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Moawad, Hassan; El-Din, S. M. S. Badr; Abdel-Aziz, R. A.

doi:10.1023/a:1004335112402

Cited by 42 publications

(6 citation statements)

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“…Yet, many rhizobia can be ineffective. In these cases, nodule formation occurs but the rhizobia provide little or no fixed nitrogen for the host [7,[25][26][27][28]. Ineffective rhizobia can potentially gain a metabolic advantage by redirecting plant carbon towards selfish ends [10,29,30] as opposed to engaging in energetically expensive nitrogen fixation [31].…”

Section: Introductionmentioning

confidence: 99%

Efficiency of partner choice and sanctions inLotusis not altered by nitrogen fertilization

et al. 2014

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Eukaryotic hosts must exhibit control mechanisms to select against ineffective bacterial symbionts. Hosts can minimize infection by less-effective symbionts ( partner choice) and can divest of uncooperative bacteria after infection (sanctions). Yet, such host-control traits are predicted to be context dependent, especially if they are costly for hosts to express or maintain. Legumes form symbiosis with rhizobia that vary in symbiotic effectiveness (nitrogen fixation) and can enforce partner choice as well as sanctions. In nature, legumes acquire fixed nitrogen from both rhizobia and soils, and nitrogen deposition is rapidly enriching soils globally. If soil nitrogen is abundant, we predict host control to be downregulated, potentially allowing invasion of ineffective symbionts. We experimentally manipulated soil nitrogen to examine context dependence in host control. We co-inoculated Lotus strigosus from nitrogen depauperate soils with pairs of Bradyrhizobium strains that vary in symbiotic effectiveness and fertilized plants with either zero nitrogen or growth maximizing nitrogen. We found efficient partner choice and sanctions regardless of nitrogen fertilization, symbiotic partner combination or growth season. Strikingly, host control was efficient even when L. strigosus gained no significant benefit from rhizobial infection, suggesting that these traits are resilient to short-term changes in extrinsic nitrogen, whether natural or anthropogenic.

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Section: Introductionmentioning

confidence: 99%

Efficiency of partner choice and sanctions inLotusis not altered by nitrogen fertilization

et al. 2014

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“…Rhizobia fix atmospheric nitrogen in exchange for photosynthates, but the interaction does not always appear cooperative. Plant and bacteria reproduce and disperse independently (Simms & Taylor 2002) and individual plants usually interact with multiple bacterial genotypes that vary from beneficial to completely ineffective mutualists (Moawad & Beck 1991;Quigley et al 1997;Moawad et al 1998;Denison 2000;Thrall et al 2000). Several authors have suggested that rhizobial cooperation could be promoted by plant traits that preferentially allocate resources to nodules harbouring cooperative strains (Denison 2000;Simms & Taylor 2002;West et al 2002b;Sprent 2003).…”

Section: Introductionmentioning

confidence: 99%

An empirical test of partner choice mechanisms in a wild legume–rhizobium interaction

Simms¹,

Taylor²,

Povich³

et al. 2005

Proc. R. Soc. B.

184

212

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Mutualisms can be viewed as biological markets in which partners of different species exchange goods and services to their mutual benefit. Trade between partners with conflicting interests requires mechanisms to prevent exploitation. Partner choice theory proposes that individuals might foil exploiters by preferentially directing benefits to cooperative partners. Here, we test this theory in a wild legumerhizobium symbiosis.Rhizobial bacteria inhabit legume root nodules and convert atmospheric dinitrogen (N 2 ) to a plant available form in exchange for photosynthates. Biological market theory suits this interaction because individual plants exchange resources with multiple rhizobia. Several authors have argued that microbial cooperation could be maintained if plants preferentially allocated resources to nodules harbouring cooperative rhizobial strains. It is well known that crop legumes nodulate non-fixing rhizobia, but allocate few resources to those nodules. However, this hypothesis has not been tested in wild legumes which encounter partners exhibiting natural, continuous variation in symbiotic benefit.Our greenhouse experiment with a wild legume, Lupinus arboreus, showed that although plants frequently hosted less cooperative strains, the nodules occupied by these strains were smaller. Our survey of wild-grown plants showed that larger nodules house more Bradyrhizobia, indicating that plants may prevent the spread of exploitation by favouring better cooperators.

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“…However, such signifi cant responses to inoculation are to be expected if legumes are grown in virgin soils. However, Moawad et al ( 1998 ) investigated the competitive ability and yield response of inoculant strains for lentil in Egypt and found that 76-88 % of nodules were occupied by native rhizobia, and there was no yield response from inoculation. However, a good response of other legumes like clover and common bean were observed, where 52-79 % of nodules were occupied by native rhizobia.…”

Section: Effects Of Inoculation In the Presence Of Indigenous Rhizobimentioning

confidence: 99%

Nitrogen-Fixing Plant-Microbe Symbioses

Rashid

Krehenbrink²,

Akhtar

2014

Sustainable Agriculture Reviews

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The symbiotic conversion of atmospheric nitrogen into nitrogenous compounds assimilated by higher organisms is an essential part of the global N cycle and a supporting pillar of agricultural practices. The nitrogen fi xing symbiosis is not confi ned only to leguminous plants but also found some other plant families. The symbiotic relationship between plants and rhizobia is initiated by the release of fl avonoids into the rhizosphere by the plant root. The release of fl avonoids are sensed by the rhizobial transcriptional regulator NodD , which leads to symbiosesspecifi c responses such as the release of Nod factors. The enzymes involved in the synthesis of basic Nod factor structure are encoded by the nodABC genes, conserved in almost all types of rhizobia. The perception of Nod factor by the plant is mediated by a receptor-like kinase, which induces intracellular calcium oscillations and leads to the deformation of root hairs through the restructuring of the cytoskeleton, leading to the formation of an infection thread. Although rhizobia are capable of synthesizing their own amino acids in the free living stage, within the infection thread rhizobia are dependent on the plant host for amino acids and other compounds.Rhizobia were initially classifi ed on the basis of their morphological, physiological characteristics and dominantly on host plant that they nodulate but after the invention of molecular techniques their molecular characteristics were taken into consideration. Thus, rhizobial taxonomy was repeatedly revised and refi ned. Currently, about 145 species of rhizobia have described from the genera Azorhizobium , Allorhizobium , Agrobacterium , Bradyrhizobium , Ensifer and Rhizobium and the taxonomic status of some genera and species has been revised. Root nodulating beta-rhizobia from different legumes have only been described recently, but the molecular evidence showed that they are existed as legume symbionts for 50 million years. Different species of beta-rhizobia contain common nodulation genes like nodABC , nodD , nifH , and these genes are very similar to the symbiotic genes of traditional rhizobia.Phylogenetic analyses are the basis to understanding the evolutionary history of individual genes or entire genomes of microorganisms. Initially, the bacterial phylogenies were reconstructed on the basis of morphological and physiological characteristics of the cell. Later, sequence analysis and chemical content analysis were introduced to further improve phylogenies. Sequencing of 16S rRNA genes not only contribute signifi cantly to the elimination of plasmid-borne characteristics from rhizobial taxonomy, but also helped in the identifi cation of beta and gamma rhizobia. Nowadays, the sequencing of housekeeping genes, DNA profi ling and the application of DNA arrays have become standard methods in bacterial taxonomy.The legume-rhizobia association contributes signifi cantly to the symbiotic biological nitrogen-fi xing process, but other microbes such as cyanobacteria, endophytic bacteria, or Frank...

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Cited by 42 publications

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Efficiency of partner choice and sanctions inLotusis not altered by nitrogen fertilization

Efficiency of partner choice and sanctions inLotusis not altered by nitrogen fertilization

An empirical test of partner choice mechanisms in a wild legume–rhizobium interaction

Nitrogen-Fixing Plant-Microbe Symbioses

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