This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Supplemental material
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Buchmann, R. C.
Right arrow Articles by Bisaro, D. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Buchmann, R. C.
Right arrow Articles by Bisaro, D. M.

 Previous Article  |  Next Article 

Journal of Virology, May 2009, p. 5005-5013, Vol. 83, No. 10
0022-538X/09/$08.00+0     doi:10.1128/JVI.01771-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Geminivirus AL2 and L2 Proteins Suppress Transcriptional Gene Silencing and Cause Genome-Wide Reductions in Cytosine Methylation{triangledown} ,{dagger}

R. Cody Buchmann,1,{ddagger} Shaheen Asad,2 Jamie N. Wolf,1 Gireesha Mohannath,1 and David M. Bisaro1*

Department of Molecular Genetics, Department of Plant Cellular and Molecular Biology, Plant Biotechnology Center, and Program in Molecular, Cellular, and Developmental Biology, The Ohio State University, Columbus, Ohio 43210,1 Plant Biotechnology Division, National Institute for Biotechnology and Genetic Engineering, Faisalabad, Pakistan2

Received 21 August 2008/ Accepted 24 February 2009

Geminiviruses replicate single-stranded DNA genomes through double-stranded intermediates that associate with cellular histone proteins. Unlike RNA viruses, they are subject to RNA-directed methylation pathways that target viral chromatin and likely lead to transcriptional gene silencing (TGS). Here we present evidence that the related geminivirus proteins AL2 and L2 are able to suppress this aspect of host defense. AL2 and L2 interact with and inactivate adenosine kinase (ADK), which is required for efficient production of S-adenosyl methionine, an essential methyltransferase cofactor. We demonstrate that the viral proteins can reverse TGS of a green fluorescent protein (GFP) transgene in Nicotiana benthamiana when overexpressed from a Potato virus X vector and that reversal of TGS by geminiviruses requires L2 function. We also show that AL2 and L2 cause ectopic expression of endogenous Arabidopsis thaliana loci silenced by methylation in a manner that correlates with ADK inhibition. However, at one exceptional locus, ADK inhibition was insufficient and TGS reversal required the transcriptional activation domain of AL2. Using restriction-sensitive PCR and bisulfite sequencing, we showed that AL2-mediated TGS suppression is accompanied by reduced cytosine methylation. Finally, using a methylation-sensitive single-nucleotide extension assay, we showed that transgenic expression of AL2 or L2 causes global reduction in cytosine methylation. Our results provide further evidence that viral chromatin methylation is an important host defense and allow us to propose that as a countermeasure, geminivirus proteins reverse TGS by nonspecifically inhibiting cellular transmethylation reactions. To our knowledge, this is the first report that viral proteins can inhibit TGS.

* Corresponding author. Mailing address: Biotechnology Center, 201 Rightmire Hall, 1060 Carmack Road, Columbus, OH 43210. Phone: (614) 292-3281. Fax: (614) 292-5379. E-mail: bisaro.1{at}osu.edu

{triangledown} Published ahead of print on 11 March 2009.

{dagger} Supplemental material for this article may be found at http://jvi.asm.org/.

{ddagger} Present address: Molecular Virology Section, Laboratory of Molecular Microbiology, the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20814.

Journal of Virology, May 2009, p. 5005-5013, Vol. 83, No. 10
0022-538X/09/$08.00+0     doi:10.1128/JVI.01771-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





Copyright © 2009 by the American Society for Microbiology.   For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»