The Red clover necrotic mosaic virus RNA-2 encoded movement protein is a second suppressor of RNA silencing

The replication complex of Red clover necrotic mosaic virus (RCNMV) has been shown to possess silencing suppression activity. Here a newly developed viral-based assay for the identification of silencing suppression activity was used to provide evidence for a second, mechanistically distinct method of silencing suppression provided for by the RCNMV movement protein (MP). This new assay relies on Turnip crinkle virus with its capsid protein replaced with green fluorescent protein to act as a reporter (TCV-sGFP). In the presence of a protein with silencing suppression activity TCV-sGFP readily moves from cell-to-cell, but in the absence of such a protein TCV-sGFP is confined to small foci of infection. This TCV-sGFP assay was used to identify MP as a suppressor of RNA silencing, to delimit essential amino acids for this activity and uncouple silencing and movement functions.