title: Identification of an RNA-silencing suppressor in the genome of Grapevine virus A.
abstract: Higher plants use post-transcriptional gene silencing (PTGS), an RNA-degradation system, as a defence mechanism against viral infections. To counteract this, plant viruses encode and express PTGS suppressor proteins. Four of the five proteins encoded by the Grapevine virus A (GVA) genome were screened using a green fluorescent protein (GFP)-based transient expression assay, and the expression product of ORF5 (protein p10) was identified as a suppressor of silencing. ORF5 p10 suppressed local and systemic silencing induced by a transiently expressed single-stranded sense RNA. This protein was active towards both a transgene and exogenous GFP mRNAs. Ectopic expression of GVA-ORF5 by a Potato virus X vector enhanced symptom severity. The findings that p10 markedly reduces the levels of small interfering RNAs (siRNAs) and that the recombinant protein is able to bind single-stranded and double-stranded forms of siRNAs and microRNAs, suggest the existence of a potential mechanism of suppression based on RNA sequestering.
authors.affiliation: Dipartimento di Protezione delle Piante e Microbiologia Applicata, Università degli Studi, Via Amendola 165/A, 70126 Bari, Italy.
authors.forename: Z Sh
authors.initials: ZS
authors.lastname: Zhou
authors.affiliation: Dipartimento di Protezione delle Piante e Microbiologia Applicata, Università degli Studi, Via Amendola 165/A, 70126 Bari, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Dell'Orco
authors.affiliation: Istituto di Virologia Vegetale CNR, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Saldarelli
authors.affiliation: Dipartimento di Protezione delle Piante e Microbiologia Applicata, Università degli Studi, Via Amendola 165/A, 70126 Bari, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Turturo
authors.affiliation: Istituto di Virologia Vegetale CNR, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Minafra
authors.affiliation: Dipartimento di Protezione delle Piante e Microbiologia Applicata, Università degli Studi, Via Amendola 165/A, 70126 Bari, Italy.
authors.forename: G P
authors.initials: GP
authors.lastname: Martelli
mesh_terms: D015870:Gene Expression; D017930:Genes, Reporter; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins / Q000032:analysis; D010935:Plant Diseases / Q000821:virology; D010942:Plant Viruses / Q000235:genetics* / Q000472:pathogenicity; D017863:Potexvirus / Q000235:genetics; D011485:Protein Binding; D034622:RNA Interference; D012328:RNA Viruses / Q000235:genetics* / Q000472:pathogenicity; D034741:RNA, Small Interfering / Q000378:metabolism; D014026:Nicotiana / Q000821:virology; D014162:Transfection; D014764:Viral Proteins / Q000502:physiology*
chemical_list: D034741:RNA, Small Interfering; D014764:Viral Proteins; D049452:Green Fluorescent Proteins