Isolation and characterization of a ntrC mutant of Bradyrhizobium (Parasponia) sp. ANU289

Udvardi, Michael K.; Lister, Diane; Day, David A.

doi:10.1099/00221287-138-5-1019

Cited by 14 publications

(6 citation statements)

References 33 publications

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“…The form of N exported from Parasponia-rhizobia to the host cells is unknown, but there is little reason to believe it should be exceptional as compared to legume rhizobia (e.g., Udvardi et al, 1992). Early work (Becking, 1983a) on the amino acid content of P. parviflora nodules indicated higher levels of the glutamate, aspartate and amides in nodules with greater N 2 fixation.…”

Section: Transfer Of the Fixed N From The Microsymbiont To The Hostmentioning

confidence: 96%

Root-based N2-fixing Symbioses: Legumes, Actinorhizal Plants, Parasponia sp. and Cycads

2005

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In the mutualistic symbioses between legumes and rhizobia, actinorhizal plants and Frankia, Parasponia sp. and rhizobia, and cycads and cyanobacteria, the N 2 -fixing microsymbionts exist in specialized structures (nodules or cyanobacterial zones) within the roots of their host plants. Despite the phylogenetic diversity among both the hosts and the microsymbionts of these symbioses, certain developmental and physiological imperatives must be met for successful mutualisms. In this review, phylogenetic and ecological aspects of the four symbioses are first addressed, and then the symbioses are contrasted and compared in regard to infection and symbio-organ development, supply of carbon to the microsymbionts, regulation of O 2 flux to the microsymbionts, and transfer of fixed-N to the hosts. Although similarities exist in the genetics, development, and functioning of the symbioses, it is evident that there is great diversity in many aspects of these root-based N 2 -fixing symbioses. Each symbiosis can be admired for the elegant means by which the host plant and microsymbiont integrate to form the mutualistic relationships so important to the functioning of the biosphere.

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Section: Transfer Of the Fixed N From The Microsymbiont To The Hostmentioning

confidence: 96%

Root-based N2-fixing Symbioses: Legumes, Actinorhizal Plants, Parasponia sp. and Cycads

2005

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“…However, expression of nitrogen fixation genes is under oxygen control (Agron et al, 1994) and does not require the Ntr system (Fischer, 1994). That means that nitrogen fixation in bacteroids is uncoupled from nitrogen assimilation with the result that mutations in the Ntr system have little or no effect on symbiotic nitrogen fixation activity (Gussin et al, 1986;Udvardi et al, 1992).…”

Section: Nitrogen Feedback-regulationmentioning

confidence: 99%

How are nitrogen fixation rates regulated in legumes?

Schulze¹

2004

Z. Pflanzenernähr. Bodenk.

137

101

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± ZusammenfassungSymbiotic nitrogen fixation by the legume-Rhizobium symbiosis is a finely regulated process that involves significant carbon and energy metabolism by the plant. At present, there are three competing theories as to how the regulation of the process is achieved at the whole plant level. Theory one (carbon supply regulation) states that nitrogen fixation rates are regulated by either current nodule assimilate supply or through metabolism of assimilates into compounds that can be used by the bacteroids. A second theory (oxygen supply regulation) assumes that oxygen diffusion into the nodules is tightly regulated and is the principal regulatory factor for nitrogen fixation rates. A third theory (N-feedback regulation) suggests that a product of nitrogen fixation or assimilation exerts a feedback regulatory impact. The paper summarizes experimental data which support or reject the mentioned theories. Moreover, implications of nitrogen fixation under P stress and of phenomena connected with the argon or acetylene induced decline in nitrogenase activity for the understanding of nitrogen fixation regulation are discussed. It is concluded that we currently have no theory that explains all aspects and experimental results concerning the regulation of nitrogen fixation in legumes. With our growing ability to impact the process, e.g., by genetic engineering, this understanding of nitrogen fixation regulation has potential to be translated into agronomically sustainable benefits. Wie werden die Stickstofffixierungsraten bei Leguminosen reguliert?Die symbiontische N 2 -Fixierung bei Leguminosen ist ein fein regulierter Prozess, der einen massiven Substanzumsatz in der Pflanze beinhaltet. Gegenwärtig gibt es drei konkurrierende Theorien über die Art, wie die Regulation des Prozesses auf Ganzpflanzenbasis erreicht wird. Eine Theorie (Regulation über die Kohlenstoffversorgung) geht von einer Abhängigkeit bzw. Regulation der N 2 -Fixierungsraten entweder durch die Assimilatversorgung der Knöllchen oder von einer Limitierung des nötigen metabolischen Umsatzes der Assimilate in für den Bakteroiden verwertbare Verbindungen aus. In der zweiten Theorie (Regulation über die Sauerstoffversorgung) wird angenommen, dass die Sauerstoffdiffusion in das Knöllchen einer strengen Regulation unterliegt und dies der prinzipielle Regulationsfaktor für die N 2 -Fixierungsraten ist. Die dritte Theorie (ªN-feedbackº-Regulation) besagt, dass ein bisher nicht zweifelsfrei identifiziertes Produkt der Stickstoffixierung oder -assimilation eine ªfeedbackª-Wirkung auf die N 2 -Fixierung ausübt. Der vorliegende Artikel fasst die bis heute gesammelten experimentellen Daten zusammen, die für oder gegen die genannten Theorien sprechen. In diesem Zusammenhang wird diskutiert, auf welche Weise die Regulation der N 2 -Fixierung unter P-Mangelbedingungen erfolgt. Schlieûlich wird diskutiert, ob die Klärung der Ursache der Azetylen-bzw. Argon-induzierten Abnahme der Nitrogenaseaktivität zum Verständnis der Regulation der N 2 -Fixierung beitragen kan...

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“…A high-affinity, energy-dependent transport system for NH 4 ϩ , detected by uptake assays with radioactive methylammonium (an NH 4 ϩ analogue), has been described in many bacterial species, including rhizobia (77,87,134,179). In rhizobia this system is activated under poor N conditions, such as the utilization of nitrate and glutamate as the sole N source, either to retrieve the NH 3 /NH 4 ϩ lost to the outside or to sense their extracellular concentration (179,191).…”

Section: Nhmentioning

confidence: 99%

Key Role of Bacterial NH ₄ ⁺ Metabolism in Rhizobium-Plant Symbiosis

Patriarca

Tatè

Iaccarino

2002

Microbiol Mol Biol Rev

159

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Symbiotic nitrogen fixation is carried out in specialized organs, the nodules, whose formation is induced on leguminous host plants by bacteria belonging to the family Rhizobiaceae. Nodule development is a complex multistep process, which requires continued interaction between the two partners and thus the exchange of different signals and metabolites. NH4+ is not only the primary product but also the main regulator of the symbiosis: either as ammonium and after conversion into organic compounds, it regulates most stages of the interaction, from the production of nodule inducers to the growth, function, and maintenance of nodules. This review examines the adaptation of bacterial NH4+ metabolism to the variable environment generated by the plant, which actively controls and restricts bacterial growth by affecting oxygen and nutrient availability, thereby allowing a proficient interaction and at the same time preventing parasitic invasion. We describe the regulatory circuitry responsible for the downregulation of bacterial genes involved in NH4+ assimilation occurring early during nodule invasion. This is a key and necessary step for the differentiation of N2-fixing bacteroids (the endocellular symbiotic form of rhizobia) and for the development of efficient nodules

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Isolation and characterization of a ntrC mutant of Bradyrhizobium (Parasponia) sp. ANU289

Cited by 14 publications

References 33 publications

Root-based N2-fixing Symbioses: Legumes, Actinorhizal Plants, Parasponia sp. and Cycads

Root-based N2-fixing Symbioses: Legumes, Actinorhizal Plants, Parasponia sp. and Cycads

How are nitrogen fixation rates regulated in legumes?

Key Role of Bacterial NH ₄ ⁺ Metabolism in Rhizobium-Plant Symbiosis

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Isolation and characterization of a ntrC mutant of Bradyrhizobium (Parasponia) sp. ANU289

Cited by 14 publications

References 33 publications

Root-based N2-fixing Symbioses: Legumes, Actinorhizal Plants, Parasponia sp. and Cycads

Root-based N2-fixing Symbioses: Legumes, Actinorhizal Plants, Parasponia sp. and Cycads

How are nitrogen fixation rates regulated in legumes?

Key Role of Bacterial NH 4 + Metabolism in Rhizobium-Plant Symbiosis

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Key Role of Bacterial NH ₄ ⁺ Metabolism in Rhizobium-Plant Symbiosis