title: Viral class 1 RNase III involved in suppression of RNA silencing.
abstract: Double-stranded RNA (dsRNA)-specific endonucleases belonging to RNase III classes 3 and 2 process dsRNA precursors to small interfering RNA (siRNA) or microRNA, respectively, thereby initiating and amplifying RNA silencing-based antiviral defense and gene regulation in eukaryotic cells. However, we now provide evidence that a class 1 RNase III is involved in suppression of RNA silencing. The single-stranded RNA genome of sweet potato chlorotic stunt virus (SPCSV) encodes an RNase III (RNase3) homologous to putative class 1 RNase IIIs of unknown function in rice and Arabidopsis. We show that RNase3 has dsRNA-specific endonuclease activity that enhances the RNA-silencing suppression activity of another protein (p22) encoded by SPCSV. RNase3 and p22 coexpression reduced siRNA accumulation more efficiently than p22 alone in Nicotiana benthamiana leaves expressing a strong silencing inducer (i.e., dsRNA). RNase3 did not cause intracellular silencing suppression or reduce accumulation of siRNA in the absence of p22 or enhance silencing suppression activity of a protein encoded by a heterologous virus. No other known RNA virus encodes an RNase III or uses two independent proteins cooperatively for RNA silencing suppression.
authors.affiliation: Department of Plant Biology and Forest Genetics, SLU, Uppsala, Sweden.
authors.forename: Jan F
authors.initials: JF
authors.lastname: Kreuze
authors.forename: Eugene I
authors.initials: EI
authors.lastname: Savenkov
authors.forename: Wilmer
authors.initials: W
authors.lastname: Cuellar
authors.forename: Xiangdong
authors.initials: X
authors.lastname: Li
authors.forename: Jari P T
authors.initials: JP
authors.lastname: Valkonen
mesh_terms: D029383:Crinivirus / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity*; D020868:Gene Silencing; D005814:Genes, Viral; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D010935:Plant Diseases / Q000235:genetics / Q000821:virology; D030821:Plants, Genetically Modified; D012330:RNA, Double-Stranded / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics* / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D043244:Ribonuclease III / Q000145:classification / Q000235:genetics* / Q000502:physiology*; D014026:Nicotiana / Q000235:genetics / Q000821:virology; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D012330:RNA, Double-Stranded; D018749:RNA, Plant; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D014764:Viral Proteins; D049452:Green Fluorescent Proteins; D043244:Ribonuclease III