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Fonseca-García C, Nava N, Lara M, Quinto C. An NADPH oxidase regulates carbon metabolism and the cell cycle during root nodule symbiosis in common bean (Phaseolus vulgaris). BMC PLANT BIOLOGY 2021; 21:274. [PMID: 34130630 PMCID: PMC8207584 DOI: 10.1186/s12870-021-03060-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Accepted: 05/20/2021] [Indexed: 05/11/2023]
Abstract
BACKGROUND Rhizobium-legume symbiosis is a specific, coordinated interaction that results in the formation of a root nodule, where biological nitrogen fixation occurs. NADPH oxidases, or Respiratory Burst Oxidase Homologs (RBOHs) in plants, are enzymes that generate superoxide (O2 •-). Superoxide produces other reactive oxygen species (ROS); these ROS regulate different stages of mutualistic interactions. For example, changes in ROS levels are thought to induce ROS scavenging, cell wall remodeling, and changes in phytohormone homeostasis during symbiotic interactions. In common bean (Phaseolus vulgaris), PvRbohB plays a key role in the early stages of nodulation. RESULTS In this study, to explore the role of PvRbohB in root nodule symbiosis, we analyzed transcriptomic data from the roots of common bean under control conditions (transgenic roots without construction) and roots with downregulated expression of PvRbohB (by RNA interference) non-inoculated and inoculated with R. tropici. Our results suggest that ROS produced by PvRBOHB play a central role in infection thread formation and nodule organogenesis through crosstalk with flavonoids, carbon metabolism, cell cycle regulation, and the plant hormones auxin and cytokinin during the early stages of this process. CONCLUSIONS Our findings provide important insight into the multiple roles of ROS in regulating rhizobia-legume symbiosis.
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Affiliation(s)
- Citlali Fonseca-García
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, Cuernavaca, Morelos, Colonia Chamilpa Mexico
| | - Noreide Nava
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, Cuernavaca, Morelos, Colonia Chamilpa Mexico
| | - Miguel Lara
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, Cuernavaca, Morelos, Colonia Chamilpa Mexico
| | - Carmen Quinto
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, Cuernavaca, Morelos, Colonia Chamilpa Mexico
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Liu A, Contador CA, Fan K, Lam HM. Interaction and Regulation of Carbon, Nitrogen, and Phosphorus Metabolisms in Root Nodules of Legumes. FRONTIERS IN PLANT SCIENCE 2018; 9:1860. [PMID: 30619423 PMCID: PMC6305480 DOI: 10.3389/fpls.2018.01860] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 11/30/2018] [Indexed: 05/19/2023]
Abstract
Members of the plant family Leguminosae (Fabaceae) are unique in that they have evolved a symbiotic relationship with rhizobia (a group of soil bacteria that can fix atmospheric nitrogen). Rhizobia infect and form root nodules on their specific host plants before differentiating into bacteroids, the symbiotic form of rhizobia. This complex relationship involves the supply of C4-dicarboxylate and phosphate by the host plants to the microsymbionts that utilize them in the energy-intensive process of fixing atmospheric nitrogen into ammonium, which is in turn made available to the host plants as a source of nitrogen, a macronutrient for growth. Although nitrogen-fixing bacteroids are no longer growing, they are metabolically active. The symbiotic process is complex and tightly regulated by both the host plants and the bacteroids. The metabolic pathways of carbon, nitrogen, and phosphate are heavily regulated in the host plants, as they need to strike a fine balance between satisfying their own needs as well as those of the microsymbionts. A network of transporters for the various metabolites are responsible for the trafficking of these essential molecules between the two partners through the symbiosome membrane (plant-derived membrane surrounding the bacteroid), and these are in turn regulated by various transcription factors that control their expressions under different environmental conditions. Understanding this complex process of symbiotic nitrogen fixation is vital in promoting sustainable agriculture and enhancing soil fertility.
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Affiliation(s)
- Ailin Liu
- Centre for Soybean Research, State Key Laboratory of Agrobiotechnology, Shatin, Hong Kong
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong
| | - Carolina A. Contador
- Centre for Soybean Research, State Key Laboratory of Agrobiotechnology, Shatin, Hong Kong
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong
| | - Kejing Fan
- Centre for Soybean Research, State Key Laboratory of Agrobiotechnology, Shatin, Hong Kong
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong
| | - Hon-Ming Lam
- Centre for Soybean Research, State Key Laboratory of Agrobiotechnology, Shatin, Hong Kong
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong
- *Correspondence: Hon-Ming Lam,
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3
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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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4
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Li X, Xi H, Sun X, Yang Y, Yang S, Zhou Y, Zhou X, Yang Y. Comparative proteomics exploring the molecular mechanism of eutrophic water purification using water hyacinth (Eichhornia crassipes). ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2015; 22:8643-8658. [PMID: 25563831 DOI: 10.1007/s11356-014-4020-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Accepted: 12/16/2014] [Indexed: 06/04/2023]
Abstract
Eutrophication is a serious threat to ecosystem stability and use of water resources worldwide. Accordingly, physical, chemical, and biological technologies have been developed to treat eutrophic water. Phytoremediation has attracted a great deal of attention, and water hyacinth (Eichhornia crassipes) is regarded as one of the best plants for purification of eutrophic water. Previous studies have shown that water hyacinths remove nitrogen (N) and phosphorus (P) via diverse processes and that they can inhibit the growth of algae. However, the molecular mechanisms responsible for these processes, especially the role of proteins, are unknown. In this study, we applied a proteomics approach to investigate the protein dynamics of water hyacinth under three eutrophication levels. The results suggested that proteins with various functions, including response to stress, N and P metabolic pathways, synthesis and secretion, photosynthesis, biosynthesis, and energy metabolism, were involved in regulating water hyacinth to endure the excess-nutrient environment, remove N and P, and inhibit algal growth. The results help us understand the mechanism of purification of eutrophic water by water hyacinth and supply a theoretical basis for improving techniques for phytoremediation of polluted water.
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Affiliation(s)
- Xiong Li
- Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, People's Republic of China
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Dragićević M, Todorović S, Bogdanović M, Filipović B, Mišić D, Simonović A. Knockout mutants as a tool to identify the subunit composition of Arabidopsis glutamine synthetase isoforms. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2014; 79:1-9. [PMID: 24657507 DOI: 10.1016/j.plaphy.2014.02.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Accepted: 02/25/2014] [Indexed: 06/03/2023]
Abstract
Glutamine synthetase (GS) is a key enzyme in nitrogen assimilation, which catalyzes the formation of glutamine from ammonia and glutamate. Plant GS isoforms are multimeric enzymes, recently shown to be decamers. The Arabidopsis genome encodes five cytosolic (GS1) proteins labeled as GLN1;1 through GLN1;5 and one chloroplastic (GS2) isoform, GLN2;0. However, as many as 11 GS activity bands were resolved from different Arabidopsis tissues by Native PAGE and activity staining. Western analysis showed that all 11 isoforms are composed exclusively of 40 kDa GS1 subunits. Of five GS1 genes, only GLN1;1, GLN1;2 and GLN1;3 transcripts accumulated to significant levels in vegetative tissues, indicating that only subunits encoded by these three genes produce the 11-band zymogram. Even though the GS2 gene also had significant expression, the corresponding activity was not detected, probably due to inactivation. To resolve the subunit composition of 11 active GS1 isoforms, homozygous knockout mutants deficient in the expression of different GS1 genes were selected from the progeny of T-DNA insertional SALK and SAIL lines. Comparison of GS isoenzyme patterns of the selected GS1 knockout mutants indicated that all of the detected isoforms consist of varying proportions of GLN1;1, GLN1;2 and GLN1;3 subunits, and that GLN1;1 and GLN1;3, as well as GLN1;2 and GLN1;3 and possibly GLN1;1 and GLN1;2 proteins combine in all proportions to form active homo- and heterodecamers.
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Affiliation(s)
- Milan Dragićević
- Institute for Biological Research "Siniša Stanković", Department for Plant Physiology, University of Belgrade, Bulevar Despota Stefana 142, 11060 Belgrade, Serbia.
| | - Slađana Todorović
- Institute for Biological Research "Siniša Stanković", Department for Plant Physiology, University of Belgrade, Bulevar Despota Stefana 142, 11060 Belgrade, Serbia.
| | - Milica Bogdanović
- Institute for Biological Research "Siniša Stanković", Department for Plant Physiology, University of Belgrade, Bulevar Despota Stefana 142, 11060 Belgrade, Serbia.
| | - Biljana Filipović
- Institute for Biological Research "Siniša Stanković", Department for Plant Physiology, University of Belgrade, Bulevar Despota Stefana 142, 11060 Belgrade, Serbia.
| | - Danijela Mišić
- Institute for Biological Research "Siniša Stanković", Department for Plant Physiology, University of Belgrade, Bulevar Despota Stefana 142, 11060 Belgrade, Serbia.
| | - Ana Simonović
- Institute for Biological Research "Siniša Stanković", Department for Plant Physiology, University of Belgrade, Bulevar Despota Stefana 142, 11060 Belgrade, Serbia.
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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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Li QG, Zhang L, Li C, Dunwell JM, Zhang YM. Comparative Genomics Suggests That an Ancestral Polyploidy Event Leads to Enhanced Root Nodule Symbiosis in the Papilionoideae. Mol Biol Evol 2013; 30:2602-11. [DOI: 10.1093/molbev/mst152] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Ortega JL, Wilson OL, Sengupta-Gopalan C. The 5' untranslated region of the soybean cytosolic glutamine synthetase β(1) gene contains prokaryotic translation initiation signals and acts as a translational enhancer in plants. Mol Genet Genomics 2012; 287:881-93. [PMID: 23080263 PMCID: PMC3881598 DOI: 10.1007/s00438-012-0724-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2012] [Accepted: 10/04/2012] [Indexed: 01/03/2023]
Abstract
Glutamine synthetase (GS) catalyzes the synthesis of glutamine from glutamate and ammonia. In plants, it occurs as two major isoforms, a cytosolic form (GS(1)) and a nuclear encoded chloroplastic form. The focus of this paper is to determine the role of the 5'UTR of a GS(1) gene. GS(1) gene constructs with and without its 5' and 3' UTRs, driven by a constitutive promoter, were agroinfiltrated into tobacco leaves and the tissues were analyzed for both transgene transcript and protein accumulation. The constructs were also tested in an in vitro transcription/translation system and in Escherichia coli. Our results showed that while the 3'UTR functioned in the destabilization of the transcript, the 5'UTR acted as a translation enhancer in plant cells but not in the in vitro translation system. The 5'UTR of the GS(1) gene when placed in front of a reporter gene (uidA), showed a 20-fold increase in the level of GUS expression in agroinfiltrated leaves when compared to the same gene construct without the 5'UTR. The 5'UTR-mediated translational enhancement is probably another step in the regulation of GS in plants. The presence of the GS(1) 5'UTR in front of the GS(1) coding region allowed for its translation in E. coli suggesting the commonality of the translation initiation mechanism for this gene between plants and bacteria.
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Affiliation(s)
- Jose Luis Ortega
- Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, NM 88003, USA
| | - Olivia L. Wilson
- Molecular Biology Graduate Program, New Mexico State University, Las Cruces, NM 88003, USA
| | - Champa Sengupta-Gopalan
- Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, NM 88003, USA,
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Betti M, García-Calderón M, Pérez-Delgado CM, Credali A, Estivill G, Galván F, Vega JM, Márquez AJ. Glutamine synthetase in legumes: recent advances in enzyme structure and functional genomics. Int J Mol Sci 2012; 13:7994-8024. [PMID: 22942686 PMCID: PMC3430217 DOI: 10.3390/ijms13077994] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Revised: 06/18/2012] [Accepted: 06/19/2012] [Indexed: 01/12/2023] Open
Abstract
Glutamine synthetase (GS) is the key enzyme involved in the assimilation of ammonia derived either from nitrate reduction, N(2) fixation, photorespiration or asparagine breakdown. A small gene family is encoding for different cytosolic (GS1) or plastidic (GS2) isoforms in legumes. We summarize here the recent advances carried out concerning the quaternary structure of GS, as well as the functional relationship existing between GS2 and processes such as nodulation, photorespiration and water stress, in this latter case by means of proline production. Functional genomic analysis using GS2-minus mutant reveals the key role of GS2 in the metabolic control of the plants and, more particularly, in carbon metabolism.
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Affiliation(s)
- Marco Betti
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +34-95-4556917; Fax: +34-95-4626853
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García-Calderón M, Chiurazzi M, Espuny MR, Márquez AJ. Photorespiratory metabolism and nodule function: behavior of Lotus japonicus mutants deficient in plastid glutamine synthetase. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2012; 25:211-219. [PMID: 22007601 DOI: 10.1094/mpmi-07-11-0200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Two photorespiratory mutants of Lotus japonicus deficient in plastid glutamine synthetase (GS(2)) were examined for their capacity to establish symbiotic association with Mesorhizobium loti bacteria. Biosynthetic glutamine synthetase (GS) activity was reduced by around 40% in crude nodule extracts from mutant plants as compared with the wild type (WT). Western blot analysis further confirmed the lack of GS(2) polypeptide in mutant nodules. The decrease in GS activity affected the nodular carbon metabolism under high CO(2) (suppressed photorespiration) conditions, although mutant plants were able to form nodules and fix atmospheric nitrogen. However, when WT and mutant plants were transferred to an ordinary air atmosphere (photorespiratory active conditions) the nodulation process and nitrogen fixation were substantially affected, particularly in mutant plants. The number and fresh weight of mutant nodules as well as acetylene reduction activity showed a strong inhibition compared with WT plants. Optical microscopy studies from mutant plant nodules revealed the anticipated senescence phenotype linked to an important reduction in starch and sucrose levels. These results show that, in Lotus japonicus, photorespiration and, particularly, GS(2) deficiency result in profound limitations in carbon metabolism that affect the nodulation process and nitrogen fixation.
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Seabra AR, Vieira CP, Cullimore JV, Carvalho HG. Medicago truncatula contains a second gene encoding a plastid located glutamine synthetase exclusively expressed in developing seeds. BMC PLANT BIOLOGY 2010; 10:183. [PMID: 20723225 PMCID: PMC3095313 DOI: 10.1186/1471-2229-10-183] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Accepted: 08/19/2010] [Indexed: 05/20/2023]
Abstract
BACKGROUND Nitrogen is a crucial nutrient that is both essential and rate limiting for plant growth and seed production. Glutamine synthetase (GS), occupies a central position in nitrogen assimilation and recycling, justifying the extensive number of studies that have been dedicated to this enzyme from several plant sources. All plants species studied to date have been reported as containing a single, nuclear gene encoding a plastid located GS isoenzyme per haploid genome. This study reports the existence of a second nuclear gene encoding a plastid located GS in Medicago truncatula. RESULTS This study characterizes a new, second gene encoding a plastid located glutamine synthetase (GS2) in M. truncatula. The gene encodes a functional GS isoenzyme with unique kinetic properties, which is exclusively expressed in developing seeds. Based on molecular data and the assumption of a molecular clock, it is estimated that the gene arose from a duplication event that occurred about 10 My ago, after legume speciation and that duplicated sequences are also present in closely related species of the Vicioide subclade. Expression analysis by RT-PCR and western blot indicate that the gene is exclusively expressed in developing seeds and its expression is related to seed filling, suggesting a specific function of the enzyme associated to legume seed metabolism. Interestingly, the gene was found to be subjected to alternative splicing over the first intron, leading to the formation of two transcripts with similar open reading frames but varying 5' UTR lengths, due to retention of the first intron. To our knowledge, this is the first report of alternative splicing on a plant GS gene. CONCLUSIONS This study shows that Medicago truncatula contains an additional GS gene encoding a plastid located isoenzyme, which is functional and exclusively expressed during seed development. Legumes produce protein-rich seeds requiring high amounts of nitrogen, we postulate that this gene duplication represents a functional innovation of plastid located GS related to storage protein accumulation exclusive to legume seed metabolism.
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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
| | - Cristina P Vieira
- Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal
| | - Julie V Cullimore
- Laboratoire des Interactions Plantes-Microorganismes, Institut National de la Recherche Agronomique - Centre National de la Recherche Scientifique, Boite Postale 52627, 31326 Castanet-Tolosan Cedex, France
| | - 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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Broyart C, Fontaine JX, Molinié R, Cailleu D, Tercé-Laforgue T, Dubois F, Hirel B, Mesnard F. Metabolic profiling of maize mutants deficient for two glutamine synthetase isoenzymes using 1H-NMR-based metabolomics. PHYTOCHEMICAL ANALYSIS : PCA 2010; 21:102-9. [PMID: 19866455 DOI: 10.1002/pca.1177] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
INTRODUCTION Maize mutants deficient for the expression of two genes encoding cytosolic glutamine synthetase (GS) isoenzymes GS1.3 and GS1.4 displayed reduced kernel number and kernel size, respectively, the effect of the mutation being cumulative in the double mutant. However, at maturity, shoot biomass production was not modified in all the mutants, indicating that the reaction catalysed by the enzyme is specifically involved in the control of grain yield. OBJECTIVE To examine the physiological impact of the GS mutations on the leaf metabolic profile during the kernel filling period, during which nitrogen is remobilized from the shoots to be further exported to the kernels. METHODOLOGY An (1)H-NMR spectroscopy metabolomic was applied to the investigation of metabolic change of the gln1.3, gln1.4 and gln1.3/1.4 double mutant. RESULTS In the three GS mutants, an increase in the amount of several N-containing metabolites such as asparagine, alanine, threonine and phophatidylcholine was observed whatever the level of nitrogen fertilisation. In addition, we found an accumulation of phenylalanine and tyrosine, two metabolites involved the primary steps of the phenylpropanoid pathway. CONCLUSION Changes in the metabolic profile of the GS mutants suggest that, when cytosolic GS activity is strongly reduced, either alternative metabolic pathways participate in the reassimilation of ammonium released during leaf protein remobilization or that premature leaf senescence is induced when kernel set and kernel filling are affected. The accumulation of phenylalanine and tyrosine in the mutant plants indicates that lignin biosynthesis is altered, thus possibly affecting ear development.
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Affiliation(s)
- Caroline Broyart
- EA 3900-BioPI Biologie des Plantes et Contrôle des Insectes Ravageurs, Faculté de Pharmacie, 1, rue des Louvels et Faculté des Sciences, 33, rue Saint Leu, 80037 Amiens cedex 1, France
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14
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Seabra AR, Carvalho H, Pereira PJB. Crystallization and preliminary crystallographic characterization of glutamine synthetase from Medicago truncatula. Acta Crystallogr Sect F Struct Biol Cryst Commun 2009; 65:1309-12. [PMID: 20054137 PMCID: PMC2802889 DOI: 10.1107/s1744309109047381] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Accepted: 11/09/2009] [Indexed: 11/11/2022]
Abstract
The condensation of ammonium and glutamate into glutamine catalyzed by glutamine synthetase (GS) is a fundamental step in nitrogen metabolism in all kingdoms of life. In plants, this is preceded by the reduction of inorganic nitrogen to an ammonium ion and therefore effectively articulates nitrogen fixation and metabolism. Although the three-dimensional structure of the dodecameric bacterial GS was determined quite some time ago, the quaternary architecture of the plant enzyme has long been assumed to be octameric, mostly on the basis of low-resolution electron-microscopy studies. Recently, the crystallographic structure of a monocotyledonous plant GS was reported that revealed a homodecameric organization. In order to unambiguously establish the quaternary architecture of GS from dicotyledonous plants, GS1a from the model legume Medicago truncatula was overexpressed, purified and crystallized. The collection of synchrotron diffraction data to 2.35 A resolution allowed the determination of the three-dimensional structure of this enzyme by molecular replacement.
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Affiliation(s)
- Ana Rita Seabra
- IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Portugal
| | - Helena Carvalho
- IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Portugal
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15
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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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16
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Berry AM, Murphy TM, Okubara PA, Jacobsen KR, Swensen SM, Pawlowski K. Novel expression pattern of cytosolic Gln synthetase in nitrogen-fixing root nodules of the actinorhizal host, Datisca glomerata. PLANT PHYSIOLOGY 2004; 135:1849-62. [PMID: 15247391 PMCID: PMC519095 DOI: 10.1104/pp.103.031534] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2003] [Revised: 04/14/2004] [Accepted: 05/02/2004] [Indexed: 05/24/2023]
Abstract
Gln synthetase (GS) is the key enzyme of primary ammonia assimilation in nitrogen-fixing root nodules of legumes and actinorhizal (Frankia-nodulated) plants. In root nodules of Datisca glomerata (Datiscaceae), transcripts hybridizing to a conserved coding region of the abundant nodule isoform, DgGS1-1, are abundant in uninfected nodule cortical tissue, but expression was not detectable in the infected zone or in the nodule meristem. Similarly, the GS holoprotein is immunolocalized exclusively to the uninfected nodule tissue. Phylogenetic analysis of the full-length cDNA of DgGS1-1 indicates affinities with cytosolic GS genes from legumes, the actinorhizal species Alnus glutinosa, and nonnodulating species, Vitis vinifera and Hevea brasilensis. The D. glomerata nodule GS expression pattern is a new variant among reported root nodule symbioses and may reflect an unusual nitrogen transfer pathway from the Frankia nodule microsymbiont to the plant infected tissue, coupled to a distinctive nitrogen cycle in the uninfected cortical tissue. Arg, Gln, and Glu are the major amino acids present in D. glomerata nodules, but Arg was not detected at high levels in leaves or roots. Arg as a major nodule nitrogen storage form is not found in other root nodule types except in the phylogenetically related Coriaria. Catabolism of Arg through the urea cycle could generate free ammonium in the uninfected tissue where GS is expressed.
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Affiliation(s)
- Alison M Berry
- Department of Environmental Horticulture, University of California, Davis, California 95616, USA.
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17
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Breuninger M, Trujillo CG, Serrano E, Fischer R, Requena N. Different nitrogen sources modulate activity but not expression of glutamine synthetase in arbuscular mycorrhizal fungi. Fungal Genet Biol 2004; 41:542-52. [PMID: 15050543 DOI: 10.1016/j.fgb.2004.01.003] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2003] [Accepted: 01/07/2004] [Indexed: 11/29/2022]
Abstract
Glutamine synthetase (GS) is a central enzyme of nitrogen metabolism that allows assimilation of nitrogen and biosynthesis of glutamine. We isolated the cDNA encoding GS from two arbuscular mycorrhizal fungi, Glomus mosseae (GmGln1) and Glomus intraradices (GiGln1). The deduced protein orthologues have a high degree of similarity (92%) with each other as well as with GSs from other fungi. GmGln1 was constitutively expressed during all stages of the fungal life cycle, i.e., spore germination, intraradical and extraradical mycelium. Feeding experiments with different nitrogen sources did not induce any change in the mRNA level of both genes independent of the symbiotic status of the fungus. However, GS activity of extraradical hypahe in G. intraradices was considerably modulated in response to different nitrogen sources. Thus, in a N re-supplementation time-course experiment, GS activity responded quickly to addition of nitrate, ammonium or glutamine. Re-feeding with ammonium produced a general increase in GS activity when compared with hyphae grown in nitrate as a sole N source.
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MESH Headings
- Amino Acid Motifs
- Amino Acid Sequence
- Base Sequence
- DNA, Complementary/chemistry
- DNA, Complementary/isolation & purification
- DNA, Fungal/chemistry
- DNA, Fungal/isolation & purification
- Enzyme Activators/metabolism
- Fungi/enzymology
- Fungi/genetics
- Fungi/growth & development
- Gene Expression Regulation, Fungal
- Glutamate-Ammonia Ligase/chemistry
- Glutamate-Ammonia Ligase/genetics
- Glutamate-Ammonia Ligase/metabolism
- Glutamine/metabolism
- Molecular Sequence Data
- Mycelium/enzymology
- Mycelium/genetics
- Mycelium/growth & development
- Mycorrhizae/metabolism
- Nitrates/metabolism
- Nitrogen/metabolism
- Phylogeny
- Quaternary Ammonium Compounds/metabolism
- RNA, Fungal/analysis
- RNA, Messenger/analysis
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Spores, Fungal/enzymology
- Spores, Fungal/genetics
- Spores, Fungal/growth & development
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Affiliation(s)
- Magdalene Breuninger
- Physiological Ecology of Plants Department, University of Tübingen, Auf der Morgenstelle 1, Tübingen 72076, Germany
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18
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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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19
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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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20
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de la Torre F, García-Gutiérrez A, Crespillo R, Cantón FR, Avila C, Cánovas FM. Functional expression of two pine glutamine synthetase genes in bacteria reveals that they encode cytosolic holoenzymes with different molecular and catalytic properties. PLANT & CELL PHYSIOLOGY 2002; 43:802-809. [PMID: 12154143 DOI: 10.1093/pcp/pcf094] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Two glutamine synthetase isogenes, GS1a and GS1b, isolated from pine have been functionally expressed in E. coli and the characteristics of individual gene products compared. When bacteria were grown at 37 degrees C most pine GS1 protein was found in the insoluble fraction but lowering of the expression temperature increased yield of both GS1 polypeptide and activity in the soluble fraction. High levels of functionally active GS1a (309 + or - 35 nkat mg(-1)) and GS1b (1,166 + or - 65 nkat mg(-1)) enzymes were obtained by decreasing the expression temperature to 10 degrees C. Purification and characterization of recombinant products showed that pine GS1 polypeptides are assembled in octameric GS holoenzymes showing structural and kinetic differences. The results are discussed with regard to the specific localization of GS1a and GS1b in different cell types of pine seedlings. The isoform GS1a may control the assimilation of the high levels of ammonium released in photosynthetic tissues, whereas GS1b enzyme could mitigate oscillations in glutamate availability providing a constant flux of glutamine for nitrogen transport in vascular cells.
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Affiliation(s)
- Fernando de la Torre
- Departamento de Biología Molecular y Bioquímica, Instituto Andaluz de Biotecnología, Unidad Asociada UMA-CSIC, Universidad de Málaga, Campus de Teatinos, E-29071 Málaga, Spain
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21
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The Biochemistry, Molecular Biology, and Genetic Manipulation of Primary Ammonia Assimilation. ADVANCES IN PHOTOSYNTHESIS AND RESPIRATION 2002. [DOI: 10.1007/0-306-48138-3_6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
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22
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Morey KJ, Ortega JL, Sengupta-Gopalan C. Cytosolic glutamine synthetase in soybean is encoded by a multigene family, and the members are regulated in an organ-specific and developmental manner. PLANT PHYSIOLOGY 2002; 128:182-193. [PMID: 11788764 DOI: 10.1104/pp.010380] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Gln synthetase (GS) is the key enzyme in N metabolism and it catalyzes the synthesis of Gln from glutamic acid, ATP, and NH4+. There are two major isoforms of GS in plants, a cytosolic form (GS1) and a chloroplastic form (GS2). In leaves, GS2 functions to assimilate ammonia produced by nitrate reduction and photorespiration, and GS1 is the major isoform assimilating NH3 produced by all other metabolic processes, including symbiotic N2 fixation in the nodules. GS1 is encoded by a small multigene family in soybean (Glycine max), and cDNA clones for the different members have been isolated. Based on sequence divergence in the 3'-untranslated region, three distinct classes of GS1 genes have been identified (alpha, beta, and gamma). Genomic Southern analysis and analysis of hybrid-select translation products suggest that each class has two distinct members. The alpha forms are the major isoforms in the cotyledons and young roots. The beta forms, although constitutive in their expression pattern, are ammonia inducible and show high expression in N2-fixing nodules. The gamma1 gene appears to be more nodule specific, whereas the gamma2 gene member, although nodule enhanced, is also expressed in the cotyledons and flowers. The two members of the alpha and beta class of GS1 genes show subtle differences in the expression pattern. Analysis of the promoter regions of the gamma1 and gamma2 genes show sequence conservation around the TATA box but complete divergence in the rest of the promoter region. We postulate that each member of the three GS1 gene classes may be derived from the two ancestral genomes from which the allotetraploid soybean was derived.
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Affiliation(s)
- Kevin J Morey
- Graduate Program in Molecular Biology, New Mexico State University, Las Cruces, New Mexico 88003, USA
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23
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Carvalho H, Lima L, Lescure N, Camut S, Salema R, Cullimore J. Differential expression of the two cytosolic glutamine synthetase genes in various organs of Medicago truncatula. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2000; 159:301-312. [PMID: 11074283 DOI: 10.1016/s0168-9452(00)00360-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
In order to clarify the physiological roles of the cytosolic forms of glutamine synthetase (GS) in Medicago truncatula, we have performed a detailed analysis of the expression of the two functional cytosolic GS genes, MtGSa and MtGSb in several organs of the plant. Transcriptional fusions were made between the 2.6 or 3.1 kbp 5' upstream regions of MtGSa or MtGSb, respectively, and the reporter gene gusA encoding beta-glucuronidase and introduced into the homologous transgenic system. MtGSa and MtGSb were found to be differentially expressed in most of the organs, both temporally and spatially. The presence of GS proteins at the sites where the promoters were active was confirmed by immunocytochemistry, providing the means to correlate gene expression with the protein products. These studies have shown that the putative MtGSa and MtGSb promoter fragments were sufficient to drive GUS expression in all the tissues and cell types where cytosolic GS proteins were located. This result indicates that the cis acting regulatory elements responsible for conferring the contrasting expression patterns are located within the region upstream of the coding sequences. MtGSa was preferentially expressed in the vascular tissues of almost all the organs examined, whereas MtGSb was preferentially expressed in the root cortex and in leaf pulvini. The location and high abundance of GS in the vascular tissues of almost all the organs analysed suggest that the enzyme encoded by MtGSa plays an important role in the production of nitrogen transport compounds. The enzyme synthesised by MtGSb appears to have more ubiquitous functions for ammonium assimilation and detoxification in a variety of organs.
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Affiliation(s)
- H Carvalho
- Instituto de Biologia Molecular e Celular, Rua do Campo Alegre, 823, 4150-, Porto, Portugal
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