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Journal articles on the topic 'Legume, symbiosis, nitrogen fixation'
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1
Zahran, Hamdi Hussein. "Rhizobium-Legume Symbiosis and Nitrogen Fixation under Severe Conditions and in an Arid Climate." Microbiology and Molecular Biology Reviews 63, no. 4 (1999): 968–89. http://dx.doi.org/10.1128/mmbr.63.4.968-989.1999.
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SUMMARY Biological N2 fixation represents the major source of N input in agricultural soils including those in arid regions. The major N2-fixing systems are the symbiotic systems, which can play a significant role in improving the fertility and productivity of low-N soils. The Rhizobium-legume symbioses have received most attention and have been examined extensively. The behavior of some N2-fixing systems under severe environmental conditions such as salt stress, drought stress, acidity, alkalinity, nutrient deficiency, fertilizers, heavy metals, and pesticides is reviewed. These major stress factors suppress the growth and symbiotic characteristics of most rhizobia; however, several strains, distributed among various species of rhizobia, are tolerant to stress effects. Some strains of rhizobia form effective (N2-fixing) symbioses with their host legumes under salt, heat, and acid stresses, and can sometimes do so under the effect of heavy metals. Reclamation and improvement of the fertility of arid lands by application of organic (manure and sewage sludge) and inorganic (synthetic) fertilizers are expensive and can be a source of pollution. The Rhizobium-legume (herb or tree) symbiosis is suggested to be the ideal solution to the improvement of soil fertility and the rehabilitation of arid lands and is an important direction for future research.
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Schulte, Carolin C. M., Khushboo Borah, Rachel M. Wheatley, et al. "Metabolic control of nitrogen fixation in rhizobium-legume symbioses." Science Advances 7, no. 31 (2021): eabh2433. http://dx.doi.org/10.1126/sciadv.abh2433.
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Rhizobia induce nodule formation on legume roots and differentiate into bacteroids, which catabolize plant-derived dicarboxylates to reduce atmospheric N2 into ammonia. Despite the agricultural importance of this symbiosis, the mechanisms that govern carbon and nitrogen allocation in bacteroids and promote ammonia secretion to the plant are largely unknown. Using a metabolic model derived from genome-scale datasets, we show that carbon polymer synthesis and alanine secretion by bacteroids facilitate redox balance in microaerobic nodules. Catabolism of dicarboxylates induces not only a higher oxygen demand but also a higher NADH/NAD+ ratio than sugars. Modeling and 13C metabolic flux analysis indicate that oxygen limitation restricts the decarboxylating arm of the tricarboxylic acid cycle, which limits ammonia assimilation into glutamate. By tightly controlling oxygen supply and providing dicarboxylates as the energy and electron source donors for N2 fixation, legumes promote ammonia secretion by bacteroids. This is a defining feature of rhizobium-legume symbioses.
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Geddes, Barney A., Jason V. S. Kearsley, Jiarui Huang, et al. "Minimal gene set from Sinorhizobium (Ensifer) meliloti pSymA required for efficient symbiosis with Medicago." Proceedings of the National Academy of Sciences 118, no. 2 (2020): e2018015118. http://dx.doi.org/10.1073/pnas.2018015118.
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Reduction of N2 gas to ammonia in legume root nodules is a key component of sustainable agricultural systems. Root nodules are the result of a symbiosis between leguminous plants and bacteria called rhizobia. Both symbiotic partners play active roles in establishing successful symbiosis and nitrogen fixation: while root nodule development is mostly controlled by the plant, the rhizobia induce nodule formation, invade, and perform N2 fixation once inside the plant cells. Many bacterial genes involved in the rhizobia–legume symbiosis are known, and there is much interest in engineering the symbiosis to include major nonlegume crops such as corn, wheat, and rice. We sought to identify and combine a minimal bacterial gene complement necessary and sufficient for symbiosis. We analyzed a model rhizobium, Sinorhizobium (Ensifer) meliloti, using a background strain in which the 1.35-Mb symbiotic megaplasmid pSymA was removed. Three regions representing 162 kb of pSymA were sufficient to recover a complete N2-fixing symbiosis with alfalfa, and a targeted assembly of this gene complement achieved high levels of symbiotic N2 fixation. The resulting gene set contained just 58 of 1,290 pSymA protein-coding genes. To generate a platform for future synthetic manipulation, the minimal symbiotic genes were reorganized into three discrete nod, nif, and fix modules. These constructs will facilitate directed studies toward expanding the symbiosis to other plant partners. They also enable forward-type approaches to identifying genetic components that may not be essential for symbiosis, but which modulate the rhizobium’s competitiveness for nodulation and the effectiveness of particular rhizobia–plant symbioses.
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Pandharikar, Gaurav, Jean-Luc Gatti, Jean-Christophe Simon, Pierre Frendo, and Marylène Poirié. "Aphid infestation differently affects the defences of nitrate-fed and nitrogen-fixing Medicago truncatula and alters symbiotic nitrogen fixation." Proceedings of the Royal Society B: Biological Sciences 287, no. 1934 (2020): 20201493. http://dx.doi.org/10.1098/rspb.2020.1493.
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Legumes can meet their nitrogen requirements through root nodule symbiosis, which could also trigger plant systemic resistance against pests. The pea aphid Acyrthosiphon pisum , a legume pest, can harbour different facultative symbionts (FS) influencing various traits of their hosts. It is therefore worth determining if and how the symbionts of the plant and the aphid modulate their interaction. We used different pea aphid lines without FS or with a single one ( Hamiltonella defensa , Regiella insecticola, Serratia symbiotica ) to infest Medicago truncatula plants inoculated with Sinorhizobium meliloti (symbiotic nitrogen fixation, SNF) or supplemented with nitrate (non-inoculated, NI). The growth of SNF and NI plants was reduced by aphid infestation, while aphid weight (but not survival) was lowered on SNF compared to NI plants. Aphids strongly affected the plant nitrogen fixation depending on their symbiotic status, suggesting indirect relationships between aphid- and plant-associated microbes. Finally, all aphid lines triggered expression of Pathogenesis-Related Protein 1 ( PR1 ) and Proteinase Inhibitor (PI) , respective markers for salicylic and jasmonic pathways, in SNF plants, compared to only PR1 in NI plants. We demonstrate that the plant symbiotic status influences plant–aphid interactions while that of the aphid can modulate the amplitude of the plant's defence response.
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Oono, Ryoko, Carolyn G. Anderson, and R. Ford Denison. "Failure to fix nitrogen by non-reproductive symbiotic rhizobia triggers host sanctions that reduce fitness of their reproductive clonemates." Proceedings of the Royal Society B: Biological Sciences 278, no. 1718 (2011): 2698–703. http://dx.doi.org/10.1098/rspb.2010.2193.
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The legume–rhizobia symbiosis is a classical mutualism where fixed carbon and nitrogen are exchanged between the species. Nonetheless, the plant carbon that fuels nitrogen (N 2 ) fixation could be diverted to rhizobial reproduction by ‘cheaters’—rhizobial strains that fix less N 2 but potentially gain the benefit of fixation by other rhizobia. Host sanctions can decrease the relative fitness of less-beneficial reproductive bacteroids and prevent cheaters from breaking down the mutualism. However, in certain legume species, only undifferentiated rhizobia reproduce, while only terminally differentiated rhizobial bacteroids fix nitrogen. Sanctions were, therefore, tested in two legume species that host non-reproductive bacteroids. We demonstrate that even legume species that host non-reproductive bacteroids, specifically pea and alfalfa, can severely sanction undifferentiated rhizobia when bacteroids within the same nodule fail to fix N 2 . Hence, host sanctions by a diverse set of legumes play a role in maintaining N 2 fixation.
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Prévost, Danielle, Pascal Drouin, Serge Laberge, Annick Bertrand, Jean Cloutier, and Gabriel Lévesque. "Cold-adapted rhizobia for nitrogen fixation in temperate regions." Canadian Journal of Botany 81, no. 12 (2003): 1153–61. http://dx.doi.org/10.1139/b03-113.
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Rhizobia from Canadian soils were selected for cold adaptation with the aim of improving productivity of legumes that are subjected to cool temperatures during the growing season. One approach was to use rhizobia associated with legume species indigenous to arctic and subarctic regions: (i) Mesorhizobium sp. isolated from Astragalus and Oxytropis spp. and (ii) Rhizobium leguminosarum from Lathryrus spp. The majority of these rhizobia are considered psychrotrophs because they can grow at 0 °C. The advantages of cold adaptation of arctic Mesorhizobium to improve legume symbiosis were demonstrated with the temperate forage legume sainfoin (Onobrychis viciifolia). In laboratory and field studies, arctic rhizobia were more efficient than temperate (commercial) rhizobia in improving growth of sainfoin and were more competitive in forming nodules. Biochemical studies on cold adaptation showed higher synthesis of cold shock proteins in cold-adapted than in nonadapted arctic rhizobia. Since arctic Mesorhizobium cannot nodulate agronomically important legumes, the nodulation genes and the bacterial signals (Nod factors) were characterized as a first step to modifying the host specificity of nodulation. Another valuable approach was to screen for cold adaptation, that is, rhizobia naturally associated with agronomic legumes cultivated in temperate areas. A superior strain of Sinorhizobium meliloti adapted for nodulation of alfalfa at low temperatures was selected and was the most efficient for improving growth of alfalfa in laboratory and field studies. This strain also performed well in improving regrowth of alfalfa after overwintering under cold and anaerobic (ice encasement) stresses, indicating a possible cross-adaptation of selected rhizobia for various abiotic stresses inherent to temperate climates.Key words: cold adaptation, legumes, symbiotic efficiency, cold shock protein, nodulation genes, anaerobiosis.
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Rivas, Raul, Encarna Velázquez, Anne Willems, et al. "A New Species of Devosia That Forms a Unique Nitrogen-Fixing Root-Nodule Symbiosis with the Aquatic Legume Neptunia natans (L.f.) Druce." Applied and Environmental Microbiology 68, no. 11 (2002): 5217–22. http://dx.doi.org/10.1128/aem.68.11.5217-5222.2002.
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ABSTRACT Rhizobia are the common bacterial symbionts that form nitrogen-fixing root nodules in legumes. However, recently other bacteria have been shown to nodulate and fix nitrogen symbiotically with these plants. Neptunia natans is an aquatic legume indigenous to tropical and subtropical regions and in African soils is nodulated by Allorhizobium undicola. This legume develops an unusual root-nodule symbiosis on floating stems in aquatic environments through a unique infection process. Here, we analyzed the low-molecular-weight RNA and 16S ribosomal DNA (rDNA) sequence of the same fast-growing isolates from India that were previously used to define the developmental morphology of the unique infection process in this symbiosis with N. natans and found that they are phylogenetically located in the genus Devosia, not Allorhizobium or Rhizobium. The 16S rDNA sequences of these two Neptunia-nodulating Devosia strains differ from the only species currently described in that genus, Devosia riboflavina. From the same isolated colonies, we also located their nodD and nifH genes involved in nodulation and nitrogen fixation on a plasmid of approximately 170 kb. Sequence analysis showed that their nodD and nifH genes are most closely related to nodD and nifH of Rhizobium tropici, suggesting that this newly described Neptunia-nodulating Devosia species may have acquired these symbiotic genes by horizontal transfer.
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Atkins, C. A. "The Legume/Rhizobium Symbiosis: Limitations to Maximizing Nitrogen Fixation." Outlook on Agriculture 15, no. 3 (1986): 128–34. http://dx.doi.org/10.1177/003072708601500305.
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Although the recent fall in the price of oil will ultimately be reflected in some reduction in the price of nitrogenous fertilizers the cost of the latter will still be sufficient to maintain interest in techniques of biological nitrogen fixation. This is attractive, in the sense that it involves direct utilization of atmospheric nitrogen as a free good but there are some costs, not yet possible to evaluate, to be set on the debit side. There is, therefore, need for much more research.
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Drew, E. A., V. V. S. R. Gupta, and D. K. Roget. "Herbicide use, productivity, and nitrogen fixation in field pea (Pisum sativum)." Australian Journal of Agricultural Research 58, no. 12 (2007): 1204. http://dx.doi.org/10.1071/ar06394.
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Grain legumes grown in low-rainfall (<300 mm per annum) cropping regions of southern Australia have at times failed to provide the rotational benefits observed in other regions, such as improved cereal yields in the season following a legume. ‘In-crop’ herbicides were identified as one possible factor that may have been negatively affecting the legume–rhizobia symbiosis. To test this hypothesis and identify possible mechanisms behind any observed effects, field trials were conducted at Waikerie (South Australia) in 2001, 2003, and 2004. Field pea (Pisum sativum L.) was grown and treated with one of several herbicides 5 weeks after sowing. Crop yellowing, biomass, nodulation, and nitrogen (N2) fixation were assessed 3 weeks after spraying, and biomass, yield, percent nitrogen derived from fixation (%Ndfa), and N2 fixation (2003, 2004) were assessed at the end of the season. Some herbicides stunted plant growth and caused crop yellowing 3 weeks after application; however, none of the herbicides affected N nutrition of peas. Despite this, in 2003, half of the herbicides assessed reduced the %Ndfa by 34–60% relative to unsprayed control plots. Herbicide effects on the measured parameters followed similar trends over each year of the 3-year study. However, effects were rarely significant in 2004 as the trials were primarily affected by low rainfall, indicating that environmental parameters play a key role in determining the severity of herbicide effects on symbiotic N2 fixation. The possible mechanisms behind herbicide-induced damage to the pea–rhizobium symbiosis are discussed, including reduced photosynthetic capacity of plants exposed to herbicides.
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Vance, C. P., and J. F. S. Lamb. "Application of biochemical studies to improving nitrogen fixation." Australian Journal of Experimental Agriculture 41, no. 3 (2001): 403. http://dx.doi.org/10.1071/ea00007.
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Improvement of symbiotic nitrogen fixation requires a multidisciplinary approach with a comprehensive program ranging from microbial ecology to plant breeding and genomics. Achievement of symbiotic nitrogen fixation requires at least 100 genes from each partner interacting in a favorable environment. The more information that we obtain from applied and fundamental studies of Rhizobium–legume and Frankia–non-legume symbioses, the greater are our chances to extend nitrogen fixation to non-fixing species. Studies with alfalfa (Medicago sativa L.) aimed at improving symbiotic nitrogen fixation have resulted in significant advances in germplasm development, plant biochemistry, microbial ecology and the understanding of plant genes involved in nodule nitrogen and carbon metabolism. However, translation to field improvement of symbiotic nitrogen fixation has proven elusive.
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Brewin, Nicholas J. "Legume root nodule symbiosis: An evolving story in biology and biotechnology." Biochemist 35, no. 4 (2013): 14–18. http://dx.doi.org/10.1042/bio03504014.
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The evolution of biological nitrogen fixation is central to the evolution of life on earth. Nitrogen is an essential component of proteins and nucleic acids and its restricted availability to living organisms has often been a major factor limiting growth. Despite the overwhelming abundance of N2 gas in the atmosphere, di-nitrogen is chemically inaccessible to most forms of life. For their growth and metabolism, most organisms use the ‘fixed’ forms of nitrogen, either as ammonium (NH4+) or as nitrate (NO3-), or derivatives thereof. However, the major input into the global nitrogen cycle is through the reductive process of biological nitrogen fixation which converts atmospheric N2 into ammonia (NH3). This process evolved in bacteria and/or archaea over 2.5 billion years ago while the planet still had a reducing atmosphere. Today, biological nitrogen fixation is still restricted to the bacteria and archaea. The legume root nodule symbiosis allows the host plant to benefit directly by association with soil bacteria, collectively termed rhizobia, which fix nitrogen as endosymbionts.
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Op den Camp, Rik H. M., Elisa Polone, Elena Fedorova, et al. "Nonlegume Parasponia andersonii Deploys a Broad Rhizobium Host Range Strategy Resulting in Largely Variable Symbiotic Effectiveness." Molecular Plant-Microbe Interactions® 25, no. 7 (2012): 954–63. http://dx.doi.org/10.1094/mpmi-11-11-0304.
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The non-legume genus Parasponia has evolved the rhizobium symbiosis independent from legumes and has done so only recently. We aim to study the promiscuity of such newly evolved symbiotic engagement and determine the symbiotic effectiveness of infecting rhizobium species. It was found that Parasponia andersonii can be nodulated by a broad range of rhizobia belonging to four different genera, and therefore, we conclude that this non-legume is highly promiscuous for rhizobial engagement. A possible drawback of this high promiscuity is that low-efficient strains can infect nodules as well. The strains identified displayed a range in nitrogen-fixation effectiveness, including a very inefficient rhizobium species, Rhizobium tropici WUR1. Because this species is able to make effective nodules on two different legume species, it suggests that the ineffectiveness of P. andersonii nodules is the result of the incompatibility between both partners. In P. andersonii nodules, rhizobia of this strain become embedded in a dense matrix but remain vital. This suggests that sanctions or genetic control against underperforming microsymbionts may not be effective in Parasponia spp. Therefore, we argue that the Parasponia-rhizobium symbiosis is a delicate balance between mutual benefits and parasitic colonization.
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Khan, Tazeen Fatima, and Md Didar-Ur-Alam. "Effects of biochar on legume-Rhizobium symbiosis in soil." Bangladesh Journal of Botany 47, no. 4 (2018): 945–52. http://dx.doi.org/10.3329/bjb.v47i4.47390.
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An in vitro study was conducted to observe the effects of tannery waste and biochar on soil bacterial population particularly legume-Rhizobium symbiosis. The study comprised a total of seven different treatments including a control. Count of total bacteria and Rhizobium was observed on initial materials and on all treated soils. A leguminous plant, cowpea, was used to study the effects on nitrogen fixation which could be further linked to legume-Rhizobium symbiosis. Bacterial population was higher in tannery waste treated soils than the corresponding biochar treated ones. It was found that waste treated soils had higher Rhizobium count than the biochar treated ones. Nitrogen fixation was found to be higher in tannery waste than biochar treatments. Although there appeared to be no adverse impact on legume-Rhizobium symbiosis, growth of bacteria particularly Rhizobium was inhibited indicating that microbial functioning of the soil might be affected and thereby likely to jeopardize agricultural production and food security.
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Uchiumi, Toshiki, Takuji Ohwada, Manabu Itakura, et al. "Expression Islands Clustered on the Symbiosis Island of the Mesorhizobium loti Genome." Journal of Bacteriology 186, no. 8 (2004): 2439–48. http://dx.doi.org/10.1128/jb.186.8.2439-2448.2004.
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ABSTRACT Rhizobia are symbiotic nitrogen-fixing soil bacteria that are associated with host legumes. The establishment of rhizobial symbiosis requires signal exchanges between partners in microaerobic environments that result in mutualism for the two partners. We developed a macroarray for Mesorhizobium loti MAFF303099, a microsymbiont of the model legume Lotus japonicus, and monitored the transcriptional dynamics of the bacterium during symbiosis, microaerobiosis, and starvation. Global transcriptional profiling demonstrated that the clusters of genes within the symbiosis island (611 kb), a transmissible region distinct from other chromosomal regions, are collectively expressed during symbiosis, whereas genes outside the island are downregulated. This finding implies that the huge symbiosis island functions as clustered expression islands to support symbiotic nitrogen fixation. Interestingly, most transposase genes on the symbiosis island were highly upregulated in bacteroids, as were nif, fix, fdx, and rpoN. The genome region containing the fixNOPQ genes outside the symbiosis island was markedly upregulated as another expression island under both microaerobic and symbiotic conditions. The symbiosis profiling data suggested that there was activation of amino acid metabolism, as well as nif-fix gene expression. In contrast, genes for cell wall synthesis, cell division, DNA replication, and flagella were strongly repressed in differentiated bacteroids. A highly upregulated gene in bacteroids, mlr5932 (encoding 1-aminocyclopropane-1-carboxylate deaminase), was disrupted and was confirmed to be involved in nodulation enhancement, indicating that disruption of highly expressed genes is a useful strategy for exploring novel gene functions in symbiosis.
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Suzuki, Shino, Toshihiro Aono, Kyung-Bum Lee, et al. "Rhizobial Factors Required for Stem Nodule Maturation and Maintenance in Sesbania rostrata-Azorhizobium caulinodans ORS571 Symbiosis." Applied and Environmental Microbiology 73, no. 20 (2007): 6650–59. http://dx.doi.org/10.1128/aem.01514-07.
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ABSTRACT The molecular and physiological mechanisms behind the maturation and maintenance of N2-fixing nodules during development of symbiosis between rhizobia and legumes still remain unclear, although the early events of symbiosis are relatively well understood. Azorhizobium caulinodans ORS571 is a microsymbiont of the tropical legume Sesbania rostrata, forming N2-fixing nodules not only on the roots but also on the stems. In this study, 10,080 transposon-inserted mutants of A. caulinodans ORS571 were individually inoculated onto the stems of S. rostrata, and those mutants that induced ineffective stem nodules, as displayed by halted development at various stages, were selected. From repeated observations on stem nodulation, 108 Tn5 mutants were selected and categorized into seven nodulation types based on size and N2 fixation activity. Tn5 insertions of some mutants were found in the well-known nodulation, nitrogen fixation, and symbiosis-related genes, such as nod, nif, and fix, respectively, lipopolysaccharide synthesis-related genes, C4 metabolism-related genes, and so on. However, other genes have not been reported to have roles in legume-rhizobium symbiosis. The list of newly identified symbiosis-related genes will present clues to aid in understanding the maturation and maintenance mechanisms of nodules.
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Doin de Moura, Ginaini Grazielli, Philippe Remigi, Catherine Masson-Boivin, and Delphine Capela. "Experimental Evolution of Legume Symbionts: What Have We Learnt?" Genes 11, no. 3 (2020): 339. http://dx.doi.org/10.3390/genes11030339.
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Rhizobia, the nitrogen-fixing symbionts of legumes, are polyphyletic bacteria distributed in many alpha- and beta-proteobacterial genera. They likely emerged and diversified through independent horizontal transfers of key symbiotic genes. To replay the evolution of a new rhizobium genus under laboratory conditions, the symbiotic plasmid of Cupriavidus taiwanensis was introduced in the plant pathogen Ralstonia solanacearum, and the generated proto-rhizobium was submitted to repeated inoculations to the C. taiwanensis host, Mimosa pudica L. This experiment validated a two-step evolutionary scenario of key symbiotic gene acquisition followed by genome remodeling under plant selection. Nodulation and nodule cell infection were obtained and optimized mainly via the rewiring of regulatory circuits of the recipient bacterium. Symbiotic adaptation was shown to be accelerated by the activity of a mutagenesis cassette conserved in most rhizobia. Investigating mutated genes led us to identify new components of R. solanacearum virulence and C. taiwanensis symbiosis. Nitrogen fixation was not acquired in our short experiment. However, we showed that post-infection sanctions allowed the increase in frequency of nitrogen-fixing variants among a non-fixing population in the M. pudica–C. taiwanensis system and likely allowed the spread of this trait in natura. Experimental evolution thus provided new insights into rhizobium biology and evolution.
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Oh, Hye-Sook, Jong-Yoon Chun, Myung-Sok Lee, Kyung-Hee Min, Suk-Ha Lee, and Choong-Ill Cheon. "Role of hsfA gene on host-specificity by Bradyrhizobium japonicum in a broad range of tropical legumes." Canadian Journal of Microbiology 46, no. 1 (1999): 81–84. http://dx.doi.org/10.1139/w99-111.
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Bradyrhizobium japonicum mutant strain NAD163, containing a 30-kb deletion mutant encompassing the hsfA gene, was inoculated onto a broad range of legume species to test host-specificity. Most legume species formed ineffective nodules except Vigna angularis var. Chibopat and Glycine max var. Pureunkong. A hsfA insertion mutant, BjjC211, gave similar results to strain NAD163, implying that many legume species require HsfA for host-specific nitrogen fixation. To determine whether other genes in the deleted region of NAD163 are also necessary, the hsfA gene was conjugally transferred into the NAD163 mutant. The transconjugant formed effective nodules on the host legume plants, which earlier had formed ineffective nodules with mutant NAD163. Thus, we conclude that the hsfA gene in the 30-kb region is the only factor responsible for host-specific nitrogen fixation in legume plants.Key words: host-specific nitrogen fixation, legume-Rhizobium symbiosis, hsfA gene, host-specificity.
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Fujita, Hironori, Seishiro Aoki, and Masayoshi Kawaguchi. "Evolutionary Dynamics of Nitrogen Fixation in the Legume–Rhizobia Symbiosis." PLoS ONE 9, no. 4 (2014): e93670. http://dx.doi.org/10.1371/journal.pone.0093670.
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Sugawara, Masayuki, Gopit R. Shah, Michael J. Sadowsky, et al. "Expression and Functional Roles of Bradyrhizobium japonicum Genes Involved in the Utilization of Inorganic and Organic Sulfur Compounds in Free-Living and Symbiotic Conditions." Molecular Plant-Microbe Interactions® 24, no. 4 (2011): 451–57. http://dx.doi.org/10.1094/mpmi-08-10-0184.
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Strains of Bradyrhizobium spp. form nitrogen-fixing symbioses with many legumes, including soybean. Although inorganic sulfur is preferred by bacteria in laboratory conditions, sulfur in agricultural soil is mainly present as sulfonates and sulfur esters. Here, we show that Bradyrhizobium japonicum and B. elkanii strains were able to utilize sulfate, cysteine, sulfonates, and sulfur-ester compounds as sole sulfur sources for growth. Expression and functional analysis revealed that two sets of gene clusters (bll6449 to bll6455 or bll7007 to bll7011) are important for utilization of sulfonates sulfur source. The bll6451 or bll7010 genes are also expressed in the symbiotic nodules. However, B. japonicum mutants defective in either of the sulfonate utilization operons were not affected for symbiosis with soybean, indicating the functional redundancy or availability of other sulfur sources in planta. In accordance, B. japonicum bacteroids possessed significant sulfatase activity. These results indicate that strains of Bradyrhizobium spp. likely use organosulfur compounds for growth and survival in soils, as well as for legume nodulation and nitrogen fixation.
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Kim, Minsoo, Yuhui Chen, Jiejun Xi, Christopher Waters, Rujin Chen, and Dong Wang. "An antimicrobial peptide essential for bacterial survival in the nitrogen-fixing symbiosis." Proceedings of the National Academy of Sciences 112, no. 49 (2015): 15238–43. http://dx.doi.org/10.1073/pnas.1500123112.
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In the nitrogen-fixing symbiosis between legume hosts and rhizobia, the bacteria are engulfed by a plant cell membrane to become intracellular organelles. In the model legume Medicago truncatula, internalization and differentiation of Sinorhizobium (also known as Ensifer) meliloti is a prerequisite for nitrogen fixation. The host mechanisms that ensure the long-term survival of differentiating intracellular bacteria (bacteroids) in this unusual association are unclear. The M. truncatula defective nitrogen fixation4 (dnf4) mutant is unable to form a productive symbiosis, even though late symbiotic marker genes are expressed in mutant nodules. We discovered that in the dnf4 mutant, bacteroids can apparently differentiate, but they fail to persist within host cells in the process. We found that the DNF4 gene encodes NCR211, a member of the family of nodule-specific cysteine-rich (NCR) peptides. The phenotype of dnf4 suggests that NCR211 acts to promote the intracellular survival of differentiating bacteroids. The greatest expression of DNF4 was observed in the nodule interzone II-III, where bacteroids undergo differentiation. A translational fusion of DNF4 with GFP localizes to the peribacteroid space, and synthetic NCR211 prevents free-living S. meliloti from forming colonies, in contrast to mock controls, suggesting that DNF4 may interact with bacteroids directly or indirectly for its function. Our findings indicate that a successful symbiosis requires host effectors that not only induce bacterial differentiation, but also that maintain intracellular bacteroids during the host–symbiont interaction. The discovery of NCR211 peptides that maintain bacterial survival inside host cells has important implications for improving legume crops.
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Lang, Claus, and Sharon R. Long. "Transcriptomic Analysis of Sinorhizobium meliloti and Medicago truncatula Symbiosis Using Nitrogen Fixation–Deficient Nodules." Molecular Plant-Microbe Interactions® 28, no. 8 (2015): 856–68. http://dx.doi.org/10.1094/mpmi-12-14-0407-r.
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The bacterium Sinorhizobium meliloti interacts symbiotically with legume plant hosts such as Medicago truncatula to form nitrogen-fixing root nodules. During symbiosis, plant and bacterial cells differentiate in a coordinated manner, resulting in specialized plant cells that contain nitrogen-fixing bacteroids. Both plant and bacterial genes are required at each developmental stage of symbiosis. We analyzed gene expression in nodules formed by wild-type bacteria on six plant mutants with defects in nitrogen fixation. We observed differential expression of 482 S. meliloti genes with functions in cell envelope homeostasis, cell division, stress response, energy metabolism, and nitrogen fixation. We simultaneously analyzed gene expression in M. truncatula and observed differential regulation of host processes that may trigger bacteroid differentiation and control bacterial infection. Our analyses of developmentally arrested plant mutants indicate that plants use distinct means to control bacterial infection during early and late symbiotic stages.
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Zgadzaj, Rafal, Ruben Garrido-Oter, Dorthe Bodker Jensen, Anna Koprivova, Paul Schulze-Lefert, and Simona Radutoiu. "Root nodule symbiosis in Lotus japonicus drives the establishment of distinctive rhizosphere, root, and nodule bacterial communities." Proceedings of the National Academy of Sciences 113, no. 49 (2016): E7996—E8005. http://dx.doi.org/10.1073/pnas.1616564113.
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Lotus japonicus has been used for decades as a model legume to study the establishment of binary symbiotic relationships with nitrogen-fixing rhizobia that trigger root nodule organogenesis for bacterial accommodation. Using community profiling of 16S rRNA gene amplicons, we reveal that in Lotus, distinctive nodule- and root-inhabiting communities are established by parallel, rather than consecutive, selection of bacteria from the rhizosphere and root compartments. Comparative analyses of wild-type (WT) and symbiotic mutants in Nod factor receptor5 (nfr5), Nodule inception (nin) and Lotus histidine kinase1 (lhk1) genes identified a previously unsuspected role of the nodulation pathway in the establishment of different bacterial assemblages in the root and rhizosphere. We found that the loss of nitrogen-fixing symbiosis dramatically alters community structure in the latter two compartments, affecting at least 14 bacterial orders. The differential plant growth phenotypes seen between WT and the symbiotic mutants in nonsupplemented soil were retained under nitrogen-supplemented conditions that blocked the formation of functional nodules in WT, whereas the symbiosis-impaired mutants maintain an altered community structure in the nitrogen-supplemented soil. This finding provides strong evidence that the root-associated community shift in the symbiotic mutants is a direct consequence of the disabled symbiosis pathway rather than an indirect effect resulting from abolished symbiotic nitrogen fixation. Our findings imply a role of the legume host in selecting a broad taxonomic range of root-associated bacteria that, in addition to rhizobia, likely contribute to plant growth and ecological performance.
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Yang, Ling-Ling, Zhao Jiang, Yan Li, En-Tao Wang, and Xiao-Yang Zhi. "Plasmids Related to the Symbiotic Nitrogen Fixation Are Not Only Cooperated Functionally but Also May Have Evolved over a Time Span in Family Rhizobiaceae." Genome Biology and Evolution 12, no. 11 (2020): 2002–14. http://dx.doi.org/10.1093/gbe/evaa152.
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Abstract Rhizobia are soil bacteria capable of forming symbiotic nitrogen-fixing nodules associated with leguminous plants. In fast-growing legume-nodulating rhizobia, such as the species in the family Rhizobiaceae, the symbiotic plasmid is the main genetic basis for nitrogen-fixing symbiosis, and is susceptible to horizontal gene transfer. To further understand the symbioses evolution in Rhizobiaceae, we analyzed the pan-genome of this family based on 92 genomes of type/reference strains and reconstructed its phylogeny using a phylogenomics approach. Intriguingly, although the genetic expansion that occurred in chromosomal regions was the main reason for the high proportion of low-frequency flexible gene families in the pan-genome, gene gain events associated with accessory plasmids introduced more genes into the genomes of nitrogen-fixing species. For symbiotic plasmids, although horizontal gene transfer frequently occurred, transfer may be impeded by, such as, the host’s physical isolation and soil conditions, even among phylogenetically close species. During coevolution with leguminous hosts, the plasmid system, including accessory and symbiotic plasmids, may have evolved over a time span, and provided rhizobial species with the ability to adapt to various environmental conditions and helped them achieve nitrogen fixation. These findings provide new insights into the phylogeny of Rhizobiaceae and advance our understanding of the evolution of symbiotic nitrogen fixation.
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Abramova, A. V., and A. G. Topaj. "Case Study of Plant-Microbial Symbiosis Model Using Evolutionary Game Theory." Mathematical Biology and Bioinformatics 13, no. 1 (2018): 130–58. http://dx.doi.org/10.17537/2018.13.130.
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Nitrogen-fixing bacteria (rhizobia) have symbiotic relationships with legumes: they inhabit legume root nodules and convert atmospheric nitrogen to a plant available form in exchange for photosynthates. Generally, this symbiotic process called biological nitrogen fixation is mutually beneficial to both plants and bacteria. Using this mechanism symbionts acquire alternative sources of hard-to-reach individual growth resources (carbon for rhizobia and nitrogen for plants). However, not all rhizobia provide fixed nitrogen to the host plant honestly: some of them can behave as a kind of cheaters. Unlimited cheating rhizobia strains propagation may potentially disrupt the symbiotic relationships. This raises the question of plant–rhizobia mutualism evolutionary stability. This paper presents the results of the legume–rhizobia interactions investigation implemented as AnyLogic agent-based models. Three modifications of interaction model ("one plant – one strain of rhizobia", "one plant – several strains of rhizobia", "one plant with root nitrogen uptake – several strains of rhizobia") in the form of evolutionary games in two populations (rhizobia and plants) are considered by the authors. Simulated natural selection is driven by populations heterogeneity: each agent has its own cooperation parameter which determines its strategy in evolutionary game. In the set of numerical experiments the following results were obtained. Simulated populations tend to become homogeneous with cooperation parameter value close to the theoretically optimal. Such degenerated structure of populations is evolutionarily stable and maximizes the total growth of the entire symbiotic system. Thus, the logic of symbionts co-development simulation itself prevents the emergence of parasitic strategies and automatically provides rational and mutually beneficial partnership sustainability. This remains true in the early stages of ontogenesis or under the assumption that life cycle duration is unlimited.
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O'Hara, G. W. "Nutritional constraints on root nodule bacteria affecting symbiotic nitrogen fixation: a review." Australian Journal of Experimental Agriculture 41, no. 3 (2001): 417. http://dx.doi.org/10.1071/ea00087.
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Root nodule bacteria require access to adequate concentrations of mineral nutrients for metabolic processes to enable their survival and growth as free-living soil saprophytes, and in their symbiotic relationship with legumes. Essential nutrients, with a direct requirement in metabolism of rhizobia are carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, potassium, calcium, magnesium, iron, manganese, copper, zinc, molybdenum, nickel, cobalt and selenium. Boron does not seem to be required by rhizobia, but is essential for the establishment of effective legume symbioses. Nutrient constraints can affect both free-living and symbiotic forms of root nodule bacteria, but whether they do is a function of a complex series of events and interactions. Important physiological characteristics of rhizobia involved in, or affected by, their mineral nutrition include nutrient uptake, growth rate, gene regulation, nutrient storage, survival, genetic exchange and the viable non-culturable state. There is considerable variation between genera, species and strains of rhizobia in their response to nutrient deficiency. The effects of nutrient deficiencies on free-living rhizobia in the soil are poorly understood. Competition between strains of rhizobia for limiting phosphorus and iron in the rhizosphere may affect their ability to nodulate legumes. Processes in the development of some legume symbioses specifically require calcium, cobalt, copper, iron, potassium, molybdenum, nickel, phosphorus, selenium, zinc and boron. Limitations of phosphorus, calcium, iron and molybdenum in particular, can reduce legume productivity by affecting nodule development and function. The effects of nutrient deficiencies on rhizobia–legume signalling are not understood. The supply of essential inorganic nutrients to bacteroids in relation to nutrient partitioning in nodule tissues and nutrient transport to the symbiosome may affect effectiveness of nitrogen fixation. An integration of molecular approaches with more traditional biochemical, physiological and field-based studies is needed to improve understanding of the agricultural importance of rhizobia response to nutrient stress.
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Gano-Cohen, Kelsey A., Peter J. Stokes, Mia A. Blanton, et al. "Nonnodulating Bradyrhizobium spp. Modulate the Benefits of Legume-Rhizobium Mutualism." Applied and Environmental Microbiology 82, no. 17 (2016): 5259–68. http://dx.doi.org/10.1128/aem.01116-16.
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ABSTRACTRhizobia are best known for nodulating legume roots and fixing atmospheric nitrogen for the host in exchange for photosynthates. However, the majority of the diverse strains of rhizobia do not form nodules on legumes, often because they lack key loci that are needed to induce nodulation. Nonnodulating rhizobia are robust heterotrophs that can persist in bulk soil, thrive in the rhizosphere, or colonize roots as endophytes, but their role in the legume-rhizobium mutualism remains unclear. Here, we investigated the effects of nonnodulating strains on the nativeAcmispon-Bradyrhizobiummutualism. To examine the effects on both host performance and symbiont fitness, we performed clonal inoculations of diverse nonnodulatingBradyrhizobiumstrains onAcmispon strigosushosts and also coinoculated hosts with mixtures of sympatric nodulating and nonnodulating strains. In isolation, nonnodulatingBradyrhizobiumstrains did not affect plant performance. In most cases, coinoculation of nodulating and nonnodulating strains reduced host performance compared to that of hosts inoculated with only a symbiotic strain. However, coinoculation increased host performance only under one extreme experimental treatment. Nearly all estimates of nodulating strain fitness were reduced in the presence of nonnodulating strains. We discovered that nonnodulating strains were consistently capable of coinfecting legume nodules in the presence of nodulating strains but that the fitness effects of coinfection for hosts and symbionts were negligible. Our data suggest that nonnodulating strains most often attenuate theAcmispon-Bradyrhizobiummutualism and that this occurs via competitive interactions at the root-soil interface as opposed toin planta.IMPORTANCERhizobia are soil bacteria best known for their capacity to form root nodules on legume plants and enhance plant growth through nitrogen fixation. Yet, most rhizobia in soil do not have this capacity, and their effects on this symbiosis are poorly understood. We investigated the effects of diverse nonnodulating rhizobia on a native legume-rhizobium symbiosis. Nonnodulating strains did not affect plant growth in isolation. However, compared to inoculations with symbiotic rhizobia, coinoculations of symbiotic and nonnodulating strains often reduced plant and symbiont fitness. Coinoculation increased host performance only under one extreme treatment. Nonnodulating strains also invaded nodule interiors in the presence of nodulating strains, but this did not affect the fitness of either partner. Our data suggest that nonnodulating strains may be important competitors at the root-soil interface and that their capacity to attenuate this symbiosis should be considered in efforts to use rhizobia as biofertilizers.
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Okubo, Takashi, Shohei Fukushima, Manabu Itakura, et al. "Genome Analysis Suggests that the Soil Oligotrophic Bacterium Agromonas oligotrophica (Bradyrhizobium oligotrophicum) Is a Nitrogen-Fixing Symbiont of Aeschynomene indica." Applied and Environmental Microbiology 79, no. 8 (2013): 2542–51. http://dx.doi.org/10.1128/aem.00009-13.
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ABSTRACTAgromonas oligotrophica(Bradyrhizobium oligotrophicum) S58Tis a nitrogen-fixing oligotrophic bacterium isolated from paddy field soil that is able to grow in extra-low-nutrient environments. Here, the complete genome sequence of S58 was determined. The S58 genome was found to comprise a circular chromosome of 8,264,165 bp with an average GC content of 65.1% lackingnodABCgenes and the typical symbiosis island. The genome showed a high level of similarity to the genomes ofBradyrhizobiumsp. ORS278 andBradyrhizobiumsp. BTAi1, including nitrogen fixation and photosynthesis gene clusters, which nodulate an aquatic legume plant,Aeschynomene indica, in a Nod factor-independent manner. Although nonsymbiotic (brady)rhizobia are significant components of rhizobial populations in soil, we found that most genes important for nodule development (ndv) and symbiotic nitrogen fixation (nifandfix) withA. indicawere well conserved between the ORS278 and S58 genomes. Therefore, we performed inoculation experiments with fiveA. oligotrophicastrains (S58, S42, S55, S72, and S80). Surprisingly, all five strains ofA. oligotrophicaformed effective nitrogen-fixing nodules on the roots and/or stems ofA. indica, with differentiated bacteroids. Nonsymbiotic (brady)rhizobia are known to be significant components of rhizobial populations without a symbiosis island or symbiotic plasmids in soil, but the present results indicate that soil-dwellingA. oligotrophicagenerally possesses the ability to establish symbiosis withA. indica. Phylogenetic analyses suggest that Nod factor-independent symbiosis withA. indicais a common trait ofnodABC- and symbiosis island-lacking strains within the members of the photosyntheticBradyrhizobiumclade, includingA. oligotrophica.
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Rigg, Jessica L., Ashlea T. Webster, Deirdre M. Harvey, et al. "Cross-host compatibility of commercial rhizobial strains for new and existing pasture legume cultivars in south-eastern Australia." Crop and Pasture Science 72, no. 9 (2021): 652. http://dx.doi.org/10.1071/cp20234.
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Perennial legumes have potential to increase pasture productivity in the high rainfall zone (600–850 mm) of south-eastern Australia through their ability to use summer rainfall and fix nitrogen (N2). Various perennial legumes are being evaluated for this environment; however, little information exists on legume–rhizobia cross-host compatibility and its consequences for biological N2 fixation. This is especially important when legumes are sown into fields with a background of competitive rhizobia such as WSM1325 or sown as a pasture mix with different host–symbiont pairs. We studied the effectiveness and cross-host compatibility of five commercial rhizobial strains for a range of pasture legumes (nine species, 18 cultivars) under controlled environment conditions, and further evaluated nodule occupancy and competitiveness of a newly established pasture (13 species, 20 cultivars) in the field, by determining nodulation and production (biomass and N2 fixation). Three of the commercial inoculant strains formed root nodules with multiple legume species; commonly however, less N2 was fixed in cases where the inoculant was not the recommended strain for the legume species. Within a legume species, cultivars could differ in their ability to form effective root nodules with multiple rhizobial strains. White clover cvv. Trophy, Haifa and Storm, strawberry clover cv. Palestine, and Talish clover cv. Permatas formed effective nodules with both TA1 and WSM1325 rhizobial strains. White clover cultivars that could not form an effective symbiosis with the common background strain WSM1325 fixed less N2. The white clover × Caucasian clover hybrid formed effective symbiosis with strain TA1 but not with other commercial strains. Some species such as birdsfoot trefoil, Talish clover, sulfur clover and tetraploid Caucasian clover formed ineffective symbiosis in the field. Until resolved, this will likely inhibit their further development as pasture plants for similar permanent pasture environments.
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Popovici, Jean, Gilles Comte, �milie Bagnarol, et al. "Differential Effects of Rare Specific Flavonoids on Compatible and Incompatible Strains in the Myrica gale-Frankia Actinorhizal Symbiosis." Applied and Environmental Microbiology 76, no. 8 (2010): 2451–60. http://dx.doi.org/10.1128/aem.02667-09.
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ABSTRACT Plant secondary metabolites, and specifically phenolics, play important roles when plants interact with their environment and can act as weapons or positive signals during biotic interactions. One such interaction, the establishment of mutualistic nitrogen-fixing symbioses, typically involves phenolic-based recognition mechanisms between host plants and bacterial symbionts during the early stages of interaction. While these mechanisms are well studied in the rhizobia-legume symbiosis, little is known about the role of plant phenolics in the symbiosis between actinorhizal plants and Frankia genus strains. In this study, the responsiveness of Frankia strains to plant phenolics was correlated with their symbiotic compatibility. We used Myrica gale, a host species with narrow symbiont specificity, and a set of compatible and noncompatible Frankia strains. M. gale fruit exudate phenolics were extracted, and 8 dominant molecules were purified and identified as flavonoids by high-resolution spectroscopic techniques. Total fruit exudates, along with two purified dihydrochalcone molecules, induced modifications of bacterial growth and nitrogen fixation according to the symbiotic specificity of strains, enhancing compatible strains and inhibiting incompatible ones. Candidate genes involved in these effects were identified by a global transcriptomic approach using ACN14a strain whole-genome microarrays. Fruit exudates induced differential expression of 22 genes involved mostly in oxidative stress response and drug resistance, along with the overexpression of a whiB transcriptional regulator. This work provides evidence for the involvement of plant secondary metabolites in determining symbiotic specificity and expands our understanding of the mechanisms, leading to the establishment of actinorhizal symbioses.
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Lodwig, E. M., A. H. F. Hosie, A. Bourdès, et al. "Amino-acid cycling drives nitrogen fixation in the legume–Rhizobium symbiosis." Nature 422, no. 6933 (2003): 722–26. http://dx.doi.org/10.1038/nature01527.
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Fagorzi, Camilla, Alexandru Ilie, Francesca Decorosi, et al. "Symbiotic and Nonsymbiotic Members of the Genus Ensifer (syn. Sinorhizobium) Are Separated into Two Clades Based on Comparative Genomics and High-Throughput Phenotyping." Genome Biology and Evolution 12, no. 12 (2020): 2521–34. http://dx.doi.org/10.1093/gbe/evaa221.
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Abstract Rhizobium–legume symbioses serve as paradigmatic examples for the study of mutualism evolution. The genus Ensifer (syn. Sinorhizobium) contains diverse plant-associated bacteria, a subset of which can fix nitrogen in symbiosis with legumes. To gain insights into the evolution of symbiotic nitrogen fixation (SNF), and interkingdom mutualisms more generally, we performed extensive phenotypic, genomic, and phylogenetic analyses of the genus Ensifer. The data suggest that SNF likely emerged several times within the genus Ensifer through independent horizontal gene transfer events. Yet, the majority (105 of 106) of the Ensifer strains with the nodABC and nifHDK nodulation and nitrogen fixation genes were found within a single, monophyletic clade. Comparative genomics highlighted several differences between the “symbiotic” and “nonsymbiotic” clades, including divergences in their pangenome content. Additionally, strains of the symbiotic clade carried 325 fewer genes, on average, and appeared to have fewer rRNA operons than strains of the nonsymbiotic clade. Initial characterization of a subset of ten Ensifer strains identified several putative phenotypic differences between the clades. Tested strains of the nonsymbiotic clade could catabolize 25% more carbon sources, on average, than strains of the symbiotic clade, and they were better able to grow in LB medium and tolerate alkaline conditions. On the other hand, the tested strains of the symbiotic clade were better able to tolerate heat stress and acidic conditions. We suggest that these data support the division of the genus Ensifer into two main subgroups, as well as the hypothesis that pre-existing genetic features are required to facilitate the evolution of SNF in bacteria.
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Herridge, D. F., J. E. Turpin, and M. J. Robertson. "Improving nitrogen fixation of crop legumes through breeding and agronomic management: analysis with simulation modelling." Australian Journal of Experimental Agriculture 41, no. 3 (2001): 391. http://dx.doi.org/10.1071/ea00041.
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The nitrogen fixed by legumes is a valuable resource in agriculture, with crop legumes alone contributing as much as 20% of the nitrogen requirements of the world’s grain and oilseed crops. Increasing legume nitrogen fixation through genetic improvement and more efficient management would have large economic benefits. Breeding for improved nitrogen fixation has, to a large extent, not been successful. Suggested reasons include the difficulty in combining single traits like nitrogen fixation with other traits, such as disease resistance, seed quality and yield, a lack of focus of programs and a lack of screening methodologies. Agronomic management of legume nitrogen fixation offers other opportunities. The challenge is to package those opportunities and provide legume growers with tools for understanding the factors determining nitrogen fixation, while at the same time providing them with site-specific management options. The potential of simulation modelling for assessing genetic and management options for enhancing nitrogen fixation of soybean grown at Warwick in south-eastern Queensland was investigated in a series of 30-year simulations using the APSIM modelling framework. The APSIM–soybean module was first adjusted to reflect observed responses of nitrogen fixation to soil nitrate. The subsequent simulations indicated that (genetically based) symbiotic nitrate tolerance would have only marginal benefits on residual soil nitrate (7 kg N/ha at sowing soil nitrate of 100 kg N/ha). Management of the crop for highest grain yield through optimising sowing dates, plant density and fallow length provided the best opportunities for increasing nitrogen fixation. The use of APSIM as a tool for managing legume nitrogen fixation appears to have merit.
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Zou, Hang, Ni-Na Zhang, Qing Pan, Jian-Hua Zhang, Juan Chen, and Ge-Hong Wei. "Hydrogen Sulfide Promotes Nodulation and Nitrogen Fixation in Soybean–Rhizobia Symbiotic System." Molecular Plant-Microbe Interactions® 32, no. 8 (2019): 972–85. http://dx.doi.org/10.1094/mpmi-01-19-0003-r.
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The rhizobium–legume symbiotic system is crucial for nitrogen cycle balance in agriculture. Hydrogen sulfide (H2S), a gaseous signaling molecule, may regulate various physiological processes in plants. However, whether H2S has regulatory effect in this symbiotic system remains unknown. Herein, we investigated the possible role of H2S in the symbiosis between soybean (Glycine max) and rhizobium (Sinorhizobium fredii). Our results demonstrated that an exogenous H2S donor (sodium hydrosulfide [NaHS]) treatment promoted soybean growth, nodulation, and nitrogenase (Nase) activity. Western blotting analysis revealed that the abundance of Nase component nifH was increased by NaHS treatment in nodules. Quantitative real-time polymerase chain reaction data showed that NaHS treatment upregulated the expressions of symbiosis-related genes nodA, nodC, and nodD of S. fredii. In addition, expression of soybean nodulation marker genes, including early nodulin 40 (GmENOD40), ERF required for nodulation (GmERN), nodulation signaling pathway 2b (GmNSP2b), and nodulation inception genes (GmNIN1a, GmNIN2a, and GmNIN2b), were upregulated. Moreover, the expressions of glutamate synthase (GmGOGAT), asparagine synthase (GmAS), nitrite reductase (GmNiR), ammonia transporter (GmSAT1), leghemoglobin (GmLb), and nifH involved in nitrogen metabolism were upregulated in NaHS-treated soybean roots and nodules. Together, our results suggested that H2S may act as a positive signaling molecule in the soybean–rhizobia symbiotic system and enhance the system’s nitrogen fixation ability.
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Ortega-Ortega, Yolanda, Janet Carrasco-Castilla, Marco A. Juárez-Verdayes, et al. "Actin Depolymerizing Factor Modulates Rhizobial Infection and Nodule Organogenesis in Common Bean." International Journal of Molecular Sciences 21, no. 6 (2020): 1970. http://dx.doi.org/10.3390/ijms21061970.
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Actin plays a critical role in the rhizobium–legume symbiosis. Cytoskeletal rearrangements and changes in actin occur in response to Nod factors secreted by rhizobia during symbiotic interactions with legumes. These cytoskeletal rearrangements are mediated by diverse actin-binding proteins, such as actin depolymerization factors (ADFs). We examined the function of an ADF in the Phaseolus vulgaris–rhizobia symbiotic interaction (PvADFE). PvADFE was preferentially expressed in rhizobia-inoculated roots and nodules. PvADFE promoter activity was associated with root hairs harbouring growing infection threads, cortical cell divisions beneath root hairs, and vascular bundles in mature nodules. Silencing of PvADFE using RNA interference increased the number of infection threads in the transgenic roots, resulting in increased nodule number, nitrogen fixation activity, and average nodule diameter. Conversely, overexpression of PvADFE reduced the nodule number, nitrogen fixation activity, average nodule diameter, as well as NODULE INCEPTION (NIN) and EARLY NODULIN2 (ENOD2) transcript accumulation. Hence, changes in ADFE transcript levels affect rhizobial infection and nodulation, suggesting that ADFE is fine-tuning these processes.
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Jourand, Philippe, Adeline Renier, Sylvie Rapior, et al. "Role of Methylotrophy During Symbiosis Between Methylobacterium nodulans and Crotalaria podocarpa." Molecular Plant-Microbe Interactions® 18, no. 10 (2005): 1061–68. http://dx.doi.org/10.1094/mpmi-18-1061.
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Some rare leguminous plants of the genus Crotalaria are specifically nodulated by the methylotrophic bacterium Methylobacterium nodulans. In this study, the expression and role of bacterial methylotrophy were investigated during symbiosis between M. nodulans, strain ORS 2060T, and its host legume, Crotalaria podocarpa. Using lacZ fusion to the mxaF gene, we showed that the methylotroph genes are expressed in the root nodules, suggesting methylotrophic activity during symbiosis. In addition, loss of the bacterial methylotrophic function significantly affected plant development. Indeed, inoculation of M. nodulans nonmethylotroph mutants in C. podocarpa decreased the total root nodule number per plant up to 60%, decreased the whole-plant nitrogen fixation capacity up to 42%, and reduced the total dry plant biomass up to 46% compared with the wild-type strain. In contrast, inoculation of the legume C. podocarpa with nonmethylotrophic mutants complemented with functional mxa genes restored the symbiotic wild phenotype. These results demonstrate the key role of methylotrophy during symbiosis between M. nodulans and C. podocarpa.
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Takanashi, Kojiro, Takayuki Sasaki, Tomohiro Kan, et al. "A Dicarboxylate Transporter, LjALMT4, Mainly Expressed in Nodules of Lotus japonicus." Molecular Plant-Microbe Interactions® 29, no. 7 (2016): 584–92. http://dx.doi.org/10.1094/mpmi-04-16-0071-r.
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Legume plants can establish symbiosis with soil bacteria called rhizobia to obtain nitrogen as a nutrient directly from atmospheric N2 via symbiotic nitrogen fixation. Legumes and rhizobia form nodules, symbiotic organs in which fixed-nitrogen and photosynthetic products are exchanged between rhizobia and plant cells. The photosynthetic products supplied to rhizobia are thought to be dicarboxylates but little is known about the movement of dicarboxylates in the nodules. In terms of dicarboxylate transporters, an aluminum-activated malate transporter (ALMT) family is a strong candidate responsible for the membrane transport of carboxylates in nodules. Among the seven ALMT genes in the Lotus japonicus genome, only one, LjALMT4, shows a high expression in the nodules. LjALMT4 showed transport activity in a Xenopus oocyte system, with LjALMT4 mediating the efflux of dicarboxylates including malate, succinate, and fumarate, but not tricarboxylates such as citrate. LjALMT4 also mediated the influx of several inorganic anions. Organ-specific gene expression analysis showed LjALMT4 mRNA mainly in the parenchyma cells of nodule vascular bundles. These results suggest that LjALMT4 may not be involved in the direct supply of dicarboxylates to rhizobia in infected cells but is responsible for supplying malate as well as several anions necessary for symbiotic nitrogen fixation, via nodule vasculatures.
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Sasakura, Fuyuko, Toshiki Uchiumi, Yoshikazu Shimoda, et al. "A Class 1 Hemoglobin Gene from Alnus firma Functions in Symbiotic and Nonsymbiotic Tissues to Detoxify Nitric Oxide." Molecular Plant-Microbe Interactions® 19, no. 4 (2006): 441–50. http://dx.doi.org/10.1094/mpmi-19-0441.
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Actinorhizal symbiosis is as important in biological nitrogen fixation as legume-rhizobium symbiosis in the global nitrogen cycle. To understand the function of hemoglobin (Hb) in actinorhizal symbiosis, we characterized a Hb of Alnus firma, AfHb1. A cDNA that encodes nonsymbiotic Hb (nonsym-Hb) was isolated from a cDNA library of A. firma nodules probed with LjHb1, a nonsym-Hb of Lotus japonicus. No homolog of symbiotic Hb (sym-Hb) could be identified by screening in the cDNA library or by polymerase chain reaction (PCR) using degenerate primers for other sym-Hb genes. The deduced amino acid sequence of AfHb1 showed 92% sequence similarity with a class 1 nonsym-Hb of Casuarina glauca. Quantitative reverse transcriptase-PCR analysis showed that AfHb1 was expressed strongly in the nodules and enhanced expression was detected under cold stress but not under hypoxia or osmotic stress. Moreover, AfHb1 was strongly induced by the application of nitric oxide (NO) donors, and the application of a NO scavenger suppressed the effect of NO donors. Acetylene reduction was strongly inhibited by the addition of NO donors. AfHb1 may support the nitrogen fixation ability of members of the genus Frankia as a NO scavenger.
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Kaiser, B. N., B. J. Shelp, P. Thumfort, and D. B. Layzell. "Oxygen limitation of N2 fixation in various legume symbioses." Canadian Journal of Plant Science 74, no. 4 (1994): 853–55. http://dx.doi.org/10.4141/cjps94-154.
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Two O2 ramping techniques (linear versus exponential) were used to investigate the response of H2 evolution from intact nodules of soybean (Glycine max (L.) Merr. 'Maple Arrow'), stem-girdled soybean, pea (Pisum sativum L. 'Juneau'), and common bean (Phaseolus vulgaris L. 'Ex Rico 23') to increasing O2 concentrations from 20 to 100% over a 30-min period. The data indicate symbiosis-specific responses to the two ramps, and possible implications for determination of O2 limitation of N2 fixation. Key words: Hydrogen evolution, legume, nitrogen fixation
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Vallis, I., and CJ Gardener. "Effect of pasture age on the efficiency of nitrogen fixation by 10 accessions of Stylosanthes spp." Australian Journal of Experimental Agriculture 25, no. 1 (1985): 70. http://dx.doi.org/10.1071/ea9850070.
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The proportion of legume nitrogen that had been symbiotically fixed in 10 accessions of Stylosanthes spp. was determined by an isotope dilution method in microplots within grazed pastures 1, 4 and 6 years after the legumes were sown in association with buffel grass at Lansdown, near Townsville, Queensland. The proportion, averaged over all accessions, varied between years from 0.79 to 0.83, but was not related to pasture age, differences in legume yield, or total uptake of soil nitrogen. Within years, the proportion in individual plots was weakly and negatively correlated with legume yield and soil nitrogen uptake 4 years after sowing, but not at other times. No significant differences in proportions between the 10 accessions of Stylosanthes were demonstrated. It is concluded that, in these pastures, the efficiency of nitrogen fixation by the legume is not greatly affected by changes in the availability of soil nitrogen as the pasture ages. Consequently, the rate of symbiotic nitrogen fixation will depend mainly on the growth of the legume.
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Rutten, Paul J., Harrison Steel, Graham A. Hood, et al. "Multiple sensors provide spatiotemporal oxygen regulation of gene expression in a Rhizobium-legume symbiosis." PLOS Genetics 17, no. 2 (2021): e1009099. http://dx.doi.org/10.1371/journal.pgen.1009099.
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Regulation by oxygen (O2) in rhizobia is essential for their symbioses with plants and involves multiple O2 sensing proteins. Three sensors exist in the pea microsymbiont Rhizobium leguminosarum Rlv3841: hFixL, FnrN and NifA. At low O2 concentrations (1%) hFixL signals via FxkR to induce expression of the FixK transcription factor, which activates transcription of downstream genes. These include fixNOQP, encoding the high-affinity cbb3-type terminal oxidase used in symbiosis. In free-living Rlv3841, the hFixL-FxkR-FixK pathway was active at 1% O2, and confocal microscopy showed hFixL-FxkR-FixK activity in the earliest stages of Rlv3841 differentiation in nodules (zones I and II). Work on Rlv3841 inside and outside nodules showed that the hFixL-FxkR-FixK pathway also induces transcription of fnrN at 1% O2 and in the earliest stages of Rlv3841 differentiation in nodules. We confirmed past findings suggesting a role for FnrN in fixNOQP expression. However, unlike hFixL-FxkR-FixK, Rlv3841 FnrN was only active in the near-anaerobic zones III and IV of pea nodules. Quantification of fixNOQP expression in nodules showed this was driven primarily by FnrN, with minimal direct hFixL-FxkR-FixK induction. Thus, FnrN is key for full symbiotic expression of fixNOQP. Without FnrN, nitrogen fixation was reduced by 85% in Rlv3841, while eliminating hFixL only reduced fixation by 25%. The hFixL-FxkR-FixK pathway effectively primes the O2 response by increasing fnrN expression in early differentiation (zones I-II). In zone III of mature nodules, near-anaerobic conditions activate FnrN, which induces fixNOQP transcription to the level required for wild-type nitrogen fixation activity. Modelling and transcriptional analysis indicates that the different O2 sensitivities of hFixL and FnrN lead to a nuanced spatiotemporal pattern of gene regulation in different nodule zones in response to changing O2 concentration. Multi-sensor O2 regulation is prevalent in rhizobia, suggesting the fine-tuned control this enables is common and maximizes the effectiveness of the symbioses.
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Rivas, Raúl, Paula García-Fraile, and Encarna Velázquez. "Taxonomy of Bacteria Nodulating Legumes." Microbiology Insights 2 (January 2009): MBI.S3137. http://dx.doi.org/10.4137/mbi.s3137.
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Over the years, the term “rhizobia” has come to be used for all the bacteria that are capable of nodulation and nitrogen fixation in association with legumes but the taxonomy of rhizobia has changed considerably over the last 30 year. Recently, several non-rhizobial species belonging to alpha and beta subgroup of Proteobacteria have been identified as nitrogen-fixing legume symbionts. Here we provide an overview of the history of the rhizobia and the widespread phylogenetic diversity of nitrogen-fixing legume symbionts.
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Ortíz, José, Carolina Sanhueza, Antònia Romero-Munar, et al. "In Vivo Metabolic Regulation of Alternative Oxidase under Nutrient Deficiency—Interaction with Arbuscular Mycorrhizal Fungi and Rhizobium Bacteria." International Journal of Molecular Sciences 21, no. 12 (2020): 4201. http://dx.doi.org/10.3390/ijms21124201.
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The interaction of the alternative oxidase (AOX) pathway with nutrient metabolism is important for understanding how respiration modulates ATP synthesis and carbon economy in plants under nutrient deficiency. Although AOX activity reduces the energy yield of respiration, this enzymatic activity is upregulated under stress conditions to maintain the functioning of primary metabolism. The in vivo metabolic regulation of AOX activity by phosphorus (P) and nitrogen (N) and during plant symbioses with Arbuscular mycorrhizal fungi (AMF) and Rhizobium bacteria is still not fully understood. We highlight several findings and open questions concerning the in vivo regulation of AOX activity and its impact on plant metabolism during P deficiency and symbiosis with AMF. We also highlight the need for the identification of which metabolic regulatory factors of AOX activity are related to N availability and nitrogen-fixing legume-rhizobia symbiosis in order to improve our understanding of N assimilation and biological nitrogen fixation.
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Kasper, Stephanie, Bradley Christoffersen, Pushpa Soti, and Alexis Racelis. "Abiotic and Biotic Limitations to Nodulation by Leguminous Cover Crops in South Texas." Agriculture 9, no. 10 (2019): 209. http://dx.doi.org/10.3390/agriculture9100209.
Full textAbstract:
Many farms use leguminous cover crops as a nutrient management strategy to reduce their need for nitrogen fertilizer. When they are effective, leguminous cover crops are a valuable tool for sustainable nutrient management. However, the symbiotic partnership between legumes and nitrogen fixing rhizobia is vulnerable to several abiotic and biotic stressors that reduce nitrogen fixation efficiency in real world contexts. Sometimes, despite inoculation with rhizobial strains, this symbiosis fails to form. Such failure was observed in a 14-acre winter cover crop trial in the Rio Grande Valley (RGV) of Texas when three legume species produced no signs of nodulation or nitrogen fixation. This study examined the role of nitrogen, phosphorus, moisture, micronutrients, and native microbial communities in the nodulation of cowpea (Vigna unguiculata L. Walp) and assessed arbuscular mycorrhizal fungi as an intervention to improve nodulation. Results from two controlled studies confirm moisture and native microbial communities as major factors in nodulation success. Micronutrients showed mixed impacts on nodulation depending on plant stress conditions. Nitrogen and phosphorus deficiencies, however, were not likely causes, nor was mycorrhizal inoculation an effective intervention to improve nodulation. Inoculation method also had a major impact on nodulation rates. Continued research on improved inoculation practices and other ways to maximize nitrogen fixation efficiency will be required to increase successful on-farm implementation.
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Anderson, A., J. A. Baldock, S. L. Rogers, W. Bellotti, and G. Gill. "Influence of chlorsulfuron on rhizobial growth, nodule formation, and nitrogen fixation with chickpea." Australian Journal of Agricultural Research 55, no. 10 (2004): 1059. http://dx.doi.org/10.1071/ar03057.
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Sulfonylurea residues have been found to inhibit the growth of some legume crops and pastures in seasons following application. Negative effects of these herbicides on symbiotic nitrogen fixation by legume crops and pastures have been demonstrated. Reductions in nitrogen fixation may result from a direct effect of the herbicide on rhizobial growth and/or an indirect effect on plant growth. In this study the influence of chlorsulfuron on the growth of chickpea rhizobia [Mesorhizobium ciceri (CC1192)], the growth of chickpea plants, and the extent of nodulation and nitrogen fixation by the chickpea/rhizobia symbiosis were examined. In vitro studies (in yeast mannitol broth and a defined medium) showed that chlorsulfuron applied at double the recommended field application rate did not influence the growth of chickpea rhizobia. An experiment using 14C-labelled chlorsulfuron was conducted to determine if rhizobial cells exposed to chlorsulfuron could deliver the herbicide to the point of root infection and nodule formation. Approximately 1% of the herbicide present in the rhizobial growth medium remained with the cell/inoculum material after rinsing with 1/4 strength Ringer’s solution. This was considered unlikely to affect chickpea growth, nodulation, or nitrogen fixation. A pot experiment was used to define the influence of chlorsulfuron on the growth, nodulation, and nitrogen fixation of chickpeas. The presence of chlorsulfuron in the soil reduced the nodulation and nitrogen fixation of the chickpea plants. Pre-exposing rhizobia to chlorsulfuron before inoculating them into pots with germinating chickpea seeds, reduced the number of nodules formed by 51%. Exposure of chickpeas and chickpea rhizobia to chlorsulfuron can adversely affect the formation and activity of symbiotic nitrogen-fixing nodules, even when only the rhizobial inoculant is exposed briefly to the herbicide.
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Wang, Xiaomi, Ying Teng, Chen Tu, et al. "Coupling between Nitrogen Fixation and Tetrachlorobiphenyl Dechlorination in a Rhizobium–Legume Symbiosis." Environmental Science & Technology 52, no. 4 (2018): 2217–24. http://dx.doi.org/10.1021/acs.est.7b05667.
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PAMPANA, SILVIA, ALESSANDRO MASONI, MARCO MARIOTTI, LAURA ERCOLI, and IDUNA ARDUINI. "NITROGEN FIXATION OF GRAIN LEGUMES DIFFERS IN RESPONSE TO NITROGEN FERTILISATION." Experimental Agriculture 54, no. 1 (2016): 66–82. http://dx.doi.org/10.1017/s0014479716000685.
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SUMMARYLegume crops are not usually fertilised with mineral N. However, there are at least two agronomic cases when it would be advantageous to distribute N fertiliser to legume crops: at sowing, before the onset of nodule functioning, and when a legume is intercropped with a cereal. We highlight the impact of various levels of fertiliser nitrogen on grain yield, nodulation capacity and biological nitrogen fixation in the four most common grain legume crops grown in central Italy. Chickpea (Cicer arietinum L.), field bean (Vicia faba L. var. minor), pea (Pisum sativum L.) and white lupin (Lupinus albus L.) were grown in soil inside growth boxes for two cropping seasons with five nitrogen fertilisation rates: 0, 40, 80, 120 and 160 kg ha−1. In both years, experimental treatments (five crops and five levels of N) were arranged in a randomised block design. We found that unfertilised plants overall yielded grain, total biomass and nitrogen at a similar level to plants supplied with 80–120 kg ha−1 of mineral nitrogen. However, above those N rates, the production of chickpea, pea and white lupin decreased, thus indicating that the high supply of N fertiliser decreased the level of N2 fixed to such an extent that the full N2-fixing potential might not be achieved. In all four grain legumes, the amount of N2 fixed was positively related to nodule biomass, which was inversely related to the rate of the N fertiliser applied. The four grain legumes studied responded differently to N fertilisation: in white lupin and chickpea, the amount of nitrogen derived from N2 fixation linearly decreased with increasing N supply as a result of a reduction in nodulation and N2 fixed per unit mass of nodules. Conversely, in field bean and pea, the decrease in N2 fixation was only due to a reduction in nodule biomass since nodule fixation activity increased with N supply. Our results suggest that the legume species and the N rate are critical factors in determining symbiotic N2-fixation responses to N fertilisation.
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Chalifour, François-P., and Louise M. Nelson. "Effects of continuous combined nitrogen supply on symbiotic dinitrogen fixation of faba bean and pea inoculated with different rhizobial isolates." Canadian Journal of Botany 65, no. 12 (1987): 2542–48. http://dx.doi.org/10.1139/b87-345.
Full textAbstract:
Combined nitrogen (N) has adverse effects on virtually all stages of the Rhizobium–legume symbiosis. Tolerance to combined N varies among legume hosts and rhizobial isolates, but the contribution of each symbiotic partner is not well established. The effects of combined N were studied in faba bean (Vicia faba L.) and pea (Pisum sativum L.), using the same Rhizobium leguminosarum isolates for both hosts. In one experiment, faba bean and pea were inoculated individually with four rhizobial isolates and grown for 28 days in the continuous presence of 0, 2.5, 5.0, or7.5 mol m−3 NH4NO3. For each isolate, faba bean was consistently more tolerant to combined N than pea as shown by significantly smaller rates of decrease in N2-fixing activity (acetylene reduction) in faba bean than in pea. The results were substantiated by those of a similar experiment in which increasing levels of 15N-labeled [Formula: see text] (5, 10, or 15 mol m−3) were supplied continuously to faba bean and pea inoculated individually with two rhizobial isolates. Comparisons of the different symbioses based on the proportion of total plant N derived from N2 fixation confirmed the conclusions reached using acetylene reduction activities.
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Materon, L. A., J. D. H. Keatinge, D. P. Beck, N. Yurtsever, K. Karuc, and S. Altuntas. "The Role of Rhizobial Biodiversity in Legume Crop Productivity in the West Asian Highlands." Experimental Agriculture 31, no. 4 (1995): 485–91. http://dx.doi.org/10.1017/s0014479700026466.
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SUMMARYThe native rhizobia capable of symbiosis with annually-sown food and forage legume crops in the Turkish highlands were surveyed and estimates made of the numbers and nitrogen fixing efficiency of native Rhizobium leguminosarum with Turkish cultivars of lentil (Lens culinaris Medik.) and vetch (Vicia sativa L.). Native rhizobia were present in medium to high numbers in most samples but the nitrogen fixation efficiency of at least half of the isolates was poor. Vetch was somewhat less specific in its rhizobial compatibility than lentil, suggesting a potential for artificial inoculation to improve the productivity and sustainability of cropping in both species especially in areas of central and eastern Anatolia where legumes are not traditionally grown.Biodiversidad en el Rhizobium leguminosarum
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Biederbeck, V. O., O. T. Bouman, C. A. Campbell, G. E. Winkleman, and L. D. Bailey. "Nitrogen benefits from four green-manure legumes in dryland cropping systems." Canadian Journal of Plant Science 76, no. 2 (1996): 307–15. http://dx.doi.org/10.4141/cjps96-053.
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Partial replacement of fallow with legume green manures has the potential to improve cereal production and agricultural sustainability in the northern Great Plains. This is possible if N gains by annual legumes and enhancement of soil N availability are optimized. The objectives of the study were to (i) determine the N distribution in different vegetative components of four annual legumes; (ii) estimate their ability to accumulate N through fixation; and (iii) compare the N uptake of the cereal crop that follows legume green manure with that of cereal grown on fallow or of cereal receiving N fertilizer. Black lentil (Lens culinaris Medik.), Tangier flatpea (Lathyrus tingitanus L.), chickling vetch (Lathyrus sativus L.), and feedpea (Pisum sativum L.) were grown in rotation with spring wheat (Tnticum aestivum L.). Nitrogen concentration in legume nodules was several times greater than in any other plant part. However, N concentration in legume shoots was, on average, 27% greater than in legume roots. Total legume N content (% × mass) ranged from 41 to 126 kg ha−1 in years of low weediness. In those years, below-ground legume N content ranged between 2 and 29 kg ha−1 and averaged 7, 8, 17 and 6 kg ha−1 for black lentil, Tangier flatpea, chickling vetch and feedpea, respectively. Estimates of N2 fixation varied between 6 and 69 kg ha−1 and averaged 18 kg ha−1 for black lentil, 16 for Tangier flatpea, 49 for chickling vetch and 40 for feedpea. Within 3 mo of green-manure incorporation, average net N mineralization across years was greatest after black lentil and chickling vetch (38 kg N ha−1). The average 49 kg N ha−1 lost through cereal grain harvest was balanced by gains through symbiotic N2 fixation when chickling vetch and feedpea were used as green manure, but black lentil and Tangier flatpea replaced only about 35% of the N removed in the grain. Key words: Symbiotic N2 fixation, N mineralization, Tangier flatpea, black lentil, chickling vetch, feedpea
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Ji, Jie, Chunyang Zhang, Zhongfeng Sun, Longlong Wang, Deqiang Duanmu, and Qiuling Fan. "Genome Editing in Cowpea Vigna unguiculata Using CRISPR-Cas9." International Journal of Molecular Sciences 20, no. 10 (2019): 2471. http://dx.doi.org/10.3390/ijms20102471.
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Cowpea (Vigna unguiculata) is widely cultivated across the world. Due to its symbiotic nitrogen fixation capability and many agronomically important traits, such as tolerance to low rainfall and low fertilization requirements, as well as its high nutrition and health benefits, cowpea is an important legume crop, especially in many semi-arid countries. However, research in Vigna unguiculata is dramatically hampered by the lack of mutant resources and efficient tools for gene inactivation in vivo. In this study, we used clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9). We applied the CRISPR/Cas9-mediated genome editing technology to efficiently disrupt the representative symbiotic nitrogen fixation (SNF) gene in Vigna unguiculata. Our customized guide RNAs (gRNAs) targeting symbiosis receptor-like kinase (SYMRK) achieved ~67% mutagenic efficiency in hairy-root-transformed plants, and nodule formation was completely blocked in the mutants with both alleles disrupted. Various types of mutations were observed near the PAM region of the respective gRNA. These results demonstrate the applicability of the CRISPR/Cas9 system in Vigna unguiculata, and therefore should significantly stimulate functional genomics analyses of many important agronomical traits in this unique crop legume.