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Interaction with a Host Ubiquitin-Conjugating Enzyme Is Required for the Pathogenicity of a Geminiviral DNA β Satellite

June 2009 , Volume 22 , Number  6
Pages  737 - 746

Omid Eini,1,2,3 Satish Dogra,1 Luke A. Selth,1 Ian B. Dry,2 John W. Randles,1 and M. Ali Rezaian1

1School of Agriculture, Food and Wine, The University of Adelaide, Waite Campus, SA 5064, Australia; 2CSIRO Plant Industry, PO Box 350, Glen Osmond, SA 5064, Australia; 3Plant Protection Department, College of Agriculture, Zanjan University, Zanjan, Iran

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Accepted 29 January 2009.

DNA β is a single-stranded satellite DNA which encodes a single gene, βC1. To better understand the role of βC1 in the pathogenicity of DNA β, a yeast two-hybrid screen of a tomato cDNA library was carried out using βC1 from Cotton leaf curl Multan virus (CLCuMV) DNA β as the bait. A ubiquitin-conjugating enzyme, designated SlUBC3, which functionally complemented a yeast mutant deficient in ubiquitin-conjugating enzymes was identified. The authenticity and specificity of the interaction between βC1 and SlUBC3 was confirmed both in vivo, using a bimolecular fluorescence complementation assay, and in vitro, using a protein-binding assay. Analysis of deletion mutants of the βC1 protein showed that a myristoylation-like motif is required both for its interaction with SlUBC3 and the induction of DNA-β-specific symptoms in host plants. The level of polyubiquitinated proteins in transgenic tobacco plants expressing βC1 was found to be reduced compared with wild-type plants. These results are consistent with the hypothesis that interaction of βC1 with SlUBC3 is required for DNA-β-specific symptom induction, and that this is possibly due to downregulation of the host ubiquitin proteasome pathway.

© 2009 The American Phytopathological Society