NITROGEN METABOLISM IN LAKES II. ROLE OF NITROGEN FIXATION IN SANCTUARY LAKE, PENNSYLVANIA1

Dear Editor,Legume/cereal intercropping systems have been regarded as the practical application of basic ecological principles such as diversity, competition and facilitation. In a recent PNAS paper, Li et al. (1) describe the novel finding that maize exudates promote faba bean nodulation and nitrogen fixation by upregulating genes involved in (iso)flavonoids synthesis (chalcone–flavanone isomerase) within faba bean, resulting in production of more genistein, a legume-to-rhizobia signal during establishment of the faba bean N2–fixing symbiosis. Although we salute the authors’ methodological efforts, there is another mechanism that could be responsible for the effect of corn root exudates on faba been nitrogen fixation observed in this article (1). The authors may misunderstand their data and the signalling role of maize exudates, thus got a defective model for the root interactions between faba bean and maize.

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Novel Reiterated Fnr-Type Proteins Control the Production of the Symbiotic Terminal Oxidase cbb3 in Rhizobium etli CFN42

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-20-10-1241 ◽

2007 ◽

Vol 20 (10) ◽

pp. 1241-1249 ◽

Cited By ~ 15

Author(s):

Manuel J. Granados-Baeza ◽

Nicolás Gómez-Hernández ◽

Yolanda Mora ◽

María J. Delgado ◽

David Romero ◽

...

Keyword(s):

Nitrogen Fixation ◽

Oxygen Affinity ◽

Structural Similarity ◽

Transcriptional Regulators ◽

Terminal Oxidase ◽

Nitrogen Fixing ◽

Rhizobium Etli ◽

High Oxygen Affinity ◽

Key Genes

Symbiotic nitrogen-fixing bacteria express a terminal oxidase with a high oxygen affinity, the cbb3-type oxidase encoded by the fixNOQP operon. Previously, we have shown that, in Rhizobium etli CFN42, the repeated fixNOQP operons (fixNOQPd and fixNOQPf) have a differential role in nitrogen fixation. Only the fixNOQPd operon is required for the establishment of an effective symbiosis; microaerobic induction of this operon is under the control of at least three transcriptional regulators, FixKf, FnrNd, and FnrNchr, belonging to the Crp/Fnr family. In this work, we describe two novel Crp/Fnr-type transcriptional regulators (StoRd and StoRf, symbiotic terminal oxidase regulators) that play differential roles in the control of key genes for nitrogen fixation. Mutations either in stoRd or stoRf enhance the microaerobic expression of both fixNOQP reiterations, increasing also the synthesis of the cbb3-type oxidase in nodules. Despite their structural similarity, a differential role of these genes was also revealed, since a mutation in stoRd but not in stoRf enhanced both the expression of fixKf and the nitrogen-fixing capacity of R. etli CFN42.

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Nitrogen fixation and bioenergetics: the role of ATP in nitrogenase catalysis

FEBS Letters ◽

10.1016/0014-5793(79)80138-6 ◽

1979 ◽

Vol 98 (1) ◽

pp. 1-8 ◽

Cited By ~ 25

Author(s):

Torbjørn Ljones

Keyword(s):

Nitrogen Fixation

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Role of Plant Hormones and Carbon/Nitrogen Metabolism in Controlling Nodule Initiation on Alfalfa Roots

Nitrogen Fixation: Fundamentals and Applications - Current Plant Science and Biotechnology in Agriculture ◽

10.1007/978-94-011-0379-4_52 ◽

1995 ◽

pp. 443-448 ◽

Cited By ~ 3

Author(s):

P. Bauer ◽

T. Coba De La Pena ◽

F. Frugier ◽

S. Poirier ◽

H. I. Mckhann ◽

...

Keyword(s):

Nitrogen Metabolism ◽

Plant Hormones ◽

Nodule Initiation

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A Possible Role of Flavodoxin in Nitrogen Fixation in Heterocysts from Anabaena

Nitrogen Fixation ◽

10.1007/978-94-011-3486-6_90 ◽

1991 ◽

pp. 431-436 ◽

Cited By ~ 2

Author(s):

M. C. Lázaro ◽

M. F. Fillat ◽

C. Gómez-Moreno ◽

M. L. Peleato

Keyword(s):

Nitrogen Fixation

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Metabolic Switching of Mycobacterium tuberculosis during Hypoxia Is Controlled by the Virulence Regulator PhoP

Journal of Bacteriology ◽

10.1128/jb.00705-19 ◽

2020 ◽

Vol 202 (7) ◽

Author(s):

Prabhat Ranjan Singh ◽

Anil Kumar Vijjamarri ◽

Dibyendu Sarkar

Keyword(s):

Mycobacterium Tuberculosis ◽

Nitrogen Metabolism ◽

Electron Acceptor ◽

Latent Infection ◽

Critical Role ◽

Hypoxic Stress ◽

Content Type ◽

Metabolic Switching ◽

Virulence Regulator

ABSTRACT Mycobacterium tuberculosis retains the ability to establish an asymptomatic latent infection. A fundamental question in mycobacterial physiology is to understand the mechanisms involved in hypoxic stress, a critical player in persistence. Here, we show that the virulence regulator PhoP responds to hypoxia, the dormancy signal, and effectively integrates hypoxia with nitrogen metabolism. We also provide evidence to demonstrate that both under nitrogen limiting conditions and during hypoxia, phoP locus controls key genes involved in nitrogen metabolism. Consistently, under hypoxia a ΔphoP strain shows growth attenuation even with surplus nitrogen, the alternate electron acceptor, and complementation of the mutant restores bacterial growth. Together, our observations provide new biological insights into the role of PhoP in integrating nitrogen metabolism with hypoxia by the assistance of the hypoxia regulator DosR. The results have significant implications on the mechanism of intracellular survival and growth of the tubercle bacilli under a hypoxic environment within the phagosome. IMPORTANCE M. tuberculosis retains the unique ability to establish an asymptomatic latent infection. To understand the mechanisms involved in hypoxic stress which play a critical role in persistence, we show that the virulence regulator PhoP is linked to hypoxia, the dormancy signal. In keeping with this, phoP was shown to play a major role in M. tuberculosis growth under hypoxia even in the presence of surplus nitrogen, the alternate electron acceptor. Our results showing regulation of hypoxia-responsive genes provide new biological insights into role of the virulence regulator in metabolic switching by sensing hypoxia and integrating nitrogen metabolism with hypoxia by the assistance of the hypoxia regulator DosR.

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The Significance of Flavonoids in the Process of Biological Nitrogen Fixation

International Journal of Molecular Sciences ◽

10.3390/ijms21165926 ◽

2020 ◽

Vol 21 (16) ◽

pp. 5926

Author(s):

Wei Dong ◽

Yuguang Song

Keyword(s):

Nitrogen Fixation ◽

Plant Species ◽

Biological Nitrogen Fixation ◽

Molecular Basis ◽

Phenylpropanoid Pathway ◽

Rhizobium Spp ◽

Microbial Symbionts ◽

Biological Nitrogen ◽

Do So

Nitrogen is essential for the growth of plants. The ability of some plant species to obtain all or part of their requirement for nitrogen by interacting with microbial symbionts has conferred a major competitive advantage over those plants unable to do so. The function of certain flavonoids (a group of secondary metabolites produced by the plant phenylpropanoid pathway) within the process of biological nitrogen fixation carried out by Rhizobium spp. has been thoroughly researched. However, their significance to biological nitrogen fixation carried out during the actinorhizal and arbuscular mycorrhiza–Rhizobium–legume interaction remains unclear. This review catalogs and contextualizes the role of flavonoids in the three major types of root endosymbiosis responsible for biological nitrogen fixation. The importance of gaining an understanding of the molecular basis of endosymbiosis signaling, as well as the potential of and challenges facing modifying flavonoids either quantitatively and/or qualitatively are discussed, along with proposed strategies for both optimizing the process of nodulation and widening the plant species base, which can support nodulation.

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