Fix Genes

2001 ◽  
pp. 707-709
Author(s):  
J. Vanderleyden ◽  
A. Van Dommelen ◽  
J. Michiels
Keyword(s):  
Fix Genes

Expression of the nodulation and nitrogen fixation genes in Rhizobium meliloti during development

Genome ◽  
1989 ◽  
Vol 31 (1) ◽  
pp. 354-360 ◽  
Author(s):  
San Chiun Shen ◽  
Shui Ping Wang ◽  
Guan Qiao Yu ◽  
Jia Bi Zhu
Keyword(s):  
Nitrogen Fixation ◽  
Rhizobium Meliloti ◽  
Abnormal Development ◽  
Wild Type ◽  
Free Living ◽  
Nod Genes ◽  
Nodule Initiation ◽  
Fix Genes ◽  
Nitrogen Fixation Genes

Genes that specify nodulation (nod genes) are only active in the free-living rhizobia or in the nodule initiation state of rhizobia. As soon as the repression of nod genes occurs in the bacteroids of the nodule, nifA is induced, while ntrC is inactivated and thus the nifA-mediated nif/fix genes are turned on. Limitation of available oxygen brings about the induction of nifA, which reflects the actual status of nif/fix gene activities in symbiotic state of rhizobia. Oxygen thus appears to be a major symbiotic signal to the expression of bacteroid nif/fix genes. Mutation of nifA or shortage of nifA product in wild-type rhizobia caused by the inhibition of multicopy nifH/fixA promoters leads to an abnormal development of nodules and premature degradation of bacteroids in nodules.Key words: nitrogen fixation, nodulation, nif/fix regulation, nifA mutant.

scholarly journals Taxonomically Different Co-Microsymbionts of a Relict Legume, Oxytropis popoviana, Have Complementary Sets of Symbiotic Genes and Together Increase the Efficiency of Plant Nodulation

2018 ◽  
Vol 31 (8) ◽  
pp. 833-841 ◽  
Author(s):  
Vera I. Safronova ◽  
Andrey A. Belimov ◽  
Anna L. Sazanova ◽  
Elizaveta R. Chirak ◽  
Alla V. Verkhozina ◽  
...  
Keyword(s):  
Root Nodules ◽  
Housekeeping Genes ◽  
Nodule Formation ◽  
Symbiotic Genes ◽  
Internal Transcribed Spacer Region ◽  
Bradyrhizobium Sp ◽  
The Common ◽  
Different Strains ◽  
Slow Growing ◽  
Fix Genes

Ten rhizobial strains were isolated from root nodules of a relict legume Oxytropis popoviana Peschkova. For identification of the isolates, sequencing of rrs, the internal transcribed spacer region, and housekeeping genes recA, glnII, and rpoB was used. Nine fast-growing isolates were Mesorhizobium-related; eight strains were identified as M. japonicum and one isolate belonged to M. kowhaii. The only slow-growing isolate was identified as a Bradyrhizobium sp. Two strains, M. japonicum Opo-242 and Bradyrhizobium sp. strain Opo-243, were isolated from the same nodule. Symbiotic genes of these isolates were searched throughout the whole-genome sequences. The common nodABC genes and other symbiotic genes required for plant nodulation and nitrogen fixation were present in the isolate Opo-242. Strain Opo-243 did not contain the principal nod, nif, and fix genes; however, five genes (nodP, nodQ, nifL, nolK, and noeL) affecting the specificity of plant-rhizobia interactions but absent in isolate Opo-242 were detected. Strain Opo-243 could not induce nodules but significantly accelerated the root nodule formation after coinoculation with isolate Opo-242. Thus, we demonstrated that taxonomically different strains of the archaic symbiotic system can be co-microsymbionts infecting the same nodule and promoting the nodulation process due to complementary sets of symbiotic genes.

Molecular genetic basis of Rhizobium–legume interactions

Genome ◽  
1989 ◽  
Vol 31 (1) ◽  
pp. 350-353 ◽  
Author(s):  
A. Kondorosi ◽  
E. Kondorosi ◽  
Z. Györgypal ◽  
Z. Banfalvi ◽  
J. Gyuris ◽  
...  
Keyword(s):  
Rhizobium Meliloti ◽  
Molecular Genetic ◽  
Nodule Development ◽  
Plant Host ◽  
Specific Expression ◽  
Nodulation Genes ◽  
Molecular Genetic Basis ◽  
Plant Signals ◽  
Nodulin Genes ◽  
Fix Genes

Recognition of the appropriate legume and nodule induction are controlled by common (nod) and host-specific nodulation (hsn) genes in Rhizobium. The nod and hsn genes are activated by the product of the regulatory nodD in conjunction with specific flavonoids excreted by the plant. Differences in the flavonoid specificity of the NodD proteins occur between different Rhizobium species, or between strains of a given species or even within one strain containing several copies of the nodD gene. Accordingly, the nodD gene controls the host-specific expression of nod and hsn genes. In addition, the nodulation genes are under not only positive but also negative regulation which is mediated by a nod-specific repressor protein. This dual control is required for optimal nodulation of the plant host. Further steps in nodule development are again controlled by the infecting Rhizobium. It was found that at least four different classes of Rhizobium fix genes are involved directly or indirectly in the expression of late nodulin genes, finally leading to the establishment of nitrogen-fixing symbiosis.Key words: Rhizobium meliloti, nodulation genes, plant signals, fix genes, alfalfa.

scholarly journals Symbiotic Burkholderia Species Show Diverse Arrangements of nif/fix and nod Genes and Lack Typical High-Affinity Cytochrome cbb3 Oxidase Genes

2016 ◽  
Vol 29 (8) ◽  
pp. 609-619 ◽  
Author(s):  
Sofie E. De Meyer ◽  
Leah Briscoe ◽  
Pilar Martínez-Hidalgo ◽  
Christina M. Agapakis ◽  
Paulina Estrada de-los Santos ◽  
...  
Keyword(s):  
16S Rrna ◽  
Gene Sequencing ◽  
Genomic Analysis ◽  
16S Rrna Gene Sequencing ◽  
Rrna Gene ◽  
Free Living ◽  
Nod Genes ◽  
Electron Transport Chains ◽  
Rrna Gene Sequencing ◽  
Fix Genes

Genome analysis of fourteen mimosoid and four papilionoid beta-rhizobia together with fourteen reference alpha-rhizobia for both nodulation (nod) and nitrogen-fixing (nif/fix) genes has shown phylogenetic congruence between 16S rRNA/MLSA (combined 16S rRNA gene sequencing and multilocus sequence analysis) and nif/fix genes, indicating a free-living diazotrophic ancestry of the beta-rhizobia. However, deeper genomic analysis revealed a complex symbiosis acquisition history in the beta-rhizobia that clearly separates the mimosoid and papilionoid nodulating groups. Mimosoid-nodulating beta-rhizobia have nod genes tightly clustered in the nodBCIJHASU operon, whereas papilionoid-nodulating Burkholderia have nodUSDABC and nodIJ genes, although their arrangement is not canonical because the nod genes are subdivided by the insertion of nif and other genes. Furthermore, the papilionoid Burkholderia spp. contain duplications of several nod and nif genes. The Burkholderia nifHDKEN and fixABC genes are very closely related to those found in free-living diazotrophs. In contrast, nifA is highly divergent between both groups, but the papilionoid species nifA is more similar to alpha-rhizobia nifA than to other groups. Surprisingly, for all Burkholderia, the fixNOQP and fixGHIS genes required for cbb3 cytochrome oxidase production and assembly are missing. In contrast, symbiotic Cupriavidus strains have fixNOQPGHIS genes, revealing a divergence in the evolution of two distinct electron transport chains required for nitrogen fixation within the beta-rhizobia.

Identification and phenotypical characterization of a cluster of fix genes, including a nif regulatory gene, from Rhizobium leguminosarum PRE

1985 ◽  
Vol 200 (3) ◽  
pp. 368-374 ◽  
Author(s):  
Resie M. P. Schetgens ◽  
Jan G. J. Hontelez ◽  
Rommert C. van den Bos ◽  
Albert van Kammen
Keyword(s):  
Rhizobium Leguminosarum ◽  
Regulatory Gene ◽  
Fix Genes

Derivation and molecular characterization of symbiotically deficient mutants of Rhizobium meliloti

1987 ◽  
Vol 33 (9) ◽  
pp. 739-747 ◽  
Author(s):  
G. Selvaraj ◽  
I. Hooper ◽  
S. Shantharam ◽  
V. N. Iyer ◽  
L. Barran ◽  
...  
Keyword(s):  
Rhizobium Meliloti ◽  
Acetylene Reduction Activity ◽  
Wild Type ◽  
Suicide Vector ◽  
Reduction Activity ◽  
Dna Restriction Fragments ◽  
Dna Restriction ◽  
Bona Fide ◽  
Fix Genes

A collection of symbiotically defective mutants of Rhizobium meliloti JJ1c10 was derived by Tn5 mutagenesis using the suicide vector pGS9. They include two Nod− and about 250 Fix− mutants. The mutants were found to be heterogenous in acetylene reduction activity and in the morphology and ultrastructure of the nodules which they induced. Over 90% were found to contain bona fide Tn5 insertions in a variety of DNA restriction fragments. When Tn5-carrying DNA segments cloned from 24 of the mutants were introduced into the equivalent location in the genome of the wild-type strain by recombination-mediated replacement, only eight produced a symbiotically defective phenotype similar to that of the original mutant. This result indicated that many of the symbiosis mutations were not directly caused by Tn5 insertion. DNA segments apparently containing mutated fix genes but not containing Tn5 were found in eight mutants by identifying cosmids carrying wild-type DNA which complemented their symbiosis defects. Probing of the DNA of these mutants with their complementing cosmids revealed no detectable physical alteration of the homologous DNA. A segment of DNA including the hsn and nifHDK genes was favoured for these non-Tn5 mutations. Three regions of the genome in which Tn5 caused fix mutations were identified. One of these was the known megaplasmid nod-nif region. The other two regions, designated fix-e5 and fix-h21, were found to be chromosomal. Mutants in one of these chromosomal regions fluoresced more intensely on calcofluor plates than the wild type.

scholarly journals Low potential electron generating enzymes serve different functions during aerobic nitrogen fixation in Azotobacter vinelandii

2021 ◽  
Author(s):  
Alexander B Alleman ◽  
Florence Mus ◽  
John W Peters
Keyword(s):  
Nitrogen Fixation ◽  
Azotobacter Vinelandii ◽  
Activation Barrier ◽  
Redox Homeostasis ◽  
Low Oxygen ◽  
High Activation Barrier ◽  
Biological Nitrogen ◽  
Diazotrophic Growth ◽  
Enzyme Complexes ◽  
Fix Genes

Biological nitrogen fixation requires large amounts of energy in the form of ATP and low potential electrons to overcome the high activation barrier for cleavage of the dinitrogen triple bond. The model aerobic nitrogen-fixing bacteria, Azotobacter vinelandii, generates low potential electrons in the form of reduced ferredoxin (Fd) and flavodoxin (Fld) using two distinct mechanisms via the enzyme complexes Rnf and Fix. Both Rnf and Fix are expressed during nitrogen fixation, and deleting either rnf1 or fix genes has little effect on diazotrophic growth. However, deleting both rnf1 and fix eliminates the ability to grow diazotrophically. Rnf and Fix both use NADH as a source of electrons, but overcoming the energetics of NADH's endergonic reduction of Fd/Fld is accomplished through different mechanisms. Rnf harnesses free energy from the proton motive force, whereas Fix uses electron bifurcation to effectively couple the endergonic reduction of Fd/Fld to the exergonic reduction of quinone. Different stoichiometries and gene expression analyses indicate specific roles for the two reactions under different conditions. In this work, complementary physiological studies and thermodynamic modeling reveal how Rnf and Fix simultaneously balance redox homeostasis in various conditions. Specifically, the Fix complex is required for efficient growth under low oxygen concentrations, while Rnf sustains homeostasis and delivers sufficient reduced Fd to nitrogenase under standard conditions. This work provides a framework for understanding how the production of low potential electrons sustains robust nitrogen fixation in various conditions.

Fix Genes

2013 ◽  
pp. 54-57
Author(s):  
A. Van Dommelen ◽  
J. Vanderleyden ◽  
J. Michiels
Keyword(s):  
Fix Genes
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