Plant-Microbe Symbiosis
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Frontiers in Plant Traffic and Transport: How membranes shape plant symbioses: signaling and transport in nodulation and arbuscular mycorrhiza (2012)

Frontiers in Plant Traffic and Transport: How membranes shape plant symbioses: signaling and transport in nodulation and arbuscular mycorrhiza (2012) | Plant-Microbe Symbiosis | Scoop.it

As sessile organisms that cannot evade adverse environmental conditions, plants have evolved various adaptive strategies to cope with environmental stresses. One of the most successful adaptations is the formation of symbiotic associations with beneficial microbes. In these mutualistic interactions the partners exchange essential nutrients and improve their resistance to biotic and abiotic stresses. In arbuscular mycorrhiza (AM) and in root nodule symbiosis (RNS), AM fungi and rhizobia, respectively, penetrate roots and accommodate within the cells of the plant host. In these endosymbiotic associations, both partners keep their plasma membranes intact and use them to control the bidirectional exchange of signaling molecules and nutrients. Intracellular accommodation requires the exchange of symbiotic signals and the reprogramming of both interacting partners. This involves fundamental changes at the level of gene expression and of the cytoskeleton, as well as of organelles such as plastids, endoplasmic reticulum (ER), and the central vacuole. Symbiotic cells are highly compartmentalized and have a complex membrane system specialized for the diverse functions in molecular communication and nutrient exchange. Here, we discuss the roles of the different cellular membrane systems and their symbiosis-related proteins in AM and RNS, and we review recent progress in the analysis of membrane proteins involved in endosymbiosis.


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Plant-Microbe Symbiosis
Beneficial associations between plants and microbes
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The theory of island biogeography applies to ectomycorrhizal fungi in subalpine tree “islands” at a fine scale

The theory of island biogeography applies to ectomycorrhizal fungi in subalpine tree “islands” at a fine scale | Plant-Microbe Symbiosis | Scoop.it
The theory of island biogeography, which predicts that species richness is a function of island size and distance from the mainland, is well tested with macro-fauna and flora. Yet, in many ways, microbes are more appropriate for testing this and other ecological theories due to their small size and short generation times that translate to an ease of replication. We used a natural experimental system of isolated “host islands” to test the generality of the theory of island biogeography. Specifically, we tested whether ectomycorrhizal fungal (EMF) richness increased with tree size and decreased with distance from forest in a subalpine basin in Yosemite National Park for two congeneric pine species, Pinus albicaulis and Pinus contorta. We determined EMF richness with next-generation sequencing, measured the size and age of each tree island (n = 40), and calculated geographic distances from each tree to the nearest forest edge. We found that EMF richness increased with island size (as measured by tree volume) and tree age for both pine species and decreased with distance from forest edge for P. albicaulis. Thus, we show the applicability of the theory to microbial symbionts in harsh, dry, and likely non-equilibrium systems. In addition, we found that despite the fact that our tree islands had a mean age of 65 yr, a pioneer community of EMF dominated. We interpret this as evidence that water stress interacts with succession to create a sustained period of early-stage fungi even in mature trees.
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Nice... I talked about exactly this in my "microbiome" course a few weeks ago.

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Impact of Agricultural Management Practices on Mycorrhizal Functioning and Soil Microbiological Parameters Under Soybean-Based Cropping Systems

Impact of Agricultural Management Practices on Mycorrhizal Functioning and Soil Microbiological Parameters Under Soybean-Based Cropping Systems | Plant-Microbe Symbiosis | Scoop.it
The use of modern agricultural techniques for enhanced production has been advocated, however, its impact on below ground microbial networks is overlooked and adversely affected. The abiotic stresses like temperature (heat, cold chilling/frost), water (drought, flooding/hypoxia), radiation (UV, ionizing radiation), chemicals (mineral deficiency/excess, pollutants heavy metals/pesticides, gaseous toxins), mechanical (wind, soil movement, submergence) are responsible for over 50% reduction in agricultural production. On the other hand, organic farming practices yield fruitful results. This has highlighted the emerging need of switching over to some eco-friendly agricultural practices which can enhance the growth of plant, improve soil quality, mitigate drought without having adverse impacts on environment. Rhizosphere which is the narrow zone surrounding the roots of plant (Hiltner 1904) contains microbial communities which have the potential to benefit plants. Arbuscular mycorrhizal fungi are obligate symbionts which form association with about 90% of the land plant species (Gadkar et al. 2001). However, agricultural practices like tillage, crop rotation, fallowing, organic farming, fertilizers, etc., influence the functioning of AMF in many ways. Soybean is rich in phytochemicals that are beneficial for human beings. The inoculation of soybean and some other crops including cereals, pulses, and other leguminous crops with AMF leads to an enhancement in abiotic stress tolerance, disease resistance, overall growth, soil carbon sequestration, nutrient uptake, etc. This chapter summarizes the overall impact of different agricultural practices on mycorrhiza and other soil microbial communities under soybean-based cropping system.
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New Native Rhizobia Strains for Inoculation of Common Bean in the Brazilian Savanna

Maximization of biological nitrogen fixation in the common bean (Phaseolus vulgaris L.) crop depends on the genetic characteristics related to the plant, the symbiotic efficiency of rhizobia, and environmental factors. The objective of this study was to evaluate the performance of rhizobia selected beforehand from Cerrado (Brazilian tropical savanna) soils in Mato Grosso do Sul. The experiments were conducted in 2007 in the municipalities of Aquidauana, Anaurilândia, Campo Grande, and Dourados, all located in the state of Mato Grosso do Sul. All procedures established followed the current recommendations of the Brazilian Ministry of Agriculture (Ministério de Agricultura, Pecuária e Abastecimento – MAPA), in accordance with the “official protocol for assessing the feasibility and agronomic efficiency of strains, and inoculant technologies linked to the process of biological nitrogen fixation in legumes”. The program for selection of rhizobia for inoculation in bean plants resulted in identification of different strains with high symbiotic efficiency, competitiveness, and genetic stability, based on the Embrapa Agropecuária Oeste collection of multifunctional microorganism cultures. In previous studies, 630 isolates of Rhizobium were evaluated. They were obtained from nodules of leucaena (380) or dry beans (250) from 87 locations, including 34 municipalities in Mato Grosso do Sul. Three of them stood out from the others: CPAO 12.5 L2, CPAO 17.5 L2, and CPAO 56.4 L2. Inoculation of these strains in bean plants demonstrated economic viability and high potential for obtaining a more effective inoculant suitable for trading purposes.

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Astromycology: The “Fungal” Frontier

Astromycology: The “Fungal” Frontier | Plant-Microbe Symbiosis | Scoop.it
Hollywood movies and horror novels have painted extraterrestrial life as green monsters, scouring the barren grounds of Mars and shooting any intruder with photon lasers. These disturbing imaginations, while far-fetched, do hold some truth about frightening outer space life forms, but not in the ways we imagine. During its orbit as the first modular space station, the satellite Mir experienced attacks from the least suspect extraterrestrial life form: mold. Splotches of fungal hyphae covered windows and control panels and gradually ate away at the hull’s interior during the latter part of the satellite’s life, and with it, any notion of a “sterile spaceship”.1

The discipline of astrobiology attempts to answer the larger mysteries about life: its origin, necessities for survival, and presence in other worlds. But astrobiology also has practical applications in considering how biological organisms may travel through space. In particular, human space travel would greatly benefit from studying a branch of fungal biology known as astromycology: the study of earth-derived fungi in space. Fungi offer both an opportunity and threat to human space travel. Problems arising from fungal intruders are both wide and relevant, ranging from providing food and decomposing biological material to breaking down spacecrafts. Interactions of intense radiation and lack of gravity with fungal growth underlie the opportunities and threats that fungi pose to human space travel.
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The arbuscular mycorrhizal fungus Rhizophagus irregularis affects arthropod colonization on sweet pepper in both the field and greenhouse

The arbuscular mycorrhizal fungus Rhizophagus irregularis affects arthropod colonization on sweet pepper in both the field and greenhouse | Plant-Microbe Symbiosis | Scoop.it
In the present study sweet pepper plants, Capsicum annuum, were planted in greenhouse and open field conditions to test the effect of the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis on phytophagous and predatory arthropod populations. Furthermore, we tested the hypothesis that AMF may increase the crop yield (number of fruits and their weight) and activity level of polyphenol oxidase (PPO) and peroxidase (POD), enzymes that seemingly decrease infestation by arthropod pests. The most abundant arthropod species found were the peach-potato aphid, Myzus persicae, western flower thrips, Frankliniella occidentalis, and the seven-spot ladybird, Coccinella septempunctata. Sweet pepper mutualism with AMF significantly reduced colonization by the peach-potato aphid under greenhouse conditions. Aphid density increased, however, on two of four pepper varieties tested under open field conditions. The density of ladybird predators did not appear directly influenced by AMF under greenhouse conditions, whereas a significantly higher predator density was found on three out of four pepper plant varieties with fungal mutualism tested under field conditions. Crop yield was significantly higher on plants with AMF mutualism under greenhouse conditions, but no clear effects were detected under field conditions. Both PPO and POD activity increased significantly and remained higher than controls until day 14 of the experiment under mutualism with AMF, although only in the greenhouse. The results suggest that under greenhouse conditions, pepper plant mutualism with AMF can increase pepper yield by reducing the numbers of the key pest, peach-potato aphid.

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Expression of 16 Nitrogenase Proteins within the Plant Mitochondrial Matrix

Expression of 16 Nitrogenase Proteins within the Plant Mitochondrial Matrix | Plant-Microbe Symbiosis | Scoop.it
The industrial production and use of nitrogenous fertilizer involves significant environmental and economic costs. Strategies to reduce fertilizer dependency are required to address the world's increasing demand for sustainable food, fibers, and biofuels. Biological nitrogen fixation, a process unique to diazatrophic bacteria, is catalyzed by the nitrogenase complex, and reconstituting this function in plant cells is an ambitious biotechnological strategy to reduce fertilizer use. Here we establish that the full array of biosynthetic and catalytic nitrogenase (Nif) proteins from the diazotroph Klebsiella pneumoniae can be individually expressed as mitochondrial targeting peptide (MTP)-Nif fusions in Nicotiana benthamiana. We show that these are correctly targeted to the plant mitochondrial matrix, a subcellular location with biochemical and genetic characteristics potentially supportive of nitrogenase function. Although Nif proteins B, D, E, F, H, J, K, M, N, Q, S, U, V, X, Y, and Z were all detectable by Western blot analysis, the NifD catalytic component was the least abundant. To address this problem, a translational fusion between NifD and NifK was designed based on the crystal structure of the nitrogenase MoFe protein heterodimer. This fusion protein enabled equimolar NifD:NifK stoichiometry and improved NifD expression levels in plants. Finally, four MTP-Nif fusion proteins (B, S, H, Y) were successfully co-expressed, demonstrating that multiple components of nitrogenase can be targeted to plant mitochondria. These results establish the feasibility of reconstituting the complete componentry for nitrogenase in plant cells, within an intracellular environment that could support the conversion of nitrogen gas into ammonia.
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Impact of Agricultural Management Practices on Mycorrhizal Functioning and Soil Microbiological Parameters Under Soybean-Based Cropping Systems - Springer

Impact of Agricultural Management Practices on Mycorrhizal Functioning and Soil Microbiological Parameters Under Soybean-Based Cropping Systems - Springer | Plant-Microbe Symbiosis | Scoop.it
The use of modern agricultural techniques for enhanced production has been advocated, however, its impact on below ground microbial networks is overlooked and adversely affected. The abiotic stresses like temperature (heat, cold chilling/frost), water (drought, flooding/hypoxia), radiation (UV, ionizing radiation), chemicals (mineral deficiency/excess, pollutants heavy metals/pesticides, gaseous toxins), mechanical (wind, soil movement, submergence) are responsible for over 50% reduction in agricultural production. On the other hand, organic farming practices yield fruitful results. This has highlighted the emerging need of switching over to some eco-friendly agricultural practices which can enhance the growth of plant, improve soil quality, mitigate drought without having adverse impacts on environment. Rhizosphere which is the narrow zone surrounding the roots of plant (Hiltner 1904) contains microbial communities which have the potential to benefit plants. Arbuscular mycorrhizal fungi are obligate symbionts which form association with about 90% of the land plant species (Gadkar et al. 2001). However, agricultural practices like tillage, crop rotation, fallowing, organic farming, fertilizers, etc., influence the functioning of AMF in many ways. Soybean is rich in phytochemicals that are beneficial for human beings. The inoculation of soybean and some other crops including cereals, pulses, and other leguminous crops with AMF leads to an enhancement in abiotic stress tolerance, disease resistance, overall growth, soil carbon sequestration, nutrient uptake, etc. This chapter summarizes the overall impact of different agricultural practices on mycorrhiza and other soil microbial communities under soybean-based cropping system.
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Establishing symbiotic nitrogen fixation in cereals and other non-legume crops: The Greener Nitrogen Revolution

Establishing symbiotic nitrogen fixation in cereals and other non-legume crops: The Greener Nitrogen Revolution | Plant-Microbe Symbiosis | Scoop.it
Haber’s invention of the synthesis of ammonia from its elements is one of the cornerstones of modern civilization. For nearly a century, agriculture has come to rely on synthetic nitrogen fertilizers produced from ammonia. This large-scale production is now supporting nearly half of the world’s population through increased food production. But whilst the use of synthetic nitrogen fertilizers brought enormous benefits, including those of the Green Revolution, the world needs to disengage from our ever-increasing reliance on nitrogen fertilizers produced from fossil fuels. Their pollution of the atmosphere and water systems has become a major global environmental and economic concern. Naturally, legume crops such as peas and beans can fix nitrogen symbiotically by interacting with soil nitrogen-fixing rhizobia, bacteria that become established intracellularly within root nodules. Ever since this was first demonstrated in 1888, consistent attempts have been made to extend the symbiotic interaction of legumes with nitrogen-fixing bacteria to non-legume crops, particularly cereals. In 1988, a fresh impetus arose from the discovery of Gluconacetobacter diazotrophicus (Gd), a non-nodulating, non-rhizobial, nitrogen-fixing bacterium isolated from the intercellular juice of sugarcane. Subsequently, strains of Gd inoculated under specific conditions were shown to intracellularly colonize the roots and shoots of the cereals: wheat, maize (corn) and rice, as well as crops as diverse as potato, tea, oilseed rape, grass and tomato. An extensive field trials programme using a seed inoculum technology based on Gd (NFix®) indicates that NFix® is able to significantly improve yields of wheat, maize, oilseed rape and grasses, in both the presence and absence of synthetic nitrogen fertilizers. Evidence suggests that these benefits are accruing through a possible combination of intracellular symbiotic nitrogen fixation, enhanced rates of photosynthesis and the presence of additional plant growth factors. Here, we discuss the research events that have led to this important development and present results demonstrating the efficacy of NFix® technology in non-legume crops, in particular cereals.

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Good plant growth promoting bacterium that fixes nitrogen for itself but I am not convinced that the crops (besides sugarcane) can acquire some of the fixed nitrogen.

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Nitrogen modulation of Medicago truncatula resistance to Aphanomyces euteiches depends on plant genotype

Nitrogen modulation of Medicago truncatula resistance to Aphanomyces euteiches depends on plant genotype | Plant-Microbe Symbiosis | Scoop.it
Nitrogen (N) availability can impact plant resistance to pathogens by regulating plant immunity. To better understand the links between N nutrition and plant defence, we analysed the impact of N availability on Medicago truncatula resistance to the root pathogen Aphanomyces euteiches. This oomycete is considered as the most limiting factor for legume production. Ten plant genotypes were tested in vitro for their resistance to A. euteiches in either complete or N-deficient medium. N-deficiency led to enhanced or reduced susceptibility depending on plant genotype. Focusing on four genotypes displaying contrasted responses we determined the impact of N-deficiency on plant growth and shoot N concentration and performed expression analyses on N- and defence-related genes as well as quantification of soluble phenolics and of root contents in different amino-acids. Our analyses suggest that N modulation of plant resistance is not linked to plant response to N deprivation nor to mechanisms previously identified to be involved in plant resistance. Furthermore our studies highlight a role of glutamine in mediating susceptibility to A. euteiches in M. truncatula.

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Gene expression analyses in tomato near isogenic lines provide evidence for ethylene and abscisic acid biosynthesis fine-tuning during arbuscular mycorrhiza development

Gene expression analyses in tomato near isogenic lines provide evidence for ethylene and abscisic acid biosynthesis fine-tuning during arbuscular mycorrhiza development | Plant-Microbe Symbiosis | Scoop.it
Plant responses to the environment and microorganisms, including arbuscular mycorrhizal fungi, involve complex hormonal interactions. It is known that abscisic acid (ABA) and ethylene may be involved in the regulation of arbuscular mycorrhiza (AM) and that part of the detrimental effects of ABA deficiency in plants is due to ethylene overproduction. In this study, we aimed to determine whether the low susceptibility to mycorrhizal colonization in ABA-deficient mutants is due to high levels of ethylene and whether AM development is associated with changes in the steady-state levels of transcripts of genes involved in the biosynthesis of ethylene and ABA. For that, tomato (Solanum lycopersicum) ethylene overproducer epinastic (epi) mutant and the ABA-deficient notabilis (not) and sitiens (sit) mutants, in the same Micro-Tom (MT) genetic background, were inoculated with Rhizophagus clarus, and treated with the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). The development of AM, as well as the steady-state levels of transcripts involved in ethylene (LeACS2, LeACO1 and LeACO4) and ABA (LeNCED) biosynthesis, was determined. The intraradical colonization in epi, not and sit mutants was significantly reduced compared to MT. The epi mutant completely restored the mycorrhizal colonization to the levels of MT with the application of 10 µM of AVG, probably due to the inhibition of the ACC synthase gene expression. The steady-state levels of LeACS2 and LeACO4 transcripts were induced in mycorrhizal roots of MT, whereas the steady-state levels of LeACO1 and LeACO4 transcripts were significantly induced in sit, and the steady-state levels of LeNCED transcripts were significantly induced in all genotypes and in mycorrhizal roots of epi mutants treated with AVG. The reduced mycorrhizal colonization in sit mutants seems not to be limited by ethylene production via ACC oxidase regulation. Both ethylene overproduction and ABA deficiency impaired AM fungal colonization in tomato roots, indicating that, besides hormonal interactions, a fine-tuning of each hormone level is required for AM development.

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Interface Symbiotic Membrane Formation in Root Nodules of Medicago truncatula: the Role of Synaptotagmins MtSyt1, MtSyt2 and MtSyt31

Interface Symbiotic Membrane Formation in Root Nodules of Medicago truncatula: the Role of Synaptotagmins MtSyt1, MtSyt2 and MtSyt31 | Plant-Microbe Symbiosis | Scoop.it
Symbiotic bacteria (rhizobia) are maintained and conditioned to fix atmospheric nitrogen in infected cells of legume root nodules. Rhizobia are confined to the asymmetrical protrusions of plasma membrane (PM): infection threads (IT), cell wall-free unwalled droplets and symbiosomes. These compartments rapidly increase in surface and volume due to the microsymbiont expansion, and remarkably, the membrane resources of the host cells are targeted to interface membrane quite precisely. We hypothesized that the change in the membrane tension around the expanding microsymbionts creates a vector for membrane traffic toward the symbiotic interface. To test this hypothesis, we selected calcium sensors from the group of synaptotagmins: MtSyt1, Medicago truncatula homolog of AtSYT1 from Arabidopsis thaliana known to be involved in membrane repair, and two other homologs expressed in root nodules: MtSyt2 and MtSyt3. Here we show that MtSyt1, MtSyt2, and MtSyt3 are expressed in the expanding cells of the meristem, zone of infection and proximal cell layers of zone of nitrogen fixation (MtSyt1, MtSyt3). All three GFP-tagged proteins delineate the interface membrane of IT and unwalled droplets and create a subcompartments of PM surrounding these structures. The localization of MtSyt1 by EM immunogold labeling has shown the signal on symbiosome membrane and endoplasmic reticulum (ER). To specify the role of synaptotagmins in interface membrane formation, we compared the localization of MtSyt1, MtSyt3 and exocyst subunit EXO70i, involved in the tethering of post-Golgi secretory vesicles and operational in tip growth. The localization of EXO70i in root nodules and arbusculated roots was strictly associated with the tips of IT and the tips of arbuscular fine branches, but the distribution of synaptotagmins on membrane subcompartments was broader and includes lateral parts of IT, the membrane of unwalled droplets as well as the symbiosomes. The double silencing of synaptotagmins caused a delay in rhizobia release and blocks symbiosome maturation confirming the functional role of synaptotagmins. In conclusion: synaptotagmin-dependent membrane fusion along with tip-targeted exocytosis is operational in the formation of symbiotic interface.

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Identification of the phosphorylation targets of symbiotic receptor‐like kinases using a high‐throughput multiplexed assay for kinase specificity

Identification of the phosphorylation targets of symbiotic receptor‐like kinases using a high‐throughput multiplexed assay for kinase specificity | Plant-Microbe Symbiosis | Scoop.it
Detecting the phosphorylation substrates of multiple kinases in a single experiment is a challenge, and new techniques are being developed to overcome this challenge. Here, we utilized a multiplexed assay for kinase specificity (MAKS) to identify the substrates directly and to map the phosphorylation site(s) of plant symbiotic receptor-like kinases. The symbiotic receptor-like kinases Nodulation Receptor-like Kinase (NORK) and Lysin motif domain-containing receptor-like kinase 3 (LYK3) are indispensable for the establishment of root nodule symbiosis. Although some interacting proteins have been identified for these symbiotic receptor-like kinases, very little is known about their phosphorylation substrates. Using this high-throughput approach, we identified several other potential phosphorylation targets for both these symbiotic receptor-like kinases. In particular, we also discovered the phosphorylation of LYK3 by NORK itself which was also confirmed by pair-wise kinase assays. Motif analysis of potential targets for these kinases revealed that the acidic motif xxxsDxxx was common to both of them. In summary, this high-throughput technique catalogs the potential phosphorylation substrates of multiple kinases in a single efficient experiment, the biological characterization of which should provide a better understanding of phosphorylation signaling cascade in symbiosis.

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Latest paper from our lab!

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Identification of Root-Secreted Compounds Involved in the Communication Between Cucumber, the Beneficial Bacillus amyloliquefaciens, and the Soil-Borne Pathogen Fusarium oxysporum | Molecular Plant...

Identification of Root-Secreted Compounds Involved in the Communication Between Cucumber, the Beneficial Bacillus amyloliquefaciens, and the Soil-Borne Pathogen Fusarium oxysporum | Molecular Plant... | Plant-Microbe Symbiosis | Scoop.it
Colonization of plant growth–promoting rhizobacteria (PGPR) is critical for exerting their beneficial effects on the plant. Root exudation is a major factor influencing the colonization of both PGPR and soil-borne pathogens within the root system. However, the tripartite interaction of PGPR, plant roots, and soil-borne pathogens is poorly understood. We screened root exudates for signals that mediate tripartite interactions in the rhizosphere. In a split-root system, we found that root colonization of PGPR strain Bacillus amyloliquefaciens SQR9 on cucumber root was significantly enhanced by preinoculation with SQR9 or the soil-borne pathogen Fusarium oxysporum f. sp. cucumerinum, whereas root colonization of F. oxysporum f. sp. cucumerinum was reduced upon preinoculation with SQR9 or F. oxysporum f. sp. cucumerinum. Root exudates from cucumbers preinoculated with SQR9 or F. oxysporum f. sp. cucumerinum were analyzed and 109 compounds were identified. Correlation analysis highlighted eight compounds that significantly correlated with root colonization of SQR9 or F. oxysporum f. sp. cucumerinum. After performing colonization experiments with these chemicals, raffinose and tryptophan were shown to positively affect the root colonization of F. oxysporum f. sp. cucumerinum and SQR9, respectively. These results indicate that cucumber roots colonized by F. oxysporum f. sp. cucumerinum or SQR9 increase root secretion of tryptophan to strengthen further colonization of SQR9. In contrast, these colonized cucumber roots reduce raffinose secretion to inhibit root colonization of F. oxysporum f. sp. cucumerinum.

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Diversity of fungal assemblages in roots of Ericaceae in two Mediterranean contrasting ecosystems

Diversity of fungal assemblages in roots of Ericaceae in two Mediterranean contrasting ecosystems | Plant-Microbe Symbiosis | Scoop.it
The plants belonging to the Ericaceae family are morphologically diverse and widely distributed groups of plants. They are typically found in soil with naturally poor nutrient status. The objective of the current study was to identify cultivable mycobionts from roots of nine species of Ericaceae (Calluna vulgaris, Erica arborea, Erica australis, Erica umbellate, Erica scoparia, Erica multiflora, Arbutus unedo, Vaccinium myrtillus, and Vaccinium corymbosum). The sequencing approach was used to amplify the Internal Transcribed Spacer (ITS) region. Results from the phylogenetic analysis of ITS sequences stored in the Genbank confirmed that most of strains (78) were ascomycetes, 16 of these were closely related to Phialocephala spp, 12 were closely related to Helotiales spp and 6 belonged to various unidentified ericoid mycorrhizal fungal endophytes. Although the isolation frequencies differ sharply according to regions and ericaceous species, Helotiales was the most frequently encountered order from the diverse assemblage of associated fungi (46.15%), especially associated with C. vulgaris (19.23%) and V. myrtillus (6.41%), mostly present in the Loge (L) and Mellousa region (M). Moreover, multiple correspondence analysis (MCA) showed three distinct groups connecting fungal order to ericaceous species in different regions.

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Effects of Nitrogen and Exogenous Rhizophagus irregularis on the Nutrient Status, Photosynthesis and Leaf Anatomy of Populus × canadensis ‘Neva’

Effects of Nitrogen and Exogenous Rhizophagus irregularis on the Nutrient Status, Photosynthesis and Leaf Anatomy of Populus × canadensis ‘Neva’ | Plant-Microbe Symbiosis | Scoop.it
The productivity of poplar is associated with large nitrogen (N) requirements. Exogenous arbuscular mycorrhizal fungi (AMF) show potential for use as bio-fertilizers. Understanding the interaction between N and exogenous AMF has theoretical and practical significance for poplar plantation. A pot experiment was conducted to assess the effects of N and exogenous Rhizophagus irregularis on plant growth, nutrient uptake, photosynthesis, water status, and leaf anatomical properties of Populus × canadensis ‘Neva’ in natural soil. The results showed that N fertilization increased plant growth, net photosynthesis, water status and the conduit diameter of midribs. The concentrations of carbon (C) and N in leaves were increased, but the phosphorus (P) concentration was decreased by N fertilization. The effectiveness of exogenous R. irregularis varied under different N levels. Under low N levels, exogenous R. irregularis-inoculated plants grew faster and exhibited superior photosynthetic capacity, water status and leaf conduit diameters than non-inoculated plants. Under high N levels, C, N and P concentrations were enhanced by exogenous R. irregularis inoculation. Furthermore, the average conduit diameter of midribs presented a significant positive correlation with plant growth parameters, photosynthesis, relative water content (RWC) and leaf C and N concentrations. It was concluded that exogenous R. irregularis exerted the strongest positive effects under low N levels by promoting plant growth and photosynthesis, and the fungus promoted plant nutrition decoupled from the level of N fertilization. Moreover, the improvement of plant physiological traits due to N fertilization or exogenous R. irregularis inoculation was accompanied by changes in internal anatomical properties.

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Adaptation Mechanisms in the Evolution of Moss Defenses to Microbes

Adaptation Mechanisms in the Evolution of Moss Defenses to Microbes | Plant-Microbe Symbiosis | Scoop.it
Bryophytes, including mosses, liverworts and hornworts are early land plants that have evolved key adaptation mechanisms to cope with abiotic stresses and microorganisms. Microbial symbioses facilitated plant colonization of land by enhancing nutrient uptake leading to improved plant growth and fitness. In addition, early land plants acquired novel defense mechanisms to protect plant tissues from pre-existing microbial pathogens. Due to its evolutionary stage linking unicellular green algae to vascular plants, the non-vascular moss Physcomitrella patens is an interesting organism to explore the adaptation mechanisms developed in the evolution of plant defenses to microbes. Cellular and biochemical approaches, gene expression profiles, and functional analysis of genes by targeted gene disruption have revealed that several defense mechanisms against microbial pathogens are conserved between mosses and flowering plants. P. patens perceives pathogen associated molecular patterns by plasma membrane receptor(s) and transduces the signal through a MAP kinase (MAPK) cascade leading to the activation of cell wall associated defenses and expression of genes that encode proteins with different roles in plant resistance. After pathogen assault, P. patens also activates the production of ROS, induces a HR-like reaction and increases levels of some hormones. Furthermore, alternative metabolic pathways are present in P. patens leading to the production of a distinct metabolic scenario than flowering plants that could contribute to defense. P. patens has acquired genes by horizontal transfer from prokaryotes and fungi, and some of them could represent adaptive benefits for resistance to biotic stress. In this review, the current knowledge related to the evolution of plant defense responses against pathogens will be discussed, focusing on the latest advances made in the model plant P. patens.

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Symbiotic interplay of fungi, algae, and bacteria within the lung lichen Lobaria pulmonaria L. Hoffm. as assessed by state-of-the-art metaproteomics2

Symbiotic interplay of fungi, algae, and bacteria within the lung lichen Lobaria pulmonaria L. Hoffm. as assessed by state-of-the-art metaproteomics2 | Plant-Microbe Symbiosis | Scoop.it
Lichens are recognized by macroscopic structures formed by a heterotrophic fungus, the mycobiont, which hosts internal autotrophic photosynthetic algal and/or cyanobacterial partners, referred to as the photobiont. We analyzed structure and functionality of the entire lung lichen Lobaria pulmonaria L. Hoffm. collected from two different sites by state-of-the-art metaproteomics. In addition to the green algae and the ascomycetous fungus, a lichenicolous fungus, as well as a complex prokaryotic community (different from the cyanobacteria) was found, the latter dominated by methanotrophic Rhizobiales. Various partner-specific proteins could be assigned to the different lichen symbionts, e.g. fungal proteins involved in vesicle transport, algal proteins functioning in photosynthesis, cyanobacterial nitrogenase and GOGAT involved in nitrogen-fixation, and bacterial enzymes responsible for methanol/C1-compounds metabolism as well as CO-detoxification. Structural and functional information on proteins expressed by the lichen community complemented and extended our recent symbiosis model depicting the functional multi-player network of single holobiont partners. Our new metaproteome analysis strongly supports the hypothesis (i) that interactions within the self-supporting association are multifaceted and (ii) that the strategy of functional diversification within the single lichen partners may support the longevity of L. pulmonaria under certain ecological conditions.

Via Jonathan Plett
Jean-Michel Ané's insight:

Nice work!

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Plant signalling in symbiosis and immunity 

Plant signalling in symbiosis and immunity  | Plant-Microbe Symbiosis | Scoop.it
Plants encounter a myriad of microorganisms, particularly at the root–soil interface, that can invade with detrimental or beneficial outcomes. Prevalent beneficial associations between plants and microorganisms include those that promote plant growth by facilitating the acquisition of limiting nutrients such as nitrogen and phosphorus. But while promoting such symbiotic relationships, plants must restrict the formation of pathogenic associations. Achieving this balance requires the perception of potential invading microorganisms through the signals that they produce, followed by the activation of either symbiotic responses that promote microbial colonization or immune responses that limit it.

Jean-Michel Ané's insight:

Very good review

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Nicolas Denancé's curator insight, March 22, 10:59 AM

Very good review

Sanjay Swami's curator insight, Today, 4:47 AM
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The actinorhizal symbiosis of the earliest divergent Frankia cluster

The actinorhizal symbiosis of the earliest divergent Frankia cluster | Plant-Microbe Symbiosis | Scoop.it
In recent years, the need to reduce reliance on synthetic nitrogen fertilizer has led to extensive research on biological nitrogen fixation, especially on root nodule symbioses. My study focuses on actinorhizal symbioses, the symbiotic interactions between members of nitrogen-fixing soil actinobacteria from the genus Frankia and a diverse group of plants from eight families, collectively called actinorhizal plants. Frankia cluster II has been shown to be sister to all other clusters. Thus, one of my aims was to gain insight into this cluster to get more information about the evolution of actinorhizal symbioses. The first sequenced genome of a member from this cluster Candidatus Frankia datiscae Dg1 originated from Pakistan. This strain contains the canonical nod genes nodABC responsible for the synthesis of lipochitooligosaccharide Nod factors. In this thesis, we obtained three Frankia inocula from North America (USA), one from Europe (France), one from Asia (Japan) and one from Oceania (Papua New Guinea). Thirteen metagenomes were sequenced based on gDNA isolated from root nodules of Datisca glomerata (Datiscaceae), Ceanothus thyrsiflorus (Rhamnaceae), Coriaria myrtifolia and Coriaria arborea (Coriariaceae). This study shows that members of Frankia cluster II come in teams, helping to explain the ability of cluster II to nodulate a wide host range, four families from two orders. The inoculum from Papua New Guinea, the only sequenced strain from the Southern Hemisphere so far, contains a new Frankia species, which was proposed as Candidatus Frankia meridionalis. All cluster II strains in this study contain the canonical nod genes nodABC, with the exception of the strain from Papua New Guinea which contains only nodB’C. All North American metagenomes also contain the sulfotransferase gene nodH. This gene shows host plant-specific expression in that it was expressed in nodules of C. thyrsiflorus but not in D. glomerata. Phylogenetic analysis and transposase frequencies of the new genomes strongly support the hypothesis that the extension of the cluster II host range from Coriaria to Datisca occurred in Eurasia and that cluster II strains came to North America via the Bering Strait. To acquire more information of the influence of the host plant on the behavior of the microsymbionts, the bacterial metabolism in nodules of D. glomerata (Cucurbitales) and C. thyrsiflorus (Rosales) were compared at the level of transcription. The system to protect nitrogenase from oxygen in Ceanothus nodules seems to be more efficient than in Datisca nodules, whereas the bacterial nitrogen metabolism is likely to be similar in both host plants. The amino acid profile of D. glomerata nodules shows that the nitrogenous solutes are dominated by glutamate and arginine, supporting the suggestion that Frankia in D. glomerata nodules exports an assimilated form of nitrogen, most likely arginine. Thus, our data show that cluster II Frankia strains differ from all other Frankia clusters with regard to the presence of the canonical nod genes and their nitrogen metabolism in symbiosis. 
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Root microbiota drive direct integration of phosphate stress and immunity 

Root microbiota drive direct integration of phosphate stress and immunity  | Plant-Microbe Symbiosis | Scoop.it
Plants live in biogeochemically diverse soils with diverse microbiota. Plant organs associate intimately with a subset of these microbes, and the structure of the microbial community can be altered by soil nutrient content. Plant-associated microbes can compete with the plant and with each other for nutrients, but may also carry traits that increase the productivity of the plant. It is unknown how the plant immune system coordinates microbial recognition with nutritional cues during microbiome assembly. Here we establish that a genetic network controlling the phosphate stress response influences the structure of the root microbiome community, even under non-stress phosphate conditions. We define a molecular mechanism regulating coordination between nutrition and defence in the presence of a synthetic bacterial community. We further demonstrate that the master transcriptional regulators of phosphate stress response in Arabidopsis thaliana also directly repress defence, consistent with plant prioritization of nutritional stress over defence. Our work will further efforts to define and deploy useful microbes to enhance plant performance.

Via Christophe Jacquet
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Biogeography of a novel clade of Ensifer meliloti associated with the Australian legume Trigonella suavissima.

Here we describe a novel clade within Ensifer meliloti and consider how geographic and ecological isolation contributed to the limited distribution of this group. Members of the genus Ensifer are best known for their ability to form nitrogen-fixing symbioses with forage legumes of three related genera, Medicago L., Melilotus Mill., and Trigonella L., which are members of the tribe Trifoleae. They have a natural distribution extending from the Mediterranean basin through west Asia, where there is an unsurpassed number of species belonging to these genera. Trigonella suavissima L. is unusual in that it is the only species in the tribe Trifolieae that is native to Australia. We compare the genetic diversity and taxonomic placement of rhizobia nodulating T. suavissima to members of an Ensifer reference collection. Our goal was to determine if the T. suavissima strains, like their plant host, are naturally limited to the Australian continent. We used multilocus sequence analysis to estimate the genetic relatedness of 56 T. suavissima symbionts to 28 Ensifer reference strains. Sequence data was partitioned according to the replicons upon which the loci are located. Results were used to construct replicon-specific phylogenetic trees. In both the chromosomal and chromid trees the Australian strains formed a distinct clade within E. meliloti. The strains also shared few alleles with Ensifer reference strains from other continents. Carbon source utilization assays revealed that the strains are also unusual in their ability to utilize 2-oxoglutarate as a sole carbon source. A strategy was outlined for locating similar strains elsewhere.

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Genome-wide identification and expression analysis of the GRAS family proteins in Medicago truncatula

The GRAS gene family performs a variety of functions in plant growth and development processes, and they also play essential roles in plant response to environmental stresses. Medicago truncatula is a diploid plant with a small genome used as a model organism. Despite the vital role of GRAS genes in plant growth regulation, few studies on these genes in M. truncatula have been conducted to date. Using the M. truncatula reference genome data, we identified 68 MtGRAS genes, which were classified into 16 groups by phylogenetic analysis, located on eight chromosomes. The structure analysis indicated that MtGRAS genes retained a relatively constant exon–intron composition during the evolution of the M. truncatula genome. Most of the closely related members in the phylogenetic tree had similar motif compositions. Different motifs distributed in different groups of the MtGRAS genes were the sources of their functional divergence. Twenty-eight MtGRAS genes were expressed in six tissues, namely root, bud, blade, seedpod, nodule, and flower tissues, suggesting their putative function in many aspects of plant growth and development. Nine MtGRAS genes were upregulated under cold, freezing, drought, ABA, and salt stress treatments, indicating that they play vital roles in the response to abiotic stress in M. truncatula. Our study provides valuable information that can be utilized to improve the quality and agronomic benefits of M. truncatula and other plants.

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LjMOT1, a high-affinity molybdate transporter from Lotus japonicus, is essential for molybdate uptake, but not for the delivery to nodules  

Molybdenum (Mo) is an essential nutrient for plants, and is required for nitrogenase activity of legumes. However, the pathways of Mo uptake from soils and then delivery to the nodules have not been characterized in legumes. In this study, we characterized a high-affinity Mo transporter (LjMOT1) from Lotus japonicus. Mo concentrations in an ethyl methanesulfonate–mutagenized line (ljmot1) decreased by 70–95% compared with wild type (WT). By comparing the DNA sequences of four AtMOT1 homologs between mutant and WT lines, one point mutation was found in LjMOT1, which altered Trp292 to a stop codon; no mutation was found in the other homologous genes. The phenotype of Mo concentrations in F2 progeny from ljmot1 and WT crosses were associated with genotypes of LjMOT1. Introduction of endogenous LjMOT1 to ljmot1 restored Mo accumulation to approximately 60–70% of the WT. Yeast expressing LjMOT1 exhibited high Mo uptake activity, and the Km was 182 nM. LjMOT1 was expressed mainly in roots, and its expression was not affected by Mo supply or rhizobium inoculation. Although Mo accumulation in the nodules of ljmot1 was significantly lower than that of WT, it was still high enough for normal nodulation and nitrogenase activity, even for cotyledons removed ljmot1 plants grown under low Mo conditions, in this case the plant growth was significantly inhibited by Mo deficiency. Our results suggest that LjMOT1 is an essential Mo transporter in L. japonicus for Mo uptake from the soil and growth, but is not Mo delivery to the nodules.
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Via Kevin Garcia
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Ecole d'été en Biologie et Ecologie intégratives 2017 

Ecole d'été en Biologie et Ecologie intégratives 2017  | Plant-Microbe Symbiosis | Scoop.it
Since 2012, TULIP has been organizing a residential training session for Masters, PhD and post-doctoral students from all over the world. A unique occasion to meet international speakers gathered in Occitanie for this occasion.
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The Mutualistic Interaction between Plants and Arbuscular Mycorrhizal Fungi

The Mutualistic Interaction between Plants and Arbuscular Mycorrhizal Fungi | Plant-Microbe Symbiosis | Scoop.it
Mycorrhizal fungi belong to several taxa and develop mutualistic symbiotic associations with over 90% of all plant species, from liverworts to angiosperms. While descriptive approaches have dominated the initial studies of these fascinating symbioses, the advent of molecular biology, live cell imaging, and “omics” techniques have provided new and powerful tools to decipher the cellular and molecular mechanisms that rule mutualistic plant-fungus interactions. In this article we focus on the most common mycorrhizal association, arbuscular mycorrhiza (AM), which is formed by a group of soil fungi belonging to Glomeromycota. AM fungi are believed to have assisted the conquest of dry lands by early plants around 450 million years ago and are found today in most land ecosystems. AM fungi have several peculiar biological traits, including obligate biotrophy, intracellular development inside the plant tissues, coenocytic multinucleate hyphae, and spores, as well as unique genetics, such as the putative absence of a sexual cycle, and multiple ecological functions. All of these features make the study of AM fungi as intriguing as it is challenging, and their symbiotic association with most crop plants is currently raising a broad interest in agronomic contexts for the potential use of AM fungi in sustainable production under conditions of low chemical input.

Via Francis Martin
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Bob Reeves's curator insight, March 8, 8:11 PM
Just think of this for a moment; how many living things in Nature (that haven't changed in 450(+?) million years) are still with us today? No adaptation via sexual re-calibration - they are just the same as they always were. And they are not on the margins of life on the planet today, they are ubiquitous, world-wide, essential partners to vascular plants - plants that didn't even exist when 'they' first evolved. 
Plants in every ecosystem support these non-evolving organisms today, feeding them with 30% or more of their photosynthates. And, did I mention, 'they' are an obligate biotroph of plants - they can't/won't exist unless they perform a valued service for their plant hosts. Maybe they've figured out how to be... Indispensable? I wish I could figure that trick out. 
Nature seems to be holding up a big neon sign saying 'Hey, hey you with the big brain - check this out - we've been waiting a very long time for you to notice us'.