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Journal of Virology, October 2007, p. 10379-10388, Vol. 81, No. 19
0022-538X/07/$08.00+0     doi:10.1128/JVI.00727-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Modification of Small RNAs Associated with Suppression of RNA Silencing by Tobamovirus Replicase Protein

Hannes Vogler,^1,, Rashid Akbergenov,^1, Padubidri V. Shivaprasad,¹ Vy Dang,^1, Monika Fasler,^1,|| Myoung-Ok Kwon,^1,# Saule Zhanybekova,^1, Thomas Hohn,¹ and Manfred Heinlein^1,2*

Department of Plant Physiology, Botanical Institute, University of Basel, Schönbeinstr. 6, CH-4056 Basel, Switzerland,¹ Institut de Biologie Moléculaire des Plantes, Laboratoire Propre du CNRS (UPR 2357) Conventionné avec l'Université Louis Pasteur (Strasbourg 1), 12 Rue du Général Zimmer, 67084 Strasbourg Cedex, France²

Received 4 April 2007/ Accepted 9 July 2007

Plant viruses act as triggers and targets of RNA silencing and have evolved proteins to suppress this plant defense response during infection. Although Tobacco mosaic tobamovirus (TMV) triggers the production of virus-specific small interfering RNAs (siRNAs), this does not lead to efficient silencing of TMV nor is a TMV-green fluorescent protein (GFP) hybrid able to induce silencing of a GFP-transgene in Nicotiana benthamiana, indicating that a TMV silencing suppressor is active and acts downstream of siRNA production. On the other hand, TMV-GFP is unable to spread into cells in which GFP silencing is established, suggesting that the viral silencing suppressor cannot revert silencing that is already established. Although previous evidence indicates that the tobamovirus silencing suppressing activity resides in the viral 126-kDa small replicase subunit, the mechanism of silencing suppression by this virus family is not known. Here, we connect the silencing suppressing activity of this protein with our previous finding that Oilseed rape mosaic tobamovirus infection leads to interference with HEN1-mediated methylation of siRNA and micro-RNA (miRNA). We demonstrate that TMV infection similarly leads to interference with HEN1-mediated methylation of small RNAs and that this interference and the formation of virus-induced disease symptoms are linked to the silencing suppressor activity of the 126-kDa protein. Moreover, we show that also Turnip crinkle virus interferes with the methylation of siRNA but, in contrast to tobamoviruses, not with the methylation of miRNA.

Published ahead of print on 18 July 2007.

H.V. and R.A. contributed equally to this study.

Present address: Sainsbury Laboratory, Colney Lane, Norwich NR4 7UH, United Kingdom.

Present address: Quintiles AG, Hochstrasse 50, CH-4053 Basel, Switzerland.

^|| Present address: Friedrich Miescher Institute for Biomedical Research, P.O. Box 2543, CH-4002 Basel, Switzerland.

^# Present address: Nextech Venture, Ltd., Scheuchzerstrasse 35, CH-8006 Zürich, Switzerland.

Present address: Center for Biomedicine, University of Basel, Mattenstrasse 28, CH-4058 Basel, Switzerland.

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