Aureusvirus P14 Is an Efficient RNA Silencing Suppressor That Binds Double-Stranded RNAs without Size Specificity

Agricultural Biotechnology Center, Plant Science Institute, P.O. Box 411, H-2101 Gödöllö, Hungary.
Journal of Virology (Impact Factor: 4.44). 07/2005; 79(11):7217-26. DOI: 10.1128/JVI.79.11.7217-7226.2005
Source: PubMed


RNA silencing is a conserved eukaryotic gene regulatory system in which sequence specificity is determined by small RNAs. Plant RNA silencing also acts as an antiviral mechanism; therefore, viral infection requires expression of a silencing suppressor. The mechanism and the evolution of silencing suppression are still poorly understood. Tombusvirus open reading frame (ORF) 5-encoded P19 is a size-selective double-stranded RNA (dsRNA) binding protein that suppresses silencing by sequestering double-stranded small interfering RNAs (siRNAs), the specificity determinant of the antiviral silencing system. To better understand the evolution of silencing suppression, we characterized the suppressor of the type member of Aureusviruses, the closest relatives of the genus Tombusvirus. We show that the Pothos latent virus (PoLV) ORF 5-encoded P14 is an efficient suppressor of both virus- and transgene-induced silencing. Findings that in vitro P14 binds dsRNAs and double-stranded siRNAs without obvious size selection suggest that P14, unlike P19, can suppress silencing by sequestering both long dsRNA and double-stranded siRNA components of the silencing machinery. Indeed, P14 prevents the accumulation of hairpin transcript-derived siRNAs, indicating that P14 inhibits inverted repeat-induced silencing by binding the long dsRNA precursors of siRNAs. However, viral siRNAs accumulate to high levels in PoLV-infected plants; therefore, P14 might inhibit virus-induced silencing by sequestering double-stranded siRNAs. Finally, sequence analyses suggest that P14 and P19 suppressors diverged from an ancient dsRNA binding suppressor that evolved as a nested protein within the common ancestor of aureusvirus-tombusvirus movement proteins.

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Available from: Zoltan Kerenyi
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    • "Both of these proteins are required for genomic RNA replication and subgenomic (sg) mRNA transcription (Reade et al., 2003). The capsid protein (p41) is translated from sg mRNA1 while overlapping silencing suppressor (p27) and movement (p19) proteins are translated from sg mRNA2; both of which are transcribed during infections (Merai et al., 2005; Xu and White, 2008, 2009). Interestingly, although aureusviruses are similar in genomic structure to tombusvirues , no DI RNAs have been found associated with any aureusvirus, even when passaged at high moi (Rubino and Russo, 1997). "
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    • "The NMD test constructs were agroinfiltrated into N. benthamiana leaves only with a P14 RNA silencing suppressor or were co-infiltrated with P14 and U1DN (referred to as control and U1DN co-infiltrated samples, respectively). P14 was co-infiltrated in these experiments for two reasons: (i) to suppress agroinfiltration-induced intense RNA silencing (39) and (ii) to serve as an internal control for RNA gel blot assays. (Although P14 was co-infiltrated in all assays shown in this article, it will not be mentioned later in the main text. "
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    • "During the last few years, the p69 encoded by Turnip yellow mosaic virus has been identified as a silencing suppressor preventing host RDRdependent secondary dsRNA synthesis (Chen et al., 2004). P14 protein encoded by Aureus viruses suppressed both virus and transgene-induced silencing by sequestering both long dsRNA and siRNA without size specificity (Merai et al., 2005). Multiple suppressors have been reported in the Citrus tristeza virus, where p20 and coat protein (CP) play important roles in suppression of the silencing signal, and p23 inhibited intracellular silencing (Lu et al., 2004). "
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