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Han F, Li H, Lyu E, Zhang Q, Gai H, Xu Y, Bai X, He X, Khan AQ, Li X, Xie F, Li F, Fang X, Wei M. Soybean-mediated suppression of BjaI/BjaR 1 quorum sensing in Bradyrhizobium diazoefficiens impacts symbiotic nitrogen fixation. Appl Environ Microbiol 2024; 90:e0137423. [PMID: 38251894 PMCID: PMC10880635 DOI: 10.1128/aem.01374-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 11/23/2023] [Indexed: 01/23/2024] Open
Abstract
The acyl-homoserine lactones (AHLs)-mediated LuxI/LuxR quorum sensing (QS) system orchestrates diverse bacterial behaviors in response to changes in population density. The role of the BjaI/BjaR1 QS system in Bradyrhizobium diazoefficiens USDA 110, which shares homology with LuxI/LuxR, remains elusive during symbiotic interaction with soybean. Here this genetic system in wild-type (WT) bacteria residing inside nodules exhibited significantly reduced activity compared to free-living cells, potentially attributed to soybean-mediated suppression. The deletion mutant strain ΔbjaR1 showed significantly enhanced nodulation induction and nitrogen fixation ability. Nevertheless, its ultimate symbiotic outcome (plant dry weight) in soybeans was compromised. Furthermore, comparative analysis of the transcriptome, proteome, and promoter activity revealed that the inactivation of BjaR1 systematically activated and inhibited genomic modules associated with nodulation and nitrogen metabolism. The former appeared to be linked to a significant decrease in the expression of NodD2, a key cell-density-dependent repressor of nodulation genes, while the latter conferred bacterial growth and nitrogen fixation insensitivity to environmental nitrogen. In addition, BjaR1 exerted a positive influence on the transcription of multiple genes involved in a so-called central intermediate metabolism within the nodule. In conclusion, our findings highlight the crucial role of the BjaI/BjaR1 QS circuit in positively regulating bacterial nitrogen metabolism and emphasize the significance of the soybean-mediated suppression of this genetic system for promoting efficient symbiotic nitrogen fixation by B. diazoefficiens.IMPORTANCEThe present study demonstrates, for the first time, that the BjaI/BjaR1 QS system of Bradyrhizobium diazoefficiens has a significant impact on its nodulation and nitrogen fixation capability in soybean by positively regulating NodD2 expression and bacterial nitrogen metabolism. Moreover, it provides novel insights into the importance of suppressing the activity of this QS circuit by the soybean host plant in establishing an efficient mutual relationship between the two symbiotic partners. This research expands our understanding of legumes' role in modulating symbiotic nitrogen fixation through rhizobial QS-mediated metabolic functioning, thereby deepening our comprehension of symbiotic coevolution theory. In addition, these findings may hold great promise for developing quorum quenching technology in agriculture.
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Affiliation(s)
- Fang Han
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Huiquan Li
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Ermeng Lyu
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Qianqian Zhang
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Haoyu Gai
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Yunfang Xu
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Xuemei Bai
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Xueqian He
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Abdul Qadir Khan
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Xiaolin Li
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai, China
- University of the Chinese Academy of Sciences, Beijing, China
| | - Fang Xie
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai, China
| | - Fengmin Li
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Xiangwen Fang
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
| | - Min Wei
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, Lanzhou, China
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Gao F, Yang J, Zhai N, Zhang C, Ren X, Zeng Y, Chen Y, Chen R, Pan H. NCR343 is required to maintain the viability of differentiated bacteroids in nodule cells in Medicago truncatula. THE NEW PHYTOLOGIST 2023; 240:815-829. [PMID: 37533094 DOI: 10.1111/nph.19180] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Accepted: 07/13/2023] [Indexed: 08/04/2023]
Abstract
Bacteroid (name for rhizobia inside nodule cells) differentiation is a prerequisite for successful nitrogen-fixing symbiosis. In certain legumes, under the regulation of host proteins, for example, a large group of NCR (nodule cysteine rich) peptides, bacteroids undergo irreversible terminal differentiation. This process causes them to lose the ability to propagate inside nodule cells while boosting their competency for nitrogen fixation. How host cells maintain the viability of differentiated bacteroids while maximizing their nitrogen-reducing activities remains elusive. Here, through mutant screen, map-based cloning, and genetic complementation, we find that NCR343 is required for the viability of differentiated bacteroids. In Medicago truncatula debino1 mutant, differentiated bacteroids decay prematurely, and NCR343 is proved to be the casual gene for debino1. NCR343 is mainly expressed in the nodule fixation zone, where bacteroids are differentiated. In nodule cells, mature NCR343 peptide is secreted into the symbiosomes. RNA-Seq assay shows that many stress-responsive genes are significantly induced in debino1 bacteroids. Additionally, a group of stress response-related rhizobium proteins are identified as putative interacting partners of NCR343. In summary, our findings demonstrate that beyond promoting bacteroid differentiation, NCR peptides are also required in maintaining the viability of differentiated bacteroids.
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Affiliation(s)
- Fengzhan Gao
- College of Biology, Hunan University, Changsha, 410082, China
| | - Jian Yang
- College of Biology, Hunan University, Changsha, 410082, China
| | - Niu Zhai
- Zhengzhou Tobacco Research Institute of CNTC, Zhengzhou, 450001, China
| | - Chao Zhang
- College of Biology, Hunan University, Changsha, 410082, China
| | - Xinru Ren
- College of Biology, Hunan University, Changsha, 410082, China
| | - Yating Zeng
- College of Biology, Hunan University, Changsha, 410082, China
| | - Yuhui Chen
- College of Life Sciences, Lanzhou University, Lanzhou, 730000, China
| | - Rujin Chen
- College of Life Sciences, Lanzhou University, Lanzhou, 730000, China
| | - Huairong Pan
- College of Biology, Hunan University, Changsha, 410082, China
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Moulin SL, Frail S, Doenier J, Braukmann T, Yeh E. The endosymbiont of Epithemia clementina is specialized for nitrogen fixation within a photosynthetic eukaryote. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.08.531752. [PMID: 37066385 PMCID: PMC10103950 DOI: 10.1101/2023.03.08.531752] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Epithemia spp. diatoms contain obligate, nitrogen-fixing endosymbionts, or "diazoplasts", derived from cyanobacteria. These algae are a rare example of photosynthetic eukaryotes that have successfully coupled oxygenic photosynthesis with oxygen-sensitive nitrogenase activity. Here, we report a newly-isolated species, E. clementina, as a model to investigate endosymbiotic acquisition of nitrogen fixation. To detect the metabolic changes associated with endosymbiotic specialization, we compared nitrogen fixation, associated carbon and nitrogen metabolism, and their regulatory pathways in the Epithemia diazoplast with its close, free-living cyanobacterial relative, Crocosphaera subtropica. Unlike C. subtropica, we show that nitrogenase activity in the diazoplast is concurrent with, and even dependent on, host photosynthesis and no longer associated with cyanobacterial glycogen storage suggesting carbohydrates are imported from the host diatom. Carbohydrate catabolism in the diazoplast indicates that the oxidative pentose pathway and oxidative phosphorylation, in concert, generates reducing equivalents and ATP and consumes oxygen to support nitrogenase activity. In contrast to expanded nitrogenase activity, the diazoplast has diminished ability to utilize alternative nitrogen sources. Upon ammonium repletion, negative feedback regulation of nitrogen fixation was conserved, however ammonia assimilation showed paradoxical responses in the diazoplast compared with C. subtropica. The altered nitrogen regulation likely favors nitrogen transfer to the host. Our results suggest that the diazoplast is specialized for endosymbiotic nitrogen fixation. Altogether, we establish a new model for studying endosymbiosis, perform the first functional characterization of this diazotroph endosymbiosis, and identify metabolic adaptations for endosymbiotic acquisition of a critical biological function.
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Affiliation(s)
- Solène L.Y. Moulin
- Department of Pathology, Stanford School of Medicine, Stanford, California, USA
| | - Sarah Frail
- Department of Biochemistry, Stanford School of Medicine, Stanford, California, USA
| | - Jon Doenier
- Department of Biochemistry, Stanford School of Medicine, Stanford, California, USA
| | - Thomas Braukmann
- Department of Pathology, Stanford School of Medicine, Stanford, California, USA
- Department of Biochemistry, Stanford School of Medicine, Stanford, California, USA
| | - Ellen Yeh
- Department of Pathology, Stanford School of Medicine, Stanford, California, USA
- Department of Microbiology & Immunology, Stanford School of Medicine, Stanford, California, USA
- Chan Zuckerberg Biohub – San Francisco, San Francisco, CA 94158
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Bao YQ, Zhang MT, Feng BY, Jieensi W, Xu Y, Xu LR, Han YY, Chen YP. Construction, Characterization, and Application of an Ammonium Transporter (AmtB) Deletion Mutant of the Nitrogen-Fixing Bacterium Kosakonia radicincitans GXGL-4A in Cucumis sativus L. Seedlings. Curr Microbiol 2023; 80:58. [PMID: 36588112 DOI: 10.1007/s00284-022-03160-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2022] [Accepted: 12/19/2022] [Indexed: 01/03/2023]
Abstract
Nitrogen is an important factor affecting crop yield, but excessive use of chemical nitrogen fertilizer has caused decline in nitrogen utilization and soil and water pollution. Reducing the utilization of chemical nitrogen fertilizers by biological nitrogen fixation (BNF) is feasible for green production of crops. However, there are few reports on how to have more ammonium produced by nitrogen-fixing bacteria (NFB) flow outside the cell. In the present study, the amtB gene encoding an ammonium transporter (AmtB) in the genome of NFB strain Kosakonia radicincitans GXGL-4A was deleted and the △amtB mutant was characterized. The results showed that deletion of the amtB gene had no influence on the growth of bacterial cells. The extracellular ammonium nitrogen (NH4+) content of the △amtB mutant under nitrogen-free culture conditions was significantly higher than that of the wild-type strain GXGL-4A (WT-GXGL-4A), suggesting disruption of NH4+ transport. Meanwhile, the plant growth-promoting effect in cucumber seedlings was visualized after fertilization using cells of the △amtB mutant. NFB fertilization continuously increased the cucumber rhizosphere soil pH. The nitrate nitrogen (NO3-) content in soil in the △amtB treatment group was significantly higher than that in the WT-GXGL-4A treatment group in the short term but there was no difference in soil NH4+ contents between groups. Soil enzymatic activities varied during a 45-day assessment period, indicating that △amtB fertilization influenced soil nitrogen cycling in the cucumber rhizosphere. The results will provide a solid foundation for developing the NFB GXGL-4A into an efficient biofertilizer agent.
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Affiliation(s)
- Yu-Qing Bao
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, 200093, China
| | - Meng-Ting Zhang
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Bao-Yun Feng
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Wulale Jieensi
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Yu Xu
- College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua, 321004, China
| | - Lu-Rong Xu
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Ying-Ying Han
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, 200093, China
| | - Yun-Peng Chen
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China.
- Ministry of Science and Technology, Shanghai Yangtze River Delta Eco-Environmental Change and Research Station, Shanghai, 200240, China.
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Succinate Transport Is Not Essential for Symbiotic Nitrogen Fixation by Sinorhizobium meliloti or Rhizobium leguminosarum. Appl Environ Microbiol 2017; 84:AEM.01561-17. [PMID: 28916561 DOI: 10.1128/aem.01561-17] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 08/31/2017] [Indexed: 01/29/2023] Open
Abstract
Symbiotic nitrogen fixation (SNF) is an energetically expensive process performed by bacteria during endosymbiotic relationships with plants. The bacteria require the plant to provide a carbon source for the generation of reductant to power SNF. While C4-dicarboxylates (succinate, fumarate, and malate) appear to be the primary, if not sole, carbon source provided to the bacteria, the contribution of each C4-dicarboxylate is not known. We address this issue using genetic and systems-level analyses. Expression of a malate-specific transporter (MaeP) in Sinorhizobium meliloti Rm1021 dct mutants unable to transport C4-dicarboxylates resulted in malate import rates of up to 30% that of the wild type. This was sufficient to support SNF with Medicago sativa, with acetylene reduction rates of up to 50% those of plants inoculated with wild-type S. melilotiRhizobium leguminosarum bv. viciae 3841 dct mutants unable to transport C4-dicarboxylates but expressing the maeP transporter had strong symbiotic properties, with Pisum sativum plants inoculated with these strains appearing similar to plants inoculated with wild-type R. leguminosarum This was despite malate transport rates by the mutant bacteroids being 10% those of the wild type. An RNA-sequencing analysis of the combined P. sativum-R. leguminosarum nodule transcriptome was performed to identify systems-level adaptations in response to the inability of the bacteria to import succinate or fumarate. Few transcriptional changes, with no obvious pattern, were detected. Overall, these data illustrated that succinate and fumarate are not essential for SNF and that, at least in specific symbioses, l-malate is likely the primary C4-dicarboxylate provided to the bacterium.IMPORTANCE Symbiotic nitrogen fixation (SNF) is an economically and ecologically important biological process that allows plants to grow in nitrogen-poor soils without the need to apply nitrogen-based fertilizers. Much research has been dedicated to this topic to understand this process and to eventually manipulate it for agricultural gains. The work presented in this article provides new insights into the metabolic integration of the plant and bacterial partners. It is shown that malate is the only carbon source that needs to be available to the bacterium to support SNF and that, at least in some symbioses, malate, and not other C4-dicarboxylates, is likely the primary carbon provided to the bacterium. This work extends our knowledge of the minimal metabolic capabilities the bacterium requires to successfully perform SNF and may be useful in further studies aiming to optimize this process through synthetic biology approaches. The work describes an engineering approach to investigate a metabolic process that occurs between a eukaryotic host and its prokaryotic endosymbiont.
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Ronneau S, Moussa S, Barbier T, Conde-Álvarez R, Zuniga-Ripa A, Moriyon I, Letesson JJ. Brucella, nitrogen and virulence. Crit Rev Microbiol 2014; 42:507-25. [PMID: 25471320 DOI: 10.3109/1040841x.2014.962480] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The brucellae are α-Proteobacteria causing brucellosis, an important zoonosis. Although multiplying in endoplasmic reticulum-derived vacuoles, they cause no cell death, suggesting subtle but efficient use of host resources. Brucellae are amino-acid prototrophs able to grow with ammonium or use glutamate as the sole carbon-nitrogen source in vitro. They contain more than twice amino acid/peptide/polyamine uptake genes than the amino-acid auxotroph Legionella pneumophila, which multiplies in a similar vacuole, suggesting a different nutritional strategy. During these two last decades, many mutants of key actors in nitrogen metabolism (transporters, enzymes, regulators, etc.) have been described to be essential for full virulence of brucellae. Here, we review the genomic and experimental data on Brucella nitrogen metabolism and its connection with virulence. An analysis of various aspects of this metabolism (transport, assimilation, biosynthesis, catabolism, respiration and regulation) has highlighted differences and similarities in nitrogen metabolism with other α-Proteobacteria. Together, these data suggest that, during their intracellular life cycle, the brucellae use various nitrogen sources for biosynthesis, catabolism and respiration following a strategy that requires prototrophy and a tight regulation of nitrogen use.
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Affiliation(s)
| | - Simon Moussa
- a UNamur, URBM 61 rue de Bruxelles , Namur , Belgium and
| | | | - Raquel Conde-Álvarez
- b Departamento de Microbiología , Edificio de Investigación, Universidad de Navarra , Pamplona , Spain
| | - Amaia Zuniga-Ripa
- b Departamento de Microbiología , Edificio de Investigación, Universidad de Navarra , Pamplona , Spain
| | - Ignacio Moriyon
- b Departamento de Microbiología , Edificio de Investigación, Universidad de Navarra , Pamplona , Spain
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Peng J, Hao B, Liu L, Wang S, Ma B, Yang Y, Xie F, Li Y. RNA-Seq and microarrays analyses reveal global differential transcriptomes of Mesorhizobium huakuii 7653R between bacteroids and free-living cells. PLoS One 2014; 9:e93626. [PMID: 24695521 PMCID: PMC3973600 DOI: 10.1371/journal.pone.0093626] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Accepted: 03/04/2014] [Indexed: 11/18/2022] Open
Abstract
Mesorhizobium huakuii 7653R occurs either in nitrogen-fixing symbiosis with its host plant, Astragalus sinicus, or free-living in the soil. The M. huakuii 7653R genome has recently been sequenced. To better understand the complex biochemical and developmental changes that occur in 7653R during bacteroid development, RNA-Seq and Microarrays were used to investigate the differential transcriptomes of 7653R bacteroids and free-living cells. The two approaches identified several thousand differentially expressed genes. The most prominent up-regulation occurred in the symbiosis plasmids, meanwhile gene expression is concentrated to a set of genes (clusters) in bacteroids to fulfill corresponding functional requirements. The results suggested that the main energy metabolism is active while fatty acid metabolism is inactive in bacteroid and that most of genes relevant to cell cycle are down-regulated accordingly. For a global analysis, we reconstructed a protein-protein interaction (PPI) network for 7653R and integrated gene expression data into the network using Cytoscape. A highly inter-connected subnetwork, with function enrichment for nitrogen fixation, was found, and a set of hubs and previously uncharacterized genes participating in nitrogen fixation were identified. The results described here provide a broader biological landscape and novel insights that elucidate rhizobial bacteroid differentiation, nitrogen fixation and related novel gene functions.
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Affiliation(s)
- Jieli Peng
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei, P. R. China
| | - Baohai Hao
- Center for Bioinformatics, School of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, P. R. China
| | - Liu Liu
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei, P. R. China
| | - Shanming Wang
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei, P. R. China
| | - Binguang Ma
- Center for Bioinformatics, School of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, P. R. China
| | - Yi Yang
- Center for Bioinformatics, School of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, P. R. China
| | - Fuli Xie
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei, P. R. China
| | - Youguo Li
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei, P. R. China
- * E-mail:
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Sallet E, Roux B, Sauviac L, Jardinaud MF, Carrère S, Faraut T, de Carvalho-Niebel F, Gouzy J, Gamas P, Capela D, Bruand C, Schiex T. Next-generation annotation of prokaryotic genomes with EuGene-P: application to Sinorhizobium meliloti 2011. DNA Res 2013; 20:339-54. [PMID: 23599422 PMCID: PMC3738161 DOI: 10.1093/dnares/dst014] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The availability of next-generation sequences of transcripts from prokaryotic organisms offers the opportunity to design a new generation of automated genome annotation tools not yet available for prokaryotes. In this work, we designed EuGene-P, the first integrative prokaryotic gene finder tool which combines a variety of high-throughput data, including oriented RNA-Seq data, directly into the prediction process. This enables the automated prediction of coding sequences (CDSs), untranslated regions, transcription start sites (TSSs) and non-coding RNA (ncRNA, sense and antisense) genes. EuGene-P was used to comprehensively and accurately annotate the genome of the nitrogen-fixing bacterium Sinorhizobium meliloti strain 2011, leading to the prediction of 6308 CDSs as well as 1876 ncRNAs. Among them, 1280 appeared as antisense to a CDS, which supports recent findings that antisense transcription activity is widespread in bacteria. Moreover, 4077 TSSs upstream of protein-coding or non-coding genes were precisely mapped providing valuable data for the study of promoter regions. By looking for RpoE2-binding sites upstream of annotated TSSs, we were able to extend the S. meliloti RpoE2 regulon by ∼3-fold. Altogether, these observations demonstrate the power of EuGene-P to produce a reliable and high-resolution automatic annotation of prokaryotic genomes.
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Affiliation(s)
- Erika Sallet
- INRA, Laboratoire des Interactions Plantes-Microorganismes-LIPM, UMR 441, Castanet-Tolosan F-31326, France
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Taté R, Cermola M, Riccio A, Diez-Roux G, Patriarca EJ. Glutathione is required by Rhizobium etli for glutamine utilization and symbiotic effectiveness. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2012; 25:331-40. [PMID: 22007600 DOI: 10.1094/mpmi-06-11-0163] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Here, we provide genetic and biochemical evidence indicating that the ability of Rhizobium etli bacteria to efficiently catabolize glutamine depends on its ability to produce reduced glutathione (l-γ-glutamyl-l-cysteinylglycine [GSH]). We find that GSH-deficient strains, namely a gshB (GSH synthetase) and a gor (GSH reductase) mutant, can use different amino acids, including histidine, alanine, and asparagine but not glutamine, as sole source of carbon, energy, and nitrogen. Moreover, l-buthionine(S,R)-sulfoximine, a GSH synthesis inhibitor, or diamide that oxidizes GSH, induced the same phenotype in the wild-type strain. Among the steps required for its utilization, glutamine uptake, occurring through the two well-characterized carriers (Aap and Bra systems) but not glutamine degradation or respiration, was largely reduced in GSH-deficient strains. Furthermore, GSH-deficient mutants of R. etli showed a reduced symbiotic efficiency. Exogenous GSH was sufficient to rescue glutamine uptake or degradation ability, as well as the symbiotic effectiveness of GSH mutants. Our results suggest a previously unknown GSH-glutamine metabolic relationship in bacteria.
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Affiliation(s)
- Rosarita Taté
- Institute Of Genetics And Biophysics, A Buzzati-Traverso, CNR, Naples, Italy
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Cloning and functional expression of an MscL ortholog from Rhizobium etli: characterization of a mechanosensitive channel. J Membr Biol 2010; 234:13-27. [PMID: 20177670 DOI: 10.1007/s00232-010-9235-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Accepted: 01/26/2010] [Indexed: 10/19/2022]
Abstract
Rhizobium etli is equipped with several systems to handle both hyper- and hypo-osmotic stress. For adaptation to hypo-osmotic stress, R. etli possesses a single gene with clear homology to MscS, four MscS-like channels and one ortholog of MscL (ReMscL, identity approximately 44% compared to Escherichia coli MscL). We subcloned and expressed the ReMscL channel ortholog from R. etli in E. coli to examine its activity by patch clamp in giant spheroplasts and characterized it at the single-channel level. We obtained evidence that ReMscL prevents the lysis of E. coli null mutant log-phase cells upon a rapid, osmotic downshock and identified a slight pH dependence for ReMscL activation. Here, we describe the facilitation of ReMscL activation by arachidonic acid (AA) and a reversible inhibitory effect of Gd(3+). The results obtained in these experiments suggest a stabilizing effect of micromolar AA and traces of Gd(3+) ions in the partially expanded conformation of the protein. Finally, we discuss a possible correlation between the number of gene paralogs for MS channels and the habitats of several microorganisms. Taken together, our data show that ReMscL may play an important role in free-living rhizobacteria during hypo-osmotic shock in the rhizosphere.
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Comparative genome-wide transcriptional profiling of Azorhizobium caulinodans ORS571 grown under free-living and symbiotic conditions. Appl Environ Microbiol 2009; 75:5037-46. [PMID: 19542345 DOI: 10.1128/aem.00398-09] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
The whole-genome sequence of the endosymbiotic bacterium Azorhizobium caulinodans ORS571, which forms nitrogen-fixing nodules on the stems and roots of Sesbania rostrata, was recently determined. The sizes of the genome and symbiosis island are 5.4 Mb and 86.7 kb, respectively, and these sizes are the smallest among the sequenced rhizobia. In the present study, a whole-genome microarray of A. caulinodans was constructed, and transcriptomic analyses were performed on free-living cells grown in rich and minimal media and in bacteroids isolated from stem nodules. Transcriptional profiling showed that the genes involved in sulfur uptake and metabolism, acetone metabolism, and the biosynthesis of exopolysaccharide were highly expressed in bacteroids compared to the expression levels in free-living cells. Some mutants having Tn5 transposons within these genes with increased expression were obtained as nodule-deficient mutants in our previous study. A transcriptomic analysis was also performed on free-living cells grown in minimal medium supplemented with a flavonoid, naringenin, which is one of the most efficient inducers of A. caulinodans nod genes. Only 18 genes exhibited increased expression by the addition of naringenin, suggesting that the regulatory mechanism responding to the flavonoid could be simple in A. caulinodans. The combination of our genome-wide transcriptional profiling and our previous genome-wide mutagenesis study has revealed new aspects of nodule formation and maintenance.
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White J, Prell J, James EK, Poole P. Nutrient sharing between symbionts. PLANT PHYSIOLOGY 2007; 144:604-14. [PMID: 17556524 PMCID: PMC1914197 DOI: 10.1104/pp.107.097741] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2007] [Accepted: 04/30/2007] [Indexed: 05/15/2023]
Affiliation(s)
- James White
- School of Biological Sciences, University of Reading, Whiteknights Reading RG6 6AJ, United Kingdom
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13
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Ludewig U, Neuhäuser B, Dynowski M. Molecular mechanisms of ammonium transport and accumulation in plants. FEBS Lett 2007; 581:2301-8. [PMID: 17397837 DOI: 10.1016/j.febslet.2007.03.034] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2007] [Revised: 03/12/2007] [Accepted: 03/14/2007] [Indexed: 10/23/2022]
Abstract
The integral membrane proteins of the ammonium transporter (AMT/Rh) family provide the major route for shuttling ammonium (NH(4)(+)/NH(3)) across bacterial, archaeal, fungal and plant membranes. These proteins are distantly related to the Rh (rhesus) glycoproteins, which are absent in higher plants, but are present in many species, including bacteria and mammals. It appears that the large nitrogen requirement of plants resulted in unique strategies to acquire, capture and/or release ammonium. The biological function of plant ammonium transporters will be discussed and compared to other AMT/Rh proteins.
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Affiliation(s)
- Uwe Ludewig
- Zentrum für Molekularbiologie der Pflanzen (ZMBP), Pflanzenphysiologie, Universität Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany.
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14
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Selle A, Willmann M, Grunze N, Gessler A, Weiss M, Nehls U. The high-affinity poplar ammonium importer PttAMT1.2 and its role in ectomycorrhizal symbiosis. THE NEW PHYTOLOGIST 2005; 168:697-706. [PMID: 16313651 DOI: 10.1111/j.1469-8137.2005.01535.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
One way to elucidate whether ammonium could act as a nitrogen (N) source delivered by the fungus in ectomycorrhizal symbiosis is to investigate plant ammonium importers. Expression analysis of a high-affinity ammonium importer from Populus tremulax tremuloides (PttAMT1.2) and of known members of the AMT1 gene family from Populus trichocarpa was performed. In addition, PttAMT1.2 function was studied in detail by heterologous expression in yeast. PttAMT1.2 expression proved to be root-specific, affected by N nutrition, and strongly increased in a N-independent manner upon ectomycorrhiza formation. The corresponding protein had a K(M) value for ammonium of c. 52 microm. From the seven members of the AMT1 gene family, one gene was exclusively expressed in roots while four genes were detectable in all poplar organs but with varying degrees of expression. Ectomycorrhiza formation resulted in a strong upregulation of three of these genes. Our results indicate an increased ammonium uptake capacity of mycorrhized poplar roots and suggest, together with the expression of putative ammonium exporter genes in the ectomycorrhizal fungus Amanita muscaria, that ammonium could be a major N source delivered from the fungus towards the plant in symbiosis.
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Affiliation(s)
- Anita Selle
- Eberhard-Karls-Universität, Physiologische Okologie der Pflanzen, Auf der Morgenstelle 1, D-72076 Tübingen, Germany
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15
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Calderón-Flores A, Du Pont G, Huerta-Saquero A, Merchant-Larios H, Servín-González L, Durán S. The stringent response is required for amino acid and nitrate utilization, nod factor regulation, nodulation, and nitrogen fixation in Rhizobium etli. J Bacteriol 2005; 187:5075-83. [PMID: 16030199 PMCID: PMC1196017 DOI: 10.1128/jb.187.15.5075-5083.2005] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A Rhizobium etli Tn5 insertion mutant, LM01, was selected for its inability to use glutamine as the sole carbon and nitrogen source. The Tn5 insertion in LM01 was localized to the rsh gene, which encodes a member of the RelA/SpoT family of proteins. The LM01 mutant was affected in the ability to use amino acids and nitrate as nitrogen sources and was unable to accumulate (p)ppGpp when grown under carbon and nitrogen starvation, as opposed to the wild-type strain, which accumulated (p)ppGpp under these conditions. The R. etli rsh gene was found to restore (p)ppGpp accumulation to a DeltarelA DeltaspoT mutant of Escherichia coli. The R. etli Rsh protein consists of 744 amino acids, and the Tn5 insertion in LM01 results in the synthesis of a truncated protein of 329 amino acids; complementation experiments indicate that this truncated protein is still capable of (p)ppGpp hydrolysis. A second rsh mutant of R. etli, strain AC1, was constructed by inserting an Omega element at the beginning of the rsh gene, resulting in a null allele. Both AC1 and LM01 were affected in Nod factor production, which was constitutive in both strains, and in nodulation; nodules produced by the rsh mutants in Phaseolus vulgaris were smaller than those produced by the wild-type strain and did not fix nitrogen. In addition, electron microscopy revealed that the mutant bacteroids lacked poly-beta-hydroxybutyrate granules. These results indicate a central role for the stringent response in symbiosis.
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Affiliation(s)
- Arturo Calderón-Flores
- Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Apdo. Postal 70228, México D.F. C.P. 04510, México
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16
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Yost CK, Del Bel KL, Quandt J, Hynes MF. Rhizobium leguminosarum methyl-accepting chemotaxis protein genes are down-regulated in the pea nodule. Arch Microbiol 2004; 182:505-13. [PMID: 15502966 DOI: 10.1007/s00203-004-0736-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2004] [Revised: 09/22/2004] [Accepted: 09/24/2004] [Indexed: 11/26/2022]
Abstract
Regulation of methyl-accepting chemotaxis protein (MCP) genes of Rhizobium leguminosarum was studied under symbiotic conditions. Transcriptional fusions using both beta-galactosidase and beta-glucuronidase genes within two different mcp genes demonstrated that mcp expression decreased significantly during nodulation. Immunoblots using an anti-MCP antibody detected MCPs in free-living cells but not in bacteroids. Down-regulation during nodulation was not dependent upon known regulatory proteins involved in induction of expression of genes involved in nitrogen fixation. Environmental conditions found in the bacteroid that may trigger down-regulation were investigated by growing free-living cultures under a variety of growth conditions. Growth under low oxygen concentration or using succinate as a sole carbon source did not lower expression of the mcp gene fusions.
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Affiliation(s)
- Christopher K Yost
- Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
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17
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Khademi S, O'Connell J, Remis J, Robles-Colmenares Y, Miercke LJW, Stroud RM. Mechanism of ammonia transport by Amt/MEP/Rh: structure of AmtB at 1.35 A. Science 2004; 305:1587-94. [PMID: 15361618 DOI: 10.1126/science.1101952] [Citation(s) in RCA: 514] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The first structure of an ammonia channel from the Amt/MEP/Rh protein superfamily, determined to 1.35 angstrom resolution, shows it to be a channel that spans the membrane 11 times. Two structurally similar halves span the membrane with opposite polarity. Structures with and without ammonia or methyl ammonia show a vestibule that recruits NH4+/NH3, a binding site for NH4+, and a 20 angstrom-long hydrophobic channel that lowers the NH4+ pKa to below 6 and conducts NH3. Favorable interactions for NH3 are seen within the channel and use conserved histidines. Reconstitution of AmtB into vesicles shows that AmtB conducts uncharged NH3.
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Affiliation(s)
- Shahram Khademi
- Department of Biochemistry and Biophysics, S412C Genentech Hall, University of California-San Francisco, 600 16th Street, San Francisco, CA 94143-2240, USA
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18
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Tatè R, Ferraioli S, Filosa S, Cermola M, Riccio A, Iaccarino M, Patriarca EJ. Glutamine utilization by Rhizobium etli. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2004; 17:720-728. [PMID: 15242166 DOI: 10.1094/mpmi.2004.17.7.720] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We undertook the study of the use of glutamine (Gln) as the source of carbon and energy by Rhizobium etli. Tn5-induced mutagenesis allowed us to identify several genes required for Gln utilization, including those coding for two broad-range amino acid transporters and a glutamate dehydrogenase. The isolated mutants were characterized by the analysis of their capacity i) to grow on different media, ii) to transport Gln (uptake assays), and iii) to utilize Gln as the C energy source (CO2 production from Gln). We show that Gln is degraded through the citric acid cycle and that its utilization as the sole C source is related to a change in the bacterial cell shape (from bacillary to coccoid form) and a high susceptibility to a thiol oxidative insult. Both these data and the analysis of ntr-dependent promoters suggested that Gln-grown bacteria are under a condition of C starvation and N sufficiency, and as expected, the addition of glucose counteracted the morphological change and increased both the bacterial growth rate and their resistance to oxidative stress. Finally, a nodulation analysis indicates that the genes involved in Gln transport and degradation are dispensable for the bacterial ability to induce and invade developing nodules, whereas those involved in gluconeogenesis and nucleotide biosynthesis are strictly required.
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Affiliation(s)
- Rosarita Tatè
- Institute of Genetics and Biophysics A. Buzzati-Traverso, CNR, Via G. Marconi 10, 80125 Naples, Italy
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19
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Patriarca EJ, Tatè R, Ferraioli S, Iaccarino M. Organogenesis of legume root nodules. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 234:201-62. [PMID: 15066376 DOI: 10.1016/s0074-7696(04)34005-2] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The N(2)-fixing nodules elicited by rhizobia on legume roots represent a useful model for studying plant development. Nodule formation implies a complex progression of temporally and spatially regulated events of cell differentiation/dedifferentiation involving several root tissues. In this review we describe the morphogenetic events leading to the development of these histologically well-structured organs. These events include (1) root hair deformation, (2) development and growth of infection threads, (3) induction of the nodule primordium, and (4) induction, activity, and persistence of the nodular meristem and/or of foci of meristematic activities. Particular attention is given to specific aspects of the symbiosis, such as the early stages of intracellular invasion and to differentiation of the intracellular form of rhizobia, called symbiosomes. These developmental aspects were correlated with (1) the regulatory signals exchanged, (2) the plant genes expressed in specific cell types, and (3) the staining procedures that allow the recognition of some cell types. When strictly linked with morphogenesis, the nodulation phenotypes of plant and bacterial mutants such as the developmental consequence of the treatment with metabolic inhibitors, metabolic intermediates, or the variation of physical parameters are described. Finally, some aspects of nodule senescence and of regulation of nodulation are discussed.
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Affiliation(s)
- Eduardo J Patriarca
- Institute of Genetics and Biophysics Adriano Buzzati-Traverso, Consiglio Nazionale delle Ricerche, 80125 Naples, Italy
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20
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Santi C, von Groll U, Ribeiro A, Chiurazzi M, Auguy F, Bogusz D, Franche C, Pawlowski K. Comparison of nodule induction in legume and actinorhizal symbioses: the induction of actinorhizal nodules does not involve ENOD40. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2003; 16:808-816. [PMID: 12971604 DOI: 10.1094/mpmi.2003.16.9.808] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Two types of root nodule symbioses are known for higher plants, legume and actinorhizal symbioses. In legume symbioses, bacterial signal factors induce the expression of ENOD40 genes. We isolated an ENOD40 promoter from an actinorhizal plant, Casuarina glauca, and compared its expression pattern in a legume (Lotus japonicus) and an actinorhizal plant (Allocasuarina verticillata) with that of an ENOD40 promoter from the legume soybean (GmENOD40-2). In the actinorhizal Allocasuarina sp., CgENOD40-GUS and GmENOD40-2-GUS showed similar expression patterns in both vegetative and symbiotic development, and neither promoter was active during nodule induction. The nonsymbiotic expression pattern of CgENOD40-GUS in the legume genus Lotus resembled the nonsymbiotic expression patterns of legume ENOD40 genes; however, in contrast to GmENOD40-2-GUS, CgENOD40-GUS was not active during nodule induction. The fact that only legume, not actinorhizal, ENOD40 genes are induced during legume nodule induction can be linked to the phloem unloading mechanisms established in the zones of nodule induction in the roots of both types of host plants.
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Affiliation(s)
- Carole Santi
- Equipe Rhizogenèse, UMR 1098, Institut de Recherche pour le Développement, 911 Avenue Agropolis, BP 64501, 34394 Montpellier cedex 5, France
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21
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Blakey D, Leech A, Thomas GH, Coutts G, Findlay K, Merrick M. Purification of the Escherichia coli ammonium transporter AmtB reveals a trimeric stoichiometry. Biochem J 2002; 364:527-35. [PMID: 12023896 PMCID: PMC1222598 DOI: 10.1042/bj20011761] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The Amt family of high-affinity ammonium transporters is a family of integral membrane proteins that are found in archaea, bacteria, fungi, plants and animals. Furthermore, the family has recently been extended to humans with the recognition that both the erythroid and non-erythroid Rhesus proteins are also ammonium transporters. The Escherichia coli AmtB protein offers a good model system for the Amt family and in order to address questions relating to both its structure and function we have overproduced a histidine-tagged form of the protein (AmtB6H) and purified it to homogeneity. We examined the quaternary structure of AmtB6H (which is active in vivo) by SDS/PAGE, gel-filtration chromatography, dynamic light scattering and sedimentation ultracentrifugation. The protein was resistant to dissociation by SDS and behaved as a stable oligomer on SDS/PAGE. By equilibrium desorption chromatography we determined the mass ratio of dodecyl beta-D-maltoside to AmtB in the detergent-solubilized complex to be 1.03+/-0.03, and this allowed us to calculate, from analytical-ultracentrifugation data, that AmtB purifies as a trimer.
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Affiliation(s)
- Dan Blakey
- Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7UH, UK
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22
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Patriarca EJ, Tatè R, Iaccarino M. Key role of bacterial NH(4)(+) metabolism in Rhizobium-plant symbiosis. Microbiol Mol Biol Rev 2002; 66:203-22. [PMID: 12040124 PMCID: PMC120787 DOI: 10.1128/mmbr.66.2.203-222.2002] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Symbiotic nitrogen fixation is carried out in specialized organs, the nodules, whose formation is induced on leguminous host plants by bacteria belonging to the family Rhizobiaceae: Nodule development is a complex multistep process, which requires continued interaction between the two partners and thus the exchange of different signals and metabolites. NH(4)(+) is not only the primary product but also the main regulator of the symbiosis: either as ammonium and after conversion into organic compounds, it regulates most stages of the interaction, from the production of nodule inducers to the growth, function, and maintenance of nodules. This review examines the adaptation of bacterial NH(4)(+) metabolism to the variable environment generated by the plant, which actively controls and restricts bacterial growth by affecting oxygen and nutrient availability, thereby allowing a proficient interaction and at the same time preventing parasitic invasion. We describe the regulatory circuitry responsible for the downregulation of bacterial genes involved in NH(4)(+) assimilation occurring early during nodule invasion. This is a key and necessary step for the differentiation of N(2)-fixing bacteroids (the endocellular symbiotic form of rhizobia) and for the development of efficient nodules.
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Affiliation(s)
- Eduardo J Patriarca
- International Institute of Genetics and Biophysics, Consiglio Nazionale delle Ricerche, 80125 Naples, Italy.
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23
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Monahan BJ, Unkles SE, Tsing I T, Kinghorn JR, Hynes MJ, Davis MA. Mutation and functional analysis of the Aspergillus nidulans ammonium permease MeaA and evidence for interaction with itself and MepA. Fungal Genet Biol 2002; 36:35-46. [PMID: 12051893 DOI: 10.1016/s1087-1845(02)00004-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The movement of ammonium across biological membranes is mediated in both prokaryotic and eukaryotic systems by ammonium transport proteins which constitute a family of related sequences (called the AMT/MEP family). Interestingly, recent evidence suggests that human and mouse Rhesus proteins which display significant relatedness to AMT/MEP sequences may function as ammonium transporters. To add to the functional understanding of ammonium transport proteins, the sequence changes in 37 loss-of-function mutations within the Aspergillus nidulans ammonium permease gene, meaA, were characterized. Together with the identification of conserved AMT/MEP residues and regions, the mutational analysis predicted regions important for uptake activity. Specifically, a major facilitator superfamily like motif (161-GAVAERGR-168 in MeaA) may be important for the translocation of ammonium across the membrane as may the conserved Pro186 residue. A specific Gly447 to Asp mutation was introduced into MeaA and this mutant protein was found to trans-inhibit the activity of endogenous MeaA and the other A. nidulans ammonium transporter, MepA. These results suggest that MeaA may interact with itself and with MepA, although any hetero-interaction is not required for ammonium transport function. In addition, cross-feeding studies showed that MeaA and to a lesser extent MepA are also required for the retention of intracellular ammonium.
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Affiliation(s)
- Brendon J Monahan
- Department of Genetics, University of Melbourne, Parkville, Victoria 3010, Australia
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24
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Dombrecht B, Marchal K, Vanderleyden J, Michiels J. Prediction and overview of the RpoN-regulon in closely related species of the Rhizobiales. Genome Biol 2002; 3:RESEARCH0076. [PMID: 12537565 PMCID: PMC151178 DOI: 10.1186/gb-2002-3-12-research0076] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2002] [Revised: 09/16/2002] [Accepted: 10/18/2002] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND In the rhizobia, a group of symbiotic Gram-negative soil bacteria, RpoN (sigma54, sigmaN, NtrA) is best known as the sigma factor enabling transcription of the nitrogen fixation genes. Recent reports, however, demonstrate the involvement of RpoN in other symbiotic functions, although no large-scale effort has yet been undertaken to unravel the RpoN-regulon in rhizobia. We screened two complete rhizobial genomes (Mesorhizobium loti, Sinorhizobium meliloti) and four symbiotic regions (Rhizobium etli, Rhizobium sp. NGR234, Bradyrhizobium japonicum, M. loti) for the presence of the highly conserved RpoN-binding sites. A comparison was also made with two closely related non-symbiotic members of the Rhizobiales (Agrobacterium tumefaciens, Brucella melitensis). RESULTS A highly specific weight-matrix-based screening method was applied to predict members of the RpoN-regulon, which were stored in a highly annotated and manually curated dataset. Possible enhancer-binding proteins (EBPs) controlling the expression of RpoN-dependent genes were predicted with a profile hidden Markov model. CONCLUSIONS The methodology used to predict RpoN-binding sites proved highly effective as nearly all known RpoN-controlled genes were identified. In addition, many new RpoN-dependent functions were found. The dependency of several of these diverse functions on RpoN seems species-specific. Around 30% of the identified genes are hypothetical. Rhizobia appear to have recruited RpoN for symbiotic processes, whereas the role of RpoN in A. tumefaciens and B. melitensis remains largely to be elucidated. All species screened possess at least one uncharacterized EBP as well as the usual ones. Lastly, RpoN could significantly broaden its working range by direct interfering with the binding of regulatory proteins to the promoter DNA.
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Affiliation(s)
- Bruno Dombrecht
- Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
| | - Kathleen Marchal
- ESAT-SCD, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
| | - Jos Vanderleyden
- Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
| | - Jan Michiels
- Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
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25
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Benelli EM, Buck M, de Souza EM, Yates MG, Pedrosa FO. Uridylylation of the PII protein from Herbaspirillum seropedicae. Can J Microbiol 2001; 47:309-14. [PMID: 11358170 DOI: 10.1139/w01-018] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The PII protein is apparently involved in the control of NifA activity in Herbaspirillum seropedicae. To evaluate the probable role of PII in signal transduction, uridylylation assays were conducted with purified H. seropedicae PII and Escherichia coli GlnD, or a cell-free extract of H. seropedicae as sources of uridylylating activity. The results showed that alpha-ketoglutarate and ATP stimulate uridylylation whereas glutamine inhibits uridylylation. Deuridylylation of PII-UMP was dependent on glutamine and inhibited by ATP and alpha-ketoglutarate. PII uridylylation and (or) deuridylylation in response to these effectors suggests that PII is a nitrogen level signal transducer in H. seropedicae.
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Affiliation(s)
- E M Benelli
- Department of Biochemistry, Federal University of Parana, Curitiba, Brazil
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26
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Tatè R, Mandrich L, Spinosa MR, Riccio A, Lamberti A, Iaccarino M, Patriarca EJ. The Rhizobium GstI protein reduces the NH4+ assimilation capacity of Rhizobium leguminosarum. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2001; 14:823-831. [PMID: 11437255 DOI: 10.1094/mpmi.2001.14.7.823] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We show that the protein encoded by the glutamine synthetase translational inhibitor (gstI) gene reduces the NH4+ assimilation capacity of Rhizobium leguminosarum. In this organism, gstI expression is regulated by the ntr system, including the PII protein, as a function of the nitrogen (N) status of the cells. The GstI protein, when expressed from an inducible promoter, inhibits glutamine synthetase II (glnII) expression under all N conditions tested. The induction of gstI affects the growth of a glutamine synthetase I (glnA-) strain and a single amino acid substitution (W48D) results in the complete loss of GstI function. During symbiosis, gstI is expressed in young differentiating symbiosomes (SBs) but not in differentiated N2-fixing SBs. In young SBs, the PII protein modulates the transcription of NtrC-regulated genes such as gstI and glnII. The evidence presented herein strengthens the idea that the endocytosis of bacteria inside the cytoplasm of the host cells is a key step in the regulation of NH4+ metabolism.
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Affiliation(s)
- R Tatè
- International Institute of Genetics and Biophysics, CNR, Naples, Italy
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27
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Salvemini F, Marini A, Riccio A, Patriarca EJ, Chiurazzi M. Functional characterization of an ammonium transporter gene from Lotus japonicus. Gene 2001; 270:237-43. [PMID: 11404021 DOI: 10.1016/s0378-1119(01)00470-x] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
NH(4)(+) is the main product of symbiotic nitrogen fixation and the external concentration of combined nitrogen plays a key regulatory role in all the different step of plant-rhizobia interaction. We report the cloning and characterization of the first member of the ammonium transporter family, LjAMT1;1 from a leguminous plant, Lotus japonicus. Sequence analysis reveals a close relationship to plant transporters of the AMT1 family. The wild type and two mutated versions of LjAMT1;1 were expressed and functionally characterized in yeast. LjAMT1;1 is transcribed in roots, leaves and nodules of L. japonicus plants grown under low nitrogen conditions, consistent with a role in uptake of NH(4)(+) by the plant cells.
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Affiliation(s)
- F Salvemini
- International Institute of Genetics and Biophysics. Via Marconi 12, 80125, Napoli, Italy
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28
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Arcondéguy T, Jack R, Merrick M. P(II) signal transduction proteins, pivotal players in microbial nitrogen control. Microbiol Mol Biol Rev 2001; 65:80-105. [PMID: 11238986 PMCID: PMC99019 DOI: 10.1128/mmbr.65.1.80-105.2001] [Citation(s) in RCA: 312] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The P(II) family of signal transduction proteins are among the most widely distributed signal proteins in the bacterial world. First identified in 1969 as a component of the glutamine synthetase regulatory apparatus, P(II) proteins have since been recognized as playing a pivotal role in control of prokaryotic nitrogen metabolism. More recently, members of the family have been found in higher plants, where they also potentially play a role in nitrogen control. The P(II) proteins can function in the regulation of both gene transcription, by modulating the activity of regulatory proteins, and the catalytic activity of enzymes involved in nitrogen metabolism. There is also emerging evidence that they may regulate the activity of proteins required for transport of nitrogen compounds into the cell. In this review we discuss the history of the P(II) proteins, their structures and biochemistry, and their distribution and functions in prokaryotes. We survey data emerging from bacterial genome sequences and consider other likely or potential targets for control by P(II) proteins.
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Affiliation(s)
- T Arcondéguy
- Department of Microbiology, John Innes Centre, Norwich, United Kingdom
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29
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Abstract
One of the paradigms of symbiotic nitrogen fixation has been that bacteroids reduce N2 to ammonium and secrete it without assimilation into amino acids. This has recently been challenged by work with soybeans showing that only alanine is excreted in 15N2 labelling experiments. Work with peas shows that the bacteroid nitrogen secretion products during in vitro experiments depend on the experimental conditions. There is a mixed secretion of both ammonium and alanine depending critically on the concentration of bacteroids and ammonium concentration. The pathway of alanine synthesis has been shown to be via alanine dehydrogenase, and mutation of this enzyme indicates that in planta there is likely to be mixed secretion of ammonium and alanine. Alanine synthesis directly links carbon catabolism and nitrogen assimilation in the bacteroid. There is now overwhelming evidence that the principal carbon sources of bacteroids are the C4-dicarboxylic acids. This is based on labelling and bacteroid respiration data, and mutation of both the dicarboxylic acid transport system (dct) and malic enzyme. L-malate is at a key bifurcation point in bacteroid metabolism, being oxidized to oxaloacetate and oxidatively decarboxylated to pyruvate. Pyruvate can be aminated to alanine or converted to acetyl-CoA where it either enters the TCA cycle by condensation with oxaloacetate or forms polyhydroxybutyrate (PHB). Thus regulation of carbon and nitrogen metabolism are strongly connected. Efficient catabolism of C4-dicarboxylates requires the balanced input and removal of intermediates from the TCA cycle. The TCA cycle in bacteroids may be limited by the redox state of NADH/NAD+ at the 2-ketoglutarate dehydrogenase complex, and a number of pathways may be involved in bypassing this block. These pathways include PHB synthesis, glutamate synthesis, glycogen synthesis, GABA shunt and glutamine cycling. Their operation may be critical in maintaining the optimum redox poise and carbon balance of the TCA cycle. They can also be considered to be overflow pathways since they act to remove or add electrons and carbon into the TCA cycle. Optimum operation of the TCA cycle has a major impact on nitrogen fixation.
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Affiliation(s)
- P Poole
- Division of Microbiology, School of Animal and Microbial Sciences, University of Reading, UK
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30
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Abstract
Completion of fungal, plant and human genomes paved the way to the identification of erythrocytic rhesus proteins and their kidney homologs as ammonium transporters.
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Affiliation(s)
- Uwe Ludewig
- Zentrum für Molekularbiologie der Pflanzen, Eberhard-Karls-Universität, Auf der Morgenstelle 1, 72076 Tübingen, Germany
| | - Nico von Wirén
- Zentrum für Molekularbiologie der Pflanzen, Eberhard-Karls-Universität, Auf der Morgenstelle 1, 72076 Tübingen, Germany
| | - Doris Rentsch
- Zentrum für Molekularbiologie der Pflanzen, Eberhard-Karls-Universität, Auf der Morgenstelle 1, 72076 Tübingen, Germany
| | - Wolf B Frommer
- Zentrum für Molekularbiologie der Pflanzen, Eberhard-Karls-Universität, Auf der Morgenstelle 1, 72076 Tübingen, Germany
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31
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Martin DE, Hurek T, Reinhold-Hurek B. Occurrence of three PII-like signal transmitter proteins in the diazotrophic proteobacterium Azoarcus sp. BH72. Mol Microbiol 2000; 38:276-88. [PMID: 11069654 DOI: 10.1046/j.1365-2958.2000.02095.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PII-like signal transmitter proteins are involved in the regulation of ammonium assimilation and nitrogen fixation. We report the identification of three PII-like proteins in the diazotrophic, endophytic proteobacterium Azoarcus sp. BH72, encoded by glnB (monocistronically transcribed) or in the glnKamtB and glnYamtY operons. Phylogenetic analysis revealed that glnB, glnK and glnY represent distinct lineages within the Proteobacteria. A combined approach of two-dimensional gel electrophoresis, Western blotting with paralogue-specific antibodies, N-terminal sequencing and marker exchange mutagenesis allowed us to analyse PII protein expression of Azoarcus sp. BH72 in vivo. GlnK and GlnB were present on all nitrogen sources. Knock-out mutant analysis revealed that GlnB was the only detectable PII protein in a glnK- background, whereas GlnY was only present in a glnK/glnB- double mutant. Nitrogen limitation enhanced transcript abundance of glnK strongly, glnY moderately and glnB not at all in wild-type, glnB-/glnK- or glnK- backgrounds respectively. Phenotypic characterization of knock-out mutants revealed that, unlike in other Proteobacteria, neither glnK nor glnB were essential for nitrogen fixation. As the growth of a double mutant was drastically impaired only on minimal media, both proteins are probably involved in the control of ammonium and nitrate assimilation. The PII-like proteins differed from each other in details of N-sensing. They were covalently modified by uridylylation upon nitrogen limitation, as shown by mass spectrometry; however, the modification patterns in relation to the supplied nitrogen source differed. The novel paralogue GlnY was unusual, as it only occurred in the uridylylated state in vivo and thus lacked a deuridylylation response to nitrogen excess.
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Affiliation(s)
- D E Martin
- Max-Planck-Institute for Terrestrial Microbiology, Group Symbiosis Research, D-35043 Marburg, Germany
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32
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Abstract
The Mep/Amt proteins constitute a new family of transport proteins that are ubiquitous in nature. Members from bacteria, yeast and plants have been identified experimentally as high-affinity ammonium transporters. We have determined the topology of AmtB, a Mep/Amt protein from Escherichia coli, as a representative protein for the complete family. This was established using a minimal set of AmtB-PhoA fusion proteins with a complementary set of AmtB-LacZ fusions. These data, accompanied by an in silico analysis, indicate that the majority of the Mep/Amt proteins contain 11 membrane-spanning helices, with the N-terminus on the exterior face of the membrane and the C-terminus on the interior. A small subset, including E. coli AmtB, probably have an additional twelfth membrane-spanning region at the N-terminus. Addition of PhoA or LacZ alpha-peptide to the C-terminus of E. coli AmtB resulted in complete loss of transport activity, as judged by measurements of [14C]-methylammonium uptake. This C-terminal region, along with four membrane-spanning helices, contains multiple residues that are conserved within the Mep/Amt protein family. Structural modelling of the E. coli AmtB protein suggests a number of secondary structural features that might contribute to function, including a putative ammonium binding site on the periplasmic face of the membrane at residue Asp-182. The implications of these results are discussed in relation to the structure and function of the related human Rhesus proteins.
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Affiliation(s)
- G H Thomas
- Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich, Norfolk NR4 7UH, UK
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Howitt SM, Udvardi MK. Structure, function and regulation of ammonium transporters in plants. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1465:152-70. [PMID: 10748252 DOI: 10.1016/s0005-2736(00)00136-x] [Citation(s) in RCA: 195] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ammonium is an important source of nitrogen for plants. It is taken up by plant cells via ammonium transporters in the plasma membrane and distributed to intracellular compartments such as chloroplasts, mitochondria and vacuoles probably via different transporters in each case. Ammonium is generally not used for long-distance transport of nitrogen within the plant. Instead, most of the ammonium transported into plant cells is assimilated locally via glutamine synthetases in the cytoplasm and plastids. Ammonium is also produced by plant cells during normal metabolism, and ammonium transporters enable it to be moved from intracellular sites of production to sites of consumption. Ammonium can be generated de novo from molecular nitrogen (N(2)) by nitrogen-fixing bacteria in some plant cells, such as rhizobia in legume root nodule cells, and at least one ammonium transporter is implicated in the transfer of ammonium from the bacteria to the plant cytoplasm. Plant physiologists have described many of these ammonium transport processes over the last few decades. However, the genes and proteins that underlie these processes have been isolated and studied only recently. In this review, we consider in detail the molecular structure, function and regulation of plant ammonium transporters. We also attempt to reconcile recent discoveries at the molecular level with our knowledge of ammonium transport at the whole plant level.
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Affiliation(s)
- S M Howitt
- Division of Biochemistry and Molecular Biology, The Australian National University, Canberra, Australia
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34
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Affiliation(s)
- G Thomas
- Department of Molecular Microbiology, John Innes Centre, Norwich, UK.
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Jack R, De Zamaroczy M, Merrick M. The signal transduction protein GlnK is required for NifL-dependent nitrogen control of nif gene expression in Klebsiella pneumoniae. J Bacteriol 1999; 181:1156-62. [PMID: 9973341 PMCID: PMC93492 DOI: 10.1128/jb.181.4.1156-1162.1999] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In Klebsiella pneumoniae, transcription of the nitrogen fixation (nif) genes is regulated in response to molecular oxygen or availability of fixed nitrogen by the coordinated activities of the nifA and nifL gene products. NifA is a nif-specific transcriptional activator, the activity of which is inhibited by interaction with NifL. Nitrogen control of NifL occurs at two levels: transcription of the nifLA operon is regulated by the global ntr system, and the inhibitory activity of NifL is controlled in response to fixed nitrogen by an unknown factor. K. pneumoniae synthesizes two PII-like signal transduction proteins, GlnB, which we have previously shown not to be involved in the response of NifL to fixed nitrogen, and the recently identified protein GlnK. We have now cloned the K. pneumoniae glnK gene, studied its expression, and shown that a null mutation in glnK prevents NifL from responding to the absence of fixed nitrogen, i.e., from relieving the inhibition of NifA activity. Hence, GlnK appears to be involved, directly or indirectly, in NifL-dependent regulation of nif gene expression in K. pneumoniae. Comparison of the GlnB and GlnK amino acid sequences from six species of proteobacteria identifies five residues (residues 3, 5, 52, 54, and 64) which serve to distinguish the GlnB and GlnK proteins.
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Affiliation(s)
- R Jack
- Nitrogen Fixation Laboratory, John Innes Centre, Norwich NR4 7UH, United Kingdom
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Waters JK, Hughes BL, Purcell LC, Gerhardt KO, Mawhinney TP, Emerich DW. Alanine, not ammonia, is excreted from N2-fixing soybean nodule bacteroids. Proc Natl Acad Sci U S A 1998; 95:12038-42. [PMID: 9751786 PMCID: PMC21761 DOI: 10.1073/pnas.95.20.12038] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Symbiotic nitrogen fixation, the process whereby nitrogen-fixing bacteria enter into associations with plants, provides the major source of nitrogen for the biosphere. Nitrogenase, a bacterial enzyme, catalyzes the reduction of atmospheric dinitrogen to ammonium. In rhizobia-leguminous plant symbioses, the current model of nitrogen transfer from the symbiotic form of the bacteria, called a bacteroid, to the plant is that nitrogenase-generated ammonia diffuses across the bacteroid membrane and is assimilated into amino acids outside of the bacteroid. We purified soybean nodule bacteroids by a procedure that removed contaminating plant proteins and found that alanine was the major nitrogen-containing compound excreted. Bacteroids incubated in the presence of 15N2 excreted alanine highly enriched in 15N. The ammonium in these assays neither accumulated significantly nor was enriched in 15N. The results demonstrate that a transport mechanism rather than diffusion functions at this critical step of nitrogen transfer from the bacteroids to the plant host. Alanine may serve only as a transport species, but this would permit physiological separation of the transport of fixed nitrogen from other nitrogen metabolic functions commonly mediated through glutamate.
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Affiliation(s)
- J K Waters
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
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