Broad bean wilt virus 1 encoded VP47 and SCP are suppressors of plant post-transcriptional gene silencing

Broad bean wilt virus 1 (BBWV-1, genus Fabavirus, family Secoviridae) is a bipartite positive single-stranded RNA (+ssRNA) virus infecting important horticultural and ornamental crops worldwide. RNA1 encodes proteins involved in virus replication, whereas RNA2 encodes the large and small coat proteins (LCP, and SCP, respectively) and two putative movement proteins with overlapping C-terminal but different sizes: 47.2 kDa (VP47) and 37 kDa (VP37). Post-transcriptional gene silencing (PTGS) is a mechanism of gene regulation and defense against pathogens such as viruses. However, most plant viruses encode proteins called viral suppressors of RNA silencing (VSRs) which able to inhibit PTGS. Previously, BBWV-1 VP37 was identified as VSR and here, we have demonstrated that VP47 and SCP, but not LCP, are also VSRs by two approaches: (i) transient expression in Nicotiana benthamiana 16c plants expressing the green fluorescent protein (GFP) constitutively, and (ii) movement complementation assays using a viral vector based on Turnip crinkle virus sequence containing GFP (pTCV-GFP). In contrast LCP but not SCP of Broad been wilt virus 2 (BBWV-2, genus Fabavirus, family Secoviridae) is a VSR, which illustrates that viruses of the same genus can interact differently with the host.