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Int. J. Mol. Sci. 2011, 12(6), 4132-4155; doi:10.3390/ijms12064132

Modulation of rosR Expression and Exopolysaccharide Production in Rhizobium leguminosarum bv. trifolii by Phosphate and Clover Root Exudates

Department of Genetics and Microbiology, Institute of Microbiology and Biotechnology, University of Maria Curie-Skłodowska, Akademicka 19 st., Lublin, 20–033, Poland
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Received: 23 May 2011 / Revised: 14 June 2011 / Accepted: 15 June 2011 / Published: 22 June 2011
(This article belongs to the Section Biochemistry, Molecular Biology and Biophysics)
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Abstract

The acidic exopolysaccharide (EPS) secreted in large amounts by the symbiotic nitrogen-fixing bacterium Rhizobium leguminosarum bv. trifolii is required for the establishment of an effective symbiosis with the host plant Trifolium spp. EPS biosynthesis in rhizobia is a very complex process regulated at both transcriptional and post-transcriptional levels and influenced by various nutritional and environmental conditions. The R. leguminosarum bv. trifolii rosR gene encodes a transcriptional regulator with a C2H2 type zinc-finger motif involved in positive regulation of EPS synthesis. In silico sequence analysis of the 450-bp long rosR upstream region revealed the presence of several inverted repeats (IR1 to IR6) and motifs with significant identity to consensus sequences recognized by PhoB and LysR-type proteins associated with phosphate- and flavonoid-dependent gene regulation in R. leguminosarum. Using a set of sequentially truncated rosR-lacZ transcriptional fusions, the role of the individual motifs and the effect of phosphate and clover root exudates on rosR expression were established. In addition, the significance of IR4 inverted repeats in the repression, and P2–10 hexamer in the activation of rosR transcription, respectively, was found. The expression of rosR increased in the presence of phosphate (0.1–20 mM) and clover root exudates (10 μM). PHO boxes and the LysR motif located upstream of the rosR translation start site were engaged in the regulation of rosR transcription. The synthesis of EPS and biofilm formation decreased at high phosphate concentrations, but increased in the presence of clover root exudates, indicating a complex regulation of these processes.
Keywords: rosR expression; exopolysaccharide synthesis; phosphate; root exudates; Rhizobium leguminosarum bv. trifolii rosR expression; exopolysaccharide synthesis; phosphate; root exudates; Rhizobium leguminosarum bv. trifolii
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Janczarek, M.; Skorupska, A. Modulation of rosR Expression and Exopolysaccharide Production in Rhizobium leguminosarum bv. trifolii by Phosphate and Clover Root Exudates. Int. J. Mol. Sci. 2011, 12, 4132-4155.

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Int. J. Mol. Sci. EISSN 1422-0067 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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