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Tobacco mosaic virus 126-kDa Protein Increases the Susceptibility of Nicotiana tabacum to Other Viruses and Its Dosage Affects Virus-Induced Gene Silencing

December 2008 , Volume 21 , Number  12
Pages  1,539 - 1,548

Phillip A. Harries, Karuppaiah Palanichelvam, Sumana Bhat, and Richard S. Nelson

Plant Biology Division, The Samuel Roberts Noble Foundation, Inc., 2510 Sam Noble Parkway, Ardmore, OK 73401, U.S.A.

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Accepted 15 August 2008.

The Tobacco mosaic virus (TMV) 126-kDa protein is a suppressor of RNA silencing previously shown to delay the silencing of transgenes in Nicotiana tabacum and N. benthamiana. Here, we demonstrate that expression of a 126-kDa protein--green fluorescent protein (GFP) fusion (126-GFP) in N. tabacum increases susceptibility to a broad assortment of viruses, including Alfalfa mosaic virus, Brome mosaic virus, Tobacco rattle virus (TRV), and Potato virus X. Given its ability to enhance TRV infection in tobacco, we tested the effect of 126-GFP expression on TRV-mediated virus-induced gene silencing (VIGS) and demonstrate that this protein can enhance silencing phenotypes. To explain these results, we examined the poorly understood effect of suppressor dosage on the VIGS response and demonstrated that enhanced VIGS corresponds to the presence of low levels of suppressor protein. A mutant version of the 126-kDa protein, inhibited in its ability to suppress silencing, had a minimal effect on VIGS, suggesting that the suppressor activity of the 126-kDa protein is indeed responsible for the observed dosage effects. These findings illustrate the sensitivity of host plants to relatively small changes in suppressor dosage and have implications for those interested in enhancing silencing phenotypes in tobacco and other species through VIGS.

Additional keywords:pathogenicity determinants, post-transcriptional gene silencing, small RNAs, synergy determinant

© 2008 The American Phytopathological Society