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Berger A, Boscari A, Frendo P, Brouquisse R. Nitric oxide signaling, metabolism and toxicity in nitrogen-fixing symbiosis. JOURNAL OF EXPERIMENTAL BOTANY 2019; 70:4505-4520. [PMID: 30968126 DOI: 10.1093/jxb/erz159] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 03/28/2019] [Indexed: 05/13/2023]
Abstract
Interactions between legumes and rhizobia lead to the establishment of a symbiotic relationship characterized by the formation of a new organ, the nodule, which facilitates the fixation of atmospheric nitrogen (N2) by nitrogenase through the creation of a hypoxic environment. Significant amounts of nitric oxide (NO) accumulate at different stages of nodule development, suggesting that NO performs specific signaling and/or metabolic functions during symbiosis. NO, which regulates nodule gene expression, accumulates to high levels in hypoxic nodules. NO accumulation is considered to assist energy metabolism within the hypoxic environment of the nodule via a phytoglobin-NO-mediated respiration process. NO is a potent inhibitor of the activity of nitrogenase and other plant and bacterial enzymes, acting as a developmental signal in the induction of nodule senescence. Hence, key questions concern the relative importance of the signaling and metabolic functions of NO versus its toxic action and how NO levels are regulated to be compatible with nitrogen fixation functions. This review analyses these paradoxical roles of NO at various stages of symbiosis, and highlights the role of plant phytoglobins and bacterial hemoproteins in the control of NO accumulation.
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Silva LS, Alves MQ, Seabra AR, Carvalho HG. Characterization of plant glutamine synthetase S-nitrosation. Nitric Oxide 2019; 88:73-86. [PMID: 31026500 DOI: 10.1016/j.niox.2019.04.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Revised: 04/05/2019] [Accepted: 04/13/2019] [Indexed: 10/27/2022]
Abstract
The identification of S-nitrosated substrates and their target cysteine residues is a crucial step to understand the signaling functions of nitric oxide (NO) inside the cells. Here, we show that the key nitrogen metabolic enzyme glutamine synthetase (GS) is a S-nitrosation target in Medicago truncatula and characterize the molecular determinants and the effects of this NO-induced modification on different GS isoenzymes. We found that all the four M. truncatula GS isoforms are S-nitrosated, but despite the high percentage of amino acid identity between the four proteins, S-nitrosation only affects the activity of the plastid-located enzymes, leading to inactivation. A biotin-switch/mass spectrometry approach revealed that cytosolic and plastid-located GSs share an S-nitrosation site at a conserved cysteine residue, but the plastidic enzymes contain additional S-nitrosation sites at non-conserved cysteines, which are accountable for enzyme inactivation. By site-directed mutagenesis, we identified Cys369 as the regulatory S-nitrosation site relevant for the catalytic function of the plastid-located GS and an analysis of the structural environment of the SNO-targeted cysteines in cytosolic and plastid-located isoenzymes explains their differential regulation by S-nitrosation and elucidates the mechanistic by which S-nitrosation of Cys369 leads to enzyme inactivation. We also provide evidence that both the cytosolic and plastid-located GSs are endogenously S-nitrosated in leaves and root nodules of M. truncatula, supporting a physiological meaning for S-nitrosation. Taken together, these results provide new insights into the molecular details of the differential regulation of individual GS isoenzymes by NO-derived molecules and open new paths to explore the biological significance of the NO-mediated regulation of this essential metabolic enzyme.
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Affiliation(s)
- Liliana S Silva
- IBMC, Instituto de Biologia Molecular e Celular da Universidade do Porto; i3S, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Rua Alfredo Allen, 4200-135 Porto, Portugal; Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, s/n, 4169-007 Porto, Portugal; Centro de Investigação em Biodiversidade e Recursos Genéticos da Universidade do Porto, Campus de Vairão, Rua Padre Armando Quintas, No 7, 4485-661, Vairão, Portugal
| | - Mariana Q Alves
- IBMC, Instituto de Biologia Molecular e Celular da Universidade do Porto; i3S, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Rua Alfredo Allen, 4200-135 Porto, Portugal
| | - Ana R Seabra
- Centro de Investigação em Biodiversidade e Recursos Genéticos da Universidade do Porto, Campus de Vairão, Rua Padre Armando Quintas, No 7, 4485-661, Vairão, Portugal
| | - Helena G Carvalho
- IBMC, Instituto de Biologia Molecular e Celular da Universidade do Porto; i3S, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Rua Alfredo Allen, 4200-135 Porto, Portugal; Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, s/n, 4169-007 Porto, Portugal; Centro de Investigação em Biodiversidade e Recursos Genéticos da Universidade do Porto, Campus de Vairão, Rua Padre Armando Quintas, No 7, 4485-661, Vairão, Portugal.
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Blanquet P, Silva L, Catrice O, Bruand C, Carvalho H, Meilhoc E. Sinorhizobium meliloti Controls Nitric Oxide-Mediated Post-Translational Modification of a Medicago truncatula Nodule Protein. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2015; 28:1353-63. [PMID: 26422404 DOI: 10.1094/mpmi-05-15-0118-r] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Nitric oxide (NO) is involved in various plant-microbe interactions. In the symbiosis between soil bacterium Sinorhizobium meliloti and model legume Medicago truncatula, NO is required for an optimal establishment of the interaction but is also a signal for nodule senescence. Little is known about the molecular mechanisms responsible for NO effects in the legume-rhizobium interaction. Here, we investigate the contribution of the bacterial NO response to the modulation of a plant protein post-translational modification in nitrogen-fixing nodules. We made use of different bacterial mutants to finely modulate NO levels inside M. truncatula root nodules and to examine the consequence on tyrosine nitration of the plant glutamine synthetase, a protein responsible for assimilation of the ammonia released by nitrogen fixation. Our results reveal that S. meliloti possesses several proteins that limit inactivation of plant enzyme activity via NO-mediated post-translational modifications. This is the first demonstration that rhizobia can impact the course of nitrogen fixation by modulating the activity of a plant protein.
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Affiliation(s)
- Pauline Blanquet
- 1 Institut National de la Recherche Agronomique, Laboratoire des Interactions Plantes-Microorganismes, UMR441, Castanet-Tolosan, France
- 2 Centre National de la Recherche Scientifique, Laboratoire des Interactions Plantes-Microorganismes, UMR2594, Castanet-Tolosan, France; and
| | - Liliana Silva
- 3 Laboratório de Biologia Molecular da Assimilação do Azoto, Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
| | - Olivier Catrice
- 1 Institut National de la Recherche Agronomique, Laboratoire des Interactions Plantes-Microorganismes, UMR441, Castanet-Tolosan, France
- 2 Centre National de la Recherche Scientifique, Laboratoire des Interactions Plantes-Microorganismes, UMR2594, Castanet-Tolosan, France; and
| | - Claude Bruand
- 1 Institut National de la Recherche Agronomique, Laboratoire des Interactions Plantes-Microorganismes, UMR441, Castanet-Tolosan, France
- 2 Centre National de la Recherche Scientifique, Laboratoire des Interactions Plantes-Microorganismes, UMR2594, Castanet-Tolosan, France; and
| | - Helena Carvalho
- 3 Laboratório de Biologia Molecular da Assimilação do Azoto, Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
| | - Eliane Meilhoc
- 1 Institut National de la Recherche Agronomique, Laboratoire des Interactions Plantes-Microorganismes, UMR441, Castanet-Tolosan, France
- 2 Centre National de la Recherche Scientifique, Laboratoire des Interactions Plantes-Microorganismes, UMR2594, Castanet-Tolosan, France; and
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Silva LS, Seabra AR, Leitão JN, Carvalho HG. Possible role of glutamine synthetase of the prokaryotic type (GSI-like) in nitrogen signaling in Medicago truncatula. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2015; 240:98-108. [PMID: 26475191 DOI: 10.1016/j.plantsci.2015.09.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Revised: 08/31/2015] [Accepted: 09/01/2015] [Indexed: 06/05/2023]
Abstract
Genes containing domains related to glutamine synthetase of the prokaryotic type (GSI-like) are widespread in higher plants, but their function is currently unknown. To gain insights into the possible role of GSI-like proteins, we characterized the GSI-like gene family of Medicago truncatula and investigated the functionality of the encoded proteins. M. truncatula contains two-expressed GSI-like genes, MtGSIa and MtGSIb, encoding polypeptides of 454 and 453 amino acids, respectively. Heterologous complementation assays of a bacterial glnA mutant indicate that the proteins are not catalytically functional for glutamine synthesis. Gene expression was investigated by qRT-PCR and western blot analysis in different organs of the plant and under different nitrogen (N) regimes, revealing that both genes are preferentially expressed in roots and root nodules, and that their expression is influenced by the N-status of the plant. Analysis of transgenic plants expressing MtGSI-like-promoter-gusA fusion, indicate that the two genes are strongly expressed in the root pericycle, and interestingly, the expression is enhanced at the sites of nodule emergence being particularly strong in specific cells located in front of the protoxylem poles. Taken together, the results presented here support a role of GSI-like proteins in N sensing and/or signaling, probably operating at the interface between perception of the N-status and the developmental processes underlying both root nodule and lateral root formation. This study indicates that GSI-like genes may represent a novel class of molecular players of the N-mediated signaling events.
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Affiliation(s)
- Liliana S Silva
- Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal; Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Portugal
| | - Ana R Seabra
- Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal
| | - José N Leitão
- Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal
| | - Helena G Carvalho
- Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal.
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Seabra AR, Carvalho HG. Glutamine synthetase in Medicago truncatula, unveiling new secrets of a very old enzyme. FRONTIERS IN PLANT SCIENCE 2015; 6:578. [PMID: 26284094 PMCID: PMC4515544 DOI: 10.3389/fpls.2015.00578] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Accepted: 07/13/2015] [Indexed: 05/03/2023]
Abstract
Glutamine synthetase (GS) catalyzes the first step at which nitrogen is brought into cellular metabolism and is also involved in the reassimilation of ammonium released by a number of metabolic pathways. Due to its unique position in plant nitrogen metabolism, GS plays essential roles in all aspects of plant development, from germination to senescence, and is a key component of nitrogen use efficiency (NUE) and plant yield. Understanding the mechanisms regulating GS activity is therefore of utmost importance and a great effort has been dedicated to understand how GS is regulated in different plant species. The present review summarizes exciting recent developments concerning the structure and regulation of GS isoenzymes, using the model legume Medicago truncatula. These include the understanding of the structural determinants of both the cytosolic and plastid located isoenzymes, the existence of a seed-specific GS gene unique to M. truncatula and closely related species and the discovery that GS isoenzymes are regulated by nitric oxide at the post-translational level. The data is discussed and integrated with the potential roles of the distinct GS isoenzymes within the whole plant context.
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Affiliation(s)
| | - Helena G. Carvalho
- *Correspondence: Helena G. Carvalho, Laboratory of Molecular Biology of Nitrogen Assimilation, Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal,
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Torreira E, Seabra AR, Marriott H, Zhou M, Llorca Ó, Robinson CV, Carvalho HG, Fernández-Tornero C, Pereira PJB. The structures of cytosolic and plastid-located glutamine synthetases from Medicago truncatula reveal a common and dynamic architecture. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2014; 70:981-93. [PMID: 24699643 PMCID: PMC3975887 DOI: 10.1107/s1399004713034718] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Accepted: 12/27/2013] [Indexed: 11/21/2022]
Abstract
The first step of nitrogen assimilation in higher plants, the energy-driven incorporation of ammonia into glutamate, is catalyzed by glutamine synthetase. This central process yields the readily metabolizable glutamine, which in turn is at the basis of all subsequent biosynthesis of nitrogenous compounds. The essential role performed by glutamine synthetase makes it a prime target for herbicidal compounds, but also a suitable intervention point for the improvement of crop yields. Although the majority of crop plants are dicotyledonous, little is known about the structural organization of glutamine synthetase in these organisms and about the functional differences between the different isoforms. Here, the structural characterization of two glutamine synthetase isoforms from the model legume Medicago truncatula is reported: the crystallographic structure of cytoplasmic GSII-1a and an electron cryomicroscopy reconstruction of plastid-located GSII-2a. Together, these structural models unveil a decameric organization of dicotyledonous glutamine synthetase, with two pentameric rings weakly connected by inter-ring loops. Moreover, rearrangement of these dynamic loops changes the relative orientation of the rings, suggesting a zipper-like mechanism for their assembly into a decameric enzyme. Finally, the atomic structure of M. truncatula GSII-1a provides important insights into the structural determinants of herbicide resistance in this family of enzymes, opening new avenues for the development of herbicide-resistant plants.
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Affiliation(s)
- Eva Torreira
- Chemical and Physical Biology, Centro de Investigaciones Biológicas – CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Ana Rita Seabra
- Molecular Biology of Nitrogen Assimilation, IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
| | - Hazel Marriott
- Chemistry Research Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, England
| | - Min Zhou
- Chemistry Research Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, England
| | - Óscar Llorca
- Chemical and Physical Biology, Centro de Investigaciones Biológicas – CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Carol V. Robinson
- Chemistry Research Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, England
| | - Helena G. Carvalho
- Molecular Biology of Nitrogen Assimilation, IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
| | - Carlos Fernández-Tornero
- Chemical and Physical Biology, Centro de Investigaciones Biológicas – CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Pedro José Barbosa Pereira
- Biomolecular Structure Group, IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
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Seabra AR, Silva LS, Carvalho HG. Novel aspects of glutamine synthetase (GS) regulation revealed by a detailed expression analysis of the entire GS gene family of Medicago truncatula under different physiological conditions. BMC PLANT BIOLOGY 2013; 13:137. [PMID: 24053168 PMCID: PMC3848809 DOI: 10.1186/1471-2229-13-137] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2013] [Accepted: 09/16/2013] [Indexed: 05/20/2023]
Abstract
BACKGROUND Glutamine Synthetase (GS, EC 6.3.1.2) is a central enzyme in nitrogen metabolism, and a key component of nitrogen use efficiency (NUE) and plant yield and thus it is extremely important to understand how it is regulated in plants. Medicago truncatula provides an excellent model system to study GS, as it contain a very simple GS gene family comprising only four expressed genes, MtGS1a and MtGS1b encoding cytosolic polypeptides, and MtGS2a and MtGS2b encoding plastid-located enzymes. To identify new regulatory mechanisms controlling GS activity, we performed a detailed expression analysis of the entire GS gene family of M. truncatula in the major organs of the plant, over a time course of nodule or seed development and during a diurnal cycle. RESULTS Individual GS transcripts were quantified by qRT-PCR, and GS polypeptides and holoenzymes were evaluated by western blot and in-gel activity under native electrophoresis. These studies revealed that all four GS genes are differentially regulated in each organ of the plant, in a developmental manner, and identified new regulatory controls, which appear to be specific to certain metabolic contexts. Studies of the protein profiles showed that the GS polypeptides assemble into organ-specific protein complexes and suffer organ-specific post-translational modifications under defined physiological conditions. Our studies also reveal that GS expression and activity are modulated during a diurnal cycle. The biochemical properties of the four isoenzymes were determined and are discussed in relation to their function in the plant. CONCLUSIONS This work provides a comprehensive overview of GS expression and regulation in the model legume M. truncatula, contributing to a better understanding of the specific function of individual isoenzymes and to the identification of novel organ-specific post-translational mechanisms of GS regulation. We demonstrate that the GS proteins are modified and/or integrated into protein-complexes that assemble into a specific composition in particular organs of the plant. Taken together, the results presented here open new avenues to explore the regulatory mechanisms controlling GS activity in plants, a subject of major importance due to the crucial importance of the enzyme for plant growth and productivity.
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Affiliation(s)
- Ana R Seabra
- Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal
- Current address: Max Planck Group for Fungal Biodiversity, Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829 Köln, Germany
| | - Liliana S Silva
- Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal
| | - Helena G Carvalho
- Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal
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Silva L, Carvalho H. Possible role of glutamine synthetase in the NO signaling response in root nodules by contributing to the antioxidant defenses. FRONTIERS IN PLANT SCIENCE 2013; 4:372. [PMID: 24065976 PMCID: PMC3777134 DOI: 10.3389/fpls.2013.00372] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2013] [Accepted: 08/31/2013] [Indexed: 05/08/2023]
Abstract
Nitric oxide (NO) is emerging as an important regulatory player in the Rhizobium-legume symbiosis. The occurrence of NO during several steps of the symbiotic interaction suggests an important, but yet unknown, signaling role of this molecule for root nodule formation and functioning. The identification of the molecular targets of NO is key for the assembly of the signal transduction cascade that will ultimately help to unravel NO function. We have recently shown that the key nitrogen assimilatory enzyme glutamine synthetase (GS) is a molecular target of NO in root nodules of Medicago truncatula, being post-translationally regulated by tyrosine nitration in relation to nitrogen fixation. In functional nodules of M. truncatula NO formation has been located in the bacteroid containing cells of the fixation zone, where the ammonium generated by bacterial nitrogenase is released to the plant cytosol and assimilated into the organic pools by plant GS. We propose that the NO-mediated GS post-translational inactivation is connected to nitrogenase inhibition induced by NO and is related to metabolite channeling to boost the nodule antioxidant defenses. Glutamate, a substrate for GS activity is also the precursor for the synthesis of glutathione (GSH), which is highly abundant in root nodules of several plant species and known to play a major role in the antioxidant defense participating in the ascorbate/GSH cycle. Existing evidence suggests that upon NO-mediated GS inhibition, glutamate could be channeled for the synthesis of GSH. According to this hypothesis, GS would be involved in the NO-signaling responses in root nodules and the NO-signaling events would meet the nodule metabolic pathways to provide an adaptive response to the inhibition of symbiotic nitrogen fixation by reactive nitrogen species.
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Affiliation(s)
| | - Helena Carvalho
- *Correspondence: Helena Carvalho, Laboratório de Biologia Molecular da Assimilação do Azoto, Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal e-mail:
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Melo PM, Silva LS, Ribeiro I, Seabra AR, Carvalho HG. Glutamine synthetase is a molecular target of nitric oxide in root nodules of Medicago truncatula and is regulated by tyrosine nitration. PLANT PHYSIOLOGY 2011; 157:1505-17. [PMID: 21914816 PMCID: PMC3252174 DOI: 10.1104/pp.111.186056] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2011] [Accepted: 09/12/2011] [Indexed: 05/20/2023]
Abstract
Nitric oxide (NO) is emerging as an important regulatory player in the Rhizobium-legume symbiosis, but its biological role in nodule functioning is still far from being understood. To unravel the signal transduction cascade and ultimately NO function, it is necessary to identify its molecular targets. This study provides evidence that glutamine synthetase (GS), a key enzyme for root nodule metabolism, is a molecular target of NO in root nodules of Medicago truncatula, being regulated by tyrosine (Tyr) nitration in relation to active nitrogen fixation. In vitro studies, using purified recombinant enzymes produced in Escherichia coli, demonstrated that the M. truncatula nodule GS isoenzyme (MtGS1a) is subjected to NO-mediated inactivation through Tyr nitration and identified Tyr-167 as the regulatory nitration site crucial for enzyme inactivation. Using a sandwich enzyme-linked immunosorbent assay, it is shown that GS is nitrated in planta and that its nitration status changes in relation to active nitrogen fixation. In ineffective nodules and in nodules fed with nitrate, two conditions in which nitrogen fixation is impaired and GS activity is reduced, a significant increase in nodule GS nitration levels was observed. Furthermore, treatment of root nodules with the NO donor sodium nitroprusside resulted in increased in vivo GS nitration accompanied by a reduction in GS activity. Our results support a role of NO in the regulation of nitrogen metabolism in root nodules and places GS as an important player in the process. We propose that the NO-mediated GS posttranslational inactivation is related to metabolite channeling to boost the nodule antioxidant defenses in response to NO.
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Planchet E, Rannou O, Ricoult C, Boutet-Mercey S, Maia-Grondard A, Limami AM. Nitrogen metabolism responses to water deficit act through both abscisic acid (ABA)-dependent and independent pathways in Medicago truncatula during post-germination. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:605-15. [PMID: 20943826 PMCID: PMC3003807 DOI: 10.1093/jxb/erq294] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The modulation of primary nitrogen metabolism by water deficit through ABA-dependent and ABA-independent pathways was investigated in the model legume Medicago truncatula. Growth and glutamate metabolism were followed in young seedlings growing for short periods in darkness and submitted to a moderate water deficit (simulated by polyethylene glycol; PEG) or treated with ABA. Water deficit induced an ABA accumulation, a reduction of axis length in an ABA-dependent manner, and an inhibition of water uptake/retention in an ABA-independent manner. The PEG-induced accumulation of free amino acids (AA), principally asparagine and proline, was mimicked by exogenous ABA treatment. This suggests that AA accumulation under water deficit may be an ABA-induced osmolyte accumulation contributing to osmotic adjustment. Alternatively, this accumulation could be just a consequence of a decreased nitrogen demand caused by reduced extension, which was triggered by water deficit and exogenous ABA treatment. Several enzyme activities involved in glutamate metabolism and genes encoding cytosolic glutamine synthetase (GS1b; EC 6.3.1.2.), glutamate dehydrogenase (GDH3; EC 1.4.1.1.), and asparagine synthetase (AS; EC 6.3.1.1.) were up-regulated by water deficit but not by ABA, except for a gene encoding Δ(1)-pyrroline-5-carboxylate synthetase (P5CS; EC not assigned). Thus, ABA-dependent and ABA-independent regulatory systems would seem to exist, differentially controlling development, water content, and nitrogen metabolism under water deficit.
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Affiliation(s)
- Elisabeth Planchet
- University of Angers, UMR1191 Seed Molecular Physiology IFR 149 QUASAV, 2 Bd Lavoisier, F-49045 Angers Cedex, France.
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Simon B, Sengupta-Gopalan C. The 3' untranslated region of the two cytosolic glutamine synthetase (GS(1)) genes in alfalfa (Medicago sativa) regulates transcript stability in response to glutamine. PLANTA 2010; 232:1151-62. [PMID: 20706735 DOI: 10.1007/s00425-010-1247-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2010] [Accepted: 07/28/2010] [Indexed: 05/20/2023]
Abstract
Glutamine synthetase (GS) catalyzes the ATP-dependent condensation of ammonia with glutamate to produce glutamine. The GS enzyme is located either in the chloroplast (GS(2)) or in the cytoplasm (GS(1)). GS(1) is encoded by a small gene family and the members exhibit differential expression pattern mostly attributed to transcriptional regulation. Based on our recent finding that a soybean GS(1) gene, Gmglnβ ( 1 ) is subject to its 3'UTR-mediated post-transcriptional regulation as a transgene in alfalfa (Medicago sativa) we have raised the question of whether the 3'UTR-mediated transcript destabilization is a more universal phenomenon. Gene constructs consisting of the CaMV35S promoter driving the reporter gene, GUS, followed by the 3'UTRs of the two alfalfa GS(1) genes, MsGSa and MsGSb, were introduced into alfalfa and tobacco. The analysis of these transformants suggests that while both the 3'UTRs promote transcript turnover, the MsGSb 3'UTR is more effective than the MsGSa 3'UTR. However, both the 3'UTRs along with Gmglnβ ( 1 ) 3'UTR respond to nitrate as a trigger in transcript turnover. More detailed analysis points to glutamine rather than nitrate as the mediator of transcript turnover. Our data suggests that the 3'UTR-mediated regulation of GS(1) genes at the level of transcript turnover is probably universal and is used for fine-tuning the expression in keeping with the availability of the substrates.
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Affiliation(s)
- Bindu Simon
- New Mexico State University, Las Cruces, NM 88003, USA
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De Michele R, Formentin E, Todesco M, Toppo S, Carimi F, Zottini M, Barizza E, Ferrarini A, Delledonne M, Fontana P, Lo Schiavo F. Transcriptome analysis of Medicago truncatula leaf senescence: similarities and differences in metabolic and transcriptional regulations as compared with Arabidopsis, nodule senescence and nitric oxide signalling. THE NEW PHYTOLOGIST 2009; 181:563-75. [PMID: 19021865 DOI: 10.1111/j.1469-8137.2008.02684.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Here, for the first time, a comprehensive transcriptomics study is presented of leaf senescence in the legume model Medicago truncatula, providing a broad overview of differentially expressed transcripts involved in this process. The cDNA-amplification fragment length polymorphism (AFLP) technique was used to identify > 500 genes, which were cloned and sorted into functional categories according to their gene ontology annotation. Comparison between the datasets of Arabidopsis and M. truncatula leaf senescence reveals common physiological events but differences in the nitrogen metabolism and in transcriptional regulation. In addition, it was observed that a minority of the genes regulated during leaf senescence were equally involved in other processes leading to programmed cell death, such as nodule senescence and nitric oxide signalling. This study provides a wide transcriptional profile for the comprehension of key events of leaf senescence in M. truncatula and highlights a possible regulative role for MADS box transcription factors in the terminal phases of the process.
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Affiliation(s)
- Roberto De Michele
- Dipartimento di Biologia, Università degli Studi di Padova, Via Ugo Bassi 58/B, I-35131 Padova, Italy
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Bernard SM, Habash DZ. The importance of cytosolic glutamine synthetase in nitrogen assimilation and recycling. THE NEW PHYTOLOGIST 2009; 182:608-620. [PMID: 19422547 DOI: 10.1111/j.1469-8137.2009.02823.x] [Citation(s) in RCA: 285] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Glutamine synthetase assimilates ammonium into amino acids, thus it is a key enzyme for nitrogen metabolism. The cytosolic isoenzymes of glutamine synthetase assimilate ammonium derived from primary nitrogen uptake and from various internal nitrogen recycling pathways. In this way, cytosolic glutamine synthetase is crucial for the remobilization of protein-derived nitrogen. Cytosolic glutamine synthetase is encoded by a small family of genes that are well conserved across plant species. Members of the cytosolic glutamine synthetase gene family are regulated in response to plant nitrogen status, as well as to environmental cues, such as nitrogen availability and biotic/abiotic stresses. The complex regulation of cytosolic glutamine synthetase at the transcriptional to post-translational levels is key to the establishment of a specific physiological role for each isoenzyme. The diverse physiological roles of cytosolic glutamine synthetase isoenzymes are important in relation to current agricultural and ecological issues.
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Affiliation(s)
- Stéphanie M Bernard
- Earth Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, USA
| | - Dimah Z Habash
- Plant Science Department, Centre for Crop Genetic Improvement, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
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Anzala F, Morère-Le Paven MC, Fournier S, Rondeau D, Limami AM. Physiological and molecular aspects of aspartate-derived amino acid metabolism during germination and post-germination growth in two maize genotypes differing in germination efficiency. JOURNAL OF EXPERIMENTAL BOTANY 2006; 57:645-53. [PMID: 16415333 DOI: 10.1093/jxb/erj054] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The Asp-derived amino acid pathway has been studied during the early stages of development in two maize genotypes, Io and F2, differing in germination efficiency and post-germination growth. In both genotypes expression of Ask2 (monofunctional Asp-kinase-2), Akh1 and Akh2 (bifunctional Asp-kinase-homo-Ser dehydrogenase-1 and 2), increased throughout germination and post-germination growth, suggesting a developmental regulation, whereas Ask1 (monofunctional Asp-kinase-1) was expressed constitutively. The major difference between Io and F2 concerned genes encoding bifunctional enzymes, particularly Akh2, the expression of which was dramatically low in F2. 15N-Asp labelling showed differences in in vivo Asp-kinase activities between the genotypes studied. Asp flux through the Met/Thr branches was higher in Io than in F2, while the latter exhibited a higher flux of Asp through the Lys branch. Physiological results, together with the higher Akh2 expression in Io, suggest that bifunctional enzyme activity, favourable to Met/Thr, was higher in Io than in F2 and that the monofunctional pathway was boosted in F2 because of the lower competition by the bifunctional pathway, thus allowing for higher flux of Asp through the Lys branch. In conclusion, it is suggested that F2 germination and post-germination growth might have been partially inhibited due to a limitation in Met and Thr availability. A negative physiological effect related to Lys accumulation in F2 is also discussed.
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Affiliation(s)
- Fabiola Anzala
- UMR INRA 1191, Physiologie Moléculaire des Semences, University of Angers, 2 Bd Lavoisier, F-49045 Angers cedex 01, France
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Sauviac L, Niebel A, Boisson-Dernier A, Barker DG, de Carvalho-Niebel F. Transcript enrichment of Nod factor-elicited early nodulin genes in purified root hair fractions of the model legume Medicago truncatula. JOURNAL OF EXPERIMENTAL BOTANY 2005; 56:2507-13. [PMID: 16043451 DOI: 10.1093/jxb/eri244] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
This article describes an efficient procedure to study Nod factor-induced gene expression in root hairs of the model legume Medicago truncatula. By developing an improved method of fracturing frozen root hairs, it has been possible to obtain a highly purified root hair fraction from M. truncatula seedlings yielding sufficient RNA for real-time quantitative RT-PCR expression analysis. After Nod factor treatment it was possible to detect up to 100-fold increases of MtENOD11 and pMtENOD11-gus transcript levels in root hair RNA. This corresponds to 5-7-fold higher induction levels than for entire root tissue preparations. Furthermore, the use of these enriched RNA samples has revealed for the first time a very significant induction (30-fold) of the MtENOD40 gene in root hairs in response to Nod factors. It is concluded that the rapid and convenient procedure described here will be particularly useful for detecting tissue-specific low-level gene expression in root hairs responding to Rhizobium Nod factors or other exogenous signals.
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Affiliation(s)
- Laurent Sauviac
- Laboratory of Plant Microbe Interactions (LIPM), CNRS-INRA, BP52627, F-31320 Castanet-Tolosan, France
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Carvalho HG, Lopes-Cardoso IA, Lima LM, Melo PM, Cullimore JV. Nodule-specific modulation of glutamine synthetase in transgenic Medicago truncatula leads to inverse alterations in asparagine synthetase expression. PLANT PHYSIOLOGY 2003; 133:243-52. [PMID: 12970490 PMCID: PMC196601 DOI: 10.1104/pp.102.017830] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2002] [Revised: 02/17/2003] [Accepted: 05/07/2003] [Indexed: 05/18/2023]
Abstract
Transgenic Medicago truncatula plants were produced harboring chimeric gene constructs of the glutamine synthetase (GS) cDNA clones (MtGS1a or MtGS1b) fused in sense or antisense orientation to the nodule-specific leghemoglobin promoter Mtlb1. A series of transgenic plants were obtained showing a 2- to 4-fold alteration in nodule GS activity when compared with control plants. Western and northern analyses revealed that the increased or decreased levels of GS activity correlate with the amount of cytosolic GS polypeptides and transcripts present in the nodule extracts. An analysis of the isoenzyme composition showed that the increased or decreased levels of GS activity were attributable to major changes in the homo-octameric isoenzyme GS1a. Nodules of plants transformed with antisense GS constructs showed an increase in the levels of both asparagine synthetase (AS) polypeptides and transcripts when compared with untransformed control plants, whereas the sense GS transformants showed decreased AS transcript levels but polypeptide levels similar to control plants. The polypeptide abundance of other nitrogen metabolic enzymes NADH-glutamic acid synthase and aspartic acid amino-transferase as well as those of major carbon metabolic enzymes phosphoenolpyruvate carboxylase, carbonic anhydrase, and sucrose synthase were not affected by the GS-gene manipulations. Increased levels of AS polypeptides and transcripts were also transiently observed in nodules by inhibiting GS activity with phosphinothricin. Taken together, the results presented here suggest that GS activity negatively regulates the level of AS in root nodules of M. truncatula. The potential role of AS in assimilating ammonium when GS becomes limiting is discussed.
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Affiliation(s)
- Helena G Carvalho
- Instituto de Biologia Molecular e Celular, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
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Melo PM, Lima LM, Santos IM, Carvalho HG, Cullimore JV. Expression of the plastid-located glutamine synthetase of Medicago truncatula. Accumulation of the precursor in root nodules reveals an in vivo control at the level of protein import into plastids. PLANT PHYSIOLOGY 2003; 132:390-9. [PMID: 12746544 PMCID: PMC166984 DOI: 10.1104/pp.102.016675] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2002] [Revised: 12/04/2002] [Accepted: 02/05/2003] [Indexed: 05/18/2023]
Abstract
In this paper, we report the cloning and characterization of the plastid-located glutamine synthetase (GS) of Medicago truncatula Gaertn (MtGS2). A cDNA was isolated encoding a GS2 precursor polypeptide of 428 amino acids composing an N-terminal transit peptide of 49 amino acids. Expression analysis, by Westerns and by northern hybridization, revealed that MtGS2 is expressed in both photosynthetic and non-photosynthetic organs. Both transcripts and proteins of MtGS2 were detected in substantial amounts in root nodules, suggesting that the enzyme might be performing some important role in this organ. Surprisingly, about 40% of the plastid GS in nodules occurred in the non-processed precursor form (preGS2). This precursor was not detected in any other organ studied and moreover was not observed in non-fixing nodules. Cellular fractionation of nodule extracts revealed that preGS2 is associated with the plastids and that it is catalytically inactive. Immunogold electron microscopy revealed a frequent coincidence of GS with the plastid envelope. Taken together, these results suggest a nodule-specific accumulation of the GS2 precursor at the surface of the plastids in nitrogen-fixing nodules. These results may reflect a regulation of GS2 activity in relation to nitrogen fixation at the level of protein import into nodule plastids.
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Affiliation(s)
- Paula M Melo
- Instituto de Biologia Molecular e Celular, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal
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