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Rice yellow stunt rhabdovirus Protein 6 Suppresses Systemic RNA Silencing by Blocking RDR6-Mediated Secondary siRNA Synthesis

August 2013 , Volume 26 , Number  8
Pages  927 - 936

Hongyan Guo,1,2,3 Xiaoguang Song,1,2,3 Chuanmiao Xie,1,2,3 Yan Huo,1,2,3 Fujie Zhang,1,2,3 Xiaoying Chen,1,2 Yunfeng Geng,1,2 and Rongxiang Fang1,2

1State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China; 2National Plant Gene Research Center, Beijing 100101, China; 3University of Chinese Academy of Sciences, Beijing 100049, China

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Accepted 23 April 2013.

The P6 protein of Rice yellow stunt rhabdovirus (RYSV) is a virion structural protein that can be phosphorylated in vitro. However its exact function remains elusive. We found that P6 enhanced the virulence of Potato virus X (PVX) in Nicotiana benthamiana and N. tabacum plants, suggesting that it might function as a suppressor of RNA silencing. We examined the mechanism of P6-mediated silencing suppression by transiently expressing P6 in both N. benthamiana leaves and rice protoplasts. Our results showed that P6 could repress the production of secondary siRNAs and inhibit systemic green fluorescent protein RNA silencing but did not interfere with local RNA silencing in N. benthamiana plants or in rice protoplasts. Intriguingly, P6 and RDR6 had overlapping subcellular localization and P6 bound both rice and Arabidopsis RDR6 in vivo. Furthermore, transgenic rice plants expressing P6 showed enhanced susceptibility to infection by Rice stripe virus. Hence, we propose that P6 is part of the RYSV's counter-defense machinery against the plant RNA silencing system and plays a role mainly in affecting RDR6-mediated secondary siRNA synthesis. Our work provides a new perspective on how a plant-infecting nucleorhabdovirus may counteract host RNA silencing-mediated antiviral defense.

© 2013 The American Phytopathological Society