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First published online February 3, 2006; 10.1104/pp.105.075556 Plant Physiology 140:1317-1330 (2006) © 2006 American Society of Plant Biologists
The Geminivirus Nuclear Shuttle Protein NSP Inhibits the Activity of AtNSI, a Vascular-Expressed Arabidopsis Acetyltransferase Regulated with the Sink-to-Source Transition1Department of Plant Pathology (M.F.C., S.G.L.) and Department of Plant Biology (R.T.), Cornell University, Ithaca, New York 14853
DNA viruses can suppress or enhance the activity of cellular acetyltransferases to regulate virus gene expression and to affect cell cycle progression in support of virus replication. A role for protein acetylation in regulating the nuclear export of the bipartite geminivirus (Begomovirus) DNA genome was recently suggested by the findings that the viral movement protein NSP, a nuclear shuttle protein, interacts with the Arabidopsis (Arabidopsis thaliana) nuclear acetyltransferase AtNSI (nuclear shuttle protein interactor), and that this interaction and NSI expression are necessary for cabbage leaf curl virus infection and pathogenicity. To further investigate the consequences of NSI-NSP interactions, and the potential role of NSI in Arabidopsis growth and development, we used a reverse yeast two-hybrid selection and deletion analysis to identify NSI mutants that failed to interact with NSP, and promoter fusions to a uidA reporter gene to analyze the pattern of NSI expression during plant development. We found that NSI self assembles into highly active enzyme complexes and that high concentrations of NSP, in the absence of viral DNA, can inhibit NSI activity in vitro. Based on our detailed analysis of three NSI missense mutants, we identified an 88-amino acid putative domain, which spans NSI residues 107 to 194, as being required for both NSI oligomerization and its interaction with NSP. Finally, we found that NSI is predominantly transcribed in vascular cells, and that its expression is developmentally regulated in a manner that resembles the sink-to-source transition. Our data indicate that NSP can inhibit NSI activity by interfering with its assembly into highly active complexes, and suggest a mechanism by which NSP can both recruit NSI to regulate nuclear export of the viral genome and down-regulate NSI activity on cellular targets, perhaps to affect cellular differentiation and favor virus replication.
1 This work was supported by the National Science Foundation (grant nos. MCB–9982622 to S.G.L. and IBN–0444119 to R.T.) and the Fundação para a Ciência e a Tecnologia, Ministério da Ciência e Ensino Superior, Portugal (a PRAXIS XXI predoctoral fellowship to M.F.C.). The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Sondra G. Lazarowitz (sgl5{at}cornell.edu). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.075556. * Corresponding author; e-mail sgl5{at}cornell.edu; fax 607–255–8835. Received December 30, 2005; returned for revision January 27, 2006; accepted January 27, 2006. This article has been cited by other articles:
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