Broad bean wilt virus 2 encoded VP53, VP37 and large capsid protein orchestrate suppression of RNA silencing in plant

Viruses encode RNA silencing suppressors to counteract host RNA silencing-mediated defense responses. In this study, we demonstrate that VP53, VP37 and LCP encoded by RNA2 of broad bean wilt virus 2 (BBWV-2), a member of the genus Fabavirus, are strong suppressors of RNA silencing triggered by single-stranded sense RNA. They, however, had no effect on suppression of RNA silencing induced by double-stranded RNA. We provide evidence that these three suppressors can significantly limit the accumulation of small interfering RNAs (siRNAs) in tissues where the GFP gene has been silenced, and prevent the long distance spread of the induced silencing signal. Gel mobility shift assays showed that all three suppressors could bind ssRNA in a size-specific manner. Interestingly, VP37 and LCP, but not VP53, could reverse the silencing of a GFP gene in leaf tissue. Furthermore, these three proteins are capable of enhancing pathogenicity of potato virus X. Collectively, our findings indicate that viruses employ a more sophisticated strategy to overcome the host defense response mediated through suppression of RNA silencing during virus infection. As far as we are aware, this is the first report of RNA silencing suppressors encoded by a virus in the genus Fabavirus.

[Production of monoclonal antibodies to broad bean wilt virus and application in virus detection]

Six hybridoma cell lines secretion monoclonal antibodies(MAbs) against broad bean wilt virus(BBWV) were produced by fusing mouse myeloma cells(SP 2/0) with spleen cells from BAL B/c immunized by the BBWV particles. The hybridoma cell lines secreted MAbs stably after cultured in vitro for 3 months or stored in liquid nitrogen and then revived for several times. The titres of ascitic fluids of six MAbs ranged from 1:256,000 to 1:640,000 when measured by indirect ELISA. In agarose gel immunodiffusion test, it showed that the six MAbs represented the same isotype of murine antibodies, IgG1. Six MAbs could detect 4 tested BBWV isolates, but didn't crossreact with other 5 plant viruses. The result of Western blot showed that all the six MAbs can react with the 44.7 kD large coat protein subunit of BBWV. This is the first report of production of MAbs against BBWV.