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Journal of Virology, November 2007, p. 11972-11981, Vol. 81, No. 21
0022-538X/07/$08.00+0     doi:10.1128/JVI.00617-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Functional Modulation of the Geminivirus AL2 Transcription Factor and Silencing Suppressor by Self-Interaction{triangledown}

Xiaojuan Yang,1 Surendranath Baliji,2 R. Cody Buchmann,1 Hui Wang,1 John A. Lindbo,3 Garry Sunter,2 and David M. Bisaro1*

Department of Molecular Genetics, Plant Biotechnology Center, and Program in Molecular, Cellular, and Developmental Biology, The Ohio State University, Columbus, Ohio 43210,1 Department of Biology, University of Texas—San Antonio, San Antonio, Texas 78249,2 Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio 446913

Received 22 March 2007/ Accepted 10 August 2007

The DNA genomes of geminiviruses have a limited coding capacity that is compensated for by the production of small multifunctional proteins. The AL2 protein encoded by members of the genus Begomovirus (e.g., Tomato golden mosaic virus) is a transcriptional activator, a silencing suppressor, and a suppressor of a basal defense. The related L2 protein of Beet curly top virus (genus Curtovirus) shares the pathogenicity functions of AL2 but lacks transcriptional activation activity. It is known that AL2 and L2 can suppress local silencing by interacting with adenosine kinase (ADK) and can suppress basal defense by interacting with SNF1 kinase. However, how the activities of these viral proteins are regulated remains an unanswered question. Here, we provide some answers by demonstrating that AL2, but not L2, interacts with itself. The zinc finger-like motif (CCHC) is required but is not sufficient for AL2 self-interaction. Alanine substitutions for the invariant cysteine residues that comprise the motif abolish self-interaction or cause aberrant subnuclear localization but do not abolish interaction with ADK and SNF1. Using bimolecular fluorescence complementation, we show that AL2:AL2 complexes accumulate primarily in the nucleus, whereas AL2:ADK and L2:ADK complexes accumulate mainly in the cytoplasm. Further, the cysteine residue mutations impair the ability of AL2 to activate the coat protein promoter but do not affect local silencing suppression. Thus, AL2 self-interaction correlates with nuclear localization and efficient activation of transcription, whereas AL2 and L2 monomers can suppress local silencing by interacting with ADK in the cytoplasm.

* Corresponding author. Mailing address: Biotechnology Center, Ohio State University, 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 22 August 2007.

Journal of Virology, November 2007, p. 11972-11981, Vol. 81, No. 21
0022-538X/07/$08.00+0     doi:10.1128/JVI.00617-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Buchmann, R. C., Asad, S., Wolf, J. N., Mohannath, G., Bisaro, D. M. (2009). Geminivirus AL2 and L2 Proteins Suppress Transcriptional Gene Silencing and Cause Genome-Wide Reductions in Cytosine Methylation. J. Virol. 83: 5005-5013 [Abstract] [Full Text]  
  • Raja, P., Sanville, B. C., Buchmann, R. C., Bisaro, D. M. (2008). Viral Genome Methylation as an Epigenetic Defense against Geminiviruses. J. Virol. 82: 8997-9007 [Abstract] [Full Text]  


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