title: Modulation of rosR expression and exopolysaccharide production in Rhizobium leguminosarum bv. trifolii by phosphate and clover root exudates.
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 C(2)H(2) 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.
authors: Department of Genetics and Microbiology, Institute of Microbiology and Biotechnology, University of Maria Curie-Skłodowska, Akademicka 19 st., Lublin, 20-033, Poland; E-Mail: anna.skorupska@poczta.umcs.lublin.pl.
authors: Monika
authors: M
authors: Janczarek
authors: Anna
authors: A
authors: Skorupska
mesh_terms: D020121:5' Untranslated Regions; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018441:Biofilms / Q000187:drug effects; D005122:Exudates and Transudates / Q000737:chemistry / Q000378:metabolism; D005419:Flavonoids / Q000737:chemistry / Q000494:pharmacology; D029902:Medicago / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D010710:Phosphates / Q000737:chemistry / Q000494:pharmacology*; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D018517:Plant Roots / Q000737:chemistry / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D016961:Rhizobium leguminosarum / Q000235:genetics / Q000502:physiology*; D013559:Symbiosis / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D020121:5' Untranslated Regions; D001426:Bacterial Proteins; D005419:Flavonoids; D010710:Phosphates; D010936:Plant Extracts; D011135:Polysaccharides, Bacterial; D012313:RNA