Plant roots and rhizosphere
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Plant roots and rhizosphere
dedicated to mechanisms associated to root development, and adaptation to abiotic stresses but also to the relations between  roots  and their surrounding microbial communities. Involvement  of hormones in the regulation of root development is now reported in the "Plant hormones" site (http://www.scoop.it/t/plant-hormones-by-christophe-jacquet).
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Arbuscular mycorrhizal phenotyping: the dos and don'ts - Montero - 2019 - New Phytologist -

Arbuscular mycorrhizal phenotyping: the dos and don'ts - Montero - 2019 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
Most plant lineages engage with Glomeromycotina fungi to form the ubiquitous arbuscular mycorrhizal (AM) symbiosis. Despite its wide occurrence in diverse plant–fungal species combinations, the interaction dynamics are strikingly uniform (Fig. 1). The events leading up to a successful mutualism start when plant and fungus advertise their presence in the rhizosphere by releasing diffusible chemical cues. In vascular plants this presymbiotic dialog results in physical contact whereby extraradical hyphae differentiate into hyphopodia on the surface of roots preceding fungal entry. Intraradical hyphal passage is followed by fungal accommodation in cortical cells to foster arbuscules. This is accompanied by the rapid formation of plant and fungal membranes in juxtaposition to each other, resulting in a magnified surface area. The mutualistic nature of the association manifests here as the reciprocal exchange of nutrients occurs. Subsequently formed fungal vesicles and spores are symptomatic of a sustained association. At the whole‐root level, symbiosis establishment is considered asynchronous as all AM fungal symbiotic structures can be found simultaneously. However, at the infection unit resolution, every stage depends on the preceding one reflecting that precise molecular programs dynamically coordinate the interaction.
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Removal of soil biota alters soil feedback effects on plant growth and defense chemistry - Wang - 2019 - New Phytologist -

Removal of soil biota alters soil feedback effects on plant growth and defense chemistry - Wang - 2019 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
We examined how the removal of soil biota affects plant–soil feedback (PSF) and defense chemistry of Jacobaea vulgaris, an outbreak plant species in Europe containing the defense compounds pyrrolizidine alkaloids (PAs).
Macrofauna and mesofauna, as well as fungi and bacteria, were removed size selectively from unplanted soil or soil planted with J. vulgaris exposed or not to above‐ or belowground insect herbivores. Wet‐sieved fractions, using 1000‐, 20‐, 5‐ and 0.2‐μm mesh sizes, were added to sterilized soil and new plants were grown. Sieving treatments were verified by molecular analysis of the inocula.
In the feedback phase, plant biomass was lowest in soils with 1000‐ and 20‐μm inocula, and soils conditioned with plants gave more negative feedback than without plants. Remarkably, part of this negative PSF effect remained present in the 0.2‐μm inoculum where no bacteria were present. PA concentration and composition of plants with 1000‐ or 20‐μm inocula differed from those with 5‐ or 0.2‐μm inocula, but only if soils had been conditioned by undamaged plants or plants damaged by aboveground herbivores. These effects correlated with leaf hyperspectral reflectance.
We conclude that size‐selective removal of soil biota altered PSFs, but that these PSFs were also influenced by herbivory during the conditioning phase.
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Persistence of root-colonizing Pseudomonas protegens in herbivorous insects throughout different developmental stages and dispersal to new host plants

Persistence of root-colonizing Pseudomonas protegens in herbivorous insects throughout different developmental stages and dispersal to new host plants | Plant roots and rhizosphere | Scoop.it
The discovery of insecticidal activity in root-colonizing pseudomonads, best-known for their plant-beneficial effects, raised fundamental questions about the ecological relevance of insects as alternative hosts for these bacteria. Since soil bacteria are limited in their inherent abilities of dispersal, insects as vectors might be welcome vehicles to overcome large distances. Here, we report on the transmission of the root-colonizing, plant-beneficial and insecticidal bacterium Pseudomonas protegens CHA0 from root to root by the cabbage root fly, Delia radicum. Following ingestion by root-feeding D. radicum larvae, CHA0 persisted inside the insect until the pupal and adult stages. The emerging flies were then able to transmit CHA0 to a new plant host initiating bacterial colonization of the roots. CHA0 did not reduce root damages caused by D. radicum and had only small effects on Delia development suggesting a rather commensal than pathogenic relationship. Interestingly, when the bacterium was fed to two highly susceptible lepidopteran species, most of the insects died, but CHA0 could persist throughout different life stages in surviving individuals. In summary, this study investigated for the first time the interaction of P. protegens CHA0 and related strains with an insect present in their rhizosphere habitat. Our results suggest that plant-colonizing pseudomonads have different strategies for interaction with insects. They either cause lethal infections and use insects as food source or they live inside insect hosts without causing obvious damages and might use insects as vectors for dispersal, which implies a greater ecological versatility of these bacteria than previously thought.
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The success story of plants and fungi - ScienceDirect

The success story of plants and fungi - ScienceDirect | Plant roots and rhizosphere | Scoop.it
Fungi and plants interact in multiple ways, many of which are important for the functioning of today’s ecosystems. A systematic study of the phylogenies and diversification rates of both kingdoms suggests that these interactions are rooted in a shared history going back more than a billion years and enabling the success of land plants.
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The Root Cap Cuticle: A Wall Structure for Seedling Establishment and Lateral Root Formation

The root cap surrounding the tip of plant roots is thought to protect the delicate stem cells in the root meristem. We discovered that the first layer of root cap cells is covered by an electron-opaque cell wall modification resembling a plant cuticle. Cuticles are polyester-based protective structures considered exclusive to aerial plant organs. Mutations in cutin biosynthesis genes affect the composition and ultrastructure of this cuticular structure, confirming its cutin-like characteristics. Strikingly, targeted degradation of the root cap cuticle causes a hypersensitivity to abiotic stresses during seedling establishment. Furthermore, lateral root primordia also display a cuticle that, when defective, causes delayed outgrowth and organ deformations, suggesting that it facilitates lateral root emergence. Our results show that the previously unrecognized root cap cuticle protects the root meristem during the critical phase of seedling establishment and promotes the efficient formation of lateral roots.
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Arbuscular mycorrhizal fungi increase grain yields: a meta‐analysis - Zhang - 2019 - New Phytologist -

Arbuscular mycorrhizal fungi increase grain yields: a meta‐analysis - Zhang - 2019 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
Increasing grain yields of food cereal crops is a major goal in future sustainable agriculture. We quantitatively analyzed the potential role of arbuscular mycorrhizal (AM) fungi in enhancing grain yields of seven cereal crops with exceptional importance for human nutrition across the globe: corn, wheat, rice, barley, sorghum, millet and oat.
We conducted a meta‐analysis for three datasets including both English and Chinese language publications: the ‘whole’ dataset including both laboratory and field studies (168 articles); the ‘field’ dataset comprising only field studies (97 studies); and the ‘field‐inoculation’ dataset including only AM fungal inoculation studies conducted in field conditions (70 articles).
We found that the AM fungal effect on grain yield was less pronounced in field and noninoculation studies. AM fungal inoculation in field led to a 16% increase (overall effect) based on the ‘field‐inoculation’ dataset; this effect was variable (77% trials had positive values), crop‐specific, lower for new cultivars released after 1950 and further modulated by soil pH.
Although there are neutral and negative effects of AM fungi on grain yields, we emphasize the importance of integrating AM fungi in sustainable agriculture to increase grain yields of cereal crops.
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Pseudomonas fluorescens increases mycorrhization and modulates expression of antifungal defense response genes in roots of aspen seedlings | BMC Plant Biology |

Pseudomonas fluorescens increases mycorrhization and modulates expression of antifungal defense response genes in roots of aspen seedlings | BMC Plant Biology | | Plant roots and rhizosphere | Scoop.it
Plants, fungi, and bacteria form complex, mutually-beneficial communities within the soil environment. In return for photosynthetically derived sugars in the form of exudates from plant roots, the microbial symbionts in these rhizosphere communities provide their host plants access to otherwise inaccessible nutrients in soils and help defend the plant against biotic and abiotic stresses. One role that bacteria may play in these communities is that of Mycorrhizal Helper Bacteria (MHB). MHB are bacteria that facilitate the interactions between plant roots and symbiotic mycorrhizal fungi and, while the effects of MHB on the formation of plant-fungal symbiosis and on plant health have been well documented, the specific molecular mechanisms by which MHB drive gene regulation in plant roots leading to these benefits remain largely uncharacterized. Here, we investigate the effects of the bacterium Pseudomonas fluorescens SBW25 (SBW25) on aspen root transcriptome using a tripartite laboratory community comprised of Populus tremuloides (aspen) seedlings and the ectomycorrhizal fungus Laccaria bicolor (Laccaria). We show that SBW25 has MHB activity and promotes mycorrhization of aspen roots by Laccaria. Using transcriptomic analysis of aspen roots under multiple community compositions, we identify clusters of co-regulated genes associated with mycorrhization, the presence of SBW25, and MHB-associated functions, and we generate a combinatorial logic network that links causal relationships in observed patterns of gene expression in aspen seedling roots in a single Boolean circuit diagram. The predicted regulatory circuit is used to infer regulatory mechanisms associated with MHB activity. In our laboratory conditions, SBW25 increases the ability of Laccaria to form ectomycorrhizal interactions with aspen seedling roots through the suppression of aspen root antifungal defense responses. Analysis of transcriptomic data identifies that potential molecular mechanisms in aspen roots that respond to MHB activity are proteins with homology to pollen recognition sensors. Pollen recognition sensors integrate multiple environmental signals to down-regulate pollenization-associated gene clusters, making proteins with homology to this system an excellent fit for a predicted mechanism that integrates information from the rhizosphere to down-regulate antifungal defense response genes in the root. These results provide a deeper understanding of aspen gene regulation in response to MHB and suggest additional, hypothesis-driven biological experiments to validate putative molecular mechanisms of MHB activity in the aspen-Laccaria ectomycorrhizal symbiosis.
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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 roots and rhizosphere | 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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Arbuscular cell invasion coincides with extracellular vesicles and membrane tubules

Arbuscular cell invasion coincides with extracellular vesicles and membrane tubules | Plant roots and rhizosphere | 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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Arbuscular mycorrhizal fungi possess a CLAVATA3/embryo surrounding region‐related gene that positively regulates symbiosis - Le Marquer - - New Phytologist -

Arbuscular mycorrhizal fungi possess a CLAVATA3/embryo surrounding region‐related gene that positively regulates symbiosis - Le Marquer - - New Phytologist - | Plant roots and rhizosphere | Scoop.it
The arbuscular mycorrhizal (AM) symbiosis is a beneficial association established between land plants and the members of a subphylum of fungi, the Glomeromycotina. How the two symbiotic partners regulate their association is still enigmatic. Secreted fungal peptides are candidates for regulating this interaction.
We searched for fungal peptides with similarities with known plant signalling peptides.
We identified CLAVATA (CLV)/EMBRYO SURROUNDING REGION (ESR)‐RELATED PROTEIN (CLE) genes in phylogenetically distant AM fungi: four Rhizophagus species and one Gigaspora species. These CLE genes encode a signal peptide for secretion and the conserved CLE C‐terminal motif. They seem to be absent in the other fungal clades. Rhizophagus irregularis and Gigaspora rosea CLE genes (RiCLE1 and GrCLE1) are transcriptionally induced in symbiotic vs asymbiotic conditions. Exogenous application of synthetic RiCLE1 peptide on Medicago truncatula affects root architecture, by slowing the apical growth of primary roots and stimulating the formation of lateral roots. In addition, pretreatment of seedlings with RiCLE1 peptide stimulates mycorrhization.
Our findings demonstrate for the first time that in addition to plants and nematodes, AM fungi also possess CLE genes. These results pave the way for deciphering new mechanisms by which AM fungi modulate plant cellular responses during the establishment of AM symbiosis.
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How do arbuscular mycorrhizal fungi handle phosphate? New insight into fine‐tuning of phosphate metabolism - Ezawa - 2018 - New Phytologist -

How do arbuscular mycorrhizal fungi handle phosphate? New insight into fine‐tuning of phosphate metabolism - Ezawa - 2018 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
Arbuscular mycorrhizal fungi form symbiotic associations with most land plants and deliver mineral nutrients, in particular phosphate, to the host. Therefore, understanding the mechanisms of phosphate acquisition and delivery in the fungi is critical for full appreciation of the mutualism in this association. Here, we provide updates on physical, chemical, and biological strategies of the fungi for phosphate acquisition, including interactions with phosphate‐solubilizing bacteria, and those on the regulatory mechanisms of phosphate homeostasis based on resurveys of published genome sequences and a transcriptome with reference to the latest findings in a model fungus. For the mechanisms underlying phosphate translocation and export to the host, which are major research frontiers in this field, not only recent advances but also testable hypotheses are proposed. Lastly, we briefly discuss applicability of the latest tools to gene silencing in the fungi, which will be breakthrough techniques for comprehensive understanding of the molecular basis of fungal phosphate metabolism.
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Nitrogen and phosphate metabolism in ectomycorrhizas - Nehls - 2018 - New Phytologist -

Nitrogen and phosphate metabolism in ectomycorrhizas - Nehls - 2018 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
Nutrient homeostasis is essential for fungal cells and thus tightly adapted to the local demand in a mycelium with hyphal specialization. Based on selected ectomycorrhizal (ECM) fungal models, we outlined current concepts of nitrogen and phosphate nutrition and their limitations, and included knowledge from Baker's yeast when major gaps had to be filled. We covered the entire pathway from nutrient mobilization, import and local storage, distribution within the mycelium and export at the plant–fungus interface. Even when nutrient import and assimilation were broad issues for ECM fungi, we focused mainly on nitrate and organic phosphorus uptake, as other nitrogen/phosphorus (N/P) sources have been covered by recent reviews. Vacuolar N/P storage and mobilization represented another focus point of this review. Vacuoles are integrated into cellular homeostasis and central for an ECM mycelium at two locations: soil‐growing hyphae and hyphae of the plant–fungus interface. Vacuoles are also involved in long‐distance transport. We further discussed potential mechanisms of bidirectional long‐distance nutrient transport (distances from millimetres to metres). A final focus of the review was N/P export at the plant–fungus interface, where we compared potential efflux mechanisms and pathways, and discussed their prerequisites.
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The origin and evolution of mycorrhizal symbioses: from palaeomycology to phylogenomics - Strullu‐Derrien - 2018 - New Phytologist -

The origin and evolution of mycorrhizal symbioses: from palaeomycology to phylogenomics - Strullu‐Derrien - 2018 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
Summary

The ability of fungi to form mycorrhizas with plants is one of the most remarkable and enduring adaptations to life on land. The occurrence of mycorrhizas is now well established in c. 85% of extant plants, yet the geological record of these associations is sparse. Fossils preserved under exceptional conditions provide tantalizing glimpses into the evolutionary history of mycorrhizas, showing the extent of their occurrence and aspects of their evolution in extinct plants. The fossil record has important roles to play in establishing a chronology of when key fungal associations evolved and in understanding their importance in ecosystems through time. Together with calibrated phylogenetic trees, these approaches extend our understanding of when and how groups evolved in the context of major environmental change on a global scale. Phylogenomics furthers this understanding into the evolution of different types of mycorrhizal associations, and genomic studies of both plants and fungi are shedding light on how the complex set of symbiotic traits evolved. Here we present a review of the main phases of the evolution of mycorrhizal interactions from palaeontological, phylogenetic and genomic perspectives, with the aim of highlighting the potential of fossil material and a geological perspective in a cross‐disciplinary approach.
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Arabidopsis γ‐glutamylcyclotransferase affects glutathione content and root system architecture during sulfur starvation - Joshi - 2019 - New Phytologist -

Arabidopsis γ‐glutamylcyclotransferase affects glutathione content and root system architecture during sulfur starvation - Joshi - 2019 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
γ‐Glutamylcyclotransferase initiates glutathione degradation to component amino acids l‐glutamate, l‐cysteine and l‐glycine. The enzyme is encoded by three genes in Arabidopsis thaliana, one of which (GGCT2;1) is transcriptionally upregulated by starvation for the essential macronutrient sulfur (S). Regulation by S‐starvation suggests that GGCT2;1 mobilizes l‐cysteine from glutathione when there is insufficient sulfate for de novo l‐cysteine synthesis.
The response of wild‐type seedlings to S‐starvation was compared to ggct2;1 null mutants.
S‐starvation causes glutathione depletion in S‐starved wild‐type seedlings, but higher glutathione is maintained in the primary root tip than in other seedling tissues. Although GGCT2;1 is induced throughout seedlings, its expression is concentrated in the primary root tip where it activates the γ‐glutamyl cycle. S‐starved wild‐type plants also produce longer primary roots, and lateral root growth is suppressed. While glutathione is also rapidly depleted in ggct2;1 null seedlings, much higher glutathione is maintained in the primary root tip compared to the wild‐type. S‐starved ggct2;1 primary roots grow longer than the wild‐type, and lateral root growth is not suppressed.
These results point to a role for GGCT2;1 in S‐starvation‐response changes to root system architecture through activity of the γ‐glutamyl cycle in the primary root tip. l‐Cysteine mobilization from glutathione is not solely a function of GGCT2;1.
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Genome and evolution of the arbuscular mycorrhizal fungus Diversispora epigaea (formerly Glomus versiforme) and its bacterial endosymbionts - Sun - 2019 - New Phytologist -

Genome and evolution of the arbuscular mycorrhizal fungus Diversispora epigaea (formerly Glomus versiforme) and its bacterial endosymbionts - Sun - 2019 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
Arbuscular mycorrhizal (AM) fungi form endosymbioses with most plants, and they themselves are hosts for Mollicutes/Mycoplasma‐related endobacteria (MRE). Despite their significance, genomic information for AM fungi and their MRE are relatively sparse, which hinders our understanding of their biology and evolution.
We assembled the genomes of the AM fungus Diversispora epigaea (formerly Glomus versiforme) and its MRE and performed comparative genomics and evolutionary analyses.
The D. epigaea genome showed a pattern of substantial gene duplication and differential evolution of gene families, including glycosyltransferase family 25, whose activities are exclusively lipopolysaccharide biosynthesis. Genes acquired by horizontal transfer from bacteria possibly function in defense against foreign DNA or viruses. The MRE population was diverse, with multiple genomes displaying characteristics of differential evolution and encoding many MRE‐specific genes as well as genes of AM fungal origin. Gene family expansion in D. epigaea may enhance adaptation to both external and internal environments, such as expansion of kinases for signal transduction upon external stimuli and expansion of nucleoside salvage pathway genes potentially for competition with MRE, whose genomes lack purine and pyrimidine biosynthetic pathways.
Collectively, this metagenome provides high‐quality references and begins to reveal the diversity within AM fungi and their MRE.
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Insights into the complex role of GRAS transcription factors in the arbuscular mycorrhiza symbiosis

Insights into the complex role of GRAS transcription factors in the arbuscular mycorrhiza symbiosis | Plant roots and rhizosphere | Scoop.it
To improve access to limiting nutrients, the vast majority of land plants forms arbuscular mycorrhizal (AM) symbioses with Glomeromycota fungi. We show here that AM-related GRAS transcription factors from different subgroups are upregulated during a time course of mycorrhization. Based on expression studies in mutants defective in arbuscule branching (ram1-1, with a deleted MtRam1 GRAS transcription factor gene) or in the formation of functional arbuscules (pt4-2, mutated in the phosphate transporter gene MtPt4), we demonstrate that the five AM-related GRAS transcription factor genes MtGras1, MtGras4, MtGras6, MtGras7, and MtRad1 can be differentiated by their dependency on MtRAM1 and MtPT4, indicating that the network of AM-related GRAS transcription factors consists of at least two regulatory modules. One module involves the MtRAM1- and MtPT4-independent transcription factor MtGRAS4 that activates MtGras7. Another module is controlled by the MtRAM1- and MtPT4-dependent transcription factor MtGRAS1. Genome-wide expression profiles of mycorrhized MtGras1 knockdown and ram1-1 roots differ substantially, indicating different targets. Although an MtGras1 knockdown reduces transcription of AM-related GRAS transcription factor genes including MtRam1 and MtGras7, MtGras1 overexpression alone is not sufficient to activate MtGras genes. MtGras1 knockdown roots display normal fungal colonization, with a trend towards the formation of smaller arbuscules.

Via Jean-Michel Ané
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The Beneficial Root-Colonizing Fungus Mortierella hyalina Promotes the Aerial Growth of Arabidopsis and Activates Calcium-Dependent Responses That Restrict Alternaria brassicae–Induced Disease Deve...

The Beneficial Root-Colonizing Fungus Mortierella hyalina Promotes the Aerial Growth of Arabidopsis and Activates Calcium-Dependent Responses That Restrict Alternaria brassicae–Induced Disease Deve... | Plant roots and rhizosphere | Scoop.it
The endophytic fungus Mortierella hyalina colonizes the roots of Arabidopsis thaliana and stimulates growth and biomass production of the aerial parts but not of roots. An exudate fraction from the fungus induces rapid and transient cytoplasmic Ca2+elevation in the roots. The Ca2+ response does not require the well-characterized (co)receptors BAK1, CERK1, and FLS2 for pathogen-associated molecular patterns, and the Ca2+ channels GLR-2.4, GLR-2.5, and GLR-3.3 or the vacuolar TWO PORE CHANNEL1, which might be involved in cytoplasmic Ca2+ elevation. We isolated an ethyl-methane-sulfonate–induced Arabidopsis mutant that is impaired in this Ca2+ response. The roots of the mutant are impaired in M. hyalina–mediated suppression of immune responses after Alternaria brassicae infection, i.e., jasmonate accumulation, generation of reactive oxygen species, as well as the activation of jasmonate-related defense genes. Furthermore, they are more colonized by M. hyalina than wild-type roots. We propose that the mutant gene product is involved in a Ca2+-dependent signaling pathway activated by M. hyalina to suppress immune responses in Arabidopsis roots.
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Plant performance response to eight different types of symbiosis - Gibert - 2019 - New Phytologist -

Plant performance response to eight different types of symbiosis - Gibert - 2019 - New Phytologist - | Plant roots and rhizosphere | 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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Gibberellins negatively regulate the development of Medicago truncatula root system

Gibberellins negatively regulate the development of Medicago truncatula root system | Plant roots and rhizosphere | Scoop.it
The root system displays a remarkable plasticity that enables plants to adapt to changing environmental conditions. This plasticity is tightly linked to the activity of root apical meristems (RAMs) and to the formation of lateral roots, both controlled by related hormonal crosstalks. In Arabidopsis thaliana, gibberellins (GAs) were shown to positively control RAM growth and the formation of lateral roots. However, we showed in Medicago truncatula that GAs negatively regulate root growth and RAM size as well as the number of lateral roots depending at least on the MtDELLA1 protein. By using confocal microscopy and molecular analyses, we showed that GAs primarily regulate RAM size by affecting cortical cell expansion and additionally negatively regulate a subset of cytokinin-induced root expansin encoding genes. Moreover, GAs reduce the number of cortical cell layers, resulting in the formation of both shorter and thinner roots. These results suggest contrasting effects of GA regulations on the root system architecture depending on plant species.
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Frontiers | The Role of Host Genetic Signatures on Root–Microbe Interactions in the Rhizosphere and Endosphere | Plant Science

Microbiomes inhabiting plants are crucial for plant productivity and well-being. A plethora of interactions between roots, microbiomes, and soil shapes the self-organization of the microbial community associated with the root system. The rhizosphere (i.e., the soil close to the root surface) and endosphere (i.e., all inner root tissues) are critical interfaces for the exchange of resources between roots and the soil environment. In recent years, next-generation sequencing technologies have enabled systemic studies of root-associated microbiomes in the endosphere and interactions between roots and microbes at the root-soil interfaces. Genetic factors such as species and genotype of host plants are the driving force of microbial community differentiation and composition. In this mini-review, we will survey the role of these factors on plant–microbe interactions by highlighting the results of next-generation genomic and transcriptomic studies in the rhizosphere and endosphere of land plants. Moreover, environmental factors such as geography and soil type shape the microbiome. Relationships between the root-associated microbiome, architectural variations and functional switches within the root system determine the health and fitness of the whole plant system. A detailed understanding of plant–microbe interactions is of fundamental agricultural importance and significance for crop improvement by plant breeding
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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 roots and rhizosphere | 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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Ectopic activation of cortical cell division during the accommodation of arbuscular mycorrhizal fungi - Russo - 2019 - New Phytologist -

Ectopic activation of cortical cell division during the accommodation of arbuscular mycorrhizal fungi - Russo - 2019 - New Phytologist - | Plant roots and rhizosphere | 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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Arbuscular mycorrhizal fungi: intraspecific diversity and pangenomes - Mathieu - 2018 - New Phytologist -

Arbuscular mycorrhizal fungi: intraspecific diversity and pangenomes - Mathieu - 2018 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
Arbuscular mycorrhizal fungi (AMF) are ubiquitous plant symbionts with an intriguing population biology. Conspecific AMF strains can vary substantially at the genetic and phenotypic levels, leading to direct and quantifiable variation in plant growth. Recent studies have shown that high intraspecific diversity is very common in AMF, and not only found in model species. Studies have also revealed how the phenotype of conspecific isolates varies depending on the plant host, highlighting the functional relevance of intraspecific phenotypic plasticity for the AMF ecology and mycorrhizal symbiosis. Recent work has also demonstrated that conspecific isolates of the model AMF Rhizophagus irregularis harbor large and highly variable pangenomes, highlighting the potential role of intraspecific genome diversity for the ecological adaptation of these symbionts.
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Evolutionary history of mycorrhizal symbioses and global host plant diversity - Brundrett - 2018 - New Phytologist -

Evolutionary history of mycorrhizal symbioses and global host plant diversity - Brundrett - 2018 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
The majority of vascular plants are mycorrhizal: 72% are arbuscular mycorrhizal (AM), 2.0% are ectomycorrhizal (EcM), 1.5% are ericoid mycorrhizal and 10% are orchid mycorrhizal. Just 8% are completely nonmycorrhizal (NM), whereas 7% have inconsistent NM–AM associations. Most NM and NM–AM plants are nutritional specialists (e.g. carnivores and parasites) or habitat specialists (e.g. hydrophytes and epiphytes). Mycorrhizal associations are consistent in most families, but there are exceptions with complex roots (e.g. both EcM and AM). We recognize three waves of mycorrhizal evolution, starting with AM in early land plants, continuing in the Cretaceous with multiple new NM or EcM linages, ericoid and orchid mycorrhizas. The third wave, which is recent and ongoing, has resulted in root complexity linked to rapid plant diversification in biodiversity hotspots.
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Partner communication and role of nutrients in the arbuscular mycorrhizal symbiosis - Lanfranco - 2018 - New Phytologist -

Partner communication and role of nutrients in the arbuscular mycorrhizal symbiosis - Lanfranco - 2018 - New Phytologist - | Plant roots and rhizosphere | Scoop.it
The evolutionary and ecological success of the arbuscular mycorrhizal (AM) symbiosis relies on an efficient and multifactorial communication system for partner recognition, and on a fine‐tuned and reciprocal metabolic regulation of each symbiont to reach an optimal functional integration. Besides strigolactones, N‐acetylglucosamine‐derivatives released by the plant were recently suggested to trigger fungal reprogramming at the pre‐contact stage. Remarkably, N‐acetylglucosamine‐based diffusible molecules also are symbiotic signals produced by AM fungi (AMF) and clues on the mechanisms of their perception by the plant are emerging. AMF genomes and transcriptomes contain a battery of putative effector genes that may have conserved and AMF‐ or host plant‐specific functions. Nutrient exchange is the key feature of AM symbiosis. A mechanism of phosphate transport inside fungal hyphae has been suggested, and first insights into the regulatory mechanisms of root colonization in accordance with nutrient transfer and status were obtained. The recent discovery of the dependency of AMF on fatty acid transfer from the host has offered a convincing explanation for their obligate biotrophism. Novel studies highlighted the importance of plant and fungal genotypes for the outcome of the symbiosis. These findings open new perspectives for fundamental research and application of AMF in agriculture.
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