Unknown,Transcriptomics,Genomics,Proteomics

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Comprehensive assessment of the regulons controlled by the FixLJ-FixK2-FixK1 cascade in Bradyrhizobium japonicum

ABSTRACT: Genome-wide transcription profiling of B. japonicum fixJ, fixK2, and fixK1 mutant strains which were grown in free-living microoxic condition, and in the case of the fixK1 mutant also in anoxic condition. Transcriptomes of nodules from soybean plants infected with the fixJ or fixK2 mutant strains were investigated, too. This study includes also the expression data of a nifA mutant grown in free-living anoxic condition. Samples from GSM210242 to GSM210286 in GEO record number GSE8478 need to be considered for the analyses. Keywords: gene regulation, genetic modification, growth conditions, symbiosis Comparison analysis of the B. japonicum fixJ, fixK2 and fixK1 mutants and the wild type grown under different oxygen conditions in culture and during symbiosis with soybean.

ORGANISM(S): Bradyrhizobium japonicum

SUBMITTER: F Hauser

PROVIDER: E-GEOD-12491 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Comprehensive assessment of the regulons controlled by the FixLJ-FixK2-FixK1 cascade in Bradyrhizobium japonicum.

Mesa Socorro S Hauser Felix F Friberg Markus M Malaguti Emmanuelle E Fischer Hans-Martin HM Hennecke Hauke H

Journal of bacteriology 20080808 20

Symbiotic N(2) fixation in Bradyrhizobium japonicum is controlled by a complex transcription factor network. Part of it is a hierarchically arranged cascade in which the two-component regulatory system FixLJ, in response to a moderate decrease in oxygen concentration, activates the fixK(2) gene. The FixK(2) protein then activates not only a number of genes essential for microoxic respiration in symbiosis (fixNOQP and fixGHIS) but also further regulatory genes (rpoN(1), nnrR, and fixK(1)). The re ...[more]

PMID: 18689489

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Project description:Bradyrhizobium japonicum RegSR regulatory proteins belong to the family of two-component regulatory systems, and orthologs are present in many Proteobacteria where they globally control gene expression mostly in a redox-responsive manner. In this work, we have performed a transcriptional profiling of wild-type and regR mutant cells grown under anoxic denitrifying conditions. The comparative analyses of wild-type and regR strains revealed that almost 620 genes induced in the wild type under denitrifying conditions were regulated (directly or indirectly) by RegR, pointing out the important role of this protein as a global regulator of denitrification. Genes controlled by RegR included nor and nos structural genes encoding nitric oxide and nitrous oxide reductase, respectively, genes encoding electron transport proteins such as cycA (blr7544), or cy2 (bll2388), genes involved in nitric oxide detoxification (blr2806-09), copper homeostasis (copCAB), as well as two regulatory genes (bll3466, bll4130). Purified RegR interacted with the promoters of norC (blr3214), nosR (blr0314), a fixK-like gene (bll3466), and bll4130 which encodes a LysR-type regulator. By using fluorescently labeled oligonucleotide extension (FLOE), we were able to identify two transcriptional start sites located at about 35 (P1) and 22 (P2) bp upstream of the putative translational start codon of norC. P1 matched with the previously mapped 5M-bM-^@M-^Yend of norC mRNA which we demonstrate in this work to be under FixK2 control. P2 is a start site modulated by RegR and specific for anoxic conditions. Moreover, qRT-PCR experiments, expression studies with a norC-lacZ fusion, and heme c-staining analyses revealed that anoxia and nitrate are required for RegR-dependent induction of nor genes, and that this control is independent of the sensor protein RegS. A total of eight Affymetrix GeneChips are included in this study. Per strain (wild-type B. japonicum 110spc4, delta regR mutant 2426) four biological replicates were processed and analyzed. Strains were grown under anoxic conditions in Bergersen minimal medium supplemented with succinate as carbon source and KNO3 as terminal electron acceptor. For comparison, a microarray expression dataset generated with B. japonicum wild-type (Hauser et al., Mol. Genet. Genomics 278:255-271, 2007) and delta regR mutant cells (Lindemann et al., J. Bacteriol. 189:8928-8943, 2007) was used.

Project description:Copper-limiting growth conditions were thought to cause an induction of genes possibly involved in copper uptake and sorting. This rationale in mind, we performed microarray analyses on B. japonicum cells grown in three variations of the BVM minimal medium. Variant 1 contained 2 M-NM-<M CuSO4 (copper excess). Variant 2 was prepared in HCl-treated glassware without any copper added (copper starvation). The residual copper concentration in this copper-starvation medium was analyzed by GF-AAS and determined to be 5 nM. Variant 3 (extreme copper limitation) was prepared like variant 2 but with the addition of 10 M-NM-<M BCS and 1 mM ascorbic acid where BCS chelates Cu(I) selectively, and ascorbic acid reduces any Cu(II) to Cu(I). Changes in the transcription profiles were recorded by the pairwise comparison of cells grown in variant 2 vs. 1, and variant 3 vs. 2. Only a small set of genes were differentially up- or down-regulated when copper-starved cells were compared with cells grown in copper excess. Most notably, five genes located adjacent to each other on the B. japonicum genome displayed an increased expression: bll4882 to bll4878. The five genes were named pcuA, pcuB, pcuC, pcuD, and pcuE (mnemonic of proteins for Cu trafficking). The genes with decreased expression are either of unknown function or M-bM-^@M-^S not surprisingly M-bM-^@M-^S play a role in copper resistance. Extreme copper limitation (variant 3 vs. 2) did not further enhance the expression of the five pcu genes. Instead, another cluster of adjacent genes was strongly up-regulated: bll0889 to bll0883, which code for unidentified transport functions. Incidentally, the list also includes the copper chaperone ScoI. Taken together, copper-limiting growth conditions have led to the de-repression of genes potentially involved in copper acquisition. Microarray-based transcriptome analysis of B. japonicum 110spc4 wild-type cells grown under normal, copper-limiting and copper excess conditions

Dataset Information

Comprehensive assessment of the regulons controlled by the FixLJ-FixK2-FixK1 cascade in Bradyrhizobium japonicum

Publications

Comprehensive assessment of the regulons controlled by the FixLJ-FixK2-FixK1 cascade in Bradyrhizobium japonicum.

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