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Is N-feedback involved in the inhibition of nitrogen fixation in drought-stressed Medicago truncatula?

Drought stress is a major factor limiting nitrogen fixation (NF) in crop production. However, the regulatory mechanism involved and the origin of the inhibition, whether local or systemic, is still controversial and so far scarcely studied in temperate forage legumes. Medicago truncatula plants were symbiotically grown with a split-root system and exposed to gradual water deprivation. Physiological parameters, NF activity, and amino acid content were measured. The partial drought treatment inhibited NF in the nodules directly exposed to drought stress. Concomitantly, in the droughted below-ground organs, amino acids accumulated prior to any drop in evapotranspiration (ET). It is concluded that drought exerts a local inhibition of NF and drives an overall accumulation of amino acids in diverse plant organs which is independent of the decrease in ET. The general increase in the majority of single amino acids in the whole plant questions the commonly accepted concept of a single amino acid acting as an N-feedback signal.

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Plant-Microbe Symbioses
Symbiotic associations between plants and microbes
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Grant Application Review: The Case of Transparency

Grant Application Review: The Case of Transparency | Plant-Microbe Symbioses | Scoop.it

When it comes to the distribution of scarce funding resources for research in the biosciences, peer review has long been the undisputed champion of decision making. In recent years, its importance has only been enhanced, as many funding agencies increasingly distribute research funds through competitive instruments, and acquiring research funding is more important than ever for success in all branches of science [1],[2]. Today, peer reviewing has gained as much legitimacy in the scientific world as well as among lay public. Directed at the scientific community, it stands for fairness and objectivity in the distribution of grants; to the general public, it guarantees awarding of public (taxpayer) funds along scientific values rather than political ones. Robustness of procedure and efficiency of distribution are the two pillars on which the legitimacy of the peer review rests.

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Land-use intensity and host plant identity interactively shape communities of arbuscular mycorrhizal fungi in roots of grassland plants

Land-use intensity and host plant identity interactively shape communities of arbuscular mycorrhizal fungi in roots of grassland plants | Plant-Microbe Symbioses | Scoop.it
We studied the effect of host plant identity and land-use intensity (LUI) on arbuscular mycorrhizal fungi (AMF, Glomeromycota) communities in roots of grassland plants. These are relevant factors for intraradical AMF communities in temperate grasslands, which are habitats where AMF are present in high abundance and diversity. In order to focus on fungi that directly interact with the plant at the time, we investigated root-colonizing communities.
Our study sites represent an LUI gradient with different combinations of grazing, mowing, and fertilization. We used massively parallel multitag pyrosequencing to investigate AMF communities in a large number of root samples, while being able to track the identity of the host.
We showed that host plants significantly differed in AMF community composition, while land use modified this effect in a plant species-specific manner. Communities in medium and low land-use sites were subsets of high land-use communities, suggesting a differential effect of land use on the dispersal of AMF species with different abundances and competitive abilities.
We demonstrate that in these grasslands, there is a small group of highly abundant, generalist fungi which represent the dominating species in the AMF community.
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Very interesting

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Soil bacteria hold the key to root cluster formation

Soil bacteria hold the key to root cluster formation | Plant-Microbe Symbioses | Scoop.it
Root clusters are bunches of hairy rootlets that enhance nutrient uptake among many plants. Since first being reported in 1974, the involvement of rhizobacteria in their formation has received conflicting support. Attempts to identify specific causative organisms have failed and their role has remained speculative.
We set up a gnotobiotic experiment using two root-clustered species, Viminaria juncea (Fabaceae) and Hakea laurina (Proteaceae), and inoculated them with two plant-growth-promoting rhizobacteria (PGPR), Bradyrhizobium elkanii and Bacillus mageratium, that produce indole-3-acetic-acid (IAA). Plants were suspended in water culture with four combinations of nitrogen and phosphorus.
Clusters only developed in the presence of PGPR in two treatments, were greatly enhanced in another four, suppressed in five, and unaffected in five. Nitrogen amendment was associated with a higher density of clusters. Bradyrhizobium promoted cluster formation in Hakea, whereas Bacillus promoted cluster formation in Viminaria and suppressed it in Hakea.
Greater root cluster numbers were due either to a larger root system induced by PGPR (indirect resource effect) and/or to more clusters per unit length of parent root (direct morphogenetic effect). The results are interpreted in terms of greater IAA production by Bradyrhizobium than Bacillus and greater sensitivity of Viminaria to IAA than Hakea.
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Wow... really??

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Comparisons of computational methods for differential alternative splicing detection using RNA-seq in plant systems

Background
Alternative Splicing (AS) as a post-transcription regulation mechanism is an important application of RNA-seq studies in eukaryotes. A number of software and computational methods have been developed for detecting AS. Most of the methods, however, are designed and tested on animal data, such as human and mouse. Plants genes differ from those of animals in many ways, e.g., the average intron size and preferred AS types. These differences may require different computational approaches and raise questions about their effectiveness on plant data. The goal of this paper is to benchmark existing computational differential splicing (or transcription) detection methods so that biologists can choose the most suitable tools to accomplish their goals.

Results
This study compares the eight popular public available software packages for differential splicing analysis using both simulated and real Arabidopsis thaliana RNA-seq data. All software are freely available. The study examines the effect of varying AS ratio, read depth, dispersion pattern, AS types, sample sizes and the influence of annotation. Using a real data, the study looks at the consistences between the packages and verifies a subset of the detected AS events using PCR studies.

Conclusions
No single method performs the best in all situations. The accuracy of annotation has a major impact on which method should be chosen for AS analysis. DEXSeq performs well in the simulated data when the AS signal is relative strong and annotation is accurate. Cufflinks achieve a better tradeoff between precision and recall and turns out to be the best one when incomplete annotation is provided. Some methods perform inconsistently for different AS types. Complex AS events that combine several simple AS events impose problems for most methods, especially for MATS. MATS stands out in the analysis of real RNA-seq data when all the AS events being evaluated are simple AS events.
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Belowground fine root productivity, traits, and trees

Belowground fine root productivity, traits, and trees | Plant-Microbe Symbioses | Scoop.it
A long-standing debate in plant ecology is how plant diversity – including species richness, functional, and phylogenetic diversity – determines primary productivity aboveground and belowground (Tilman et al., 1997; Cadotte et al., 2009). A leading mechanism linking diversity and productivity posits that diverse assemblages of plants are more likely to complement each other in resource acquiring abilities, leading to greater biomass production than one would expect in low diversity communities, an outcome known as overyielding (Cardinale et al., 2007). Much of our understanding of the relationship between biodiversity and primary productivity comes from grassland communities and experiments. Forest trees are less tractable experimentally for biodiversity productivity studies than grasses and herbs and therefore require observational and correlative studies (Chisholm et al., 2013). Because of this, we know surprisingly little about how long-lived forest trees directly interact with each other belowground and compete for limiting soil resources, and in particular, if they partition space or nutrients to reduce interspecific competition – a classic explanation for species co-existence in diverse communities. Aboveground plant stems are easily measured and identified whereas belowground plant roots are buried, making species interactions and basic patterns of occurrence and co-occurrence difficult to observe. While researchers have used a variety of DNA-based methods to identify roots and explore species interactions and rooting profiles for some time now (Jackson et al., 1999; Hiiesalu et al., 2012) there have been fewer studies done in closed canopy forests (Jones et al., 2011). In this issue of New Phytologist, Valverde-Barrantes et al. (2014, pp. 731–742) use DNA identification of fine roots to dissect complex belowground interactions in a temperate hardwood forest and test several interrelated hypotheses on the relationship between: belowground species, functional, and phylogenetic diversity; soil resource availability; and productivity.
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Durch N2-Fixierung kann der Luftstickstoff für das Pflanzenwachstum genutzt werden

Durch N2-Fixierung kann der Luftstickstoff für das Pflanzenwachstum genutzt werden | Plant-Microbe Symbioses | Scoop.it
In einem geschlossenen Ökosystem stammt das für das Pflanzenwachstum erforderliche Nitrat aus dem Abbau der Biomasse. Nitrat kann, im Gegensatz zu anderen Pflanzennährstoffen wie Phosphat, nicht durch eine Verwitterung von Gesteinen nachgeliefert werden. Kleinere Mengen von Nitrat werden durch Blitze erzeugt und mit dem Regenwasser eingetragen (in unseren Breiten jährlich circa 5 kg N/ha). Durch menschliche Einflüsse (Autoverkehr, Massentierhaltung etc.) kann heute der jährliche Eintrag von Nitrat, anderen Stickoxiden und NH3 durch das Regenwasser je nach Verschmutzungsgrad der Luft zwischen 15 bis 70 kg N/ha betragen. Bei der landwirtschaftlichen Produktion muss der durch die Entnahme der Ernteprodukte verursachte Stickstoffverlust durch Düngung ausgeglichen werden. So werden zum Beispiel beim Maisanbau etwa jährlich 200 kg N/ha in Form von Nitrat- und Ammoniumdünger eingebracht. Als Ausgangsstoff wird dafür Ammoniak durch die Haber-Bosch-Synthese aus Stickstoff und Wasserstoff hergestellt:
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Plasticity in ploidy: a generalized response to stress

Endoreduplication, the replication of the genome without mitosis, leads to an increase in the cellular ploidy of an organism over its lifetime, a condition termed ‘endopolyploidy’. Endopolyploidy is thought to play significant roles in physiology and development through cellular, metabolic, and genetic effects. While the occurrence of endopolyploidy has been observed widely across taxa, studies have only recently begun to characterize and manipulate endopolyploidy with a focus on its ecological and evolutionary importance. No compilation of these examples implicating endoreduplication as a generalized response to stress has thus far been made, despite the growing evidence supporting this notion. We review here the recent literature of stress-induced endopolyploidy and suggest that plants employ endoreduplication as an adaptive, plastic response to mitigate the effects of stress.
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The importance of fungi and mycology for addressing major global challenges

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Alleviation of salt stress in germination of Vigna radiata L. by two halotolerant Bacilli sp. isolated from saline habitats of Gujarat

Alleviation of salt stress in germination of Vigna radiata L. by two halotolerant Bacilli sp. isolated from saline habitats of Gujarat | Plant-Microbe Symbioses | Scoop.it
Fifty halotolerant bacterial strains were isolated from the alkaline saline soil from the Ajod village of Vadodara district of Gujarat. All strains grew well in media supplemented with 5 % NaCl, but two strains (BR5 and BN7) could grow even at 18 % NaCl concentration. These two strains were characterized for their plant growth promoting characteristics. Both the strains were able to solubilize significant amount of phosphate and produce IAA. Both the strains also showed nitrogen fixing, siderophore production and antifungal properties against root rot pathogen of Vigna. radiata L., Fusarium sp. Potential of these halotolerant bacteria to ameliorate salt stress in V. radiata L. plants grown in saline soil inoculated with these bacteria was assessed. Both halotolerant bacteria were found to increase germination percentage, root length and shoot length compared to un inoculated control plants. Both these cultures were subjected to 16S rRNA gene sequencing and BLAST analysis, among which, BR5 showed 99 % similarity with Bacillus subtilis and BN7 showed 99 % similarity with B. megaterium.
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Ten Simple Rules for Finishing Your PhD

Ten Simple Rules for Finishing Your PhD | Plant-Microbe Symbioses | Scoop.it

After years of research and with completion in sight, the final year of the PhD often represents the most challenging time of a student's career, in which the ultimate reward is the PhD honor itself. A large investment in time, energy, and motivation is needed, with many tasks to be completed; concluding experiments must be carried out, results interpreted, and a research story mapped out in preparation for writing the final thesis. All the while, administrative obligations need attention (e.g., university credits and mandatory documents), papers may need to be published, students mentored, and due consideration paid to planning for the next career move. Without some form of strategic action plan and the employment of project management skills, students run the risk of becoming overwhelmed and run down or of not meeting their final deadlines. Personal time management and stress resilience are competences that can be developed and honed during this final period of the PhD.

Here, we present ten simple rules on how to deal with time issues and conflict situations when facing the last year of a PhD in science. The rules focus on defining research goals in advance and designing a plan of action. Moreover, we discuss the importance of managing relationships with supervisors and colleagues, as well as early career planning.


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The liverwort Pellia endiviifolia shares microtranscriptomic traits that are common to green algae and land plants

The liverwort Pellia endiviifolia shares microtranscriptomic traits that are common to green algae and land plants | Plant-Microbe Symbioses | Scoop.it
Liverworts are the most basal group of extant land plants. Nonetheless, the molecular biology of liverworts is poorly understood. Gene expression has been studied in only one species, Marchantia polymorpha. In particular, no microRNA (miRNA) sequences from liverworts have been reported.
Here, Illumina-based next-generation sequencing was employed to identify small RNAs, and analyze the transcriptome and the degradome of Pellia endiviifolia.
Three hundred and eleven conserved miRNA plant families were identified, and 42 new liverwort-specific miRNAs were discovered. The RNA degradome analysis revealed that target mRNAs of only three miRNAs (miR160, miR166, and miR408) have been conserved between liverworts and other land plants. New targets were identified for the remaining conserved miRNAs. Moreover, the analysis of the degradome permitted the identification of targets for 13 novel liverwort-specific miRNAs. Interestingly, three of the liverwort microRNAs show high similarity to previously reported miRNAs from Chlamydomonas reinhardtii.
This is the first observation of miRNAs that exist both in a representative alga and in the liverwort P. endiviifolia but are not present in land plants. The results of the analysis of the P. endivifolia microtranscriptome support the conclusions of previous studies that placed liverworts at the root of the land plant evolutionary tree of life.
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Reaction of the hemochromogen test with the heme protein leghemeoglobin obtained from soybean root nodules

The hemochromogen test for blood relies on the reaction of pyridine with the heme group of hemoglobin. Leghemoglobin, a heme protein found in the root nodules of nitrogen fixing plants, has been tested in this paper for reactivity with the hemochromogen test. Root nodules from soybean plants were used for this testing due to their high leghemoglobin content. It was found that prepared extractions from soybean root nodules produced a positive reaction with the hemochromogen test; however, directly tested (non-extracted) root nodules produced negative hemochromogen test results. In addition, stains prepared from the root nodules on fabric did not react with the hemochromogen reagent in this study.
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ALLEVIATION OF ADVERSE IMPACT OF SALINITY ON FABA BEAN (VICIA FABA L.) BY ARBUSCULAR MYCORRHIZAL FUNGI

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Temporal patterns of orchid mycorrhizal fungi in meadows and forests as revealed by 454 pyrosequencing

Temporal patterns of orchid mycorrhizal fungi in meadows and forests as revealed by 454 pyrosequencing | Plant-Microbe Symbioses | Scoop.it
Orchid mycorrhizal (OrM) symbionts play a key role in the growth of orchids, but the temporal variation and habitat partitioning of these fungi in roots and soil remain unclear.
Temporal changes in root and rhizosphere fungal communities of Cypripedium calceolus, Neottia ovata and Orchis militaris were studied in meadow and forest habitats over the vegetation period by using 454 pyrosequencing of the full internal transcribed spacer (ITS) region.
The community of typical OrM symbionts differed by plant species and habitats. The root fungal community of N. ovata changed significantly in time, but this was not observed in C. calceolus and O. militaris. The rhizosphere community included a low proportion of OrM symbionts that exhibited a slight temporal turnover in meadow habitats but not in forests. Habitat differences in OrM and all fungal associates are largely attributable to the greater proportion of ectomycorrhizal fungi in forests.
Temporal changes in OrM fungal communities in roots of certain species indicate selection of suitable fungal species by plants. It remains to be elucidated whether these shifts depend on functional differences inside roots, seasonality, climate or succession.
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Fungal associations of basal vascular plants: reopening a closed book?

Fungal associations of basal vascular plants: reopening a closed book? | Plant-Microbe Symbioses | Scoop.it
The widely held hypothesis that Glomeromycota fungi alone formed the ancestral land plant–fungus symbiosis (Pirozynski & Dalpé, 1989; Selosse & Le Tacon, 1998; Wang & Qiu, 2006; Parniske, 2008) has recently been challenged by new lines of evidence from molecular, cytological, functional and palaeontological studies. First, liverworts of the earliest divergent clade, the Haplomitriopsida, form a mutualistic mycorrhiza-like relationship, whereby there is reciprocal exchange of plant carbon (C) for fungal nitrogen (N) and phosphorus (P), with members of the Mucoromycotina (Bidartondo et al., 2011; Field et al., 2014), a fungal lineage considered basal or sister to the Glomeromycota (James et al., 2006; Lin et al., 2014). Secondly, other basal plants, including complex and simple thalloid liverworts and hornworts, enter into associations with both Mucoromycotina and Glomeromycota fungi, sometimes simultaneously (Bidartondo et al., 2011; Desirò et al., 2013). Thirdly, dual partnerships involving fungi with affinities to Glomeromycota and Mucoromycotina have been reported in fossils of early vascular plants from the Devonian (Strullu-Derrien et al., 2014).

Turning to the fungal associations of the extant representatives of the early diverging vascular plant lineages, the glomeromycete identity of fungi in ferns (Monilophyta) has never been questioned – a consensus borne out by cytology and limited DNA sequencing data (Wang & Qiu, 2006; Ogura-Tsujita et al., 2013). By contrast, the unusual cytology of fungal colonization in lycopods (Lycopodiophyta), highly reminiscent of the cytology reported in the Haplomitriopsida genus Treubia (Duckett et al., 2006), suggested unique fungal partnerships or ‘lycopodioid mycothallus interactions’ (Duckett & Ligrone, 1992; Schmid & Oberwinkler, 1993) until a molecular study detected Glomeromycota in this group (Winther & Friedman, 2008), thus ‘laying to rest over a century of speculations and uncertainty’ surrounding their identity (Leake et al., 2008). However, Winther & Friedman's study, and a more recent investigation proposing a basidiomycete as the main symbiont in a member of the Lycopodiaceae (Horn et al., 2013; but see rebuttal in Strullu-Derrien et al., 2014 criticizing their limited molecular and microscopical data), used methods that do not detect Mucoromycotina fungi. Therefore, it remains to be determined whether members of the Mucoromycotina related to the fungi known to enter into mutualism with basal liverworts (Field et al., 2014) also form associations with vascular plants. To test this possibility, we carried out molecular and microscopical analyses of the fungal associations of all the major lineages of lycopods and ferns.
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plantDARIO: web based quantitative and qualitative analysis of small RNA-seq data in plants

plantDARIO: web based quantitative and qualitative analysis of small RNA-seq data in plants | Plant-Microbe Symbioses | Scoop.it
High-throughput sequencing techniques have made it possible to assay an organism's entire repertoire of small non-coding RNAs (ncRNAs) in an efficient and cost-effective manner. The moderate size of small RNA-seq datasets makes it feasible to provide free web services to the research community that provide many basic features of a small RNA-seq analysis, including quality control, read normalization, ncRNA quantification, and the prediction of putative novel ncRNAs. DARIO is one such system that so far has been focussed on animals. Here we introduce an extension of this system to plant short non-coding RNAs (sncRNAs). It includes major modifications to cope with plant-specific sncRNA processing. The current version of plantDARIO covers analyses of mapping files, small RNA-seq quality control, expression analyses of annotated sncRNAs, including the prediction of novel miRNAs and snoRNAs from unknown expressed loci and expression analyses of user-defined loci. At present Arabidopsis thaliana, Beta vulgaris, and Solanum lycopersicum are covered. The web tool links to a plant specific visualization browser to display the read distribution of the analyzed sample. The easy-to-use platform of plantDARIO quantifies RNA expression of annotated sncRNAs from different sncRNA databases together with new sncRNAs, annotated by our group. The plantDARIO website can be accessed at http://plantdario.bioinf.uni-leipzig.de/.
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Plasma membrane protein trafficking in plant–microbe interactions: a plant cell point of view

Plasma membrane protein trafficking in plant–microbe interactions: a plant cell point of view | Plant-Microbe Symbioses | Scoop.it

In order to ensure their physiological and cellular functions, plasma membrane (PM) proteins must be properly conveyed from their site of synthesis, i.e., the endoplasmic reticulum, to their final destination, the PM, through the secretory pathway. PM protein homeostasis also relies on recycling and/or degradation, two processes that are initiated by endocytosis. Vesicular membrane trafficking events to and from the PM have been shown to be altered when plant cells are exposed to mutualistic or pathogenic microbes. In this review, we will describe the fine-tune regulation of such alterations, and their consequence in PM protein activity. We will consider the formation of intracellular perimicrobial compartments, the PM protein trafficking machinery of the host, and the delivery or retrieval of signaling and transport proteins such as pattern-recognition receptors, producers of reactive oxygen species, and sugar transporters.

 

 


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Biological nitrogen fixation in non-legume plants

Biological nitrogen fixation in non-legume plants | Plant-Microbe Symbioses | Scoop.it
Background Nitrogen is an essential nutrient in plant growth. The ability of a plant to supply all or part of its requirements from biological nitrogen fixation (BNF) thanks to interactions with endosymbiotic, associative and endophytic symbionts, confers a great competitive advantage over non-nitrogen-fixing plants.

Scope Because BNF in legumes is well documented, this review focuses on BNF in non-legume plants. Despite the phylogenic and ecological diversity among diazotrophic bacteria and their hosts, tightly regulated communication is always necessary between the microorganisms and the host plant to achieve a successful interaction. Ongoing research efforts to improve knowledge of the molecular mechanisms underlying these original relationships and some common strategies leading to a successful relationship between the nitrogen-fixing microorganisms and their hosts are presented.

Conclusions Understanding the molecular mechanism of BNF outside the legume–rhizobium symbiosis could have important agronomic implications and enable the use of N-fertilizers to be reduced or even avoided. Indeed, in the short term, improved understanding could lead to more sustainable exploitation of the biodiversity of nitrogen-fixing organisms and, in the longer term, to the transfer of endosymbiotic nitrogen-fixation capacities to major non-legume crops.
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Abscisic acid promotes pre-emergence stages of lateral root development in Medicago truncatula

The plant root system is important for plant anchorage and nutrition. Among the different characteristics of the root system, root branching is a major factor of plasticity and adaptation to changing environments. Indeed, many biotic and abiotic stresses, such as drought or symbiotic interactions, influence root branching. Many studies concerning root development and root branching were performed on the model plant Arabidopsis thaliana, but this model plant has a very simplified root structure and is not able to establish any symbiotic interactions. We have recently described seven stages for lateral root development in the model legume Medicago truncatula and found significant differences in the tissular contribution of root cell layers to the formation of new lateral roots (LR). We have also described two transgenic lines expressing the DR5:GUS and DR5:VENUS-N7 reporter genes that are useful to follow LR formation at early developmental stages. Here, we describe the use of these transgenic lines to monitor LR developmental responses of M. truncatula to the phytohormone abscisic acid (ABA) which is a major actor of stress and symbiotic interactions. We show that ABA promotes the formation of new lateral root primordia and their development, mostly at the late, pre-emergence stage.
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Plant-microorganism-soil interactions influence the Fe availability in the rhizosphere of cucumber plants

Iron (Fe) is a very important element for plants, since it is involved in many biochemical processes and, often, for the low solubility of the natural Fe sources in soil, plants suffer from Fe – deficiency, especially when grown on calcareous soils. Among the numerous plant growth-promoting rhizobacteria (PGPR) that colonize the rhizosphere of agronomically important crops, Azospirillum brasilense has been shown to exert strong stimulating activities on plants, by inducing alterations of the root architecture and an improvement of mineral nutrition, which could result from an enhancement of ion uptake mechanisms as well as by increased bioavailability of nutrients. Some studies have also established that A. brasilense can act as biocontrol agent, by preventing the growth and/or virulence of phytopathogens, most likely through the production of microbial siderophores that sequester Fe from the soil. Despite microbial siderophores complexed with Fe could be an easily accessible Fe source for plants, the possible involvement of A. brasilense in improving Fe nutrition in plants suffering from the micronutrient deficiency has not been investigated yet. Within the present research, the characterization of the physiological and biochemical effects induced by Fe starvation and PGPR inoculation in cucumber plants (Cucumis sativus L. cv. Chinese Long) was carried out. The analyses of root exudates released by hydroponically grown plants highlighted that cucumber plants respond differently depending on the nutritional status. In addition, following the cultivation period on calcareous soil, also the root exudates found in the extracts suggested a peculiar behaviour of plants as a function of the treatment. Interestingly, the presence of the inoculum in soil allowed a faster recovery of cucumber plants from Fe-deficiency symptoms, i.e. increase in the chlorophyll content, in the biomass and in the Fe content of leaves. These observations might suggest a feasible application of A. brasilense in alleviating symptoms generated by Fe-limiting growth condition in cucumber plants.
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Structure and Biological Roles of Sinorhizobium fredii HH103 Exopolysaccharide

Structure and Biological Roles of Sinorhizobium fredii HH103 Exopolysaccharide | Plant-Microbe Symbioses | Scoop.it
Here we report that the structure of the Sinorhizobium fredii HH103 exopolysaccharide (EPS) is composed of glucose, galactose, glucuronic acid, pyruvic acid, in the ratios 5:2:2:1 and is partially acetylated. A S. fredii HH103 exoA mutant (SVQ530), unable to produce EPS, not only forms nitrogen fixing nodules with soybean but also shows increased competitive capacity for nodule occupancy. Mutant SVQ530 is, however, less competitive to nodulate Vigna unguiculata. Biofilm formation was reduced in mutant SVQ530 but increased in an EPS overproducing mutant. Mutant SVQ530 was impaired in surface motility and showed higher osmosensitivity compared to its wild type strain in media containing 50 mM NaCl or 5% (w/v) sucrose. Neither S. fredii HH103 nor 41 other S. fredii strains were recognized by soybean lectin (SBL). S. fredii HH103 mutants affected in exopolysaccharides (EPS), lipopolysaccharides (LPS), cyclic glucans (CG) or capsular polysaccharides (KPS) were not significantly impaired in their soybean-root attachment capacity, suggesting that these surface polysaccharides might not be relevant in early attachment to soybean roots. These results also indicate that the molecular mechanisms involved in S. fredii attachment to soybean roots might be different to those operating in Bradyrhizobium japonicum.
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Gibberellins Interfere with Symbiosis Signaling and Gene Expression, and Alter Colonization by Arbuscular Mycorrhizal Fungi in Lotus japonicus.

Arbuscular mycorrhiza (AM) is a mutualistic plant–fungal interaction that confers great advantages for plant growth. Arbuscular mycorrhizal (AM) fungi enter the host root and form symbiotic structures that facilitate nutrient supplies between the symbionts. The phytohormones gibberellins (GAs) are known to inhibit AM fungal infection. However, our transcriptome analysis and phytohormone quantification revealed GA accumulation in the roots of Lotus japonicus infected with AM fungi, suggesting that de novo GA synthesis plays a role in AM development. We found pleiotropic effects of GAs on the AM fungal infection. In particular, the morphology of AM fungal colonization was drastically altered by the status of GA signaling in the host root. Exogenous GA treatment inhibited AM hyphal entry into the host root and suppressed expression of RAM1 and RAM2 homologs that function in hyphal entry and arbuscule formation. On the other hand, inhibition of GA biosynthesis or suppression of GA signaling also affected AM development in the host root. Low GA conditions suppressed SbtM1 expression that is required for AM fungal colonization, and reduced hyphal branching in the host root. The reduced hyphal branching and SbtM1 expression caused by inhibition of GA biosynthesis were recovered by GA treatment, supporting that insufficient GA signaling causes the inhibitory effects on AM development. Most studies have focused on the negative role of GA signaling, whereas our study demonstrates that GA signaling also positively interacts with symbiotic responses and promotes AM colonization of the host root.
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Photo by tenten156

Photo by tenten156 | Plant-Microbe Symbioses | Scoop.it
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Kevin Garcia's comment, December 23, 3:17 PM
Oops! He called it Medicago lupurina instead of Medicago lupulina!
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The Root Hair “Infectome” of Medicago truncatula Uncovers Changes in Cell Cycle Genes and Reveals a Requirement for Auxin Signaling in Rhizobial Infection

Nitrogen-fixing rhizobia colonize legume roots via plant-made intracellular infection threads. Genetics has identified some genes involved but has not provided sufficient detail to understand requirements for infection thread development. Therefore, we transcriptionally profiled Medicago truncatula root hairs prior to and during the initial stages of infection. This revealed changes in the responses to plant hormones, most notably auxin, strigolactone, gibberellic acid, and brassinosteroids. Several auxin responsive genes, including the ortholog of Arabidopsis thaliana Auxin Response Factor 16, were induced at infection sites and in nodule primordia, and mutation of ARF16a reduced rhizobial infection. Associated with the induction of auxin signaling genes, there was increased expression of cell cycle genes including an A-type cyclin and a subunit of the anaphase promoting complex. There was also induction of several chalcone O-methyltransferases involved in the synthesis of an inducer of Sinorhizobium meliloti nod genes, as well as a gene associated with Nod factor degradation, suggesting both positive and negative feedback loops that control Nod factor levels during rhizobial infection. We conclude that the onset of infection is associated with reactivation of the cell cycle as well as increased expression of genes required for hormone and flavonoid biosynthesis and that the regulation of auxin signaling is necessary for initiation of rhizobial infection threads.
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Scooped by Jean-Michel Ané
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Ectomycorrhizal colonization and growth of the hybrid larch F1 under elevated CO2 and O3

Ectomycorrhizal colonization and growth of the hybrid larch F1 under elevated CO2 and O3 | Plant-Microbe Symbioses | Scoop.it
We studied the colonization of ectomycorrhizal fungi and species abundance of a hybrid larch (F1) under elevated CO2 and O3. Two-year-old seedlings were planted in an Open-Top-Chamber system with treatments: Control (O3 < 6 nmol/mol), O3 (60 nmol/mol), CO2 (600 μmol/mol), and CO2 + O3. After two growing seasons, ectomycorrhiza (ECM) colonization and root biomass increased under elevated CO2. Additionally, O3 impaired ECM colonization and species richness, and reduced stem biomass. However, there was no clear inhibition of photosynthetic capacity by O3. Concentrations of Al, Fe, Mo, and P in needles were reduced by O3, while K and Mg in the roots increased. This might explain the distinct change in ECM colonization rate and diversity. No effects of combined fumigation were observed in any parameters except the P concentration in needles. The tolerance of F1 to O3 might potentially be related to a shift in ECM community structure.
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