Plant-Microbe Symbiosis
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Rescooped by Jean-Michel Ané from Publications from The Sainsbury Laboratory
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The plant membrane-associated REM1.3 remorin accumulates in discrete perihaustorial domains and enhances susceptibility to Phytophthora infestans

The plant membrane-associated REM1.3 remorin accumulates in discrete perihaustorial domains and enhances susceptibility to Phytophthora infestans | Plant-Microbe Symbiosis | Scoop.it

Filamentous pathogens such as the oomycete Phytophthora infestans infect plants by developing specialized structures termed haustoria inside the host cells. Haustoria are thought to enable secretion of effector proteins into the plant cells. Haustorium biogenesis is therefore critical for pathogen accommodation in the host tissue. Haustoria are enveloped by a specialized host-derived membrane, the extrahaustorial membrane (EHM), which is distinct from the plant plasma membrane. The mechanisms underlying the biogenesis of the EHM are unknown. Remarkably, several plasma membrane localised proteins are excluded from the EHM but the remorin REM1.3 accumulates around P. infestans haustoria. Here, we used overexpression, co-localization with reporter proteins, and super-resolution microscopy in cells infected by P. infestans to reveal discrete EHM domains labelled by REM1.3 and P. infestans effector AVRblb2. Moreover, SYT1 synaptotagmin, another previously identified perihaustorial protein, localized to subdomains which are mainly not labelled by REM1.3 and AVRblb2. Functional characterization of REM1.3 revealed that it is a susceptibility factor that promotes infection by P. infestans. This activity, and REM1.3 recruitment to the EHM, require REM1.3 membrane binding domain. Our results implicate REM1.3 membrane micro-domains in plant susceptibility to an oomycete pathogen.


Via Kamoun Lab @ TSL, The Sainsbury Lab
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I know that it is not a symbiont but... some people will guess why I am scooping this :-)

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Plant-Microbe Symbiosis
Beneficial associations between plants and microbes
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Development and nitrate reductase activity of sugarcane inoculated with five diazotrophic strains

Diazotrophs are able to stimulate plant growth. This study aimed at evaluating the effect of inoculation of five diazotrophic strains on growth promotion and nitrate reductase (NR, EC 1.7.1.1) activity in sugarcane. An experiment was carried out from three stages of cultivation: sprouting, tubes, and in hydroponics. On the first two stages, seven treatments were adopted: uninoculated control; mixed inoculation with five strains; and individual inoculation with Gluconacetobacter diazotrophicus (Gd), Herbaspirillum rubrisubalbicans (Hr), Herbaspirillum seropedicae (Hs), Nitrospirillum amazonense (Na), and Paraburkholderia tropica (Pt). The four treatments showing the best performance were transferred to the hydroponic system for analysis of NR activity. Hs, Pt, and the mixture of all strains led to the highest seedling biomass in tubes, followed by Hr. In hydroponics, the mixture and the strain Hr had the highest growth-promoting effect. NR activity was influenced by inoculation only under low N supply conditions, with positive effect of Hr, Pt, and the mixture.

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Growth promotion of peanut (Arachis hypogaea L.) and maize (Zea mays L.) plants by single and mixed cultures of efficient phosphate solubilizing bacteria that are tolerant to abiotic stress and pes...

Growth promotion of peanut (Arachis hypogaea L.) and maize (Zea mays L.) plants by single and mixed cultures of efficient phosphate solubilizing bacteria that are tolerant to abiotic stress and pes... | Plant-Microbe Symbiosis | Scoop.it
The aims of this study were, to analyze in vitro phosphate solubilization activity of six native peanut bacteria and to determine the effect of single and mixed inoculation of these bacteria on peanut and maize plants. Ability to produce organic acids and cofactor PQQ, to solubilize FePO4 and AlPO4 and phosphatase activity were analyzed. Also, the ability to solubilize phosphate under abiotic stress and in the presence of pesticides of the selected bacteria was determined. The effect of single and mixed bacterial inocula was analyzed on seed germination, maize plant growth and in a crop rotation plant assay with peanut and maize. The six strains produced gluconic acid and five released cofactor PQQ into the medium. All bacteria showed ability to solubilize phosphate from FePO4 and AlPO4 and phosphatase activity. The ability of the bacteria to solubilize tricalcium phosphate under abiotic stress and in presence of pesticides indicated encouraging results. Bacterial inoculation on peanut and maize increased seed germination, plant́s growth and P content.

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Interactions of arbuscular mycorrhizal and endophytic fungi improve seedling survival and growth in post-mining waste

The impact of fungal endophytes and the modulating role of arbuscular mycorrhizal fungi (AMF) on the vitality of Verbascum lychnitis, grown in the laboratory in a substratum from a post-mining waste dump was investigated. We report that inoculation with a single endophyte negatively affected the survival rate and biomass production of most of the plant-endophyte consortia examined. The introduction of arbuscular mycorrhiza fungi into this setup (dual inoculation) had a beneficial effect on both biomass yield and survivability. V. lychnitis co-inoculated with AMF and Cochliobolus sativus, Diaporthe sp., and Phoma exigua var. exigua yielded the highest biomass, exceeding the growth rate of both non-inoculated and AMF plants. AMF significantly improved the photosynthesis rates of the plant-endophyte consortia, which were negatively affected by inoculation with single endophytes. The abundance of PsbC, a photosystem II core protein previously shown to be upregulated in plants colonized by Epichloe typhina, exhibited a significant increase when the negative effect of the fungal endophyte was attenuated by AMF.

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Activity, diversity and function of arbuscular mycorrhizae vary with changes in agricultural management intensity

Many beneficial soil microbes are sensitive to chemical and mechanical disturbances associated with conventional row crop agriculture, including arbuscular mycorrhizal (AM) fungi. AM fungi provide agricultural benefits through multiple mechanisms including increasing crop pathogen resistance, helping with crop nutrient acquisition, and increasing soil carbon storage. Conversion to less intensive row crop agricultural management systems such as biologically-based organic and no-till may reduce the negative effects of conventional management to AM fungi. In this study, AM fungus activity (via glomalin production), spore diversity, community structure, and community stability were surveyed over 20 years in no-till, biologically-based organic, and conventionally managed plots at the W.K. Kellogg Biological Station Long Term Ecological Research Site in Michigan, USA. A complementary greenhouse experiment tested for direct effects of AM fungal inocula from these different agricultural management treatments on growth of corn and wheat plants. Soil glomalin increased in no-till and organic management systems, most likely due to decreases in disturbance associated with tillage and chemical inputs. No-till management slightly increased AM fungus diversity and community stability. AM fungus community structure significantly differed between conventional and no-till treatments, with an indicator species analysis showing that Acaulospora spp. were characteristic of conventional management, while Glomus spp. and Gigaspora spp. were associated with no-till management. AM fungal inocula from organically-managed treatments increased wheat, but not corn, growth. Overall, conversion from long-term conventional row crop agricultural management to no-till or biologically-based organic systems increased soil glomalin, but did not uniformly improve AM fungus diversity or crop plant benefits. In the future, novel agricultural systems combining organic management with conservation tillage may further improve AM fungal benefits to soils and crops.

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Ectomycorrhizal symbiosis enhances tolerance to low phosphorous through expression of phosphate transporter genes in masson pine (Pinus massoniana)

Ectomycorrhizal symbiosis promotes the growth of masson pine (Pinus massoniana) in low-phosphorus (low-P) conditions; however, the mechanism underlying this phenomenon has not yet been fully described. Here, we cloned four members of the Pht1 phosphate transporter protein family (GenBank accession: AMR43649.1 to AMR43652.1) encoding phosphate transporters in masson pine (PmPTs) by rapid amplification of cDNA ends (RACE) and characterized them in Boletus edulis and Pisolithus tinctorius colonized plants under low-P stress. PmPT1 to PmPT4 encoded 548, 548, 535, 535 amino acid polypeptides, respectively, containing the typical domain of the Pi:H+ symporter (PHS-transporter). Homology multiple sequence alignment indicated that these PmPTs were highly similar to phosphate transporters from other species. The polypeptides were characterized by high hydropathicity and contained 12 putative intra-membrane regions and 1 cytoplasmic loop. The temporal and spatial expression profiles showed higher expression of these PmPTs in ectomycorrhiza (ECM)-inoculated plants compared to non-inoculated ones. In addition, expressions of these PmPT members shared a similar pattern and might be intensively activated by low-P stress or inhibited under P excess. Interestingly, the ECM-colonized plants accumulated more phosphate compared to non-ECM-colonized specimens when exposed to low-P. Therefore, enhanced low-P tolerance in ECM-inoculated masson pine to low-P stress was at least partially dependent on the up-regulation of phosphate transporter genes, reflecting that the intimate interaction between plants and ECM fungi resulted in the improvement of P nutrition.

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Mass spectrometry imaging: towards mapping the elemental and molecular composition of the rhizosphere

Mass spectrometry imaging: towards mapping the elemental and molecular composition of the rhizosphere | Plant-Microbe Symbiosis | Scoop.it
This short review provides perspective regarding the use of mass spectrometry imaging (MSI) to study the rhizosphere. It also serves to complement the multi-omic-focused review by White et al. in this journals’ issue. MSI is capable of elucidating chemical distributions within samples of interest in situ, and thus can provide spatial context to MS omics data in complementary experimental endeavors. Most MSI-based studies of plant-microbe interactions have focused on the phyllosphere and on the “associated rhizosphere” (our term for material that is not removed during harvesting). Sample preparation for these in situ analyses tends to be a limiting factor. These studies, however, have provided valuable insights into the spatial arrangement of proteins, peptides, lipids, and other metabolites within these systems. We intend this short review to be a primer on the fundamentals of MSI and its role in plant-microbe analysis. Lastly, we offer a perspective on the future of MSI and its use in understanding the molecular transformations beyond what we call the associated rhizosphere, one which extends to the rest of rhizosphere and into the bulk soil.

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VARIABILIDAD DE AISLADOS DIAZOTRÓFICOS SIMBIÓTICOS EN DIFERENTES CONDICIONES AGROECOLÓGICAS DEL SUR DEL ECUADOR

El estudio consistió en la determinación de la variabilidad de aislados diazotróficos simbióticos procedentes del cultivo de frijol común (Phaseolus vulgaris L.) en diferentes zonas agroecológicas de la provincia de Loja, Ecuador. Se muestrearon un total de 9 cantones con diferentes zonas agroclimáticas, las cuales se geo-referenciaron mediante el Sistema de Posicionamiento Global. La determinación de la variabilidad de los aislados se realizó mediante caracterización morfológica de las colonias obtenidas, donde se evaluó la tinción al Gram, crecimiento, color, producción de mucus, bordes y elevación. La caracterización bioquímica se llevó a cabo mediante el crecimiento de los aislados en medios selectivos: Mac Conkey, Agar Kligler, Extracto de Levadura Manitol Agar-Rojo Congo y Peptona Glucosa Agar. Los resultados mostraron una alta variabilidad de los parámetros morfológicos evaluados en las diferentes condiciones agroclimáticas. De un total de 45 aislados iniciales, 24 de ellos presentaron diferencias en al menos un parámetro evaluado, con características que concuerdan con aquellas pertenecientes al género Rhizobium. El análisis bioquímico corroboró los requerimientos nutricionales de las bacterias pertenecientes al género Rhizobium, tanto en la fermentación de lactosa en medio Mac Conkey como el crecimiento en los medios Kligler y Peptona Glucosa Agar. El crecimiento en medio Extracto de Levadura Manitol Agar-Rojo Congo demostró la pureza de los aislados. Estos resultados sientan las bases para ulteriores estudios moleculares de identificación genética y análisis fenotípicos de cepas nativas en interacción con frijol común para elevar la eficiencia del proceso de fijación simbiótica del nitrógeno en este cultivo.

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Unknown risks to soil biodiversity from commercial fungal inoculants

To the Editor — Soil is the most biodiverse ecosystem on Earth but also the most unknown. More than any other ecosystem, soils have been impacted by humans, but consequences for soil biodiversity continue to be ignored1.
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Populus trichocarpa encodes small, effector-like secreted proteins that are highly induced during mutualistic symbiosis

Populus trichocarpa encodes small, effector-like secreted proteins that are highly induced during mutualistic symbiosis | Plant-Microbe Symbiosis | Scoop.it
During symbiosis, organisms use a range of metabolic and protein-based signals to communicate. Of these protein signals, one class is defined as ‘effectors’, i.e., small secreted proteins (SSPs) that cause phenotypical and physiological changes in another organism. To date, protein-based effectors have been described in aphids, nematodes, fungi and bacteria. Using RNA sequencing of Populus trichocarpa roots in mutualistic symbiosis with the ectomycorrhizal fungus Laccaria bicolor, we sought to determine if host plants also contain genes encoding effector-like proteins. We identified 417 plant-encoded putative SSPs that were significantly regulated during this interaction, including 161 SSPs specific to P. trichocarpa and 15 SSPs exhibiting expansion in Populus and closely related lineages. We demonstrate that a subset of these SSPs can enter L. bicolor hyphae, localize to the nucleus and affect hyphal growth and morphology. We conclude that plants encode proteins that appear to function as effector proteins that may regulate symbiotic associations.

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Genetic diversity of symbiotic Paraburkholderia species isolated from nodules of Mimosa pudica (L.) and Phaseolus vulgaris (L.) grown in soils of the Brazilian Atlantic Forest (Mata Atlântica)

Some species of the genus Paraburkholderia that are able to nodulate and fix nitrogen in symbiosis with legumes are called β-rhizobia and represent a group of ecological and biotechnological importance. We used Mimosa pudica and Phaseolus vulgaris to trap 427 rhizobial isolates from rhizospheric soil of Mimoseae trees in the Brazilian Atlantic Forest. Eighty-four representative strains were selected according to the 16S rRNA haplotypes and taxonomically characterized using a concatenated 16S rRNA-recA phylogeny. Most strains were assembled in the genus Paraburkholderia, including Paraburkholderia sabiae and Pa. nodosa. Mesorhizobium (α-rhizobia) and Cupriavidus (β-rhizobia) were also isolated, but in smaller proportions. Multilocus sequence analysis and BOX-PCR analyses indicated that six clusters of Paraburkholderia represent potential new species. In the phylogenetic analysis of the nodC gene, the majority of the strains were positioned in the same groups as in the 16S rRNA-recA tree, indicative of stability and vertical inheritance, but we also identified horizontal transfer of nodC in Pa. sabiae. All α- and β-rhizobial species were trapped by both legumes, although preferences of the host plants for specific rhizobial species have been observed.
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Biological control of plant diseases

Biological control is the control of disease by the application of biological agents to a host animal or plant that prevents the development of disease by a pathogen. With regard to plant diseases the biocontrol agents are usually bacterial or fungal strains isolated from the endosphere or rhizosphere. Viruses can also be used as biocontrol agents and there is a resurgent interest in the use of bacterial viruses for control of plant diseases. The degree of disease suppression achieved with biological agents can be comparable to that achieved with chemicals. Our understanding of the ways in which biocontrol agents protect plants from disease has developed considerably in recent years with the application of genomics and genetic modification techniques. We have uncovered mechanisms by which biocontrol agents interact with the host plant and other members of the microbial community associated with the plant. Understanding these mechanisms is crucial to the isolation of effective biocontrol agents and the development of biocontrol strategies for plant diseases. This review looks at recent developments in our understanding of biocontrol agents for plant diseases and how they work.

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Detection of plant pathogens using real‐time PCR: how reliable are late Ct values? l  Grosdidier et al. 

Effective detection of pathogens from complex substrates is a challenging task. Molecular approaches such as real-time PCR can detect pathogens present even in low quantities. However, weak real-time PCR signals, as represented by high cycle threshold (Ct) values, may be questionable. Therefore, setting a reliable Ct threshold to declare a positive reaction is important for specific detection. In this study, five methods were assessed for their performance in determining a Ct cut-off value. These methods were based on the widely used probability of detection (POD) or receiver-operating characteristic (ROC) approaches. Two important forest pathogens, Hymenoscyphus fraxineus and Fusarium circinatum, were used to set up three experimental frameworks that combined two types of substrates (seed lots and spore traps) and different PCR machines. The ROC-based method emerged as the most complete and flexible method under various experimental conditions. It was demonstrated that the ROC method leads to a cut-off value below which late Ct results can reliably be considered indicative of positive test results. This cut-off value must be determined for each experimental approach used. The method based on the distribution of a previously determined set of Ct values corresponding to false-positives appeared to be better adapted to detecting false-negative results, and thus useful for testing potentially invasive pathogens.


Via Petter Françoise
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Petter Françoise's curator insight, March 28, 5:23 AM
Interpreting late Ct values can indeed be a challenge. A workshop on setting Ct cut-off values for real-time PCR was organized by EPPO in 2013: http://archives.eppo.int/MEETINGS/2013_conferences/cut-off_values.htm.

An article was also published on this topic in the EPPO Bulletin Chandelier A, Planchon V, Oger R, 2010. Determination of cycle cut off in real-time PCR for the detection of regulated plant pathogens. EPPO Bulletin 40 ,52–8.
Rescooped by Jean-Michel Ané from Plant roots and rhizosphere
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Live imaging of root–bacteria interactions in a microfluidics setup

Live imaging of root–bacteria interactions in a microfluidics setup | Plant-Microbe Symbiosis | Scoop.it
Plant roots play a dominant role in shaping the rhizosphere, the environment in which interaction with diverse microorganisms occurs. Tracking the dynamics of root–microbe interactions at high spatial resolution is currently limited because of methodological intricacy. Here, we describe a microfluidics-based approach enabling direct imaging of root–bacteria interactions in real time. The microfluidic device, which we termed tracking root interactions system (TRIS), consists of nine independent chambers that can be monitored in parallel. The principal assay reported here monitors behavior of fluorescently labeled Bacillus subtilis as it colonizes the root of Arabidopsis thaliana within the TRIS device. Our results show a distinct chemotactic behavior of B. subtilis toward a particular root segment, which we identify as the root elongation zone, followed by rapid colonization of that same segment over the first 6 h of root–bacteria interaction. Using dual inoculation experiments, we further show active exclusion of Escherichia coli cells from the root surface after B. subtilis colonization, suggesting a possible protection mechanism against root pathogens. Furthermore, we assembled a double-channel TRIS device that allows simultaneous tracking of two root systems in one chamber and performed real-time monitoring of bacterial preference between WT and mutant root genotypes. Thus, the TRIS microfluidics device provides unique insights into the microscale microbial ecology of the complex root microenvironment and is, therefore, likely to enhance the current rate of discoveries in this momentous field of research.

Via Christophe Jacquet
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Substrate utilization by endophytic bacteria Paenibacillus polymyxa P2b-2R that may facilitate bacterial entrance and survival inside diverse plant hosts

Bacterial endophytes are thought to enter plants either through pre-existing openings in plant tissues or by creating openings by hydrolyzing major plant cell wall components. A lodgepole endophyte, Paenibacillus polymyxa P2b-2R, consistently formed endophytic colonies when inoculated in diverse plant hosts, viz., lodgepole pine, western red cedar, corn, canola, and tomato. We were interested to know, whether or not this bacterial strain possesses enzymes that can hydrolyze three major plant cell wall components namely cellulose, xylan, and pectin to facilitate entrance into the host plants. Using a BIOLOG assay, we also tested this bacterial strain’s ability to utilize carbon sources that might facilitate its entrance and hence its survival inside host plants. Paenibacillus polymyxa P2b-2R hydrolyzed sodium carboxymethylcellulose, beechwood xylan, and sodium polypectate and utilized 39 of the 95 carbon sources (41%) tested. Of the 39 carbon substrates oxidized by P2b-2R, the “carbohydrates” group represents the largest source of utilizable carbon (23 out of 39). Thus, it can be concluded that P. polymyxa P2b-2R is able to degrade major cell wall components (cellulose, xylan, and pectin) and utilize some of the available carbon substrates, possibly to gain entry and survive inside the plant and form endophytic colonies thereafter.

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Impact of tree species on barley rhizosphere-associated fungi in an agroforestry ecosystem as revealed by 18S rDNA PCR-DGGE

Agroforestry systems have been considered a form of sustainable land use. Woody species in agroforestry systems can improve soil physicochemical properties by supplying leaf or stem litter. However, little is known about fungal community structure and diversity in agroforestry systems. In the present study, the culture-independent 18S rDNA-based polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method was used to investigate fungal community structure in rhizosphere and bulk soil in Populus euramevicana-barley and Taxodium distichum-barley agroforestry systems. DGGE profiling and cluster analysis revealed that the fungal community structure in the rhizosphere was more complex than that of bulk soil. Our results also indicated that the rhizosphere fungal community in barley was less affected by T. distichum than by P. euramevicana. In addition, an increase in the relative abundance of certain rhizosphere fungal populations was detected in this agroforestry system. Sequencing of prominent DGGE bands revealed an increase in the rhizosphere of a fungal species belonging to the genera Chaetomium, which includes potential biocontrol agents. A rare cellulolytic fungus, Acremonium alcalophilum, was found in the bulk soil from P. euramevicana and barley grown under P. euramevicana. Taken together, our findings may provide new insights into agroforestry practices.

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Transport of nitrogen and zinc to rhodes grass by arbuscular mycorrhiza and roots as affected by different nitrogen sources (NH4+-N and NO3−-N)

We investigated the effect of mineral nitrogen forms on transfer of nitrogen (N) and zinc (Zn) from attached compartments to rhodes grass (Chloris gayana) colonised with arbuscular mycorrhizal fungi (AMF). After being pre-cultivated in substrates with adequate nutrient supply and either AMF inoculated (+AM) or left non-inoculated (−AM), rhodes grass was positioned adjacent to an outer compartment holding a similar substrate but applied with labelled nitrogen (15N) either as ammonium (NH4+) or nitrate (NO3−), and a high supply of Zn (150 mg kg−1 DS). Plant roots together with fungal mycelium were either allowed to explore the outer compartment (with root access) or only mycorrhizal hyphae were allowed (without root access). Within each access treatment, biomasses of rhodes grass were not significantly affected by AMF inoculation or N form. AMF contribution to plant 15N uptake was about double in NH4+ compared with NO3−-supplied treatments while the mycorrhizal influence on plant Zn uptake was insignificant. Without root access, the shoot 15N/Zn concentration ratio was up to ten-fold higher in +AM than –AM treatments and this ratio increase was clearly more pronounced in NH4+ than NO3−-supplied treatments. In conclusion, rhodes grass in symbiosis with the tested AMF acquired more N when supplied with ammonium. Moreover, there is clear indication that although the AMF have transported both nutrients (N and Zn), N was preferentially transferred as compared to Zn. We confirmed that, while rhodes grass is not able to prevent excessive Zn uptake via roots under conditions of high Zn, mycorrhiza is able to avoid excessive Zn supply to the host plant when the fungus alone has access to contaminated patches.

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Physiological and molecular insights into rice-arbuscular mycorrhizal interactions under arsenic stress

Physiological and molecular insights into rice-arbuscular mycorrhizal interactions under arsenic stress | Plant-Microbe Symbiosis | Scoop.it
The symbiotic associations between plants, microbes and fungi are examples of living in harmony. The intimate association between the arbuscular mycorrhizal fungi (AMF) and their host plants benefits the latter in nutrient (viz., phosphate, nitrogen etc.) acquisition in exchange of carbohydrates. Arsenic (As) accumulation in rice grains has become a serious issue in some parts of world having high As levels in soil and groundwater. To this end, experiments have demonstrated ameliorative potential of AMF colonization on As stress in rice. AMF colonization not only influences As concentrations in grains but also the speciation of As and reduces the ratios of inorganic/organic As concentrations. Positive influences of AMF colonization have also been linked to alteration in transport of As and phosphate, photosynthetic reactions and improved growth. A role of 14-3-3 proteins in AMF colonization under As stress is also suggested in recent studies. Importantly, grain yield has been found to increase in presence of AMF colonization. In this review, we discuss the molecular intricacies of rice-AMF in the context of As stress.

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Interactions between phenolic compounds present in dry olive residues and the arbuscular mycorrhizal symbiosis

The use of “alpeorujo” (dry olive residue) has been proposed as an organic amendment in order to enhance soil structure and to increase C storage in soils. The aim of this work is to study how aqueous alpeorujo (ADOR) extracts bioremediated with white-rot fungi and three representative phenolic acids present in this extract (protocatechuic, vanillic and caffeic acid) affect the growth of the arbuscular mychorrhizal fungus Rhizophagus custos in monoxenic culture. Our results show that ADOR decreased mycorrhization parameters; however, this negative effect ceased after ADOR bioremediation. Although protocatechuic and vanillic acids have drastic negative effects at high concentrations, these phenols enhance mycorrhization processes at low concentrations and caffeic acid negatively affects symbiosis at low concentrations. Finally, the capacity of root biomass to dissipate individual phenols was also estimated, in which mycorrhized roots improve phenol dissipation in the growth medium in the presence of different phenols. This study highlights the important role played by arbuscular mycorrhiza in protecting plants from phytotoxicity.

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Local signalling pathways regulate the Arabidopsis root developmental response to Mesorhizobium loti inoculation 

Numerous reports have shown that various rhizobia can interact with non-host plant species, improving mineral nutrition and promoting plant growth. To further investigate the effects of such non-host interactions on root development and functions, we inoculated Arabidopsis thaliana with the model nitrogen fixing rhizobacterium Mesorhizobium loti (strain MAFF303099). In vitro, we show that root colonization by M. loti remains epiphytic and that M. loti cells preferentially grow at sites where primary and secondary roots intersect. Besides resulting in an increase in shoot biomass production, colonization leads to transient inhibition of primary root growth, strong promotion of root hair elongation and increased apoplasmic acidification in periphery cells of a sizeable part of the root system. Using auxin mutants, axr1-3 and aux1-100, we show that a plant auxin pathway plays a major role in inhibiting root growth but not in promoting root hair elongation, indicating that root developmental responses involve several distinct pathways. Finally, using a split root device, we demonstrate that root colonization by M. loti, as well as by the bona fide plant growth promoting rhizobacteria Azospirillum brasilense and Pseudomonas, affect root development via local transduction pathways restricted to the colonised regions of the root system.
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Common bean proteomics: Present status and future strategies

Common bean (Phaseolus vulgaris L.) is a legume of appreciable importance and usefulness worldwide to the human population providing food and feed. It is rich in high-quality protein, energy, fiber and micronutrients especially iron, zinc, and pro-vitamin A; and possesses potentially disease-preventing and health-promoting compounds. The recently published genome sequence of common bean is an important landmark in common bean research, opening new avenues for understanding its genetics in depth. This legume crop is affected by diverse biotic and abiotic stresses severely limiting its productivity. Looking at the trend of increasing world population and the need for food crops best suited to the health of humankind, the legumes will be in great demand, including the common bean mostly for its nutritive values. Hence the need for new research in understanding the biology of this crop brings us to utilize and apply high-throughput omics approaches. In this mini-review our focus will be on the need for proteomics studies in common bean, potential of proteomics for understanding genetic regulation under abiotic and biotic stresses and how proteogenomics will lead to nutritional improvement. We will also discuss future proteomics-based strategies that must be adopted to mine new genomic resources by identifying molecular switches regulating various biological processes.

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Biofilm formation enables free-living nitrogen-fixing rhizobacteria to fix nitrogen under aerobic conditions

Biofilm formation enables free-living nitrogen-fixing rhizobacteria to fix nitrogen under aerobic conditions | Plant-Microbe Symbiosis | Scoop.it
The multicellular communities of microorganisms known as biofilms are of high significance in agricultural setting, yet it is largely unknown about the biofilm formed by nitrogen-fixing bacteria. Here we report the biofilm formation by Pseudomonas stutzeri A1501, a free-living rhizospheric bacterium, capable of fixing nitrogen under microaerobic and nitrogen-limiting conditions. P. stutzeri A1501 tended to form biofilm in minimal media, especially under nitrogen depletion condition. Under such growth condition, the biofilms formed at the air–liquid interface (termed as pellicles) and the colony biofilms on agar plates exhibited nitrogenase activity in air. The two kinds of biofilms both contained large ovoid shape ‘cells’ that were multiple living bacteria embedded in a sac of extracellular polymeric substances (EPSs). We proposed to name such large ‘cells’ as A1501 cyst. Our results suggest that the EPS, especially exopolysaccharides enabled the encased bacteria to fix nitrogen while grown under aerobic condition. The formation of A1501 cysts was reversible in response to the changes of carbon or nitrogen source status. A1501 cyst formation depended on nitrogen-limiting signaling and the presence of sufficient carbon sources, yet was independent of an active nitrogenase. The pellicles formed by Azospirillum brasilense, another free-living nitrogen-fixing rhizobacterium, which also exhibited nitrogenase activity and contained the large EPS-encapsuled A1501 cyst-like ‘cells’. Our data imply that free-living nitrogen-fixing bacteria could convert the easy-used carbon sources to exopolysaccharides in order to enable nitrogen fixation in a natural aerobic environment.

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Terpenoids in plant and arbuscular mycorrhiza-reinforced defence against herbivorous insects

Terpenoids in plant and arbuscular mycorrhiza-reinforced defence against herbivorous insects | Plant-Microbe Symbiosis | Scoop.it
Background Plants, though sessile, employ various strategies to defend themselves against herbivorous insects and convey signals of an impending herbivore attack to other plant(s). Strategies include the production of volatiles that include terpenoids and the formation of symbiotic associations with fungi, such as arbuscular mycorrhiza (AM). This constitutes a two-pronged above-ground/below-ground attack–defence strategy against insect herbivores.
Scope Terpenoids represent an important constituent of herbivore-induced plant volatiles that deter herbivores and/or attract their predators. Terpenoids serve as airborne signals that can induce defence responses in systemic undamaged parts of the plant and also prime defence responses in neighbouring plants. Colonization of roots by AM fungi is known to influence secondary metabolism in plants; this includes alteration of the concentration and composition of terpenoids, which can boost both direct and indirect plant defence against herbivorous insects. Enhanced nutrient uptake facilitated by AM, changes in plant morphology and physiology and increased transcription levels of certain genes involved in the terpenoid biosynthesis pathway result in alterations in plant terpenoid profiles. The common mycorrhizal networks of external hyphae have added a dimension to the two-pronged plant defence strategy. These act as conduits to transfer defence signals and terpenoids.
Conclusion Improved understanding of the roles of terpenoids in plant and AM defences against herbivory and of interplant signalling in natural communities has significant implications for sustainable management of pests in agricultural ecosystems.
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The influence of environmental factors on communities of arbuscular mycorrhizal fungi associated with Chenopodium ambrosioides revealed by MiSeq sequencing investigation

The influence of environmental factors on communities of arbuscular mycorrhizal fungi associated with Chenopodium ambrosioides revealed by MiSeq sequencing investigation | Plant-Microbe Symbiosis | Scoop.it
Arbuscular mycorrhizal fungi (AMF) affect multiple ecosystem functions and processes, the assemblages of which vary across ecosystems. However, the influences of environmental factors on AMF communities which may shape these communities are still largely unknown. In this study, AMF communities from roots and rhizosphere soils of Chenopodium ambrosioides in different natural soils were investigated. The root habitat showed significantly smaller numbers of OTUs and lower community richness compared to the rhizosphere soil habitat. Most OTUs in the root habitat were shared by the soil habitat from the same sampling site, indicating that rhizosphere soils represent a pool of AMF species, a fraction of which is recruited by plants. Most of the AMF in root habitats were Glomeraceae, suggesting recruitment preferences of AMF by plants. The relative contributions of environmental factors to explain variations in AMF community composition and phylogenetic structure were assessed. The results revealed soil properties predominantly explained the variation, followed by geographic and climate parameters which explained a small fraction independently, while the host plant showed few explanations. Overall, our results indicated that soil and root habitats as well as soil characters, especially pH, nitrogen and micronutrients (Zn and Cu) affected AMF communities significantly.

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Does a foliar endophyte improve plant fitness under flooding?

Although endophytic fungi are ubiquitous in plants, their full range of ecological effects has yet to be characterized, particularly in non-agronomic systems. In this study, we compared the responses of two congeneric bluegrass species to flooding. Both plant species co-occur in subalpine zones of the Rocky Mountains. Marsh bluegrass (Poa leptocoma) commonly hosts a vertically transmitted fungal endophyte (Epichloë sp.) and naturally grows in wetter conditions than does nodding bluegrass (Poa reflexa), which lacks an epichloid endophyte. We investigated the novel hypothesis that endophyte symbiosis promotes host fitness under flooded conditions, contributing to niche differentiation between the two bluegrass species. We used a factorial greenhouse experiment to test whether endophyte presence improved survival, growth, or reproduction of P. leptocoma under flooded versus non-flooded edaphic conditions by experimentally removing the endophyte from half of the plants. We compared P. leptocoma responses to those of the endophyte-free congener. In contrast to expectations generated from the natural distributions of the two plant species, endophyte presence was more beneficial to P. leptocoma under ambient soil moisture than under flooding. Increased benefits of symbiosis in drier soils are consistent with studies of other grass endophytes. Flooded soils also unexpectedly improved the growth of P. reflexa more than that of the wet habitat specialist, P. leptocoma. While our results demonstrate an overall benefit of fungal symbiosis in this system, ecological factors other than flooding per se likely underlie the observed geographical distributions of these congeneric grasses in nature.

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Small Molecules Belowground: The Role of Specialized Metabolites in the Rhizosphere

Small Molecules Belowground: The Role of Specialized Metabolites in the Rhizosphere | Plant-Microbe Symbiosis | Scoop.it

Soil communities are diverse taxonomically and functionally. This ecosystem experiences highly complex networks of interactions, but may also present functionally independent entities. Plant roots, a metabolically active hotspot in the soil, take an essential part in belowground interactions. While plants are known to release an extremely high portion of the fixated carbon to the soil, less is known about the composition and role of C-containing compounds in the rhizosphere, in particular those involved in chemical communication. Specialized metabolites (or secondary metabolites) produced by plants and their associated microbes have a critical role in various biological activities that modulate the behavior of neighboring organisms. Thus, elucidating the chemical composition and function of specialized metabolites in the rhizosphere is a key element in understanding interactions in this belowground environment. Here, we review key classes of specialized metabolites that occur as mostly non-volatile compounds in root exudates or are emitted as volatile organic compounds (VOCs). The role of these metabolites in belowground interactions and response to nutrient deficiency, as well as their tissue and cell type-specific biosynthesis and release are discussed in detail.


Via Jonathan Plett
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