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Plant-Microbe Symbioses
Symbiotic associations between plants and microbes
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Characterization of winter microbial communities in the purple pitcher plant (Sarracenia purpurea)

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ARBUSCULAR MYCORRHIZAL FUNGI COLONIZING THE PLANT COMMUNITIES IN ERITREA, NORTHEAST AFRICA

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Common and divergent roles of plant hormones in nodulation and arbuscular mycorrhizal symbioses

All of the classical plant hormones have been suggested to influence nodulation, including some that interact with the Autoregulation of Nodulation (AON) pathway. Leguminous plants strictly regulate the number of nodules formed through this AON pathway via a root-shoot-root loop that acts to suppress excessive nodulation. A related pathway, the Autoregulation of Mycorrhization (AOM) pathway controls the more ancient, arbuscular mycorrhizal (AM) symbiosis. A comparison of the published responses to the classical hormones in these 2 symbioses shows that most influence the symbioses in the same direction. This may be expected if they affect the symbioses via common components of these symbiotic regulatory pathways. However, some hormones influence these symbioses in opposite directions, suggesting a more complex relationship, and probably one that is not via the common components of these pathways. In a recent paper we showed, using a genetic approach, that strigolactones and brassinosteroids do not act downstream of the AON genes examined and argued that they probably act independently to promote nodule formation. Recently it has been shown that the control of nodulation via the AON pathway involves mobile CLE peptide signals. It is therefore suggested that a more direct avenue to determine if the classical hormones play a direct role in the autoregulatory pathways is to further examine whether CLE peptides and other components of these processes can influence, or be influenced by, the classical hormones. Such studies and other comparisons between the nodulation and mycorrhizal symbioses should allow the role of the classical hormones in these critical symbioses to be rapidly advanced.
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Carbon and nitrogen metabolism in arbuscular mycorrhizal maize plants under low temperature stres

The effects of arbuscular mycorrhizal (AM) fungus Glomus tortuosum on C and N metabolism of Zea mays L. grown under low temperature stress was investigated. Maize plants inoculated or not inoculated with AM fungus were grown in the growth chamber at 25 °C for four weeks and subsequently subjected to two temperature treatments (15 °C low temperature and 25 °C as an ambient control) for two weeks. Low temperature stress significantly decreased AM colonization, plant height and biomass. The total N content, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase activities of AM plants were higher than those of non-AM plants. AM plants had a higher net photosynthetic rate (Pn) compared to non-AM plants, although low temperature inhibited the Pn. Compared with non-AM plants, AM plants exhibited higher leaf soluble sugars, reducing sugars, root sucrose and fructose contents, sucrose phosphate synthase and amylase activities at low temperature conditions. Moreover, low temperature stress increased the C/N ratio in the leaves of maize plants, and AM colonization decreased the root C/N ratio. These results suggested a difference in the C and N metabolism of maize plants at ambient and low temperature regimes. AM symbiosis modulated C metabolic enzymes, thereby inducing an accumulation of soluble sugars, which may have contributed to an increased tolerance to low temperature and therefore higher Pn in maize plants.
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Physiological and biochemical characterization of Azospirillum brasilense strains commonly used as plant growth-promoting rhizobacteria

Azospirillum is a plant growth-promoting rhizobacteria (PGPR) genus vastly studied and utilized as agriculture inoculants. Isolation of new strains under different environmental conditions allows the access to the genetic diversity and improves the success of inoculation procedures. Historically, the isolation of this genus has been performed by the use of some traditional culture media. In this work we characterized the physiology and biochemistry of five different A. brasilense strains, commonly used as cereal inoculants. The aim of this work is to contribute to pose into revision some concepts concerning the most used protocols to isolate and characterize this bacterium. We characterized their growth in different traditional and non-traditional culture media, evaluated some PGPR mechanisms and characterized their profiles of fatty acid methyl esters and carbon-source utilization. This work shows, for the first time, differences in both profiles, and ACC deaminase activity of A. brasilense strains. Also, we show unexpected results obtained in some of the evaluated culture media. Results obtained here and an exhaustive knowledge revision revealed that it is not appropriate to conclude about bacterial species without analyzing several strains. Also, it is necessary to continue developing studies and laboratory techniques to improve the isolation and characterization protocols.

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Mycorrhizae support oaks growing in a phylogenetically distant neighbourhood

Mycorrhizae support oaks growing in a phylogenetically distant neighbourhood | Plant-Microbe Symbioses | Scoop.it

Host-plants may rarely leave their ancestral niche and in which case they tend to be surrounded by phylogenetically distant neighbours. Phylogenetically isolated host-plants might share few mutualists with their neighbours and might suffer from a decrease in mutualist support. In addition host plants leaving their ancestral niche might face a deterioration of their abiotic and biotic environment and might hence need to invest more into mutualist partners. We tested whether phylogenetic isolation of hosts from neighbours decreases or increases abundance and activity of their mutualists and whether mutualist activity may help to compensate deterioration of the environment. We study oak-hosts and their ectomycorrhizal fungi mutualists established in the litter layer formed by the phylogenetically closely or distantly related neighbourhood. We find that oaks surrounded by phylogenetically distant neighbours show increased abundance and enzymatic activity of ectomycorrhizal fungi in the litter. Moreover, oaks surrounded by phylogenetically distant neighbours also show delayed budburst but ectomycorrhizal fungi activity partly compensates this negative effect of phylogenetic isolation. This suggests decreased nutrient availability in a phylogenetically distant litter partly compensated by increased litter-degradation by ectomycorrhizal fungi activity. Most observed effects of phylogenetic isolation cannot be explained by a change in baseline soil fertility (as reflected by nutritional status of fresh oak litter, or soil microbial biomass and activity) nor by simple reduction of percentages of oak neighbours, nor by the presence of gymnosperms. Our results show that colonizing new niche represented by the presence of distantly related neighbours may delay plant phenology but may be supported by mycorrhizal mutualists. Studies on other host-plant species are required to generalize our findings.

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Expression of novel cytosolic malate dehydrogenases (cMDH) in Lupinus angustifolius nodules during phosphorus starvation

During P deficiency, the increased activity of malate dehydrogenase (MDH, EC 1.1.1.37) can lead to malate accumulation. Cytosolic- and nodule-enhanced MDH (cMDH and neMDH, respectively) are known isoforms, which contribute to MDH activity in root nodules. The aim of this study was to investigate the role of the cMDH isoforms in nodule malate supply under P deficiency. Nodulated lupins (Lupinus angustifolius var. Tanjil) were hydroponically grown at adequate P (+P) or low P (–P). Total P concentration in nodules decreased under P deficiency, which coincided with an increase in total MDH activity. A consequence of higher MDH activity was the enhanced accumulation of malate derived from dark CO2 fixation via PEPC and not from pyruvate. Although no measurable neMDH presence could be detected via PCR, gene-specific primers detected two 1 kb amplicons of cMDH, designated LangMDH1 (corresponding to +P, HQ690186) andLangMDH2 (corresponding to–P, HQ690187), respectively. Sequencing analyses of these cMDH amplicons showed them to be 96% identical on an amino acid level. There was a high degree of diversification between proteins detected in this study and other known MDH proteins, particularly those from other leguminous plants. Enhanced malate synthesis in P-deficient nodules was achieved via increased anaplerotic CO2fixation and subsequent higher MDH activities. Novel isoforms of cytosolic MDH may be involved, as shown by gene expression of specific genes under P deficiency.

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Transcriptional networks leading to symbiotic nodule organogenesis

Transcriptional networks leading to symbiotic nodule organogenesis | Plant-Microbe Symbioses | Scoop.it

The symbiosis with nitrogen-fixing bacteria leading to root nodules is a relatively recent evolutionary innovation and limited to a distinct order of land plants. It has long been a mystery how plants have invented this complex trait. However, recent advances in molecular genetics of model legumes has elucidated genes involved in the development of root nodules, providing insights into this process. Here we discuss how the de novo assembly of transcriptional networks may account for the predisposition to nodulate. Transcriptional networks and modes of gene regulation from the arbuscular mycorrhizal symbiosis, nitrate responses and aspects of lateral root development have likely all contributed to the emergence and development of root nodules.

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Great review

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Global biogeography of Alnus-associated Frankia actinobacteria

Global biogeography of Alnus-associated Frankia actinobacteria | Plant-Microbe Symbioses | Scoop.it
  • Macroecological patterns of microbes have received relatively little attention until recently. This study aimed to disentangle the determinants of the global biogeographic community of Alnus-associated actinobacteria belonging to the Frankia alni complex.
  • By determining a global sequence similarity threshold for the nitrogenase reductase (nifH) gene, we separated Frankia into operational taxonomic units (OTUs) and tested the relative effects of Alnus phylogeny, geographic relatedness, and climatic and edaphic variables on community composition at the global scale.
  • Based on the optimal nifH gene sequence similarity threshold of 99.3%, we distinguished 43 Frankia OTUs from root systems of 22Alnus species on four continents. Host phylogeny was the main determinant of Frankia OTU-based community composition, but there was no effect on the phylogenetic structure of Frankia. Biogeographic analyses revealed the strongest cross-continental links over the Beringian land bridge.
  • Despite the facultative symbiotic nature of Frankia, phylogenetic relations among Alnus species play a prominent role in structuring root-associated Frankia communities and their biogeographic patterns. Our results suggest that Alnus species exert strong phylogenetically determined selection pressure on compatible Actinobacteria.
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Identification and functional characterization of a sulfate transporter induced by both sulfur starvation and mycorrhiza formation in Lotus japonicus

Identification and functional characterization of a sulfate transporter induced by both sulfur starvation and mycorrhiza formation in Lotus japonicus | Plant-Microbe Symbioses | Scoop.it
  • Arbuscular mycorrhizas (AMs) are one of the most widespread symbioses in the world. They allow plants to receive mineral nutrients from the symbiotic fungus which in turn gets back up to 20% of plant carbon and completes its life cycle. Especially in low-nutrient conditions, AM fungi are capable of significantly improving plant phosphate and nitrogen acquisition, but fewer data are available about sulfur (S) nutrition.
  • We focused on S metabolism in Lotus japonicus upon mycorrhizal colonization under sulfur starvation or repletion. We investigated both tissue sulfate concentrations and S-related gene expression, at cell-type or whole-organ level.
  • Gene expression and sulfate tissue concentration showed that Rhizophagus irregularis colonization can improve plant S nutritional status under S starvation. A group 1 sulfate transporter, LjSultr1;2, induced by both S starvation and mycorrhiza formation, was identified. Its transcript was localized in arbuscule-containing cells, which was confirmed with a promoter-GUS assay, and its function was verified through phenotyping of TILLING mutants in nonmycorrhizal seedlings.
  • LjSultr1;2 thus appears to encode a key protein involved in plant sulfate uptake. In contrast to phosphate transporters, a single gene,LjSultr1;2, seems to mediate both direct and symbiotic pathways of S uptake in L. japonicus.
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MiR171h restricts root symbioses and shows like its target

Background

Legumes have the unique capability to undergo root nodule and arbuscular mycorrhizal symbiosis. Both types of root endosymbiosis are regulated by NSP2, which is a target of microRNA171h (miR171h). Although, recent data implies that miR171h specifically restricts arbuscular mycorrhizal symbiosis in the root elongation zone of Medicago truncatula roots, there is limited knowledge available about the spatio-temporal regulation of miR171h expression at different physiological and symbiotic conditions.

Results

We show that miR171h is functionally expressed from an unusual long primary transcript, previously predicted to encode two identical miR171h strands. Both miR171h and NSP2 transcripts display a complex regulation pattern, which involves the symbiotic status and the fertilization regime of the plant. Quantitative Real-time PCR revealed that miR171h and NSP2 transcript levels show a clear anti-correlation in all tested conditions except in mycorrhizal roots, where NSP2transcript levels were induced despite of an increased miR171h expression. This was also supported by a clear correlation of transcript levels of NSP2 and MtPt4, a phosphate transporter specifically expressed in a functional AM symbiosis. MiR171h is strongly induced in plants growing in sufficient phosphate conditions, which we demonstrate to be independent of the CRE1 signaling pathway and which is also not required for transcriptional induction of NSP2 in mycorrhizal roots.In situ hybridization and promoter activity analysis of both genes confirmed the complex regulation involving the symbiotic status, P and N nutrition, where both genes show a mainly mutual exclusive expression pattern. Overexpression of miR171h in M. truncatula roots led to a reduction in mycorrhizal colonization and to a reduced nodulation by Sinorhizobium meliloti.

Conclusion

The spatio-temporal expression of miR171h and NSP2 is tightly linked to the nutritional status of the plant and, together with the results from the overexpression analysis, points to an important function of miR171h to integrate the nutrient homeostasis in order to safeguard the expression domain of NSP2 during both, arbuscular mycorrhizal and root nodule symbiosis.

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Phosphate transport of fungi to plant roots requires proton pump

Phosphate transport of fungi to plant roots requires proton pump | Plant-Microbe Symbioses | Scoop.it
Phosphorous (P) is a component of DNA and plays an important role in energy metabolism; therefore it is essential for all organisms. Plants are able to take it up from the soil in the form of salts, namely phosphates. But in many soils phosphate is already depleted and the world’s phosphate resources, which can be used to produce fertilizer, are declining. Nevertheless, crop plants need an optimal P-supply to gain high yields. To overcome this problem, a special community of plants and fungi could become more important in the future. About 80% of all land plants live in a kind of marriage with arbuscular mycorrhizal fungi. This relationship secures the plants’ phosphate nutrition while the fungi are rewarded with sugars. Scientists around Franziska Krajinski from the Max Planck Institute of Molecular Plant Physiology recently discovered that a special proton pump facilitates the transport of fungal phosphate into the plant. (Plant Cell, DOI: 10.1105/tpc.113.120436).
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Jennifer Mach's comment, August 3, 7:11 AM
Check out the source paper at The Plant Cell: http://www.plantcell.org/content/early/2014/04/29/tpc.113.120436.abstract
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Nodulation competitiveness as a requisite for improved rhizobial inoculants of Trifolium pratense

Nodulation competitiveness as a requisite for improved rhizobial inoculants of Trifolium pratense | Plant-Microbe Symbioses | Scoop.it

Red clover (Trifolium pratense L.) is used in the improvement of grasslands in Uruguay and has been inoculated with commercial strain U204 of Rhizobium leguminosarum bv trifolii since 1970s. Native-naturalized rhizobia strains present in soil are the basis for selecting and developing new inoculants. With this aim, we evaluated the diversity of red clover rhizobia in Uruguayan red clover pastures both historically inoculated with U204 and non-inoculated ones. Thirty-eight different enterobacterial repetitive intergenic consensus (ERIC) PCR genomic fingerprints were identified, albeit surprisingly only one of 80 isolates showed an ERIC profile similar to U204. Under controlled conditions, red clover plants inoculated with one of the native isolates, strain 317, produced more biomass than those inoculated with the commercial U204. ERIC-PCR was also used to show that strain 317 competed for nodulation better than U204 in a field with previous history of inoculation. Moreover, both U204 and 317 were tagged with a gusA reporter gene and their competitiveness for nodulation assessed in various soil types. Again, strain 317 appeared more competitive than U204, particularly in soils with previous history of inoculation. Our results reinforce the long-known idea of assessing the actual needs of inoculation of legumes in different soils and suggest that the indigenous isolate 317 is an effective and competitive strain that can be used for development of a new red clover inoculant.

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ARBUSCULAR MYCORRHIZAL SYMBIOSIS, ECOSYSTEM PROCESSES AND ENVIRONMENTAL CHANGES IN TROPICAL SOILS

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Interaction with ectomycorrhizal fungi and endophytic Methylobacterium affects nutrient uptake and growth of pine seedlings in vitro

Tissues of Scots pine (Pinus sylvestris L.) contain several endophytic microorganisms of which Methylobacterium extorquens DSM13060 is a dominant species throughout the year. Similar to other endophytic bacteria, M. extorquens is able to colonize host plant tissues without causing any symptoms of disease. In addition to endophytic bacteria, plants associate simultaneously with a diverse set of microorganisms. Furthermore, plant-colonizing microorganisms interact with each other in a species- or strain-specific manner. Several studies on beneficial microorganisms interacting with plants have been carried out, but few deal with interactions between different symbiotic organisms and specifically, how these interactions affect the growth and development of the host plant. Our aim was to study how the pine endophyte M. extorquens DSM13060 affects pine seedlings and how the co-inoculation with ectomycorrhizal (ECM) fungi [Suillus variegatus (SV) or Pisolithus tinctorius (PT)] alters the response of Scots pine. We determined the growth, polyamine and nutrient contents of inoculated and non-inoculated Scots pine seedlings in vitro. Our results show that M. extorquens is able to improve the growth of seedlings at the same level as the ECM fungi SV and PT do. The effect of co-inoculation using different symbiotic organisms was seen in terms of changes in growth and nutrient uptake. Inoculation using M. extorquens together with ECM fungi improved the growth of the host plant even more than single ECM inoculation. Symbiotic organisms also had a strong effect on the potassium content of the seedling. The results indicate that interaction between endophyte and ECM fungus is species dependent, leading to increased or decreased nutrient content and growth of pine seedlings.

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"Ménage à trois"

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An increasing opine carbon bias in artificial exudation systems and genetically modified plant rhizospheres leads to an increasing reshaping of bacterial populations

To investigate how exudation shapes root-associated bacterial populations, transgenic Arabidopsis thaliana plants that exuded the xenotopic compound octopine at low and high rates were grown in a non-sterile soil. Enumerations of both cultivable and octopine-degrading bacteria demonstrated that the ratios of octopine degraders increased along with octopine concentration. An artificial exudation system was also set up in which octopine was brought at four different ratios. The density of octopine-degrading bacteria directly correlated with the input of octopine. Bacterial diversity was analyzed by rrs-amplicon pyrosequencing. Ensifer and Pseudomonas were significantly more frequently detected in soil amended with artificial exudates. However, the density of Pseudomonas increased as a response to carbon supplementation while that of Ensifer only correlated with octopine concentrations possibly in relation with two opposed colonization strategies of rhizosphere bacteria, i.e. copiotrophy and oligotrophy.

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Glomus mosseae bioprotection against aster yellows phytoplasma (16srI-B) and Spiroplasma citri infection in Madagascar periwinkle

Glomus mosseae bioprotection against aster yellows phytoplasma (16srI-B) and Spiroplasma citri infection in Madagascar periwinkle | Plant-Microbe Symbioses | Scoop.it

The bio-control potential of arbuscular mycorrhizal fungus Glomus mosseae against two pathogenic microorganisms aster yellows (AY) phytoplasma and Spiroplasma citri has been examined in Madagascar periwinkle (Catharanthus roseus). G. mosseae had a positive influence on healthy C. roseus plants andS. citri infection. It provided bioprotection against S. citri pathogen and induced significant degree of resistance to spiroplasma infection. Besides, symptom expression significantly reduced and shoot height, leaves number, root fresh and dry weight increased in spiroplasma-infected plants treated with mycorrhiza fungus. Although, G. mosseae had no positive effect on phytoplasma disease. The root architectures were affected by the phytoplasma pathogen, and the root surface area dramatically decreased in G. mosseaetreated AY-infected periwinkles compared with the control. Nitrogen and Phosphorus concentrations notably increased in spiroplasma + G. mosseae compared with control plants. Potassium concentration did not differ significantly in all mycorrhizal treated and untreated infected plants except in G. mosseae treated healthy plants. The spore density and root colonization rate did not vary in both pathogen treatmentsG. mosseae + spiroplasma and G. mosseae + phytoplasma. To our knowledge, this is the first report showing the bioprotective effect of G. mosseae on S. citri. The possible mechanisms involved in complex interaction between plants, cell wall-less bacteria and arbuscular mycorrhizal fungi (AMF) are discussed and the underlying mechanisms for the functioning of AMF are hypothesized.

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Paul Laski's curator insight, August 25, 9:50 AM

Wonder if this would work on citrus greening phytoplasma?

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β-Glucosidase BGLU42 is a MYB72-dependent key regulator of rhizobacteria-induced systemic resistance and modulates iron deficiency responses in Arabidopsis roots

β-Glucosidase BGLU42 is a MYB72-dependent key regulator of rhizobacteria-induced systemic resistance and modulates iron deficiency responses in Arabidopsis roots | Plant-Microbe Symbioses | Scoop.it
  • Selected soil-borne rhizobacteria can trigger an induced systemic resistance (ISR) that is effective against a broad spectrum of pathogens. In Arabidopsis thaliana, the root-specific transcription factor MYB72 is required for the onset of ISR, but is also associated with plant survival under conditions of iron deficiency. Here, we investigated the role of MYB72 in both processes.
  • To identify MYB72 target genes, we analyzed the root transcriptomes of wild-type Col-0, mutant myb72 and complemented35S:FLAG-MYB72/myb72 plants in response to ISR-inducing Pseudomonas fluorescens WCS417.
  • Five WCS417-inducible genes were misregulated in myb72 and complemented in 35S:FLAG-MYB72/myb72. Amongst these, we uncovered β-glucosidase BGLU42 as a novel component of the ISR signaling pathway. Overexpression of BGLU42 resulted in constitutive disease resistance, whereas the bglu42 mutant was defective in ISR. Furthermore, we found 195 genes to be constitutively upregulated in MYB72-overexpressing roots in the absence of WCS417. Many of these encode enzymes involved in the production of iron-mobilizing phenolic metabolites under conditions of iron deficiency. We provide evidence that BGLU42 is required for their release into the rhizosphere.
  • Together, this work highlights a thus far unidentified link between the ability of beneficial rhizobacteria to stimulate systemic immunity and mechanisms induced by iron deficiency in host plants.
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RNA-seq transcriptome profiling reveals that Medicago truncatula nodules acclimate N2 fixation before emerging P deficiency reaches the nodules

Legume nodules are plant tissues with an exceptionally high concentration of phosphorus (P), which, when there is scarcity of P, is preferentially maintained there rather than being allocated to other plant organs. The hypothesis of this study was that nodules are affected before the P concentration in the organ declines during whole-plant P depletion. Nitrogen (N2) fixation and P concentration in various organs were monitored during a whole-plant P-depletion process in Medicago truncatula. Nodule gene expression was profiled through RNA-seq at day 5 of P depletion. Until that point in time P concentration in leaves reached a lower threshold but was maintained in nodules. N2-fixation activity per plant diverged from that of fully nourished plants beginning at day 5 of the P-depletion process, primarily because fewer nodules were being formed, while the activity of the existing nodules was maintained for as long as two weeks into P depletion. RNA-seq revealed nodule acclimation on a molecular level with a total of 1140 differentially expressed genes. Numerous genes for P remobilization from organic structures were increasingly expressed. Various genes involved in nodule malate formation were upregulated, while genes involved in fermentation were downregulated. The fact that nodule formation was strongly repressed with the onset of P deficiency is reflected in the differential expression of various genes involved in nodulation. It is concluded that plants follow a strategy to maintain N2 fixation and viable leaf tissue as long as possible during whole-plant P depletion to maintain their ability to react to emerging new P sources (e.g. through active P acquisition by roots).

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A European perspective of innovations towards mitigation of nitrogen-related greenhouse gases

A European perspective of innovations towards mitigation of nitrogen-related greenhouse gases | Plant-Microbe Symbioses | Scoop.it

Technology design and effectiveness studies available in the scientific literature demonstrate future mitigation potentials of nitrogen-related greenhouse gases. Here we investigate ‘innovations’ influencing such emissions. These innovations mainly address agriculture: reduced meat diets, urban gardening, genetically modified crops, and precision farming, but also more distant options such as vertical farming and cultured meat production, that is, indoor agriculture. While the latter approaches, which allow full management of effluents, seem very promising in terms of emission control, the cost estimates available would rule out any practical relevance. Technologies that currently seem more realistic offer much smaller mitigation potential. Information on energy need, greenhouse gas emissions, and land requirements feed into a semi-quantitative assessment, which delivers information in a format useful for existing European policy tools.

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Hum... interesting...

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Proteome reference maps of the Lotus japonicus nodule and root

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Genetic variation in horizontally transmitted fungal endophytes of pine needles reveals population structure in cryptic species

• Premise of the study: Fungal endophytes comprise one of the most ubiquitous groups of plant symbionts, inhabiting healthy leaves and stems of all major lineages of plants. Together, they comprise immense species richness, but little is known about the fundamental processes that generate their diversity. Exploration of their population structure is needed, especially with regard to geographic distributions and host affiliations.

• Methods: We take a multilocus approach to examine genetic variation within and among populations of Lophodermium australe, an endophytic fungus commonly associated with healthy foliage of pines in the southeastern United States. Sampling focused on two pine species ranging from montane to coastal regions of North Carolina and Virginia.

• Key results: Our sampling revealed two genetically distinct groups withinLophodermium australe. Our analysis detected less than one migrant per generation between them, indicating that they are distinct species. The species comprising the majority of isolates (major species) demonstrated a panmictic structure, whereas the species comprising the minority of isolates (crypticspecies) demonstrated isolation by distance. Distantly related pine species hosted the same Lophodermium species, and host species did not influence genetic structure.

• Conclusions: We present the first evidence for isolation by distance in a foliar fungal endophyte that is horizontally transmitted. Cryptic species may be common among microbial symbionts and are important to delimit when exploring their genetic structure and microevolutionary processes. The hyperdiversity of endophytic fungi may be explained in part by cryptic species without apparent ecological and morphological differences as well as genetic diversification within rare fungal species across large spatial scales.

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Staying in touch: mechanical signals in plant–microbe interactions

Staying in touch: mechanical signals in plant–microbe interactions | Plant-Microbe Symbioses | Scoop.it

Mechanical stimulations play a significant role in the day to day existence of plants. Plants exhibit varied responses depending on the nature and intensity of these stimuli. In this review, we present recent literature on the responses of plants to mechanical stimuli, focusing primarily on those exerted during plant–microbe interactions. We discuss how microbes are able to apply mechanical stimuli on plants and how some plant responses to pathogenic and symbiotic microbes present striking similarities with responses to mechanical stimuli applied, for instance, using micro-needles. We hypothesize that appropriate responses of plants to pathogenic and symbiotic microbes may require a tight integration of both chemical and mechanical stimulations exerted by these microbes.

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Effects of flower dimorphism and light environment on arbuscular mycorrhizal colonisation in a cleistogamous herb

Although it is known that floral dimorphism contributes to the maintenance of mixed breeding systems, the consequences of producing progeny of a contrasting genetic background and seeds with differential resource allocation has been practically ignored regarding establishment of belowground organisms–plant interactions. This article evaluates the combined effect of floral dimorphism with cross type and light environment on interactions between Ruellia nudiflora and arbuscular mycorrhizal fungi (AMF). R. nudiflora produces cleistogamous (CL) flowers that exhibit obligate self-pollination and chasmogamous (CH) flowers with facultative self- (CHs) or cross- (CHc) pollination. We evaluated the establishment of the plant–AMF interaction in progeny derived from each floral type, under two light conditions (shaded versus open). We established different scenarios depending on the existence of inbreeding depression (ID) and whether the differential resource allocation (DRA) to CH and CL flowers affected the R. nudiflora–AMF interaction. We predicted that under shaded light conditions there might be an intensification of ID, having a negative effect on AMF colonisation. The percentages of hyphae and vesicles in the harvested roots was significantly higher in the shaded plants (F ≥ 4.11, < 0.05), while progeny of CHc and CHs presented a higher percentage of hyphae and vesicle colonisation compared to CL progeny (F = 15.26, < 0.01). The results show that DRA to CH flowers and light availability both determines the establishment of R. nudiflora–AMF interaction. The results also suggest that even under stressful light conditions, endogamy does not affect this interaction, which may explain the success of R. nudiflora as an invasive species.

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Rhizopogon vinicolor genome sequence v1.0

Rhizopogon vinicolor genome sequence v1.0 | Plant-Microbe Symbioses | Scoop.it

Rhizopogon vinicolor Smith is an ectomycorrhizal (EM) fungus in family Rhizopogonaceae of order Boletales.  Genus Rhizopogon produce sexual basidiospores within hypogeous sporocarps (false truffles) and rely upon excavation and consumption of these sporocarps by mammals for spore dispersal. While genus Rhizopogon associates with many EM host trees in family Pinaceae, R. vinicolor is an obligate EM symbiont of Pseudotsuga menziesii(Douglas fir) (Massicotte et al. 1994). Along with its sister species, Rhizopogon vesiculosusR. vinicolormakes up a major component of the EM fungal community colonizing the roots of P. menziesii across all forest age classes (Twieg et al 2007) and is especially abundant in young stands following disturbance (Luoma et al 2006).  P. menziesii is a tree of major ecological and economic importance. It is a dominant overstory tree in coniferous forests of the North American Pacific Northwest and it has been planted on a global scale as a source of high quality timber. R. vinicolor occurs throughout the natural and introduced range of P. menziesii and is an important factor in the establishment and maintenance of P. menziesii forests.   

R. vinicolor and R. vesiculosus produce sporocarps that are difficult to distinguish morphologically yet they differ greatly in life history. They can occur in relatively equal abundance when found at the same site but R. vinicolor typically produces smaller genets and possesses little population structure on the landscape scale while R. vesiculosus produces larger genets and shows patterns of inbreeding at the landscape scale (Kretzer et al 2005, Beiler et al 2010, Dunham et al 2013). In addition to producing smaller genets in width, R. vinicolorexplores the soil to a lesser depth than R. vesiculosus and displays vertical partitioning into the upper soil horizon when co-occuring with R. vesiculosus (Beiler et al. 2012).

The genome of Rhizopogon vinicolor will enable phylogenomic and population genomic studies of genusRhizopogon and will allow for the study of genetic mechanisms that underly EM host specificity.  Along with the genome of Rhizopogon vesiculosus, this genome will allow deeper inquiry into the ecology and evolutionary biology of sympatric EM sister species.

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