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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 Symbioses | 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.


Via Kamoun Lab @ TSL
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Plant-Microbe Symbioses
Symbiotic associations between plants and microbes
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Physcomitrella patens Has Kinase-LRR R Gene Homologs and Interacting Proteins

Physcomitrella patens Has Kinase-LRR R Gene Homologs and Interacting Proteins | Plant-Microbe Symbioses | Scoop.it
Plant disease resistance gene (R gene)-like sequences were screened from the Physcomitrella patens genome. We found 603 kinase-like, 475 Nucleotide Binding Site (NBS)-like and 8594 Leucine Rich Repeat (LRR)-like sequences by homology searching using the respective domains of PpC24 (Accession No. BAD38895), which is a candidate kinase-NBS-LRR (kinase-NL) type R-like gene, as a reference. The positions of these domains in the genome were compared and 17 kinase-NLs were predicted. We also found four TIR-NBS-LRR (TIR-NL) sequences with homology to Arabidopsis TIR-NL (NM_001125847), but three out of the four TIR-NLs had tetratricopeptide repeats or a zinc finger domain in their predicted C-terminus. We also searched for kinase-LRR (KLR) type sequences by homology with rice OsXa21 andArabidopsis thaliana FLS2. As a result, 16 KLRs with similarity to OsXa21 were found. In phylogenetic analysis of these 16 KLRs, PpKLR36, PpKLR39, PpKLR40, and PpKLR43 formed a cluster with OsXa21. These four PpKLRs had deduced transmembrane domain sequences and expression of all four was confirmed. We also found 14 homologs of rice OsXB3, which is known to interact with OsXa21 and is involved in signal transduction. Protein–protein interaction was observed between the four PpKLRs and at least two of the XB3 homologs in Y2H analysis.
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Adequate Rhizobia Populations Help Protect Soybean Yields

Adequate Rhizobia Populations Help Protect Soybean Yields | Plant-Microbe Symbioses | Scoop.it
Maintaining adequate levels of rhizobia organisms in the soil can help increase nitrogen (N) fixation, potentially leading to higher yields, according to DuPont Pioneer agronomy experts. When a field is planted with soybeans in a corn-soy rotation, the rhizobia populations tend to remain adequate. However, when growers change from soybeans to other crops, such as continuous corn, rhizobia populations drop.

"Too little or too much water in a field also may impact rhizobia populations, but the effects are difficult to detect," says Paul Carter, DuPont Pioneer senior agronomy research manager. "There are some indications drought may curb rhizobia numbers and limit the soybean plant's ability to fix nitrogen."
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Eco-evolutionary feedbacks drive species interactions

Eco-evolutionary feedbacks drive species interactions | Plant-Microbe Symbioses | Scoop.it
In the biosphere, many species live in close proximity and can thus interact in many different ways. Such interactions are dynamic and fall along a continuum between antagonism and cooperation. Because interspecies interactions are the key to understanding biological communities, it is important to know how species interactions arise and evolve. Here, we show that the feedback between ecological and evolutionary processes has a fundamental role in the emergence and dynamics of species interaction. Using a two-species artificial community, we demonstrate that ecological processes and rapid evolution interact to influence the dynamics of the symbiosis between a eukaryote (Saccharomyces cerevisiae) and a bacterium (Rhizobium etli). The simplicity of our experimental design enables an explicit statement of causality. The niche-constructing activities of the fungus were the key ecological process: it allowed the establishment of a commensal relationship that switched to ammensalism and provided the selective conditions necessary for the adaptive evolution of the bacteria. In this latter state, the bacterial population radiates into more than five genotypes that vary with respect to nutrient transport, metabolic strategies and global regulation. Evolutionary diversification of the bacterial populations has strong effects on the community; the nature of interaction subsequently switches from ammensalism to antagonism where bacteria promote yeast extinction. Our results demonstrate the importance of the evolution-to-ecology pathway in the persistence of interactions and the stability of communities. Thus, eco-evolutionary dynamics have the potential to transform the structure and functioning of ecosystems. Our results suggest that these dynamics should be considered to improve our understanding of beneficial and detrimental host–microbe interactions.
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Microbes Will Feed the World, or Why Real Farmers Grow Soil, Not Crops

Microbes Will Feed the World, or Why Real Farmers Grow Soil, Not Crops | Plant-Microbe Symbioses | Scoop.it
It's not just better crops that will feed the world -- it's better microbes.
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I would rather say "better crops able to associate with better microbes".

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Identification of effective Pb resistant bacteria isolated from Lens culinaris growing in lead contaminated soils

Soil bacteria are a new phytoremediation system for the removal of heavy metals from soils. In this study, fifteen soil bacteria were isolated from root nodules of lentil growing in heavy metals contaminated soils, particularly by lead. Molecular characterization of the collection showed a large diversity, including Agrobacterium tumefaciens, Rahnella aquatilis, Pseudomonas, and Rhizobium sp. These soil bacteria had a wide range of tolerance to heavy metals. Among them, strains of A. tumefaciens and R. aquatilis tolerated up to 3.35 mM Pb; whereas Pseudomonas tolerated up to 3.24 mM Pb. The inoculation of lentil grown hydroponically with inoculums formed by these efficient and Pb resistant bacteria enhanced plant biomass. The treatment of this symbiosis by 1 mM Pb for 10 days or by 2 mM Pb for 3 days demonstrated that lentil had Pb accumulation capacity and can be considered a Pb accumulator plant, elsewhere, roots accumulated more Pb than shoots, and the inoculation decreased the Pb up take by the plants, suggesting that this symbiosis should be investigated for use in phytostabilization of Pb-contaminated soils. At the same time, a modulation in the antioxidant enzyme activity and a specific duration was required for the induction of the superoxide dismutase (SOD), peroxidase (POX), and ascorbate peroxidase (APX) response and to adapt to Pb stress. These results suggested that these enzymes may be involved in the main mechanism of antioxidative defense in lentil exposed to Pb oxidative stress.

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Relative importance of an arbuscular mycorrhizal fungus (Rhizophagus intraradices) and root hairs in plant drought tolerance

Both arbuscular mycorrhizal (AM) fungi and root hairs play important roles in plant uptake of water and mineral nutrients. To reveal the relative importance of mycorrhiza and root hairs in plant water relations, a bald root barley (brb) mutant and its wild type (wt) were grown with or without inoculation of the AM fungus Rhizophagus intraradices under well-watered or drought conditions, and plant physiological traits relevant to drought stress resistance were recorded. The experimental results indicated that the AM fungus could almost compensate for the absence of root hairs under drought-stressed conditions. Moreover, phosphorus (P) concentration, leaf water potential, photosynthetic rate, transpiration rate, stomatal conductance, and water use efficiency were significantly increased by R. intraradices but not by root hairs, except for shoot P concentration and photosynthetic rate under the drought condition. Root hairs even significantly decreased root P concentration under drought stresses. These results confirm that AM fungi can enhance plant drought tolerance by improvement of P uptake and plant water relations, which subsequently promote plant photosynthetic performance and growth, while root hairs presumably contribute to the improvement of plant growth and photosynthetic capacity through an increase in shoot P concentration.

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Very interesting

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Insights into the history of a bacterial group II intron remnant from the genomes of the nitrogen-fixing symbionts Sinorhizobium meliloti and Sinorhizobium medicae

Insights into the history of a bacterial group II intron remnant from the genomes of the nitrogen-fixing symbionts Sinorhizobium meliloti and Sinorhizobium medicae | Plant-Microbe Symbioses | Scoop.it
Group II introns are self-splicing catalytic RNAs that act as mobile retroelements. In bacteria, they are thought to be tolerated to some extent because they self-splice and home preferentially to sites outside of functional genes, generally within intergenic regions or in other mobile genetic elements, by mechanisms including the divergence of DNA target specificity to prevent target site saturation. RmInt1 is a mobile group II intron that is widespread in natural populations of Sinorhizobium melilotiand was first described in the GR4 strain. Like other bacterial group II introns, RmInt1 tends to evolve toward an inactive form by fragmentation, with loss of the 3′ terminus. We identified genomic evidence of a fragmented intron closely related to RmInt1 buried in the genome of the extant S. meliloti/S. medicae species. By studying this intron, we obtained evidence for the occurrence of intron insertion before the divergence of ancient rhizobial species. This fragmented group II intron has thus existed for a long time and has provided sequence variation, on which selection can act, contributing to diverse genetic rearrangements, and to generate pan-genome divergence after strain differentiation. The data presented here suggest that fragmented group II introns within intergenic regions closed to functionally important neighboring genes may have been microevolutionary forces driving adaptive evolution of these rhizobial species.
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Arbuscular mycorrhizal fungi as a tool to ameliorate the phytoremediation potential of poplar: biochemical and molecular aspects

Poplar is a suitable species for phytoremediation, able to tolerate high concentrations of heavy metals (HMs). Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with the roots of most land plants; they improve nutrient uptake and enhance phytoextraction of HMs while alleviating stress in the host plant. This review summarizes previous results from field and greenhouse studies conducted by us and dealing with this topic. In a field trial on a highly Zn- and Cu-contaminated site, differences in plant survival and growth were observed among 168 clones originating from natural populations of Populus alba L. and Populus nigra L. from northern Italy. After two and a half years from planting, the density, activity and metabolic versatility of the culturable fraction of the soil bacteria in the HM-polluted field was higher in the soil close to where larger poplar plants were growing, in spite of comparable HM concentrations recorded in these soils. One well-performing clone of P. alba (AL35), which accumulated a higher concentration of both metals and had high foliar polyamine (PA) levels, was used for further investigation. In a greenhouse study, AL35 cuttings pre-inoculated with AMF (Glomus mosseae or Glomus intraradices) and then transferred to pots containing soil, collected from the HM-polluted site, displayed growth comparable to that of controls grown on unpolluted soil, in spite of higher Cu and Zn accumulation. Such plants also showed an overall up-regulation of metallothionein (MT) and PA biosynthetic genes, together with increased PA levels. A genome-wide transcriptomic (cDNA-AFLP) analysis allowed the identification of a number of genes, mostly belonging to stress-related functional categories of defense and secondary metabolism, that were differentially regulated in mycorrhizal vs. non mycorrhizal plants. A proteomic analysis revealed that, depending on sampling time, changes in protein profiles were differentially affected by AMF and/or HMs. It is concluded that soil-borne microorganisms affect plant performance on HM-polluted soil. In particular, mycorrhizal plants exhibited increased capacity for phytostabilization of HMs, together with improved growth. Their greater stress tolerance may derive from the protective role of PAs, and from the strong modulation in the expression profiles of stress-related genes and proteins.

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Symbiotic

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Symbiotic... 

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Nitrogen fixation and symbiosis-induced accumulation of mineral nutrients by cowpea (Vigna unguiculata L. Walp.)

Little information currently exists on the relationship between rhizobial symbiosis and mineral accumulation in nodulated legumes. The aim of this study was to measure fixed nitrogen (N) in whole plants and in young fully expanded trifoliate leaves of cowpea genotypes, and to relate this to mineral accumulation in the leaves. The data revealed marked differences between high and low N2-fixing genotypes, with the former consistently showing greater %N, plant or leaf total N, and amount of N fixed compared with the latter. There was a 2.0–3.8-fold difference in amount of N fixed at whole-plant level between high- and low-fixing cowpea genotypes at Taung, South Africa, and 2.4–4.0-fold at Manga, Ghana. Furthermore, the genotypes with high N2 fixation consistently exhibited greater concentration and content of minerals (e.g. P, K, Mg, S, Na, Fe, Cu, Zn, Mn and B) in their trifoliate leaves, whereas those that recorded low N2 fixation accumulated lesser amounts of mineral nutrients in leaves. In a nodulation assay, we found that rhizobial isolates TUT53b2vu and TUT33b4vu, which exhibited higher symbiotic efficiency (measured here as nodule number, nodule fresh weight, and plant dry matter yield), also elicited greater mineral accumulation in cowpea shoots, while strains with low N2-fixing ability induced limited mineral accumulation. These results, together with a correlation analysis, show that, at least in nodulated cowpea, there is a strong relationship between N2-fixing efficiency and mineral accumulation, two traits that could be exploited in breeding programs for improved human nutrition and health
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Host plant and arbuscular mycorrhizal fungi show contrasting responses to temperature increase: Implications for dioecious plants

Host plant and arbuscular mycorrhizal fungi show contrasting responses to temperature increase: Implications for dioecious plants | Plant-Microbe Symbioses | Scoop.it

Individual plants live in complex environments where they interact with other organisms such as herbivores, pollinators, fungi and pathogens. The influence of rising temperature on biotic interactions has begun to receive attention, and is an important research frontier currently. However, the belowground interactions with organisms such as arbuscular mycorrhizal (AM) fungi have received little attention so far. In this study, we investigated the response of the dioecious plant Antennaria dioica and its AM fungi to increased temperature in a controlled environment simulating the period of growth of A. dioica in central Finland. Specifically, we evaluated the effect of rising temperature on plant survival, growth, flowering and physiology in plants growing with or without AM fungi. Overall, increased temperature had a positive effect on plant survival, but a negative effect on the growth and flowering compared with the control temperature, while it did not affect the physiological parameters analyzed. Females suffered more of rising temperature in terms of reduced flowering, but a larger proportion of plants survived compared to males. In contrast, the rising temperature had positive effects on the frequency of AM fungal colonization in roots regardless of sex, but sex-specific differences were observed in the amount of extraradical hyphae and the number of spores produced. These findings suggest than the sexes in dioecious species and their associated fungi respond differently to increasing temperature. If rising temperature affects host plants and symbionts in a contrasting way, a potential functional mismatch might appear.

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Agricultural Science: New Nitrogen fixation technology for legume crops fares

Agricultural Science: New Nitrogen fixation technology for legume crops fares | Plant-Microbe Symbioses | Scoop.it

Most farmers in Uganda and the entire East African region are focusing on growing cereal and root crops while gradually abandoning production of legume crop varieties which they think may not be commercially viable.
However, there are efforts by development partners to revamp production of legume crops such as groundnuts, climbing beans, cow peas and soya beans. Farmers are now being encouraged to apply rhizobia to increase soil nitrogen for improved production of the crops in question.

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Effects of co-inoculation of native Rhizobium and Pseudomonas strains on growth parameters and yield of two contrasting Phaseolus vulgaris L. genotypes under Cuban soil conditions

Effects of co-inoculation of native Rhizobium and Pseudomonas strains on growth parameters and yield of two contrasting Phaseolus vulgaris L. genotypes under Cuban soil conditions | Plant-Microbe Symbioses | Scoop.it

Plant growth-promoting rhizobacteria (PGPR) have been isolated from legume nodules, displaying a potential to enhance nodulation, growth and yield of legume plants when co-inoculated with Rhizobium. This study genetically characterizes bacteria isolated from bean root nodules in Cuba and investigates the effect ofRhizobium–Pseudomonas co-inoculation on common bean (Phaseolus vulgaris L.) genotypes under two different Cuban soil conditions. Bacteria were identified by partial sequencing of the 16S rDNA gene. Growth-promoting effects of Rhizobium pisi–Pseudomonas monteilii co-inoculation were evaluated under field conditions in consecutive years. Two contrasting bean genotypes (BAT-477 and DOR-364) were co-inoculated and grown in two different soil types (Cambisol and Oxisol) in Cuban farm areas. Several growth parameters were evaluated at three time points during the crop cycle (21, 42 and 87 days after planting). In total, 20 strains were isolated belonging to six different genera, i.e. Arthrobacter, Chryseobacterium,Enterobacter, Stenotrophomonas, Pseudomonas and Rhizobium. It was observed that nativeRhizobium–Pseudomonas co-inoculation as compared to single Rhizobium inoculation increased the nodulation, growth parameters and yield of the different genotypes. The response of BAT-477 was more pronounced than that of DOR-364. These findings contribute to the understanding of the interplay betweenRhizobium, PGPR and the plant host under different soil conditions. Importantly, co-inoculation with R. pisiand P. monteilii could be an effective biofertilization strategy for common bean production.

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Do Soybeans Need Nitrogen Fertilizer?

Do Soybeans Need Nitrogen Fertilizer? | Plant-Microbe Symbioses | Scoop.it

Nitrogen fixation takes a considerable amount of energy in the form of sugars produced by photosynthesis in the crop. "Estimates of the amount of energy this takes range widely but could be in the vicinity of 10 percent of the energy captured in photosynthesis, at least during part of the season," Nafziger said. "Because photosynthesis also powers growth and yield, it seems logical that the crop might not be able to produce enough sugars to go around, especially at high yield levels, and that either yields will suffer or nitrogen fixation will be reduced."

Would adding nitrogen fertilizer fix this problem and result in higher yields?

Nafiziger explained that he has looked at adding nitrogen fertilizer in a series of trials over the past several years, with some of the research funded by the Illinois Soybean Association. These studies involve application of urea, in some cases with Agrotain® (urease inhibitor) or as ESN (slow-release nitrogen) during mid-season, usually in July.

Yields ranged widely among these studies, from in the 30s to nearly 90 bushels per acre. But in only one case did adding nitrogen fertilizer significantly increase yield (by 6 bushels per acre), he said. There was no relationship between yield level and response to nitrogen fertilizer.

"These results provide no support for the idea that the higher the yield, the more response to fertilizer nitrogen. In fact, yields above 70 bushels seemed more likely to show yield decreases from adding nitrogen, though these differences were small and not statistically significant," he said.

While these results don’t prove that adding nitrogen fertilizer can’t increase soybean yields, Nafziger said it’s clear that it shows that an increase cannot be expected.

 

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Patterns of divergence of a large family of nodule cysteine-rich peptides in accessions of Medicago truncatula

Patterns of divergence of a large family of nodule cysteine-rich peptides in accessions of Medicago truncatula | Plant-Microbe Symbioses | Scoop.it

The nodule cysteine-rich (NCR) groups of defensin-like (DEFL) genes are one of the largest gene families expressed in the nodules of some legume plants. They have only been observed in the inverted repeat loss clade (IRLC) of legumes, which includes the model legume Medicago truncatula. NCRs are reported to play an important role in plant–microbe interactions. To understand their diversity we analyzed their expression and sequence polymorphisms among four accessions of M. truncatula. A significant expression and nucleotide variation was observed among the genes. We then used 26 accessions to estimate the selection pressures shaping evolution among the accessions by calculating the nucleotide diversity at non-synonymous and synonymous sites in the coding region. The mature peptides of the orthologous NCRs had signatures of both purifying and diversifying selection pressures, unlike the seed DEFLs, which predominantly exhibited purifying selection. The expression, sequence variation and apparent diversifying selection in NCRs within the Medicago species indicates rapid and recent evolution, and suggests that this family of genes is actively evolving to adapt to different environments and is acquiring new functions.

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Nice work!

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Fungal associations in Horneophyton ligneri from the Rhynie Chert (c. 407 million year old) closely resemble those in extant lower land plants: novel insights into ancestral plant–fungus symbioses.

Fungal associations in Horneophyton ligneri from the Rhynie Chert (c. 407 million year old) closely resemble those in extant lower land plants: novel insights into ancestral plant–fungus symbioses. | Plant-Microbe Symbioses | Scoop.it
Fungi (Eumycota) form close associations with plants, with which they have co-existed since the dawn of life on land, but their diversity in early terrestrial ecosystems is still poorly understood.We studied petrographic sections of exceptionally well-preserved petrified plants from the 407 million yr-old Rhynie Chert (Scotland, UK). For comparative purposes, we illustrate fungal associations in four extant lower land plants.We document two new endophytes in the plant Horneophyton lignieri: Palaeoglomus boullardii (sp. nov. Glomeromycota) colonizes parenchyma in a discontinuous zone of the outer cortex of the aerial axes, forming arbuscule-like structures, vesicles and spores;Palaeoendogone gwynne-vaughaniae (gen. nov., sp. nov. Mucoromycotina) colonizes parenchyma in the basal part of the plant, where it is present in intercellular spaces and as intracellular coils but absent from rhizoids.Critical comparisons between the newly discovered Horneophyton endophytes, fungi previously described from the Rhynie Chert and fungal colonization in extant lower land plants reveal several features characteristic of both Mucoromycotina and Glomeromycota. A reappraisal of fungal associations in early land plants indicates that they are more diverse than assumed hitherto, overturning the long-held paradigm that the early endophytes were exclusively Glomeromycota.
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Wilhelms Best AGRI: Mycorrhizal Rootstock Infection for fruit trees

Use this advice for your mycorrhizal rootstock infection by Wilhelms Best. You must optimize this advice for your own production. Use 25 kg for 12.500 plants...
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Rhizobium tibeticum activated with a mixture of flavonoids alleviates nickel toxicity in symbiosis with fenugreek (Trigonella foenum graecum L.)

The objective of this study is to explore the response of an activated Rhizobium tibeticum inoculum with a mixture of hesperetin (H) and apigenin (A) to improve the growth, nodulation, and nitrogen fixation of fenugreek (Trigonella foenum graecum L.) grown under nickel (Ni) stress. Three different sets of fenugreek seed treatments were conducted, in order to investigate the activated R. tibeticumpre-incubation effects on nodulation, nitrogen fixation and growth of fenugreek under Ni stress. Group (I): uninoculated seeds with R. tibeticum, group (II): inoculated seeds with uninduced R. tibeticumgroup (III): inoculated seeds with induced R. tibeticum. The present study revealed that Ni induced deleterious effects on rhizobial growth, nod gene expression, nodulation, phenylalanine ammonia-lyase (PAL) and glutamine synthetase activities, total flavonoids content and nitrogen fixation, while the inoculation with an activated R. tibeticum significantly improved these values compared with plants inoculated with uninduced R. tibeticum. PAL activity of roots plants inoculated with inducedR. tibeticum and grown hydroponically at 75 and 100 mg L−1 Ni and was significantly increased compared with plants receiving uninduced R. tibeticum. The total number and fresh mass of nodules, nitrogenase activity of plants inoculated with induced cells grown in soil treated up to 200 mg kg−1 Ni were significantly increased compared with plants inoculated with uninduced cells. Plants inoculated with induced R. tibeticum dispalyed a significant increase in the dry mass compared with those treated with uninduced R. tibeticum. Activation of R. tibeticum inoculum with a mixture of hesperetin and apigenin has been proven to be practically important in enhancing nodule formation, nitrogen fixation and growth of fenugreek grown in Ni contaminated soils.

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Arsenic-tolerant plant-growth-promoting bacteria isolated from arsenic-polluted soils in South Korea

The Janghang smelter in Chungnam, South Korea started in 1936 was subsequently shutdown in 1989 due to heavy metal (loid) pollution concerns in the vicinity. Thus, there is a need for the soil in the area to be remediated to make it usable again especially for agricultural purposes. The present study was conducted to exploit the potential of arsenic (As)-tolerant bacteria thriving in the vicinity of the smelter-polluted soils to enhance phytoremediation of hazardous As. We studied the genetic and taxonomic diversity of 21 As-tolerant bacteria isolated from soils nearer to and away from the smelter. These isolates belonging to the genera Brevibacterium, Pseudomonas, Microbacterium,Rhodococcus, Rahnella, and Paenibacillus, could tolerate high concentrations of arsenite (As(III)) and arsenate (As(V)) with the minimum inhibitory concentration ranging from 3 to >20 mM for NaAsO2 and 140 to 310 mM NaH2AsO4 · 7H2O, respectively. All isolates exhibited As(V) reduction except Pseudomonas koreensis JS123, which exhibited both oxidation and reduction of As. Moreover, all the 21 isolates produced indole acetic acid (IAA), 13 isolates exhibited 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, 12 produced siderophore, 17 solubilized phosphate, and 13 were putative nitrogen fixers under in vitro conditions. Particularly,Rhodococcus aetherivorans JS2210, P. koreensis JS2214, and Pseudomonas sp. JS238 consistently increased root length of maize in the presence of 100 and 200 μM As(V). Possible utilization of these As-tolerant plant-growth-promoting bacteria can be a potential strategy in increasing the efficiency of phytoremediation in As-polluted soils.

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Viability and morphology of Tuber aestivum spores after passage through the gut of Sus scrofa

Viability and morphology of Tuber aestivum spores after passage through the gut of Sus scrofa | Plant-Microbe Symbioses | Scoop.it

Truffles have hypogeous fruit bodies that are dependent on mycophagous animals for spore dispersal. In our study we assessed the effect of passage through the gut of Sus scrofa on the morphology and viability ofTuber aestivum asci and ascospores. Light and Atomic Force Microscopy showed that passage through the gut freed spores from the asci, eroded the walls of free spores and modified their structure but spores were still viable. We believe this was the reason for the observed improvement in forming mycorrhizas with oak. These results confirm the role of wild boars in long distance dispersal of Tuber and support the theory that pigs play a significant role in truffle survival and territorial expansion during climatic changes.

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Boaring... just kidding. It's very interesting but I would have not imagined that someone could work on that... I love science!

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Soil microbial community responses to sulfadiazine-contaminated manure in different soil microhabitats

Soil microbial community responses to sulfadiazine-contaminated manure in different soil microhabitats | Plant-Microbe Symbioses | Scoop.it

Veterinary antibiotics such as sulfadiazine (SDZ) are applied with manure to agricultural soil. Antimicrobial effects of SDZ on soil microbial community structures and functions were reported for homogenized bulk soils. In contrast, field soil is structured. The resulting microhabitats are often hot spots that account for most of the microbial activity and contain strains of different antibiotic sensitivity or resilience. We therefore hypothesize that effects of SDZ are different in diverse soil microhabitats. We combined the results of laboratory and field experiments that evaluated the fate of SDZ and the response of the microbial community in rhizosphere, earthworm burrow, and soil macroaggregate microhabitats. Microbial communities were characterized by phenotypic phospholipid fatty acid (PLFA) and genotypic 16S rRNA gene patterns (DGGE) and other methods. Data was evaluated by principle component analyses followed by two-way ANOVA with post-hoc tests. Extractable SDZ concentrations in rhizosphere soil were not clearly different and varied by a factor 0.7–1.2 from those in bulk soil. In contrast to bulk soil, the extractable SDZ content was two-fold larger in earthworm burrows, which are characterized by a more hydrophobic organic matter along the burrow surface. Also, extractable SDZ was larger by up to factor 2.6 in the macroaggregate surface soil. The rhizosphere effect clearly increased the microbial biomass. Nonetheless, in the 10 mg SDZ kg−1 treatment, the biomass deceased by about 20% to the level of uncontaminated bulk soil. SDZ contamination lowered the total PLFA concentrations by 14% in the rhizosphere and 3% in bulk soil of the field experiment. Structural shifts represented by Pseudomonas DGGE data were larger in SDZ-contaminated earthworm burrows compared to bulk soils. In the laboratory experiment, a functional shift was indicated by a four-fold reduced acid phosphatase activity in SDZ-contaminated burrows compared to bulk soil. Structural and functional shifts after SDZ contamination were larger by a factor of 2.5 in the soil macroaggregate surface versus interior, but this relation reversed over the long-term under field conditions. Overall, the combined effects of soil microhabitat, microbial community composition, and exposure to SDZ influenced the microbial susceptibility towards antibiotics under laboratory and field conditions.

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Bradyrhizobium manausense sp. nov., isolated from effective nodules of Vigna unguiculata grown in Brazilian Amazon rainforest soils.

Root nodule bacteria were trapped with cowpea (Vigna unguiculata) from soils with different cultivation histories collected in the Amazon rainforest in North Brazil. Analysis of the 16S rRNA gene sequences of six strains (BR 3351T, BR 3307, BR 3310, BR 3315, BR 3323 BR and BR 3361) isolated from cowpea nodules showed that they formed a distinct group within the genus Bradyrhizobium that was separate from current type strains. Phylogenetic analyses of three housekeeping genes (glnII, recA and rpoB) revealed Bradyrhizobium huanghuaihaiense CCBAU 23303T to be the closest type strain (96% sequence similarity or less). Chemotaxonomic data, including fatty acid profiles (with majority being C16:0 and Summed feature 8), the slow growth rate and carbon compound utilization patterns supported the assignment of the strains to the genus Bradyrhizobium. The results of DNA-DNA hybridisations, antibiotic resistance and physiological tests, differentiated our strains from the closest validly named Bradyrhizobium species. Symbiosis-related genes for nodulation (nodC) and nitrogen fixation (nifH) grouped the novel Bradyrhizobium strains together with B. iriomotense strain EK05T with 94% and 96% sequence similarity, respectively. Based on the data, these six strains represent a novel species for which the name Bradyrhizobium manausense sp. nov. (BR 3351T = HAMBI 3596T), is proposed.
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Protein actors sustaining arbuscular mycorrhizal symbiosis: underground artists break the silence

Protein actors sustaining arbuscular mycorrhizal symbiosis: underground artists break the silence | Plant-Microbe Symbioses | Scoop.it

The roots of most land plants can enter a relationship with soil-borne fungi belonging to the phylum Glomeromycota. This symbiosis with arbuscular mycorrhizal (AM) fungi belongs to the so-called biotrophic interactions, involving the intracellular accommodation of a microorganism by a living plant cell without causing the death of the host. Although profiling technologies have generated an increasing depository of plant and fungal proteins eligible for sustaining AM accommodation and functioning, a bottleneck exists for their functional analysis as these experiments are difficult to carry out with mycorrhiza. Nonetheless, the expansion of gene-to-phenotype reverse genetic tools, including RNA interference and transposon silencing, have recently succeeded in elucidating some of the plant-related protein candidates. Likewise, despite the ongoing absence of transformation tools for AM fungi, host-induced gene silencing has allowed knockdown of fungal gene expression in planta for the first time, thus unlocking a technological limitation in deciphering the functional pertinence of glomeromycotan proteins during mycorrhizal establishment. This review is thus intended to draw a picture of our current knowledge about the plant and fungal protein actors that have been demonstrated to be functionally implicated in sustaining AM symbiosis mostly on the basis of silencing approaches.

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A fun way to address this topic...

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Rhizobial genomes galore

Rhizobial genomes galore | Plant-Microbe Symbioses | Scoop.it
he past year has seen a bonanza for rhizobial genome sequences. Here is a list of the the papers that I am aware of that were published in 2013 or 2014. Apart from the first two, they represent some of the fruits of the genome sequencing that Wayne Reeve persuaded the Joint Genome Institute to carry out. I know that many rhizobium researchers around the world provided strains and DNA for this effort, and there are many more genome sequences in the pipeline but not yet published. Some of these can already be accessed on the JGI web site or in the NCBI database. These genome sequences represent a great resource for rhizobium researchers. They will suggest new experiments – but even those who are not in a position to carry out lab work have the opportunity to use this free information to gain new insights through careful analysis in silico.
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By fair means or foul

By fair means or foul | Plant-Microbe Symbioses | Scoop.it
When thinking about microbes, one may imagine primitive and ultimately solitary creatures concerned only with their own reproduction. In fact, scientists usually study micro-organisms in isolation from other cells, without possibility for interaction. The underlying assumption is that wherever they are found – in a primordial sludge, a petri dish in a lab, maybe even inside another living being – they are solely concerned with their own ability to reproduce. As a result, they will battle any other organism they encounter for space, nutrients and the resulting ability to divide faster.
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