Plant-Microbe Symbiosis
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Plant-Microbe Symbiosis
Beneficial associations between plants and microbes
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Scooped by Jean-Michel Ané
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Why NZ has to ban synthetic nitrogen fertiliser

David Attenborough did not mince words in his address to the United Nations this week.

“Right now we are facing a manmade disaster of global scale, our greatest threat in thousands of years: climate change,” he said. “If we don’t take action, the collapse of our civilisations and the extinction of much of the natural world is on the horizon.”

We’ve literally got 12 years before the planet is going to hell in a handbasket, taking us with it. That is unless we radically transform society. Like, now. Or preferably, yesterday.

One part of society that urgently needs a fundamental and far reaching transformation is agriculture. It makes up 49% of New Zealand’s emissions.

But what do we do about it?

We need to be farming far fewer cows, that much is obvious to anyone who isn’t living in the the fantasy world of unproven methane vaccines. But reducing the herd won’t be enough.

There’s a hidden climate (and river) killer that drives the industrialisation of agriculture.

Synthetic nitrogen fertiliser. We have to ban it.

Jean-Michel Ané's insight:

This position is too extreme and not realistic but it would be good to have a discussion about a reduction of their use.

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Rescooped by Jean-Michel Ané from Plant roots and rhizosphere
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Microbial Interkingdom Interactions in Roots Promote Arabidopsis Survival 

Microbial Interkingdom Interactions in Roots Promote Arabidopsis Survival  | Plant-Microbe Symbiosis | Scoop.it
Roots of healthy plants are inhabited by soil-derived bacteria, fungi, and oomycetes that have evolved independently in distinct kingdoms of life. How these microorganisms interact and to what extent those interactions affect plant health are poorly understood. We examined root-associated microbial communities from three Arabidopsis thaliana populations and detected mostly negative correlations between bacteria and filamentous microbial eukaryotes. We established microbial culture collections for reconstitution experiments using germ-free A. thaliana. In plants inoculated with mono- or multi-kingdom synthetic microbial consortia, we observed a profound impact of the bacterial root microbiota on fungal and oomycetal community structure and diversity. We demonstrate that the bacterial microbiota is essential for plant survival and protection against root-derived filamentous eukaryotes. Deconvolution of 2,862 binary bacterial-fungal interactions ex situ, combined with community perturbation experiments in planta, indicate that biocontrol activity of bacterial root commensals is a redundant trait that maintains microbial interkingdom balance for plant health.

Via Christophe Jacquet
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Rescooped by Jean-Michel Ané from Plant roots and rhizosphere
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Identification of Arbuscular Mycorrhiza Fungi Responsive microRNAs and Their Regulatory Network in Maize 

Identification of Arbuscular Mycorrhiza Fungi Responsive microRNAs and Their Regulatory Network in Maize  | Plant-Microbe Symbiosis | Scoop.it
Maize can form symbiotic relationships with arbuscular mycorrhiza (AM) fungus to increase productivity and resistance, but the miRNAs in maize responsible for this process have not been discovered. In this study, 155 known and 28 novel miRNAs were identified by performing high-throughput sequencing of sRNA in maize roots colonized by AM fungi. Similar to the profiles in other AM-capable plants, a large proportion of identified maize miRNAs were 24 nt in length. Fourteen and two miRNAs were significantly down- and up-regulated in response to AM fungus Glomus intraradices inoculation, respectively, suggesting potential roles of these miRNAs in AM symbiosis. Interestingly, 12 of 14 significantly down-regulated known maize miRNAs belong to the miR399 family, which was previously reported to be involved in the interaction between Medicago truncatula and AM fungi. This result indicated that the miR399 family should regulate AM symbiosis conservatively across different plant lineages. Pathway and network analyses showed that the differentially expressed miRNAs might regulate lipid metabolism and phosphate starvation response in maize during the symbiosis process via their target genes. Several members of the miR399 family and the miR397 family should be involved in controlling the fatty acid metabolism and promoting lipid delivering from plants to AM fungi. To the best of our knowledge, this is the first report on miRNAs mediating fatty acids from plant to AM fungi. This study provides insight into the regulatory roles of miRNAs in the symbiosis between plants and AM fungi. View Full-Text

Via Christophe Jacquet
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Genetic conflict with a parasitic nematode disrupts the legume–rhizobia mutualism

Genetic conflict with a parasitic nematode disrupts the legume–rhizobia mutualism | Plant-Microbe Symbiosis | Scoop.it
Genetic variation for partner quality in mutualisms is an evolutionary paradox. One possible resolution to this puzzle is that there is a tradeoff between partner quality and other fitness‐related traits. Here, we tested whether susceptibility to parasitism is one such tradeoff in the mutualism between legumes and nitrogen‐fixing bacteria (rhizobia). We performed two greenhouse experiments with the legume Medicago truncatula. In the first, we inoculated each plant with the rhizobia Ensifer meliloti and with one of 40 genotypes of the parasitic root‐knot nematode Meloidogyne hapla. In the second experiment, we inoculated all plants with rhizobia and half of the plants with a genetically variable population of nematodes. Using the number of nematode galls as a proxy for infection severity, we found that plant genotypes differed in susceptibility to nematode infection, and nematode genotypes differed in infectivity. Second, we showed that there was a genetic correlation between the number of mutualistic structures formed by rhizobia (nodules) and the number of parasitic structures formed by nematodes (galls). Finally, we found that nematodes disrupt the rhizobia mutualism: nematode‐infected plants formed fewer nodules and had less nodule biomass than uninfected plants. Our results demonstrate that there is genetic conflict between attracting rhizobia and repelling nematodes in Medicago. If genetic conflict with parasitism is a general feature of mutualism, it could account for the maintenance of genetic variation in partner quality and influence the evolutionary dynamics of positive species interactions.

Via Christophe Jacquet
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Medicago AP2-Domain Transcription Factor WRI5a Is a Master Regulator of Lipid Biosynthesis and Transfer during Mycorrhizal Symbiosis

Medicago AP2-Domain Transcription Factor WRI5a Is a Master Regulator of Lipid Biosynthesis and Transfer during Mycorrhizal Symbiosis | Plant-Microbe Symbiosis | Scoop.it
Most land plants have evolved a mutualistic symbiosis with arbuscular mycorrhiza (AM) fungi that improve nutrient acquisition from the soil. In return, up to 20% of host plant photosynthate is transferred to the mycorrhizal fungus in the form of lipids and sugar. Nutrient exchange must be regulated by both partners in order to maintain a reliable symbiotic relationship. However, the mechanisms underlying the regulation of lipid transfer from the plant to the AM fungus remain elusive. Here, we show that the Medicago truncatula AP2/EREBP transcription factor WRI5a, and likely its two homologs WRI5b/Erf1 and WRI5c, are master regulators of AM symbiosis controlling lipid transfer and periarbuscular membrane formation. We found that WRI5a binds AW-box cis-regulatory elements in the promoters of M. truncatula STR, which encodes a periarbuscular membrane-localized ABC transporter required for lipid transfer from the plant to the AM fungus, and MtPT4, which encodes a phosphate transporter required for phosphate transfer from the AM fungus to the plant. The hairy roots of the M. truncatula wri5a mutant and RNAi composite plants displayed impaired arbuscule formation, whereas overexpression of WRI5a resulted in enhanced expression of STR and MtPT4, suggesting that WRI5a regulates bidirectional symbiotic nutrient exchange. Moreover, we found that WRI5a and RAM1 (Required for Arbuscular Mycorrhization symbiosis 1), which encodes a GRAS-domain transcription factor, regulate each other at the transcriptional level, forming a positive feedback loop for regulating AM symbiosis. Collectively, our data suggest a role for WRI5a in controlling bidirectional nutrient exchange and periarbuscular membrane formation via the regulation of genes involved in the biosynthesis of fatty acids and phosphate uptake in arbuscule-containing cells.

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Mycobiome diversity: high-throughput sequencing and identification of fungi

Mycobiome diversity: high-throughput sequencing and identification of fungi | Plant-Microbe Symbiosis | Scoop.it
Fungi are major ecological players in both terrestrial and aquatic environments by cycling organic matter and channelling nutrients across trophic levels. High-throughput sequencing (HTS) studies of fungal communities are redrawing the map of the fungal kingdom by hinting at its enormous — and largely uncharted — taxonomic and functional diversity. However, HTS approaches come with a range of pitfalls and potential biases, cautioning against unwary application and interpretation of HTS technologies and results. In this Review, we provide an overview and practical recommendations for aspects of HTS studies ranging from sampling and laboratory practices to data processing and analysis. We also discuss upcoming trends and techniques in the field and summarize recent and noteworthy results from HTS studies targeting fungal communities and guilds. Our Review highlights the need for reproducibility and public data availability in the study of fungal communities. If the associated challenges and conceptual barriers are overcome, HTS offers immense possibilities in mycology and elsewhere.

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Modulation of nitrogen metabolism of maize plants inoculated with Azospirillum brasilense and Herbaspirillum seropedicae

Maize is highly responsive to the application of nitrogen to achieve high productivity. Inoculation with diazotrophic bacteria can improve plant growth with low N fertilization. The objective was to evaluate the inoculation of two species of diazotrophs on N metabolism in maize plants, in the presence of two concentrations of nitrogen in a hydroponic system. A factorial arrangement composed of two N levels (3.0 and 0.3 mM), with the presence of Hs—Herbaspirillum seropedicae, and Ab—Azospirillum brasilense or not. The parameters used were dry mass; N, P, and K accumulation; nitrate reductase activity; soluble fractions in roots and leaves. The inoculation altered the N metabolism and promoted greater development of maize plants, as well as a higher accumulation of P and K in the shoots. A more intensive process of N assimilation was evidenced when the plants were inoculated with H. seropedicae, leading to increased levels of NO3− and reduced N-amino, sugars, and NH4+ in leaves associated with high N level, opposite of A. brasilense.

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Nice PGPR effect... but not more than that.

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Genetic diversity of symbiotic bacteria nodulating common bean (Phaseolus vulgaris) in western Kenya

Genetic diversity of symbiotic bacteria nodulating common bean (Phaseolus vulgaris) in western Kenya | Plant-Microbe Symbiosis | Scoop.it
Biological nitrogen fixation (BNF) in legumes plays a critical role in improving soil fertility. Despite this vital role, there is limited information on the genetic diversity and BNF of bacteria nodulating common bean (Phaseolus vulgaris L.). This study evaluated the genetic diversity and symbiotic nitrogen fixation of bacteria nodulating common bean in soils of Western Kenya. The genetic diversity was determined using 16S rRNA gene partial sequences while BNF was estimated in a greenhouse experiment. The sequences of the native isolates were closely affiliated with members from the genera Pantoea, Klebsiella, Rhizobium, Enterobacter and Bacillus. These results show that apart from rhizobia, there are non-rhizobial strains in the nodules of common bean. The symbiotic efficiency (SE) of native isolates varied and exhibited comparable or superior BNF compared to the local commercial inoculants (CIAT 899 and Strain 446). Isolates (MMUST 003 [KP027691], MMUST 004 [KP027687], MMUST 005 [KP027688], KSM 001 [KP027682], KSM 002 [KP027680], KSM 003 [KP027683] and KSM 005 [KP027685]) recorded equal or significantly higher SE (p < 0.05) compared to N supplemented treatments. The results demonstrate the presence of genetic diversity of native bacteria nodulating bean that are effective in N fixation. These elite bacterial strains should be exploited as candidates for the development of Phaseolus vulgaris inoculants.

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Mesorhizobium carmichaelinearum sp. nov., isolated from Carmichaelineae spp. root nodules

Five strains of Gram-stain-negative, rod-shaped bacteria were isolated from Carmichaelia and Montigena root nodules. Based on 16S rRNA gene phylogeny, they were shown to belong to the genus Mesorhizobium , and to be most closely related to Mesorhizobium jarvisii ATCC 33669T (100–99.6 % sequence similarity), Mesorhizobium huakuii IAM 14158T (99.9–99.6 %), Mesorhizobium japonicum MAFF303099T (99.8–99.6 %) and Mesorhizobium erdmanii USDA 3471T (99.8–99.5 %). Additionally, the strains formed distinct groups based on housekeeping gene analysis and were most closely related to M. jarvisii ATCC 33669T (89.6–89.5 and 97.6–97.3 % sequence similarity for glnII and recA, respectively), M. erdmanii USDA 3471T (94.3–94.0 and 94.9–94.1 %), M. japonicum MAFF303099T (90.0–89.9 and 96.7–96.2 %) and M. huakuii IAM 14158T (89.9–90.0 and 95.4–94.9 %). Chemotaxonomic data supported the assignment of the strains to the genus Mesorhizobium and DNA–DNA hybridizations, average nucleotide identity analysis, matrix-assisted laser desorption ionization time-of-flight MS analysis, physiological and biochemical tests differentiated them genotypically and phenotypically from their nearest neighbouring species. Therefore, these strains are considered to represent a novel species, for which the name Mesorhizobium carmichaelinearum sp. nov. is proposed. The type strain is ICMP 18942T (=MonP1N1T=LMG 28414T).

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Common mycorrhizal networks activate salicylic acid defense responses of trifoliate orange (Poncirus trifoliata)

Citrus canker, caused by Xanthomonas axonopodis pv. citri (‘Xac’), is an important disease in citrus crops. Arbuscular mycorrhizal fungi (AMF) form symbiotic interactions with host plants and further affect their disease resistance, possibly by modulating the activity of salicylic acid (SA), a key phytohormone in disease resistance. Common mycorrhizal networks (CMNs) can interconnect plants, but it is not yet clear whether CMNs promote resistance to citrus canker and, if so, whether SA signaling is involved in this process. To test this possibility, we used a two‐chambered rootbox to establish CMNs between trifoliate orange (Poncirus trifoliata) seedlings in chambers inoculated (treated) or not (neighboring) with the AMF, Paraglomus occultum. A subset of the AMF‐inoculated seedlings were also inoculated with Xac (+AMF + Xac). At 2 days post‐inoculation (dpi), compared with the +AMF − Xac treatment, neighboring seedlings in +AMF + Xac treatment had lower expression levels of the SA biosynthetic genes, PtPAL, PtEPS1, and PtPBS3, but higher SA levels, which attributed to the up‐regulation of PtPAL and PtPBS3 in treated seedlings and the transfer of SA, via CMNs, to the neighboring seedlings. At 4 dpi, the pathogenesis‐related (PR) protein genes, PtPR1, PtPR4, and PtPR5, and the transcriptional regulatory factor gene, PtNPR1, were activated in neighboring seedlings of +AMF + Xac treatment. At 9 dpi, root phenylalanine ammonia‐lyase activity and total soluble phenol and lignin concentrations increased in neighboring seedlings of +AMF + Xac treatment, likely due to their linkage and signal transfer, via CMNs. These findings support the hypothesis that CMNs transfer the SA signal from infected to neighboring healthy seedlings, to activate defense responses and affording protection to neighboring plants against citrus canker infection.

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Generation of transgenic cell suspension cultures of the model legume Medicago truncatula: a rapid method for Agrobacterium mediated gene transfer

Plant cell suspension cultures are used in basic research and applied biotechnology. In both cases, the transfer and stable integration of heterologous genes is a required technique. This report describes a rapid method for transformation of cell cultures of Medicago truncatula, the model species for the legume family. Accession A17 from the cultivar Jemalong is the reference genotype selected for the sequencing of the genome and therefore most studies on Medicago are carried out on this accession line. However, this line has a low embryogenic capacity and is poorly responsive to transformation protocols that rely on somatic embryogenesis. An alternative method for transformation of suspension cultures of this line, which does not depend on leaf transformation or somatic embryogenesis, was therefore needed. The method described herein uses Agrobacterium tumefaciens mediated gene transfer, allowing the transformation of Medicago callus tissue and the following establishment of liquid suspension cell cultures approximately 2 months after transformation. Kanamycin resistance was used to select for positive transformation events and the screening was facilitated by visualization of a fluorescent marker, which was fused to the gene of interest. This new protocol reduces the time between transformation and cell culture establishment, and allows the generation of transgenic suspension cultures of Medicago reference accession A17.

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Rescooped by Jean-Michel Ané from Regulation of the plant-microbe interactions
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Novel Positive Regulator of the Early Stages of the Root Nodule Symbiosis Identified by Phosphoproteomics 

Novel Positive Regulator of the Early Stages of the Root Nodule Symbiosis Identified by Phosphoproteomics  | Plant-Microbe Symbiosis | Scoop.it

Signals and signaling pathways underlying the symbiosis between legumes and rhizobia have been studied extensively over the past decades. In a previous phosphoproteomic study on the Medicago truncatula - Sinorhizobium meliloti symbiosis, we identified plant proteins that are differentially phosphorylated upon the perception of rhizobial signals, called Nod factors. In this study, we provide experimental evidence that one of these proteins, Early Phosphorylated Protein 1 (EPP1), is required for the initiation of this symbiosis. Upon inoculation with rhizobia, MtEPP1 expression was induced in curled root hairs. Down-regulation of MtEPP1 in M. truncatula roots almost abolished calcium spiking, reduced the expression of essential symbiosis-related genes (MtNIN, MtNF-YB1, MtERN1, and MtENOD40), and strongly decreased nodule development. Phylogenetic analyses revealed that orthologs of MtEPP1 are present in legumes and specifically in plant species able to host arbuscular mycorrhizal fungi, suggesting a possible role in this association too. Short chitin oligomers induced the phosphorylation of MtEPP1 like Nod factors. However, the down-regulation of MtEPP1 affected the colonization of M. truncatula roots by arbuscular mycorrhizal fungi only moderately. Altogether, these findings indicate that MtEPP1 is essential for the establishment of the legume-rhizobia symbiosis but might plays a limited role in the arbuscular mycorrhizal symbiosis.

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Via Oswaldo Valdes-Lopez
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Mechanism of application nursery cultivation arbuscular mycorrhizal seedling in watermelon in the field

Arbuscular mycorrhizal fungi (AMF) colonisation of plant root facilitates the absorption of nutrients such as phosphorus (P) and enhances plant biotic and abiotic resistance generally. However, arbuscular mycorrhiza (AM) colonisation decreases with application of chemical fertiliser. Here, we investigated whether AMF inoculation in nurseries would facilitate AM colonisation and take physiological and ecological functions in watermelon (Citrullus lanatus) in the field. Pot experiments were carried out to study the change of AMF colonised seedling on physiology and gene expression in nursery site. Field experiments were performed to investigate the effect of nursery AMF inoculation on yield, quality and disease resistance of watermelon in the field. The results showed that nursery‐inoculated seedlings produced more dry matter and root surface area than non‐inoculated seedlings. Expression of the secretory purple acid phosphatase (PAP) genes ClaPAP10 and ClaPAP26 was up‐regulated following AMF colonisation. Accordingly, acid phosphatase activities at the root surface and P concentrations in seedling were enhanced. After transplantation to the field, the shoot dry matter and P concentration in old stem were higher in the nursery AMF inoculated seedlings than that in non‐AMF inoculated seedling. AMF inoculation also induced increase of yields and decrease of wilt disease indexes and soluble sugar content. In addition, acid phosphatase activities and AMF spore densities were increased by nursery‐inoculation in watermelon rhizosphere soil in the field. In conclusion, nursery colonisation AMF seedling enhanced watermelon growth and yield by improving the root growth and P acquisition in nursery cultivating stage, as well as optimised soil properties in the field. Nursery cultivation of watermelon seedling with AMF was an effective technique to reduce wilt disease in continuous cropped management in watermelon.

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Rescooped by Jean-Michel Ané from Transport in plants and fungi
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The ectomycorrhizal contribution to tree nutrition

The ectomycorrhizal contribution to tree nutrition | Plant-Microbe Symbiosis | Scoop.it
Trees can be associated with dozens of fungi helping them to acquire resources from forest soils. The most widespread mutualistic association in boreal and temperate forests is the ectomycorrhizal symbiosis. This symbiosis involves mushroom-forming fungi of basidiomycota, ascomycota, and some zygomycota clades and the roots of woody plant species, including oaks, poplars or pines. Although the impact of this association on ecosystem production and tree nutrition is investigated for about a century, our understanding on the molecular mechanisms that control water and nutrient fluxes between plant and fungal partners is still limited. Here, we review the recent knowledge on the ectomycorrhizal contribution to tree nutrition. We specifically highlight the molecular mechanisms driving the acquisition, translocation and release of water and nutrients in ectomycorrhizal systems. We particularly focus on the transport of macronutrients, including nitrogen, phosphorus, potassium, sulphur and calcium, micronutrients, and water by the symbiotic partner. We also provide background on the evolution, diversity, and importance of this symbiosis, identify knowledge gaps, and propose future research directions.

Via Kevin Garcia
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Arbuscular mycorrhizal fungi alleviate root damage stress induced by simulated coal mining subsidence ground fissures 

Arbuscular mycorrhizal fungi alleviate root damage stress induced by simulated coal mining subsidence ground fissures  | Plant-Microbe Symbiosis | Scoop.it
Coal mining results in surface subsidence and induces the development of ground fissures that damage surrounding plant roots. Very few studies have explored the stress of root damage caused by ground fissures and whether arbuscular mycorrhizal fungi (AMF) can relieve root damage stress induced by ground fissures. In the present study we simulated ground fissure induced root damage, examined the resultant changes in endogenous hormones, root system morphology, leaf area, leaf chlorophyll content, nutrient content and biomass of maize, and examined the ameliorative effects of AMF on maize with root damage. Ground fissures led to significantly higher levels of endogenous abscisic acid (ABA) but significantly reduced levels of indole-3-acetic acid (IAA), gibberellins (GA) and cytokinin (CTK). In addition, ground fissures led to significantly reduced root biomass, total root length, root tip number, total root volume, plant nutrient content, leaf chlorophyll content and leaf area. The shoot biomass of root damaged maize decreased significantly by 46%. By contrast, AMF increased IAA and CTK levels in maize roots, reduced ABA levels, improved the hormone balance of damaged plants, increased total root length, root tip number, total root volume, leaf area and leaf chlorophyll content, increased nutrient content and increased shoot biomass by 34%. Overall, by simulating coal mining subsidence ground fissures, the study investigated the effects of root damage stress on plant biomass, found that AMF can alleviate the mechanical damages to the root system, and provided a theoretical basis for microbial remediation in areas subject to subsidence due to coal mining.

Via Christophe Jacquet
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Lipo‐chitooligosaccharides promote lateral root formation and modify auxin homeostasis in Brachypodium distachyon 

Lipo‐chitooligosaccharides promote lateral root formation and modify auxin homeostasis in Brachypodium distachyon  | Plant-Microbe Symbiosis | Scoop.it
Lipo‐chitooligosaccharides (LCOs) are microbial symbiotic signals that also influence root growth. In Medicago truncatula, LCOs stimulate lateral root formation (LRF) synergistically with auxin. However, the molecular mechanisms of this phenomenon and whether it is restricted to legume plants are not known.
We have addressed the capacity of the model monocot Brachypodium distachyon (Brachypodium) to respond to LCOs and auxin for LRF. For this, we used a combination of root phenotyping assays, live‐imaging and auxin quantification, and analysed the regulation of auxin homeostasis genes.
We show that LCOs and a low dose of the auxin precursor indole‐3‐butyric acid (IBA) stimulated LRF in Brachypodium, while a combination of LCOs and IBA led to different regulations. Both LCO and IBA treatments locally increased endogenous indole‐3‐acetic acid (IAA) content, whereas the combination of LCO and IBA locally increased the endogenous concentration of a conjugated form of IAA (IAA‐Ala). LCOs, IBA and the combination differentially controlled expression of auxin homeostasis genes.
These results demonstrate that LCOs are active on Brachypodium roots and stimulate LRF probably through regulation of auxin homeostasis. The interaction between LCO and auxin treatments observed in Brachypodium on root architecture opens interesting avenues regarding their possible combined effects during the arbuscular mycorrhizal symbiosis.

Via Christophe Jacquet
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A Resurrected Scenario: Single Gain and Massive Loss of Nitrogen-Fixing Nodulation

A Resurrected Scenario: Single Gain and Massive Loss of Nitrogen-Fixing Nodulation | Plant-Microbe Symbiosis | Scoop.it
N2-fixing nodulation symbiosis is a complex and important agronomic trait. It occurs in phylogenetically separated lineages, and its evolution may be explained by two alternative hypotheses: (i) single gain followed by massively parallel loss, or (ii) parallel evolution and fewer losses. The latter hypothesis is widely accepted, but the first hypothesis is supported by recent phylogenomic data.

Molecular and developmental commonalities across distinct lineages support a common origin of nodulation. Moreover, recent comparative genomics studies revealed parallel loss of key nodulation genes in non-nodulating species.

These findings support a single gain of nodulation followed by massively parallel loss in most descendant lineages. Such massive loss may have been triggered by reductions in global atmospheric CO2 levels.
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Non‐random association patterns in a plant‐mycorrhizal fungal network reveal host‐symbiont specificity

Arbuscular mycorrhizal (AM) fungi are obligate plant symbionts that have important functions in most terrestrial ecosystems, but there remains an incomplete understanding of host‐fungus specificity and the relationships between species or functional groups of plants and AM fungi. Here, we aimed to provide a comprehensive description of plant‐AM fungal interactions in a biodiverse semi‐natural grassland. We sampled all plant species in a 1000 m2 homogeneous plot of dry calcareous grassland in two seasons (summer and autumn) and identified root‐colonizing AM fungi by SSU rDNA sequencing. In the network of 33 plant and 100 AM fungal species, we found a significant effect of both host plant species and host plant functional group on AM fungal richness and community composition. Comparison with network null models revealed a larger‐than‐random degree of partner selectivity among plants. Grasses harbored a larger number of AM fungal partners and were more generalist in partner selection, compared with forbs. More generalist partner association and lower specialization were apparent among obligately, compared with facultatively, mycorrhizal plant species and among locally more abundant plant species. This study provides the most complete dataset of co‐occurring plant and AM fungal taxa to date, showing that at this particular site, the interaction network is assembled non‐randomly, with moderate selectivity in associations between plant species and functional groups and their fungal symbionts.

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That's not really novel...

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Yield components of lucerne were affected by sowing dates and inoculation treatments

Yield components of lucerne were affected by sowing dates and inoculation treatments | Plant-Microbe Symbiosis | Scoop.it

Inoculation with specific rhizobia increased lucerne yield in N-deficient soils.


Spring sowing promoted faster establishment and higher above and below ground yields.


Higher yields for inoculated treatments were linked to increased leaf area, N fixation and higher RUEshoot.


Lower yields in late sowings were associated with decreased RUEshoot and longer phyllochrons, indicating carbon demand to roots.


The inoculation effect was temporary and uninoculated plants established effective nodulation over time.
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Symbiotic Effectivity of Dual and Tripartite Associations on Soybean (Glycine max L. Merr.) Cultivars Inoculated With Bradyrhizobium japonicum and AM Fungi

Symbiotic Effectivity of Dual and Tripartite Associations on Soybean (Glycine max L. Merr.) Cultivars Inoculated With Bradyrhizobium japonicum and AM Fungi | Plant-Microbe Symbiosis | Scoop.it
Soybean (Glycine max L. Merr.) is regarded worldwide as indisputably one of the most important crops for human food and animal feed. The presence of symbiotic bacteria and fungi is essential for soybean breeding, especially in low-input agricultural systems. Research on the cooperation between different microbial symbionts is a key to understanding how the health and productivity of the plant is supported. The symbiotic effectivity of dual and tripartite symbiotic agents was investigated in two pot experiments on different soybean cultivars with special regard to compatibility. In the Selection experiment, two out of sixteen soybean cultivars (Aliz, Emese) were chosen on the basis of their drought tolerance and used in all the other investigations. In the Compatibility experiment, the compatible coupling of symbiotic partners was selected based on the efficiency of single and co-inoculation with two Bradyrhizobium japonicum strains and two commercial arbuscular mycorrhizal fungal (AMF) products. Significant differences were found in the infectivity and effectivity of the microsymbionts. The rhizobial and AMF inoculation generally improved plant production, photosynthetic efficiency and root activity, but this effect depended on the type of symbiotic assotiation. Despite the low infectivity of AMF, inocula containing fungi were more beneficial than those containing only rhizobia. In the Drought Stress (DS) experiment, co-inoculated and control plants were grown in chernozem soil originating from organic farms. Emese was more resistant to drought stress than Aliz and produced a bigger root system. Under DS, the growth parameters of both microbially inoculated cultivars were better than that of control, proving that even drought tolerant genotypes can strengthen their endurance due to inoculation with AMF and nitrogen fixing bacteria. Root electrical capacitance (CR) showed a highly significant linear correlation with root and shoot dry mass and leaf area. The same root biomass was associated with higher CR in inoculated hosts. As CR method detects the absorptive surface increasing due to inoculation, it may be used to check the efficiency of the microbial treatment.

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The transcriptomic response to a short day to long day shift in leaves of the reference legume Medicago truncatula

Photoperiodic flowering aligns plant reproduction to favourable seasons of the year to maximise successful production of seeds and grains. However understanding of this process in the temperate legumes of the Fabaceae family, which are important both agriculturally and ecologically, is incomplete. Previous work in the reference legume Medicago truncatula has shown that the FT-like gene MtFTa1 is a potent floral activator. While MtFTa1 is upregulated by long-day photoperiods (LD) and vernalisation, the molecular basis of this is unknown as functional homologues of key regulatory genes present in other species, notably CONSTANS in A. thaliana, have not been identified. In LD MtFTa1 maintains a near constant diurnal pattern of expression unlike its homologue FT in A. thaliana, which has a notable peak in expression at dusk. This suggests a different manner of regulation. Furthermore, M. truncatula possesses other FT-like genes such as two LD induced MtFTb genes which may also act in the regulation of flowering time. MtFTb genes have a diurnal pattern of expression with peaks at both four and sixteen hours after dawn. This study utilises RNA-Seq to analyse the transcriptome of M. truncatula leaves to identify genes which may regulate or be co-expressed with these FT-like genes following a shift from short-day photoperiods to inductive long-days. Specifically this study focuses on the first four hours of the day in the young leaves, which coincides with the first diurnal peak of the FTb genes. Following differential expression analysis at each timepoint, genes which alter their pattern of expression are distinguished from those which just alter their magnitude of expression (and those that do neither). It goes on to categorise these genes into groups with similar patterns of expression using c-means clustering and identifies a number of potential candidate photoperiod flowering time genes for future studies to consider.

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Tracing Rhizophagus irregularis isolate IR27 in Ziziphus mauritiana roots under field conditions

Arbuscular mycorrhizal fungi (AMF) play a major role as biofertilizer for sustainable agriculture. Nevertheless, it is still poorly documented whether inoculated AMF can successfully establish in field soils as exotic AMF and improve plant growth and productivity. Further, the fate of an exogenous inoculum is still poorly understood. Here, we pre-inoculated two cultivars (Tasset and Gola) of the fruit tree Ziziphus mauritiana (jujube) with the exotic AM fungus Rhizophagus irregularis isolate IR27 before transplantation in the field. In two experiments, tracking and quantification of R. irregularis IR27 were assessed in a 13-month-old jujube and an 18-month-old jujube in two fields located in Senegal. Our results showed that the inoculant R. irregularis IR27 was quantitatively traced and discriminated from native R. irregularis isolates in roots by using a qPCR assay targeting a fragment of the RNA polymerase II gene (RPB1), and that the inoculum represented only fractions ranging from 11 to 15% of the Rhizophagus genus in the two plantations 13 and 18 months after transplantation, respectively. This study validates the use of the RPB1 gene as marker for a relative quantification of a mycorrhizal inoculant fungus isolate in the field.

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Arbuscular mycorrhiza under water — Carbon‒phosphorus exchange between rice and arbuscular mycorrhizal fungi under different flooding regimes 

Arbuscular mycorrhizal fungi (AMF) are commonly present in wetlands, but their functional role there is not well understood. We have quantified the carbon (C) allocation from rice to AMF under different flooding regimes, using stable isotope labeling (13CO2), and assessed the potential phosphorus (P) delivery from AMF to rice by profiling the expression of plant and fungal P transporter genes. The results showed that the plant-assimilated C was allocated to AMF under all flooding regimes, as evidenced by the significant enrichment of 13C in the AMF signature fatty acids. The plant C allocation to AMF declined at increased flooding intensity, and was strikingly greater at the growth stage when the rice plants had a higher nutrient requirement. The gene expression profiles and rice P levels strongly indicated that a considerable amount of P was transported to plants via the mycorrhizal pathway under wetland conditions, although AMF colonization did not improve rice growth. This work provides the first solid evidence of C‒P exchange in AM symbiosis under flooded conditions, although it is reduced compared to non-flooded conditions. Nonetheless, this means that AMF may have an important function in wetlands, which opens new perspectives on the application of symbiotic AMF in wetlands.

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19th International Meeting on Frankia and Actinorhizal Plants

It has been 40 years since the first meeting dedicated to Frankia and actinorhizal plants, which was held at Petersham, Massachusetts (reported in Torrey and Tjepkema, 1979). Since then biennial meetings have been organised and held in different venues around the globe (Table 1). The most recent meeting, the “19th International Meeting on Frankia and Actinorhizal Plants”, organised in Hammamet, Tunisia from 17th to 19th of March, 2018, gathered scientists from Algeria, Argentina, Belgium, China, Egypt, France, India, Portugal, Senegal, Sweden, UK, USA and Tunisia. The event was a stimulating opportunity for active researchers to share many advances since the previous meeting held in Montpellier, France (Franche et al. 2016) and to discuss new perspectives in this research field.

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Seven steps towards health and happiness in the lab

Seven steps towards health and happiness in the lab | Plant-Microbe Symbiosis | Scoop.it
Studies show that if we are happy, we work better and are both more creative and more productive1,2. Here are seven key principles that I follow as a PI to make the staff and researchers in my lab as happy as possible, and to maintain a nurturing and collaborative environment:

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