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Rescooped by Muhammad Afridi from Rhizobium Research
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A Paradigm for Endosymbiotic Life: Cell Differentiation of Rhizobium Bacteria Provoked by Host Plant Factors

A Paradigm for Endosymbiotic Life: Cell Differentiation of Rhizobium Bacteria Provoked by Host Plant Factors | Biological nitrogen fixing microbes information | Scoop.it

Symbiosis between Rhizobium bacteria and legumes leads to the formation of the root nodule. The endosymbiotic bacteria reside in polyploid host cells as membrane-surrounded vesicles where they reduce atmospheric nitrogen to support plant growth by supplying ammonia in exchange for carbon sources and energy. The morphology and physiology of endosymbionts, despite their common function, are highly divergent in different hosts. In galegoid plants, the endosymbionts are terminally differentiated, uncultivable polyploid cells, with remarkably elongated and even branched Y-shaped cells. Bacteroid differentiation is controlled by host peptides, many of which have antibacterial activity and require the bacterial function of BacA. Although the precise and combined action of several hundred host peptides and BacA has yet to be discovered, similarities, especially to certain insect-bacterium symbioses involving likewise host peptides for manipulation of endosymbionts, suggest convergent evolution. Rhizobium-legume symbiosis provides a rich source of information for understanding host-controlled endosymbiotic life in eukaryotic cells.

 

Eva Kondorosi, Peter Mergaert,and Attila Kereszt (2013) Annual Review Microniology 67: 611-628 (Volume publication date September 2013)DOI: 10.1146/annurev-micro-092412-155630

 


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Rescooped by Muhammad Afridi from Plant Breeding and Genomics News
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Wheat genotypes with high early vigour accumulate more nitrogen and have higher photosynthetic nitrogen use efficiency during early growth

Wheat genotypes with high early vigour accumulate more nitrogen and have higher photosynthetic nitrogen use efficiency during early growth | Biological nitrogen fixing microbes information | Scoop.it

Genotypic differences in early growth and nitrogen (N) uptake among 24 wheat (Triticum aestivum L.) genotypes were assessed in a field trial. At late tillering, large genetic variation was observed for shoot biomass (23–56 g m–2 ground area) and N uptake (1.1–1.8 g m–2 ground area). A strong correlation between aboveground biomass and N uptake was observed. Variation around this relationship was also found, with some genotypes having similar N uptake but large differences in aboveground biomass. A controlled environment experiment was conducted to investigate the underlying mechanisms for this variation in aboveground biomass using three vigorous genotypes (38–19, 92–11 and CV97) and a non-vigorous commercial cultivar (Janz). Vigorous genotypes had lower specific leaf N in the youngest fully expanded leaf than Janz. However, there was no difference in chlorophyll content, maximum Rubisco activity or the rate of electron transport per unit area. This suggests that Janz invested more N in non-photosynthetic components than the vigorous lines, which could explain the higher photosynthetic N use efficiency of the vigorous genotypes. The results suggest that the utilisation of wheat genotypes with high early vigour could improve the efficiency of N use for biomass production in addition to improving N uptake during early growth.


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Rescooped by Muhammad Afridi from Rhizobium Research
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Calcium-Dependent Regulation of Genes for Plant Nodulation in Rhizobium leguminosarum Detected by iTRAQ Quantitative Proteomic Analysis - Journal of Proteome Research (ACS Publications)

Calcium-Dependent Regulation of Genes for Plant Nodulation in Rhizobium leguminosarum Detected by iTRAQ Quantitative Proteomic Analysis - Journal of Proteome Research (ACS Publications) | Biological nitrogen fixing microbes information | Scoop.it

Rhizobia, the nitrogen-fixing bacterial symbionts of legumes, represent an agricultural application of primary relevance and a model of plant–microbe molecular dialogues. We recently described rhizobium proteome alterations induced by plant flavonoids using iTRAQ. Herein, we further extend that experimentation, proving that the transient elevation in cytosolic calcium is a key signaling event necessary for the expression of the nodulation (nod) genes. Ca2+ involvement in nodulation is a novel issue that we recently flagged with genetic and physiological approaches and that hereby we demonstrate also by proteomics. Exploiting the multiple combinations of 4-plex iTRAQ, we analyzed Rhizobium leguminosarum cultures grown with or without the nod gene-inducing plant flavonoid naringenin and in the presence or absence of the extracellular Ca2+ chelator EGTA. We quantified over a thousand proteins, 189 of which significantly altered upon naringenin and/or EGTA stimulation. The expression of NodA, highly induced by naringenin, is strongly reduced when calcium availability is limited by EGTA. This confirms, from a proteomic perspective, that a Ca2+ influx is a necessary early step in flavonoid-mediated legume nodulation by rhizobia. We also observed other proteins affected by the different treatments, whose identities and roles in nodulation and rhizobium physiology are likewise discussed.

 

J. Proteome Res., (2013). Publication Date (Web): September 16,  


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Rescooped by Muhammad Afridi from Amazing Science
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Nitrogen fixing trees help to quicken the pace of reforestation

Nitrogen fixing trees help to quicken the pace of reforestation | Biological nitrogen fixing microbes information | Scoop.it

Researchers have discovered that trees can switch on their ability to fix Nitrogen from the atmosphere with a little help from the Rhizobium bacteria. This finding has a huge implication on the ongoing projects of reforestation on denuded lands.

 

A study was carried out on a square mile area of the Panama Canal watershed where the forest was recovering after clearing activities. Different land use options were studied and the carbon storage, runoff and biodiversity were carefully monitored. A comparison was made between mature tropical forests, native trees in forest restoration plots and abandoned pastureland.

 

Jefferson Hall, one of the researchers, said, “This is the first solid case showing how nitrogen fixation by tropical trees directly affects the rate of carbon recovery after agricultural fields are abandoned. Trees turn nitrogen fixation on and off according to the need for nitrogen in the system.”

 

It was observed that trees which were able to fix the atmospheric nitrogen were also able to add carbon nine times quicker than ordinary trees. In fact Nitrogen fixing trees were able to add 50,000 kilograms of carbon per hectare during the first 12 years of growth.

 

Tropical forests act as carbon sinks drawing away carbon from the air. As the scourge of the Global warming increases it is important that freed land which has been denuded by industrial or agricultural use be quickly repaired and reforested. Nitrogen fixing trees will help to quicken the pace of reforestation.

 


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Rescooped by Muhammad Afridi from Rhizobium Research
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The Sinorhizobium meliloti ntrX gene is involved in succinoglycan production, motility, and symbiotic nodulation on alfalfa.

Rhizobia establish a symbiotic relationship with their host legumes to induce the formation of nitrogen-fixing nodules. This process is regulated by many rhizobium regulators, including some two-component regulatory systems (TCSs). NtrY/NtrX, a TCS that was first identified in Azorhizobium caulinodans, is required for free-living nitrogen metabolism and symbiotic nodulation on Sesbania rostrata. However, its functions in a typical rhizobium such as Sinorhizobium meliloti remain unclear. Here we found that the S. meliloti response regulator NtrX but not the histidine kinase NtrY is involved in the regulation of exopolysaccharide production, motility, and symbiosis with alfalfa. A plasmid-insertion mutant of ntrX formed mucous colonies, which overproduced succinoglycan, an exopolysaccharide, by upregulating its biosynthesis genes. This mutant also exhibited motility defects due to reduced flagella and decreased expression of flagellins and regulatory genes. The regulation is independent of the known regulatory systems of ExoR/ExoS/ChvI, EmmABC and ExpR. Alfalfa plants inoculated with the ntrX mutant were small and displayed symptoms of nitrogen starvation. Interestingly, the deletion mutant of ntrY showed a phenotype similar to that of the parent strain. These findings demonstrate that the S. meliloti NtrX is a new regulator of succinoglycan production and motility that is not genetically coupled with NtrY.

 Wang D, Xue H, Wang Y, Yin R, Xie F, Luo L. (2013).  Appl Environ Microbiol. Sep 13. [Epub ahead of print]


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Ironing Out Nitrogen Fixation - Chemical & Engineering News

Bacteria make nitrogenases and use them to convert N2 in air to NH3, a process called nitrogen fixation. The process is a primary source of nitrogen in proteins, nucleic acids, and other biomolecules.
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