ViralZone: Suppressor of RNA silencing

Virally encoded protein which suppresses host RNA-mediated gene silencing (also called post-transcriptional gene silencing or PTGS in plants).

The most common form of RNA-mediated gene silencing is RNA interference (RNAi), a sequence-specific RNA-degradation mechanism that operates as a natural antiviral system in plants and invertebrates cells. RNAi is mediated by small interfering RNAs (siRNA) of about 21- to 25-nt that target homologous RNAs for destruction. RNA silencing by endogenous micro-RNAs (miRNAs) may also play a role in the antiviral defences of mammals. miRNAs differ from siRNAs in that they generally base pair imperfectly with target RNAs and inhibit their translation by an unknown mechanism.

siRNAs assemble into RNA-induced complexes (RISCs) to serve as guides for the host endonuclease AGO, which targets the viral RNA for degradation.

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). 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.

-Through interaction with and inhibition of components of the host RISC machinery.

Family/Genus	Virus	Viral proteins	Reference	Mechanism of action
Alphaflexiviridae, Potexvirus		Triple gene block protein 1		-
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
Bromoviridae, Cucumovirus	Cucumber mosaic virus	Protein 2b	Inhibition of Argonaute 1
	Tomato aspermy virus	Protein 2b		Sequesters siRNA duplexes
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		-
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		-
Luteoviridae, Polerovirus		P0 protein		May prevent RISC assembly and target AGO1 to degradation
Potyviridae, Potyvirus	Turnip mosaic virus	P1/HC-Pro		-
Potyviridae, Ipomovirus	Cucumber vein yellowing virus	P1b protein		Sequesters siRNA duplexes
Reoviridae, Phytoreovirus	Rice gall dwarf virus	Pns11	-	-
	Rice dwarf virus	Pns10		-
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	Soil-borne wheat mosaic virus	P19		-
	Peanut clump virus	P15		-
	Barley stripe mosaic virus	Gamma-B		-
	Tobacco mosaic virus	Small replicase subunit		-
	Tobacco rattle virus	P16		-

Suppressor of RNA silencing

Matching UniProtKB/Swiss-Prot entries

Protein 2b

Protein AC4 (Protein AL4)

Protein V2

Protein B2

Protein C2 (Protein L2)

Capsid protein (Coat protein) (p38)

Movement protein (MP)

Movement protein P1 (Cell-to-cell transport protein)

Non-structural protein 1 (NS1) (NS1A)

Non-structural protein NS-S

Suppressor of silencing P0 (28 kDa protein) (Protein ORF0)

RNA silencing suppressor p14

RNA silencing suppressor p19 (19 kDa symptom severity modulator)

RNA silencing suppressor (21 kDa protein) (p21)

69 kDa protein (p69)

RNA2 polyprotein (Genome polyprotein M) (P2)

Genome polyprotein

Replicase polyprotein

Replicase large subunit (EC 2.1.1.-) (EC 2.7.7.-) (EC 2.7.7.48) (EC 3.6.4.13) (183 kDa protein) (RNA-directed RNA polymerase)

Movement and silencing protein TGBp1 (25 kDa protein) (Silencing suppressor P25) (Triple gene block 1 protein) (TGBp1)

Transcriptional activator protein (TrAP) (Protein AC2) (Protein AL2)

Protein E3 (p25)

RNA silencing suppressor

Suppressor of RNA silencing p3 (Protein NS3) (Protein p3)