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Applied and Environmental Microbiology, March 2009, p. 1223-1228, Vol. 75, No. 5
0099-2240/09/$08.00+0     doi:10.1128/AEM.02015-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Plant Phenolic Compound p-Coumaric Acid Represses Gene Expression in the Dickeya dadantii Type III Secretion System ^,

Yan Li,^1,2, Quan Peng,^1, Dija Selimi,³ Qi Wang,² Amy O. Charkowski,³ Xin Chen,⁴ and Ching-Hong Yang^1*

Department of Biological Sciences, University of Wisconsin—Milwaukee, Milwaukee, Wisconsin 53211,¹ Department of Plant Pathology, College of Agronomy & Biotechnology, China Agricultural University, Beijing 100094, China,² Department of Plant Pathology, University of Wisconsin—Madison, Madison, Wisconsin 53706,³ Department of Chemistry, Duke University, Durham, North Carolina 27708⁴

Received 26 August 2008/ Accepted 16 December 2008

The type III secretion system (T3SS) is a major virulence factor in many gram-negative bacterial pathogens. This secretion system translocates effectors directly into the cytosol of eukaryotic host cells, where the effector proteins facilitate bacterial pathogenesis by interfering with host cell signal transduction and other cellular processes. Plants defend themselves against bacterial pathogens by recognizing either the type 3 effectors or their actions and initiating a cascade of defense responses that often results in programmed cell death of the plant cell being attacked. Here we show that a plant phenolic compound, p-coumaric acid (PCA), represses the expression of T3SS genes of the plant pathogen Dickeya dadantii, suggesting that plants can also defend against bacterial pathogens by manipulating the expression of the T3SS. PCA repressed the expression of T3SS regulatory genes through the HrpX/Y two-component system, a core regulator of the T3SS, rather than through the global regulator GacS/A, which indirectly regulates the T3SS. A further analysis of several PCA analogs suggests that the para positioning of the hydroxyl group in the phenyl ring and the double bond of PCA may be important for its biological activity.

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* Corresponding author. Mailing address: Department of Biological Sciences, University of Wisconsin—Milwaukee, Milwaukee, WI 53211. Phone: (414) 229-6331. Fax: (414) 229-3926. E-mail: chyang{at}uwm.edu

Published ahead of print on 29 December 2008.

Supplemental material for this article may be found at http://aem.asm.org/.

Yan Li and Quan Peng contributed equally in this work.

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Applied and Environmental Microbiology, March 2009, p. 1223-1228, Vol. 75, No. 5
0099-2240/09/$08.00+0     doi:10.1128/AEM.02015-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

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