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Journal of Bacteriology, November 2005, p. 7805-7814, Vol. 187, No. 22
0021-9193/05/$08.00+0     doi:10.1128/JB.187.22.7805-7814.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Novel Virulence Gene of Pseudomonas syringae pv. tomato Strain DC3000

Karen Preiter,¹ David M. Brooks,^1, Alejandro Penaloza-Vazquez,² Aswathy Sreedharan,² Carol L. Bender,² and Barbara N. Kunkel^1*

Department of Biology, Washington University, St. Louis, Missouri 63130,¹ Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, Oklahoma 74078²

Received 3 June 2005/ Accepted 28 August 2005

Previously, we conducted a mutant screen of Pseudomonas syringae pv. tomato strain DC3000 to identify genes that contribute to virulence on Arabidopsis thaliana plants. Here we describe the characterization of one mutant strain, DB4H2, which contains a single Tn5 insertion in PSPTO3576, an open reading frame that is predicted to encode a protein belonging to the TetR family of transcriptional regulators. We demonstrate that PSPTO3576 is necessary for virulence in DC3000 and designate the encoded protein TvrR (TetR-like virulence regulator). TvrR, like many other TetR-like transcriptional regulators, negatively regulates its own expression. Despite the presence of a putative HrpL binding site in the tvrR promoter region, tvrR is not regulated by HrpL, an alternative sigma factor that regulates the expression of many known DC3000 virulence genes. tvrR mutant strains grow comparably to wild-type DC3000 in culture and possess an intact type III secretion system. However, tvrR mutants do not cause disease symptoms on inoculated A. thaliana and tomato plants, and their growth within plant tissue is significantly impaired. We demonstrate that tvrR mutant strains are able to synthesize coronatine (COR), a phytotoxin required for virulence of DC3000 on A. thaliana. Given that tvrR mutant strains are not defective for type III secretion or COR production, tvrR appears to be a novel virulence factor required for a previously unexplored process that is necessary for pathogenesis.

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* Corresponding author. Mailing address: Department of Biology, Campus Box 1137, 1 Brookings Dr., St. Louis, MO 63130. Phone: (314) 935-7284. Fax: (314) 935-4432. E-mail: kunkel{at}biology.wustl.edu.

Present address: East Central College, Union, MO 63084.

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Journal of Bacteriology, November 2005, p. 7805-7814, Vol. 187, No. 22
0021-9193/05/$08.00+0     doi:10.1128/JB.187.22.7805-7814.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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