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J. Bacteriol. doi:10.1128/JB.01507-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

OryR is a LuxR-family protein involved in inter-kingdom signaling between pathogenic Xanthomonas oryzae pv. oryzae and rice

Bacteriology Group, International Centre for Genetic Engineering & Biotechnology, Trieste, Italy; and Plant Bacteriology Group, International Centre for Genetic Engineering & Biotechnology, Biosafety Outstation, Ca'Tron, Treviso, Italy

^* To whom correspondence should be addressed. Email: venturi{at}icgeb.org.

	Abstract

Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial leaf blight (BLB) in rice, contains a regulator in the genome, called OryR, which belongs to the N-acyl homoserine lactone (AHL) dependent quorum sensing (QS) of LuxR sub-family proteins. We previously reported that Xoo however does not make AHLs, does not possess a LuxI-family AHL synthase and that the OryR protein is solubilized by a compound present in rice. In this study we provide further evidence that OryR interacts with a rice signal molecule (RSM) and that the concentration increases when rice is infected with Xoo. We also report three OryR target promoters which are regulated differently; (i) the neighboring proline iminopeptidase (pip) virulence gene which is positively regulated by OryR in the presence of the RSM, (ii) the oryR promoter which is negatively autoregulated independently of the RSM and (iii) the 1,4--cellobiosidase cbsA gene which is positively regulated by OryR independently of the RSM. It is also shown that the RSM for OryR is small in size, not related to AHLs and not able to activate the broad range AHL-biosensor A. tumefaciens NT1(pZLQR). Furthermore OryR does not regulate the production of the quorum sensing diffusible signal factor (DSF) present in the Xanthomonas genus. OryR has therefore unique features being an important regulator involved in the inter-kingdom communication between host and pathogen.