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Identification of an RNA-silencing suppressor in the genome of Grapevine virus A

Z. Sh. Zhou^1,

M. Dell'Orco^1,

C. Turturo^1,,

¹ Dipartimento di Protezione delle Piante e Microbiologia Applicata, Università degli Studi, Via Amendola 165/A, 70126 Bari, Italy
² Istituto di Virologia Vegetale CNR, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy

Correspondence
P. Saldarelli
p.saldarelli{at}ba.ivv.cnr.it

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.

These authors contributed equally to this work.

Present address: International Centre for Genetic Engineering and Biotechnology (ICGEB), Biosafety Unit (Ca' Tron), Via Piovega 23, 31050 Ca' Tron di Roncade, Treviso, Italy.

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