Suppressor of RNA silencing

RNA-mediated gene silencing (also known as RNA interference, RNAi) is a conserved sequence-specific gene regulation system, which has an essential role in the maintenance of cell genome integrity, and, in higher plants and insects, it also operates as an adaptive inducible antiviral defense mechanism. It consists in sequence-specific recognition and inhibition of target genes expression by endogenous (gene, development, stress response regulation) or virus-derived short silencing RNAs (sRNAs) .

Target genes expression can be inhibited post-translationally (post-transcriptional gene silencing or PTGS): target dsRNAs are recognized by Dicer-like enzymes (DCL) and diced into small interfering RNAs duplexes (siRNA) of about 21- to 24-nt, which interact with Argonaute (AGO) proteins and associated proteins to form RNA-induced complexes (RISCs) to target homologous RNAs for destruction. PTGS can also be performed by endogenous microRNAs (miRNAs). miRNAs differ from siRNAs in that they are encoded by cellular genes and generally base pair imperfectly with homologous RNAs to target them for destruction or inhibit their translation.

Target genes expression can also be inhibited by heavy methylation of concerned DNA loci (transcriptional gene silencing or TGS).

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To counteract host RNAi antiviral defense, viruses from almost all plant virus genera (and also from some animal viruses) encode viral suppressors of RNA silencing (VSRs) which inhibit key steps of cellular RNAi system . They are often multifunctional and play important roles in viral replication, coating, movement, and pathogenesis, in addition to suppressing host RNA silencing-based antiviral immunity.


VSRs suppress RNA silencing pathways mainly:

-through dsRNA binding. Sequestering siRNA duplexes prevents small RNA loading into the AGO effector proteins to assemble the RNA-induced silencing complex (RISC). Sequestering long dsRNA duplexes inhibits siRNA biogenesis.

-by interacting with and inhibiting components of the host RISC machinery.

-by inhibiting enzymes necessary for host cell-mediated DNA methylation.

Family/Genus Virus Viral proteins Reference Mechanism of action
Alphaflexiviridae, Potexvirus Triple gene block protein 1 -
Betaflexiviridae, Carlavirus Potato virus M Triple gene block protein 1, ORF6 Sequesters siRNA duplexes (ORF6)
Betaflexiviridae, Citrivirus Citrus leaf blotch virus Movement protein
Betaflexiviridae, Trichovirus Apple chlorotic leaf spot virus 50 kDa movement protein
Betaflexiviridae, Vitivirus Grapevine virus A ORF5 p10 Sequesters siRNA duplexes
Bromoviridae, Cucumovirus Cucumber mosaic virus Protein 2b sequestering siRNA and long dsRNA
Tomato aspermy virus Protein 2b Sequesters siRNA duplexes
Bromoviridae, Ilarvirus Tobacco streak virus Protein 2b - -
Bunyaviridae, Tospovirus Tomato spotted wilt virus NSs Sequesters both long dsRNA and double-stranded siRNA or miRNA
Closteroviridae, Closterovirus Beet yellows virus P21 Sequesters siRNA duplexes
Citrus tristeza virus p23, capsid protein, p20 -
Closteroviridae, Crinivirus Sweet potato chlorotic stunt virus P22 Sequesters siRNA duplexes
Tomato chlorosis virus P22 Sequesters siRNA duplexes
Dicistroviridae, Cripavirus Drosophila C virus DCV-1A Sequesters long dsRNA and inhibits siRNA biogenesis
Cricket paralysis virus CrPV-1A Interaction with Argonaute 2 and inhibition of RISC
Geminiviridae, Begomovirus Mungbean yellow mosaic virus-Vigna TrAP/AC2 -
Tomato leaf curl Java virus V2 -
Tomato leaf curl China virus V2 ?Sequesters siRNA duplexes
Tomato yellow leaf curl virus C4 -
Luteoviridae , Polerovirus Beet western yellows virus P0 protein Targets AGO1 to degradation
Luteoviridae, Enamovirus Pea enation mosaic virus-1 P0 protein Targets AGO1 to degradation
Nanoviridae , Babuvirus Banana bunchy top virus Clink , MP -
Nodaviridae, Alphanodavirus Flock house virus B2 protein Interaction with Dicer leads to suppression of siRNA biogenesis
Nodaviridae, Alphanodavirus Flock house virus B2 protein Interaction with Dicer leads to suppression of siRNA biogenesis
Nodamura virus B2 protein Interaction with Dicer leads to suppression of siRNA biogenesis
Potyviridae, Potyvirus HC-Pro Prevents accumulation of siRNA
Potyviridae, Ipomovirus Cucumber vein yellowing virus P1b protein Sequesters siRNA duplexes
Potyviridae, Poacevirus Triticum mosaic virus P1 protein -
Potyviridae, Tritimovirus Wheat streak mosaic virus P1 protein -
Reoviridae, Phytoreovirus Rice gall dwarf virus Pns11, Pns12 -
Rice dwarf virus Pns10 -
Reoviridae, Oryzavirus Rice ragged stunt virus Pns6 -
Rice dwarf virus Pns10 -
Secoviridae, Comovirus Cowpea mosaic virus small capsid protein -
Tenuivirus Rice stripe virus NS3 Sequesters siRNA duplexes
Sobemovirus Cocksfoot mottle virus P1
Rice yellow mottle virus P1
Tombusviridae, Tombusvirus Carnation Italian ringspot virus p19 Sequesters siRNA duplexes
Tombusviridae, Aureusvirus Pothos latent virus Protein p14 Sequesters both long dsRNA and double-stranded siRNA
Tombusviridae, Dianthovirus Red clover necrotic mosaic virus MP -
Tombusviridae, Carmovirus Turnip crinkle virus Capsid protein P38 Competes for and inhibits Argonaute 1
Tymoviridae, Tymovirus Turnip yellow mosaic virus p69 -
Virgaviridae, Furovirus Soil-borne wheat mosaic virus P19 -
Virgaviridae, Pecluvirus Peanut clump virus P15 -
Virgaviridae, Hordeivirus Barley stripe mosaic virus Gamma-B -
Virgaviridae, tobamovirus Tobacco mosaic virus Small replicase subunit -
Virgaviridae, Tobravirus Tobacco rattle virus P16 -
Hypovirus Cryphonectria hypovirus 1 P29 -