Azorhizobium caulinodansNitrogen Fixation(nif/fix)Gene Regulation: Mutagenesis of thenifA─24/─12 Promoter Element, Characterization of antrA(rpoN)Gene, and Derivation of a Model

Stigter, John

doi:10.1094/mpmi-6-238

Cited by 34 publications

(42 citation statements)

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“…FixL is an O 2 -regulated hemoprotein with kinase and phosphatase activities that phosphorylates FixJ, the transcriptional activator component (14). Genes homologous to fixLJ have also been identified in Bradyrhizobium japonicum and in Azorhizobium caulinodans, but in these organisms, unlike the situation in S. meliloti, NifA expression is not controlled by FixLJ (22,34,53,54). In all these three species, fixLJ genes are required for expression of fixK (fixK2 in B. japonicum) genes under micro-oxic conditions (3,12,23).…”

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FnrN controls symbiotic nitrogen fixation and hydrogenase activities in Rhizobium leguminosarum biovar viciae UPM791

et al. 1997

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Rhizobium leguminosarum bv. viciae UPM791 contains a second copy of the fnrN gene, which encodes a redox-sensitive transcriptional activator functionally homologous to Escherichia coli Fnr. This second copy (fnrN2) is located in the symbiotic plasmid, while fnrN1 is in the chromosome. Isolation and sequencing of the fnrN2 gene revealed that the deduced amino acid sequence of FnrN2 is 87.5% identical to the sequence of FnrN1, including a conserved cysteine-rich motif characteristic of Fnr-like proteins. Individual R. leguminosarum fnrN1 and fnrN2 mutants exhibited a Fix ؉ phenotype and near wild-type levels of nitrogenase and hydrogenase activities in pea (Pisum sativum L.) nodules. In contrast, an fnrN1 fnrN2 double mutant formed ineffective nodules lacking both nitrogenase and hydrogenase activities. Unlike the wild-type strain and single fnrN1 or fnrN2 mutants, the fnrN1 fnrN2 double mutant was unable to induce micro-oxic or bacteroid activation of the hypBFCDEX operon, which encodes proteins essential for hydrogenase synthesis. In the search for symbiotic genes that could be controlled by FnrN, a fixNOQP operon, putatively encoding a micro-oxically induced, bacteroid-specific cbb 3 -type terminal cytochrome oxidase, was isolated from strain UPM791 and partially sequenced. The fixNOQP operon was present in a single copy located in the symbiotic plasmid, and an anaerobox was identified in the fixN promoter region. Consistent with this, a fixNOQP-lacZ fusion was shown to be highly induced in micro-oxic cells of the wild-type strain. A high level of micro-oxic induction was also observed in single fnrN1 and fnrN2 mutants, but no detectable induction was observed in the fnrN1 fnrN2 double mutant. The lack of expression of fixNOQP in the fnrN1 fnrN2 double mutant is likely to cause the observed Fix ؊ phenotype. These data demonstrate that, contrary to the situation in other rhizobia, FnrN controls both hydrogenase and nitrogenase activities of R. leguminosarum bv. viciae UPM791 in the nodule and suggest that this strain lacks a functional fixK gene.

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FnrN controls symbiotic nitrogen fixation and hydrogenase activities in Rhizobium leguminosarum biovar viciae UPM791

et al. 1997

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“…It is able to grow in the free-living state at the expense of dinitrogen and also to fix nitrogen symbiotically in the stem and root nodules of the tropical legume Sesbania rostrata (9)(10)(11). A model of the regulation of nifandfix gene expression in A. caulinodans has been proposed (20,21,35,46). Transcription of nifA is controlled by both oxygen and ammonia via the fixLJ, fixK, and ntrBClntrYX gene products.…”

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Functional analysis of the fixNOQP region of Azorhizobium caulinodans

1994

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The deduced amino acid sequences of four open reading frames identified upstream of thefixGHI region in Azorhizobium caulinodans are very similar to the putative terminal oxidase complex coded by the fixNOQP operons from Rhizobium meliloti and Bradyrhizobium japonicum. The expression of the A. caulinodansfixNOQP genes, which was maximal under microaerobiosis, was positively regulated by FixK and independent of NifA. In contrast to the Fix-phenotype of B.japonicum and R. melilotifixN mutants, anA. caulinodansfixNO-deleted mutant strain retained 50%o of the nitrogenase activity of the wild type in the symbiotic state. In addition, the nitrogenase activity was scarcely reduced under free-living conditions. Analysis of membrane fractions of A.caulinodans wild-type and mutant strains suggests that the fixNOQP region encodes two proteins with covalently bound hemes, tentatively assigned tofixO andfixP. Spectral analysis showed a large decrease in the c-type cytochrome content of thefixN mutant compared with the wild type. These results provide evidence for the involvement of FixNOQP proteins in a respiratory process. The partial impairment in nitrogen fixation of thefixN mutant in planta may be due to the activity of an alternative terminal oxidase compensating for the loss of the oxidase complex encoded byfixNOQP.

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“…When the base equivalent to position Ϫ28 in the 4521 promoter is mutagenized in either the Klebsiella pneumoniae nifH (2) or the Caulobacter crescentus flbG (32) promoters, the resulting promoter activity is essentially that of the wild type or only slightly decreased, just as in the case of the 4521 promoter. Mutations in the position Ϫ27 equivalent, which is G in the 54 consensus but is replaced by an A in the 4521 wild-type promoter, have no activity in the case of the K. pneumoniae nifL promoter (17) but result in approximately 40% of wild-type activity in the Azorhizobium caulinodans nifA promoter (41). In addition, changing the bases in the equivalent Ϫ28/Ϫ27 positions in the Bradyrhizobium japonicum fixR nifA promoter from TG to CT does not appear to affect promoter activity, indicating that position Ϫ27 may not be important for activity of a subset of 54 -type promoters.…”

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An early A-signal-dependent gene in Myxococcus xanthus has a sigma 54-like promoter

Keseler

Kaiser

1995

J Bacteriol

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A-signaling plays an essential role in the early stages of Myxococcus xanthus fruiting body development. Expression of the 4521 gene, which is regulated at the level of RNA accumulation, depends on starvation and on A-signaling. To identify the cis-acting regulatory elements which allow gene 4521 to respond to the nutritional and A-factor signals, the 4521 transcription start site was mapped. The region just upstream of the start site showed sequence similarity to the 54 family of promoters and to the developmentally regulated mbhA promoter of M. xanthus. A mutational analysis of this region established that the bases which were conserved between the 54 consensus, mbhA, and 4521 promoters were also important for 4521 promoter activity. Changes which altered the spacing between two conserved regions centered around positions ؊14 and ؊24 abolished promoter activity. In contrast, mutations in a putative ؊10 region for a 70 -like promoter had little effect on expression of 4521. Despite their similar promoter regions, the regulation of the 4521 and mbhA genes was shown to differ with respect to timing of expression and requirement for a solid surface and extracellular signals. This suggests a model in which different activator proteins may be responsible for regulating expression of these two genes.In response to nutrient limitation in its environment, Myxococcus xanthus enters a developmental cycle in which about 100,000 cells aggregate to build a multicellular structure, the fruiting body. Once inside the fruiting body, the individual rod-shaped cells are able to undergo morphological and physiological differentiation to form ovoid, environmentally resistant, and metabolically dormant spores (39). Progress through this developmental program is highly coordinated and involves intercellular communication. Mutational analysis has shown that at least five extracellular signals are required for progress through different stages of the developmental program (6, 9, 26). One of the extracellular signals required early in development is the A-signal, which consists of a mixture of amino acids or small peptides. These signaling molecules have to be present in a narrow concentration range at 1 to 2 h after the onset of starvation and serve as a cell density signal (24). In the absence of extracellular A-signal, as in the asg class of mutants, development arrests prior to aggregation of the cells into mounds (22).To begin to understand how the information conveyed by the A-signal is transduced inside the cell and exerts its normal function in facilitating progress through development, a gene whose expression is dependent on the A-signaling process has been studied. This gene, subsequently called 4521, was identified by a transcriptional fusion of a promoterless lacZ gene to its promoter. The fusion was generated by transposition of Tn5lac into the transcribed region (20). In an otherwise wildtype cell, the ⍀4521 Tn5lac fusion begins to be expressed early in the developmental process, around 1.5 h after the onset of starvation...

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Azorhizobium caulinodansNitrogen Fixation(nif/fix)Gene Regulation: Mutagenesis of thenifA─24/─12 Promoter Element, Characterization of antrA(rpoN)Gene, and Derivation of a Model

Cited by 34 publications

References 0 publications

FnrN controls symbiotic nitrogen fixation and hydrogenase activities in Rhizobium leguminosarum biovar viciae UPM791

FnrN controls symbiotic nitrogen fixation and hydrogenase activities in Rhizobium leguminosarum biovar viciae UPM791

Functional analysis of the fixNOQP region of Azorhizobium caulinodans

An early A-signal-dependent gene in Myxococcus xanthus has a sigma 54-like promoter

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