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