Plant-Microbe Symbiosis
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Ok, thanks! A new mutualism between Chlamydomonas and Methylobacteria facilitates growth on amino acids and peptides

Nitrogen is a key nutrient for land plants and phytoplankton in terrestrial and aquatic ecosystems. The model alga Chlamydomonas reinhardtii can grow efficiently on several inorganic nitrogen sources (e.g. ammonium, nitrate, nitrite) as well as many amino acids. In this study, we show that Chlamydomonas is unable to use proline, hydroxyproline, and peptides that contain these amino acids. However, we discovered that algal growth on these substrates is supported in association with Methylobacterium spp., and that a mutualistic carbon-nitrogen metabolic exchange between Chlamydomonas and Methylobacterium spp. is established. Specifically, the mineralization of these amino acids and peptides by Methylobacterium spp. produces ammonium that can be assimilated by Chlamydomonas, and CO2 photosynthetically fixed by Chlamydomonas yields glycerol that can be assimilated by Methylobacterium. As Chlamydomonas is an algal ancestor to land plants and Methylobacterium is a plant growth-promoting bacterium (PGPB), this new model mutualism may facilitate insights into the ecology and evolution of plant-bacterial interactions and design principles of synthetic ecology.

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Plant-Microbe Symbiosis
Beneficial associations between plants and microbes
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US10188104B2 - Combinations of lipo-chitooligosaccharides and methods for use in enhancing plant growth

US10188104B2 - Combinations of lipo-chitooligosaccharides and methods for use in enhancing plant growth | Plant-Microbe Symbiosis | Scoop.it
Disclosed are methods of enhancing plant growth, comprising treating plant seed or the plant that germinates from the seed with an effective amount of at least two lipo-chitooligosaccharides, wherein upon harvesting the plant exhibits at least one of increased plant yield measured in terms of bushels/acre, increased root number, increased root length, increased root mass, increased root volume and increased leaf area, compared to untreated plants or plants harvested from untreated seed.
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Extensive membrane systems at the host–arbuscular mycorrhizal fungus interface

Extensive membrane systems at the host–arbuscular mycorrhizal fungus interface | Plant-Microbe Symbiosis | Scoop.it
During arbuscular mycorrhizal (AM) symbiosis, cells within the root cortex develop a matrix-filled apoplastic compartment in which differentiated AM fungal hyphae called arbuscules reside. Development of the compartment occurs rapidly, coincident with intracellular penetration and rapid branching of the fungal hypha, and it requires much of the plant cell’s secretory machinery to generate the periarbuscular membrane that delimits the compartment. Despite recent advances, our understanding of the development of the periarbuscular membrane and the transfer of molecules across the symbiotic interface is limited. Here, using electron microscopy and tomography, we reveal that the periarbuscular matrix contains two types of membrane-bound compartments. We propose that one of these arises as a consequence of biogenesis of the periarbuscular membrane and may facilitate movement of molecules between symbiotic partners. Additionally, we show that the arbuscule contains massive arrays of membrane tubules located between the protoplast and the cell wall. We speculate that these tubules may provide the absorptive capacity needed for nutrient assimilation and possibly water absorption to enable rapid hyphal expansion.

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An MAP kinase interacts with LHK1 and regulates nodule organogenesis in Lotus japonicus

Symbiosis receptor-like kinase (SymRK) is a key protein mediating the legume-Rhizobium symbiosis. Our previous work has identified an MAP kinase kinase, SIP2, as a SymRK-interacting protein to positively regulate nodule organogenesis in Lotus japonicus, suggesting that an MAPK cascade might be involved in Rhizobium-legume symbiosis. In this study, LjMPK6 was identified as a phosphorylation target of SIP2. Stable transgenic L. japonicus with RNAi silencing of LjMPK6 decreased the numbers of nodule primordia (NP) and nodule, while plants overexpressing LjMPK6 increased the numbers of nodule, infection threads (ITs), and NP, indicating that LjMPK6 plays a positive role in nodulation. LjMPK6 could interact with a cytokinin receptor, LHK1 both in vivo and in vitro. LjMPK6 was shown to compete with LHP1 to bind to the receiver domain (RD) of LHK1and to downregulate the expression of two LjACS (1-aminocyclopropane-1-carboxylic acid synthase) genes and ethylene levels during nodulation. This study demonstrated an important role of LjMPK6 in regulation of nodule organogenesis and ethylene production in L. japonicus.

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Do arbuscular mycorrhizal fungi play a role in the ability of rare plant species to colonize abandoned fields? 

Do arbuscular mycorrhizal fungi play a role in the ability of rare plant species to colonize abandoned fields?  | Plant-Microbe Symbiosis | Scoop.it
Soil microbes from dry grassland do not support plant performance on abandoned fields.


The abandoned field microbial community enhances plant survival and size.


Seedling inoculation supports specialist species more than seed inoculation.


Mycorrhizal inoculation potential is not a good predictor of AMF root colonization.


AMF root colonization is not affected by soil community origin or plant specificity.
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Mycorrhiza response and phosphorus acquisition efficiency of sorghum cultivars differing in strigolactone composition

Aims
The function of strigolactone isomers in sorghum phosphorus acquisition efficiency (PAE) is still a matter of speculation. Therefore, the objective of this study was to investigate the effects of cultivar-specific strigolactone composition on sorghum growth indices, responsiveness of arbuscular mycorrhizal fungi (AMF), and PAE.

Methods
Two Striga-resistant (orobanchol-producing) and two Striga-susceptible (5-deoxystrigol-producing) sorghum (Sorghum bicolor (L.) Moench) cultivars were planted with and without AMF inoculation as well as with and without P fertilization. Growth indices and AMF colonization were measured 30 days after sowing from pot trial plants in a growth chamber.

Results
AMF colonization was highest in Tetron and lowest in IS9830, both Striga-resistant cultivars. Conversely, PAE was lowest in Tetron and highest in IS9830 and revealed strong positive relationships with root length, leaf area and shoot DW.

Conclusions
Although the strigolactone composition had no clear general effects on the growth indices of the four different sorghum cultivars, breeders should consider it for combining efficient AM symbiosis and high PAE values.
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SNARE Proteins LjVAMP72a and LjVAMP72b Are Required for Root Symbiosis and Root Hair Formation in Lotus japonicus

SNARE Proteins LjVAMP72a and LjVAMP72b Are Required for Root Symbiosis and Root Hair Formation in Lotus japonicus | Plant-Microbe Symbiosis | Scoop.it
SNARE (soluble N-ethyl maleimide sensitive factor attachment protein receptor) proteins mediate membrane trafficking in eukaryotic cells. Both LjVAMP72a and LjVAMP72b are members of R-SNARE and belong to a symbiotic subgroup of VAMP72 in Lotus japonicus. Their sequences are closely related and both were induced in the root upon rhizobial inoculation. The expression level of LjVAMP72a in the nodules was higher than in the leaves or roots; however, LjVMAP72b was expressed constitutively in the leaves, roots, and nodules. Immunoblot analysis showed that not only LjVAMP72a but also LjVAMP72b were accumulated in a symbiosome-enriched fraction, suggesting its localization in the symbiosome membrane during nodulation. Since there was 89% similarity between LjVAMP72a and LjVAMP72b, knockdown mutant by RNAi suppressed both genes. The suppression of both genes impaired root nodule symbiosis (RNS). The number of bacteroids and the nitrogen fixation activity were severely curtailed in the nodules formed on knockdown roots (RNAi-LjVAMP72a/72b). Arbuscular mycorrhization (AM) was also attenuated in knockdown roots, indicating that LjVAMP72a and LjVAMP72b were required to establish not only RNS but also AM. In addition, transgenic hairy roots of RNAi-LjVAMP72a/72b suppressed the elongation of root hairs without infections by rhizobia or arbuscular mycorrhizal fungi. Amino acid alignment showed the symbiotic subclade of VAMP72s containing LjVAMP72a and LjVAMP72b were a conserved six amino acid region (HHQAQD) within the SNARE motif. Taken together, our data suggested that LjVAMP72a and LjVAMP72b positively controlled both symbioses and root hair formation by affecting the secretory pathway.

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Heterologous expression of nifA or nodD genes improves chickpea- Mesorhizobium symbiotic performance

Plant growth assays showed that nifA overexpression was able to improve the symbiotic effectiveness of V-15b, while nodD overexpression lead to the improvement of ST-2 and PMI-6. Hydroponic assays showed that plants inoculated with V15bnifA+ and PMI6nodD+ started developing nodules earlier than those inoculated with the corresponding control strains. In addition, the number of nodules was always higher in plants inoculated with the strains overexpressing the symbiotic genes. Analysis of histological sections of nodules formed by V15bnifA+ showed a more developed fixation zone when compared with control. On the other hand, nodules induced by PMI6nodD+ did not show a senescent zone, which was observed in nodules from plants inoculated with the control strain. Plants inoculated with PMI6nodD+ and ST2nodD+ showed a higher number of infection threads than the corresponding control inoculations.

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Medicago LINC Complexes Function in Nuclear Morphology, Nuclear Movement, and Root Nodule Symbiosis

Medicago LINC Complexes Function in Nuclear Morphology, Nuclear Movement, and Root Nodule Symbiosis | Plant-Microbe Symbiosis | Scoop.it
olved in cellular and developmental processes across eukaryotic life, often driven by Linker of Nucleoskeleton and Cytoskeleton (LINC) complexes, which bridge the nuclear envelope (NE) via the interaction of Klarsicht/ANC-1/Syne-1 Homology (KASH) and Sad1/UNC-84 (SUN) proteins. Arabidopsis (Arabidopsis thaliana) LINC complexes are involved in nuclear movement and positioning in several cell types. Observations since the 1950s have described targeted nuclear movement and positioning during symbiosis initiation between legumes and rhizobia, but it has not been established whether these movements are functional or incidental. Here, we identify and characterize LINC complexes in the model legume Medicago truncatula. We show that LINC complex characteristics such as NE localization, dependence of KASH proteins on SUN protein binding for NE enrichment, and direct SUN-KASH binding are conserved between plant species. Using a SUN dominant-negative strategy, we demonstrate that LINC complexes are necessary for proper nuclear shaping and movement in Medicago root hairs, and are important for infection thread initiation and nodulation.
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Nice work!!

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Misdiagnosis of mycorrhizas and inappropriate recycling of data can lead to false conclusions

We draw attention to a worrying trend for the uncritical use of ‘recycled’ mycorrhizal data to compile host species lists that include obvious errors or undertake risky analyses that correlate mycorrhizal colonisation levels with environmental or physiological factors despite inherent limitations in datasets. We are not suggesting that all meta‐studies are wrong, only that more care should be taken to resolve what can safely be done with recycled mycorrhizal data in the future. We also recommend that mycorrhizal species lists should be checked against standard references since the majority of EM hosts and NM plant belong to families that are well resolved. However, additional research is required in cases where plant families have multiple root types within genera or occur in habitats where mycorrhizal associations are often suppressed (see Brundrett & Tedersoo, 2018). We hope that the mycorrhizal science community will work together more closely in the future to develop and enforce standards for mycorrhizal diagnosis and to share carefully corrected datasets for realistic meta‐studies.

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The role of plant–mycorrhizal mutualisms in deterring plant invasions: Insights from an individual‐based model

Understanding the factors that determine invasion success for non‐native plants is crucial for maintaining global biodiversity and ecosystem functioning. One hypothesized mechanism by which many exotic plants can become invasive is through the disruption of key plant–mycorrhizal mutualisms, yet few studies have investigated how these disruptions can lead to invader success. We present an individual‐based model to examine how mutualism strengths between a native plant (Impatiens capensis) and mycorrhizal fungus can influence invasion success for a widespread plant invader, Alliaria petiolata (garlic mustard). Two questions were investigated as follows: (a) How does the strength of the mutualism between the native I. capensis and a mycorrhizal fungus affect resistance (i.e., native plant maintaining >60% of final equilibrium plant density) to garlic mustard invasion? (b) Is there a non‐linear relationship between initial garlic mustard density and invasiveness (i.e., garlic mustard representing >60% of final equilibrium plant density)? Our findings indicate that either low (i.e., facultative) or high (i.e., obligate) mutualism strengths between the native plant and mycorrhizal fungus were more likely to lead to garlic mustard invasiveness than intermediate levels, which resulted in higher resistance to garlic mustard invasion. Intermediate mutualism strengths allowed I. capensis to take advantage of increased fitness when the fungus was present but remained competitive enough to sustain high numbers without the fungus. Though strong mutualisms had the highest fitness without the invader, they proved most susceptible to invasion because the loss of the mycorrhizal fungus resulted in a reproductive output too low to compete with garlic mustard. Weak mutualisms were more competitive than strong mutualisms but still led to garlic mustard invasion. Furthermore, we found that under intermediate mutualism strengths, the initial density of garlic mustard (as a proxy for different levels of plant invasion) did not influence its invasion success, as high initial densities of garlic mustard did not lead to it becoming dominant. Our results indicate that plants that form weak or strong mutualisms with mycorrhizal fungi are most vulnerable to invasion, whereas intermediate mutualisms provide the highest resistance to an allelopathic invader.

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The impact of dispersal, plant genotype and nematodes on arbuscular mycorrhizal fungal colonization 

The impact of dispersal, plant genotype and nematodes on arbuscular mycorrhizal fungal colonization  | Plant-Microbe Symbiosis | Scoop.it
While the majority of parasitic and mutualistic microbes have the potential for long-range dispersal, the high turnover in community composition among nearby hosts has often been interpreted to reflect dispersal constraints. To resolve this apparent contradiction, we need further insights into the relative importance of dispersal limitation, host genotype and the biotic environment on the colonization process. We focused on the important root symbionts, the arbuscular mycorrhizal (AM) fungi. We studied AM fungal colonization ability in a controlled mesocosm setting, where we placed Plantago lanceolata plants belonging to four different genotypes in sterile soil at 10, 30 and 70 cm from a central AM fungal inoculated P. lanceolata plant. In part of the mesocosms, we also inoculated the source plants with nematodes. AM fungi colonized receiver plants <1 m away over the course of ten weeks, with a strong effect of distance from source plant on AM fungal colonization. Plant genotype influenced AM fungal colonization during the early stages of colonization, while nematode inoculation had no effect on AM fungal colonization. Overall, the effect of both dispersal limitation and plant genetic variation may underlie the small-scale heterogeneity found in natural AM fungal communities.

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Mucoromycotina fine root endophyte fungi form nutritional mutualisms with vascular plants.

Fungi and plants have engaged in intimate symbioses that are globally widespread and have driven terrestrial biogeochemical processes since plant terrestrialisation >500 Mya. Recently, hitherto unknown nutritional mutualisms involving ancient lineages of fungi and non-vascular plants have been discovered. However, their extent and functional significance in vascular plants remains uncertain. Here, we provide first evidence of abundant carbon-for-nitrogen exchange between an early-diverging vascular plant (Lycopodiaceae) and Mucoromycotina (Endogonales) fine root endophyte regardless of changes in atmospheric CO2 concentration. Furthermore, we provide evidence that the same fungi also colonize neighbouring non-vascular and flowering plants. These findings fundamentally change our understanding of the evolution, physiology, interrelationships and ecology of underground plant-fungal symbioses in terrestrial ecosystems by revealing an unprecedented nutritional role of Mucoromycotina fungal symbionts in vascular plants.

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Genotype and rhizobium inoculation modulate the assembly of soybean rhizobacterial communities

Rhizosphere bacterial communities are vital for plants, yet the composition of rhizobacterial communities and the complex interactions between roots and microbiota, or between microbiota, are largely unknown. In this study, we investigated the structure and composition of rhizobacterial communities in two soybean cultivars and their recombinant inbred lines (RILs) contrasting in nodulation through 16S rRNA amplicon sequencing in two years of field trials. Our results demonstrate that soybean plants are able to select microbes from bulk soils at the taxonomic and functional level. Soybean genotype significantly influenced the structure of rhizobacterial communities, and resulted in dramatically different co‐occurrence networks of rhizobacterial communities between different genotypes of soybean plants. Furthermore, the introduction of exogenous rhizobia through inoculation altered soybean rhizobacterial communities in genotype dependent manner. Rhizobium inoculation not only stimulated the proliferation of potential beneficial microbes, but also increased connections in rhizobacterial networks and changed the hub microbes, all of which led to the association of distinctive bacterial communities. Taken together, we demonstrated that the assembly of soybean rhizobacterial communities was determined by both genotype and the introduction of exogenous rhizobia. These findings bolster the feasibility of root microbiome engineering through inoculation of specific microbial constituents.

Via Oswaldo Valdes-Lopez
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WillistonPlantPath's comment, January 30, 3:06 PM
Great paper. Thanks Oswaldo!
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Arbuscular cell invasion coincides with extracellular vesicles and membrane tubules

Arbuscular cell invasion coincides with extracellular vesicles and membrane tubules | Plant-Microbe Symbiosis | Scoop.it
During establishment of arbuscular mycorrhizal symbioses, fungal hyphae invade root cells producing transient tree-like structures, the arbuscules, where exchange of photosynthates for soil minerals occurs. Arbuscule formation and collapse lead to rapid production and degradation of plant and fungal membranes, their spatiotemporal dynamics directly influencing nutrient exchange. We determined the ultra-structural details of both membrane surfaces and the interstitial apoplastic matrix by transmission electron microscopy tomography during growth and senescence of Rhizophagus irregularis arbuscules in rice. Invasive growth of arbuscular hyphae was associated with abundant fungal membrane tubules (memtubs) and plant peri-arbuscular membrane evaginations. Similarly, the phylogenetically distant arbuscular mycorrhizal fungus, Gigaspora rosea, and the fungal maize pathogen, Ustilago maydis, developed memtubs while invading host cells, revealing structural commonalities independent of the mutualistic or parasitic outcome of the interaction. Additionally, extracellular vesicles formed continuously in the peri-arbuscular interface from arbuscule biogenesis to senescence, suggesting an involvement in inter-organismic signal and nutrient exchange throughout the arbuscule lifespan.

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Plant performance response to eight different types of symbiosis

Plant performance response to eight different types of symbiosis | Plant-Microbe Symbiosis | Scoop.it
Almost all plant species interact with one or more symbioses somewhere within their distribution range.
Bringing together plant trait data and growth responses to symbioses spanning 552 plant species, we provide for the first time on a large scale (597 studies) a quantitative synthesis on plant performance differences between eight major types of symbiosis, including mycorrhizas, N‐fixing bacteria, fungal endophytes and ant–plant interactions.
Frequency distributions of plant growth responses varied considerably between different types of symbiosis, in terms of both mean effect and ‘risk’, defined here as percentage of experiments reporting a negative effect of symbiosis on plants. Contrary to expectation, plant traits were poor predictors of growth response across and within all eight symbiotic associations. Our analysis showed no systematic additive effect when a host plant engaged in two functionally different symbioses.
This synthesis suggests that plant species’ ecological strategies have little effect in determining the influence of a symbiosis on host plant growth. Reliable quantification of differences in plant performance across symbioses will prove valuable for developing general hypotheses on how species become engaged in mutualisms without a guarantee of net returns.
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Quorum Sensing and Biofilm Formation in Pathogenic and Mutualistic Plant-Bacterial Interactions

Bacterial quorum sensing plays a cardinal role in determining the outcomes of plant interactions with pathogenic and mutualistic bacteria. This review dwells on the current understanding of how bacterial quorum sensing molecules, their cognate receptors and signaling pathways enable bacteria to interact with a plant host as a community. Suitable habitat niches on the plant, nutritional abundance as well as stress situations can all contribute to the formation of bacterial biofilms on plants and the abundance of nutrients such as host sugar molecules can not only serve as signals, but also as energy substrates and building blocks for biofilm formation. While biofilm formation is increasingly shown to be key to pathogenesis of bacterial plant pathogens, the modulation of plant immunity through QS signals is critical to the tolerance and establishment of mutualistic plant-microbe relationships. A new role for the versatile stress hormone salicylic acid as a possible quorum quenching molecule in plant-pathogen interactions is emerging and will be discussed. Furthermore, genetic studies coupled with -omics scale analysis of gene expression, advances in microscopy and the recent use of interdisciplinary approaches including molecular modeling and docking simulations and in silico and in vitro screening of small molecule compound libraries have provided novel insights into plant biofilm processes. The potential in targeting quorum interactions to control bacterial diseases of plants is discussed.

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A first glimpse at genes important to the Azolla–Nostoc symbiosis

Azolla is a small genus of diminutive aquatic ferns with a surprisingly vast potential to benefit the environment and agriculture, as well as to provide insight into the evolution of plant-cyanobacterial symbioses. This capability is derived from the unique relationship Azolla spp. have with their obligate, nitrogen-fixing cyanobacterial symbiont, Nostoc azollae, that resides in their leaves. Although previous work has specified the importance of the exchange of ammonium and sucrose metabolites between these two partners, we have yet to determine the underlying molecular mechanisms that make this symbiosis so successful. The newly sequenced and annotated reference genome of Azolla filiculoides has allowed us to investigate gene expression profiles of A. filiculoides—both with and without its obligate cyanobiont, N. azollae—revealing genes potentially essential to the Azolla-Nostoc symbiosis. We observed the absence of differentially expressed glutamine synthetase (GS) and glutamate synthase (GOGAT) genes, leading to questions about how A. filiculoides regulates the machinery it uses for nitrogen assimilation. Ushering A. filiculoides into the era of transcriptomics sets the stage to truly begin to understand the uniqueness of the Azolla-Nostoc symbiosis.

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Nitrogen transfer from one plant to another depends on plant biomass production between conspecific and heterospecific species via a common arbuscular mycorrhizal network

The formation of a common mycorrhizal network (CMN) between roots of different plant species enables nutrient transfers from one plant to another and their coexistence. However, almost all studies on nutrient transfers between CMN-connected plants have separately, but not simultaneously, been demonstrated under the same experimentation. Both conspecific and heterospecific seedlings of Cinnamomum camphora, Bidens pilosa, and Broussonetia papyrifera native to a karst habitat in southwest China were concurrently grown in a growth microcosm that had seven hollowed compartments (six around one in the center) being covered by 35.0-μm and/or 0.45-μm nylon mesh. The Ci. camphora in the central compartment was supplied with or without Glomus etunicatum and 15N to track N transfers between CMN-connected conspecific and heterospecific seedlings. The results showed as follows: significant greater nitrogen accumulations, biomass productions, 15N content, % Ntransfer, and the Ntransfer amount between receiver plant species ranked as Br. papyrifera≈Bi. pilosa > Ci. camphora under both M+ and M−, and as under M+ than under M− for Ci. camphora but not for both Bi. Pilosa and Br. papyrifera; the CMN transferred more nitrogen (15N content, % Ntransfer, and Ntransfer amount) from the donor Ci. camphora to the heterospecific Br. papyrifera and Bi. pilosa, with a lower percentage of nitrogen derived from transfer (%NDFT). These findings suggest that the CMN may potentially regulate the nitrogen transfer from a donor plant to individual heterospecific receiver plants, where the ratio of nitrogen derived from transfer depends on the biomass strength of the individual plants.

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Fungal endophytes of Populus trichocarpa alter host phenotype, gene expression and rhizobiome composition

Mortierella and Ilyonectria include common species of soil fungi which are frequently detected as root endophytes in many plants including Populus spp. However, the ecological roles of these and other endophytic fungi with respect to plant growth and function are still not well understood. The functional ecology of two key taxa from the Populus rhizobiome, Mortierella elongata PMI93 and Ilyonectria europaea PMI82, was studied by coupling forest soil bioassays with environmental metatranscriptomics. Using soil bioassay experiments amended with fungal inoculants, M. elongata was observed to promote the growth of Populus. This response was cultivar independent. In contrast, I. europaea had no visible effect on Populus growth. Metatranscriptomic studies reveal that these fungi impact rhizophytic and endophytic activities in Populus and induce shifts in soil and root microbial communities. Differential expression of core genes in P. trichocarpa roots was observed in response to both fungal species. Expression of Populus genes for lipid signaling and nutrient uptake were up-regulated and expression of genes associated with gibberellin signaling were altered in plants inoculated with M elongata, but not I. europaea. Up-regulation of genes for growth promotion, down-regulation of genes for several LRR-receptors/kinases, and alteration of expression of genes associated with plant defense responses (e.g., JA/ET/SA pathways) also suggest that M. elongata manipulates plant defenses while promoting plant growth.

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NIN acts as a Network Hub Controlling a Growth Module Required for Rhizobial Infection

The symbiotic infection of root cells by nitrogen-fixing rhizobia bacteria during nodulation requires the transcription factor Nodule Inception (NIN). Our root hair transcriptomic study extends NIN's regulon to include RHIZOBIUM POLAR GROWTH (RPG) and genes involved in cell wall modification, gibberellin biosynthesis, and a comprehensive group of nutrient (N, P, S) uptake and assimilation genes, suggesting that NIN's recruitment to nodulation was based on its role as a growth module, a role shared with other NIN-Like Proteins (NLPs). The expression of JA-genes in nin suggests involvement of NIN in the resolution of growth versus defence outcomes. We find that the regulation of the growth module component Nodulation Pectate Lyase (NPL) by NIN, and its function in rhizobial infection, is conserved in hologalegina legumes, highlighting its recruitment as a major event in the evolution of nodulation. We find that NPL is secreted to the infection chamber and the lumen of the infection thread. Gene network analysis using the transcription factor mutants ern1 and nf-ya1 confirms hierarchical control of NIN over NF-YA1 and shows that ERN1 acts independently to control infection. We conclude that while NIN shares function with other NLPs, the conscription of key infection genes to NIN's control has made it a central regulatory hub for rhizobial infection.

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Ectopic activation of cortical cell division during the accommodation of arbuscular mycorrhizal fungi

Ectopic activation of cortical cell division during the accommodation of arbuscular mycorrhizal fungi | Plant-Microbe Symbiosis | Scoop.it
Arbuscular mycorrhizas (AMs) between plants and soil fungi are widespread symbioses with a major role in soil nutrient uptake.
In this study we investigated the induction of root cortical cell division during AM colonization by combining morphometric and gene expression analyses with promoter activation and protein localization studies of the cell‐plate‐associated exocytic marker TPLATE.
Our results show that TPLATE promoter is activated in colonized cells of the root cortex where we also observed the appearance of cells that are half the size of the surrounding cells. Furthermore, TPLATE‐green fluorescent protein recruitment to developing cell plates highlighted ectopic cell division events in the inner root cortex during early AM colonization. Lastly, transcripts of TPLATE, KNOLLE and Cyclinlike 1 (CYC1) are all upregulated in the same context, alongside endocytic markers Adaptor‐Related Protein complex 2 alpha 1 subunit (AP2A1) and Clathrin Heavy Chain 2 (CHC2), known to be active during cell plate formation. This pattern of gene expression was recorded in wild‐type Medicago truncatula roots, but not in a common symbiotic signalling pathway mutant where fungal colonization is blocked at the epidermal level.
Altogether, these results suggest the activation of cell‐division‐related mechanisms by AM hosts during the accommodation of the symbiotic fungus.
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The Influence of Bt Maize Cultivation on Communities of Arbuscular Mycorrhizal Fungi Revealed by MiSeq Sequencing

The Influence of Bt Maize Cultivation on Communities of Arbuscular Mycorrhizal Fungi Revealed by MiSeq Sequencing | Plant-Microbe Symbiosis | Scoop.it
The cultivation of transgenic Bacillus thuringiensis (Bt) has received worldwide attention since Bt crops were first released. Its ecological risks on arbuscular mycorrhizal fungi (AMF) have been widely studied. In this study, after cultivation for five seasons, the AMF diversity and community composition of two Bt maize varieties, 5422Bt1 (event Bt11) and 5422CBCL (event MO10), which both express Cry1Ab protein, and their isoline non-Bt maize 5422, as well as Bt straw after cultivation had been returned to subsequent conventional maize variety, were analyzed using Illumina MiSeq sequencing. A total of 263 OTUs (operational taxonomic units) from 511,847 sequenced affiliated with the AMF which belonged to Mucoromycota phylum Glomeromycotina subphylum were obtained. No significant difference was detected in the AMF diversity and richness (Shannon, Simpson, ACE, and Chao 1 indices) and community composition in rhizosphere soils and roots between Bt and non-Bt treatment revealed by NMDS (non-metric multidimensional scaling) and NPMANOVA (non-parametric multivariate analysis). Moreover, Glomus was the most dominant genus in all samples. Although there was no significant difference in the AMF community in roots and rhizosphere soils between the Bt and non-Bt maize treatments, total phosphorus (TP), total nitrogen (TN), organic carbon (OC), and pH were driving factors affecting the AMF community, and their composition varied between rhizosphere soils and roots during the maturity period of the fifth season. Compared to our previous study, the results were identical. In conclusion, no significant difference was observed between the Bt and non-Bt treatments, and the Illumina MiSeq method had higher throughput and higher quality read cover, which gave us comprehensive insight into AMF communities in agro-ecosystems.
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D14-LIKE: An essential protein for the establishment of arbuscular mycorrhizal symbiosis

Low nutrition availability in the soil can be a major limitation of plant growth. To improve nutrient acquisition, the majority of land plants engage in symbiosis with arbuscular mycorrhizal (AM) fungi. The accommodation of fungal colonisation structures in the roots requires their radical reprogramming. This starts during pre-symbiotic communication, where signals are exchanged between the fungus and plant across the rhizosphere. The receptor D14-LIKE emerged as a vital component of this pre-symbiotic communication when it was found to be absolutely required for symbiosis in rice. However, the broader relevance of the receptor, both in terms of functional conservation across plant species and its relation to other pre-symbiotic plant signalling components, remained unclear. The aim of this thesis was to elucidate these two key points. To address the fragmented picture of fungal signals, plant receptors and signalling pathways, a large scale transcriptomic experiment in rice was conducted to tie D14L together with other distinct pre-symbiotic components. In the absence of D14L-mediated signalling, rice was found to be compromised in the perception of germinated spore exudates, as well as specific chitinaceous signals, meaning that normal transcriptional reprogramming could not be achieved in response to any of these treatments. In addition, the functional conservation of D14L signalling was explored using trans-species complementation experiments. It was found that the Arabidopsis homolog AtKAI2 could complement the developmental phenotype of the d14l rice mutant, but not symbiosis. Likewise, D14La from early diverging Marchantia polymorpha and Marachantia paleacea could rescue developmental phenotypes in d14l rice, but again failed to complement symbiosis. This demonstrated a functional separation between developmental and symbiotic signalling. The data generated during my PhD foster D14L as a central node for multiple inputs to pre-symbiotic reprogramming, and provides new insights into pre-symbiotic communication mechanisms which are required for the successful establishment of symbiosis.
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Interactions between arbuscular mycorrhizal fungi and non-host Carex capillacea

A topic of confusion over the interactions between arbuscular mycorrhizal (AM) fungi and plants is the mycorrhizal status of some plant families such as Cyperaceae, which is generally considered to be non-mycorrhizal. Here, we conducted experiments to explore how the abiotic environmental conditions and AM network influence the interactions between AM fungi and Carex capillacea. We grew Carex capillacea alone or together with a mycorrhizal host species Medicago sativa in the presence or absence of AM fungi (soil inoculum from Mount Segrila and Rhizophagus intraradices from the Chinese Bank of the Glomeromycota, BGC). Plants were grown in a growth chamber and at two elevational sites of Mount Segrila, respectively. The results indicate that mycorrhizal host plants ensured the presence of an active AM fungal network whether under growth chamber or alpine conditions. The AM fungal network significantly depressed the growth of C. capillacea, especially when native inocula were used and the plants grew under alpine site conditions, although root colonization of C. capillacea increased in most cases. Moreover, the colonization level of C. capillacea was much higher (≤ 30%) when growing under alpine conditions compared with growth chamber conditions (< 8.5%). Up to 20% root colonization by Rhizophagus intraradices was observed in monocultures under alpine conditions. A significant negative relationship was found between shoot phosphorus concentrations in M. sativa and shoot dry mass of C. capillacea. These results indicate that growing conditions, AM network, and inoculum source are all important factors affecting the susceptibility of C. capillacea to AM fungi, and growing conditions might be a key driver of the interactions between AM fungi and C. capillacea.

Jean-Michel Ané's insight:

They get "colonization" even in the non-inoculated control... 

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Global plant–symbiont organization and emergence of biogeochemical cycles resolved by evolution-based trait modelling

Global plant–symbiont organization and emergence of biogeochemical cycles resolved by evolution-based trait modelling | Plant-Microbe Symbiosis | Scoop.it
One of the most distinct but unresolved global patterns is the apparent variation in plant–symbiont nutrient strategies across biomes. This pattern is central to our understanding of plant–soil–nutrient feedbacks in the land biosphere, which, in turn, are essential for our ability to predict the future dynamics of the Earth system. Here, we present an evolution-based trait-modelling approach for resolving (1) the organization of plant–symbiont relationships across biomes worldwide and (2) the emergent consequences for plant community composition and land biogeochemical cycles. Using game theory, we allow plants to use different belowground strategies to acquire nutrients and compete within local plant–soil–nutrient cycles in boreal, temperate and tropical biomes. The evolutionarily stable strategies that emerge from this analysis allow us to predict the distribution of belowground symbioses worldwide, the sequence and timing of plant succession, the bistability of ecto- versus arbuscular mycorrhizae in temperate and tropical forests, and major differences in the land carbon and nutrient cycles across biomes. Our findings imply that belowground symbioses have been central to the evolutionary assembly of plant communities and plant–nutrient feedbacks at the scale of land biomes. We conclude that complex global patterns emerge from local between-organism interactions in the context of Darwinian natural selection and evolution, and that the underlying dynamics can be mechanistically probed by our low-dimensional modelling approach.

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