protein RACK 1 is highjacked for promoting viral protein‐triggered ROS production necessary for robust viral replication.