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Journal of Bacteriology, November 2008, p. 7200-7208, Vol. 190, No. 21
0021-9193/08/$08.00+0     doi:10.1128/JB.00804-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Aromatic Amino Acid-Dependent Expression of Indole-3-Pyruvate Decarboxylase Is Regulated by TyrR in Enterobacter cloacae UW5{triangledown}

R. Julie Ryu and Cheryl L. Patten*

Biology Department, University of New Brunswick, P.O. Box 4400, Fredericton, New Brunswick E3B 5A3, Canada

Received 8 June 2008/ Accepted 22 August 2008

The plant growth-promoting rhizobacterium Enterobacter cloacae UW5 synthesizes the plant growth hormone indole-3-acetic acid (IAA) via the indole-3-pyruvate pathway utilizing the enzyme indole-3-pyruvate decarboxylase that is encoded by ipdC. In this bacterium, ipdC expression and IAA production occur in stationary phase and are induced by an exogenous source of tryptophan, conditions that are present in the rhizosphere. The aim of this study was to identify the regulatory protein that controls the expression of ipdC. We identified a sequence in the promoter region of ipdC that is highly similar to the recognition sequence for the Escherichia coli regulatory protein TyrR that regulates genes involved in aromatic amino acid transport and metabolism. Using a tyrR insertional mutant, we demonstrate that TyrR is required for IAA production and for induction of ipdC transcription. TyrR directly induces ipdC expression, as was determined by real-time quantitative reverse transcription-PCR, by ipdC promoter-driven reporter gene activity, and by electrophoretic mobility shift assays. Expression increases in response to tryptophan, phenylalanine, and tyrosine. This suggests that, in addition to its function in plant growth promotion, indolepyruvate decarboxylase may be important for aromatic amino acid uptake and/or metabolism.

* Corresponding author. Mailing address: Biology Department, University of New Brunswick, P.O. Box 4400, Fredericton, New Brunswick E3B 5A3, Canada. Phone: (506) 447-3354. Fax: (506) 453-3583. E-mail: pattenc{at}unb

{triangledown} Published ahead of print on 29 August 2008.

Journal of Bacteriology, November 2008, p. 7200-7208, Vol. 190, No. 21
0021-9193/08/$08.00+0     doi:10.1128/JB.00804-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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