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Frontiers | Effector candidates in the secretome of Piriformospora indica, a ubiquitous plant-associated fungus

Frontiers | Effector candidates in the secretome of Piriformospora indica, a ubiquitous plant-associated fungus | MycorWeb Plant-Microbe Interactions | Scoop.it
One of the emerging systems in plant-microbe interaction is the study of proteins, referred to as effectors, secreted by microbes in order to modulate host cells function and structure and to promote microbial growth on plant tissue. Current knowledge on fungal effectors derives mainly from biotrophic and hemibiotrophic plant fungal pathogens that have a limited host range. Here, we focus on effectors of Piriformospora indica, a soil borne endophyte forming intimate associations with roots of a wide range of plant species. Complete genome sequencing provides an opportunity to investigate the role of effectors during the interaction of this mutualistic fungus with plants. We describe in silico analyses to predict effectors of P. indica and we explore effector features considered here to mine a high priority protein list for functional analysis.
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Rescooped by Francis Martin from Plant-Microbe Symbiosis
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Root-Associated Fungi Shared Between Arbuscular Mycorrhizal and Ectomycorrhizal Conifers in a Temperate Forest

Root-Associated Fungi Shared Between Arbuscular Mycorrhizal and Ectomycorrhizal Conifers in a Temperate Forest | MycorWeb Plant-Microbe Interactions | Scoop.it
Arbuscular mycorrhizal and ectomycorrhizal symbioses are among the most important drivers of terrestrial ecosystem dynamics. Historically, the two types of symbioses have been investigated separately because arbuscular mycorrhizal and ectomycorrhizal plant species are considered to host discrete sets of fungal symbionts (i.e., arbuscular mycorrhizal and ectomycorrhizal fungi, respectively). Nonetheless, recent studies based on high-throughput DNA sequencing technologies have suggested that diverse non-mycorrhizal fungi (e.g., endophytic fungi) with broad host ranges play roles in relationships between arbuscular mycorrhizal and ectomycorrhizal plant species in forest ecosystems. By analyzing an Illumina sequencing dataset of root-associated fungi in a temperate forest in Japan, we statistically examined whether co-occurring arbuscular mycorrhizal (Chamaecyparis obtusa) and ectomycorrhizal (Pinus densiflora) plant species could share non-mycorrhizal fungal communities. Among the 919 fungal operational taxonomic units (OTUs) detected, OTUs in various taxonomic lineages were statistically designated as “generalists,” which associated commonly with both coniferous species. The list of the generalists included fungi in the genera Meliniomyces, Oidiodendron, Cladophialophora, Rhizodermea, Penicillium, and Mortierella. Meanwhile, our statistical analysis also detected fungi preferentially associated with Chamaecyparis (e.g., Pezicula) or Pinus (e.g., Neolecta). Overall, this study provides a basis for future studies on how arbuscular mycorrhizal and ectomycorrhizal plant species interactively drive community- or ecosystem-scale processes. The physiological functions of the fungi highlighted in our host-preference analysis deserve intensive investigations for understanding their roles in plant endosphere and rhizosphere.


Via Jean-Michel Ané
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The origin and evolution of mycorrhizal symbioses: from palaeomycology to phylogenomics - Strullu‐Derrien - - New Phytologist - Wiley Online Library

The origin and evolution of mycorrhizal symbioses: from palaeomycology to phylogenomics - Strullu‐Derrien - - New Phytologist - Wiley Online Library | MycorWeb Plant-Microbe Interactions | Scoop.it
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.

Via Jonathan Plett
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Debate: On the place of mankind in evolution, ethics and nutrition

Debate: On the place of mankind in evolution, ethics and nutrition | MycorWeb Plant-Microbe Interactions | Scoop.it
This anthropocentric vision describing humans as the ultimate step of evolution goes together with moral and religious developments described in several religions that propose that humanity was chosen by God or indicating that God has created us in his own image or else that God can occasionally present Himself under a human appearance. The last of these is not unique to monotheist religions as in polytheist Greek or Latin religions, where gods can easily acquire a human appearance, in particular to seduce attractive young women. Beyond the anecdote, these dated phylogenetic trees and those much more ancestral beliefs reflect the propensity of humankind to consider itself as superior to other biological organisms. Or is it to reassure ourselves?
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Extracellular Vesicle RNA: A Universal Mediator of Microbial Communication?

Extracellular Vesicle RNA: A Universal Mediator of Microbial Communication? | MycorWeb Plant-Microbe Interactions | Scoop.it
Both extracellular RNAs and extracellular vesicles (EVs) have recently garnered attention as novel mediators of intercellular communication in eukaryotes and prokaryotes alike. EVs not only permit export of RNA, but also facilitate delivery and trans-kingdom exchange of these and other biomolecules, for instance between microbes and their hosts. In this Opinion article, we propose that EV-mediated export of RNA represents a universal mechanism for interkingdom and intrakingdom communication that is conserved among bacterial, archaeal, and eukaryotic microbes. We speculate how microbes might use EV RNA to influence target cell gene expression or manipulate host immune responses.

Via Jonathan Plett
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The genome and microbiome of a dikaryotic fungus (Inocybe terrigena, Inocybaceae) revealed by metagenomics

The genome and microbiome of a dikaryotic fungus (Inocybe terrigena, Inocybaceae) revealed by metagenomics | MycorWeb Plant-Microbe Interactions | Scoop.it
Recent advances in molecular methods have increased our understanding of various fungal symbioses. However, little is known about genomic and microbiome features of most uncultured symbiotic fungal clades. Here, we analysed the genome and microbiome of Inocybaceae (Agaricales, Basidiomycota), a largely uncultured ectomycorrhizal clade known to form symbiotic associations with a wide variety of plant species. We used metagenomic sequencing and assembly of dikaryotic fruiting‐body tissues from Inocybe terrigena (Fr.) Kuyper, to classify fungal and bacterial genomic sequences, and obtained a nearly complete fungal genome containing 93% of core eukaryotic genes. Comparative genomics reveals that I. terrigena is more similar to ectomycorrhizal and brown rot fungi than to white rot fungi. The reduction in lignin degradation capacity has been independent from and significantly faster than in closely related ectomycorrhizal clades supporting that ectomycorrhizal symbiosis evolved independently in Inocybe. The microbiome of I. terrigena fruiting‐bodies includes bacteria with known symbiotic functions in other fungal and non‐fungal host environments, suggesting potential symbiotic functions of these bacteria in fungal tissues regardless of habitat conditions. Our study demonstrates the usefulness of direct metagenomics analysis of fruiting‐body tissues for characterizing fungal genomes and microbiome.
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Fungal Phytotoxin Lasiojasmonate A Activates the Plant Jasmonic Acid Pathway | Journal of Experimental Botany | Oxford Academic

Jasmonates are signaling compounds that regulate plant responses to stress. Jasmonic acid (JA) is the direct precursor of the bioactive plant hormone JA-Ile, the ligand of the COI1-JAZ co-receptor complex. JA, its methyl ester and three furanonyl esters were recently isolated from the grapevine pathogen Lasiodiplodia mediterannea sp. The JA ester lasiojasmonate A (LasA) is the first reported naturally occurring JA-furanone, whose mode of action is currently unexplored. Here we show that LasA activates many JA-regulated responses in planta, including protein degradation, gene expression, and physiological processes. These in vivo effects required LasA conversion into JA, formation of JA-Ile and its recognition by the plant JA-Ile perception complex. These data suggest a mode of action of the natural fungal LasA as an inactive JA pool that can be transformed into the bioactive JA-Ile form. We propose that fungal production of JA derivates such as LasA occur at late infection stages to induce plant JA responses such as cell death, and facilitate fungal infection.

Via Philip Carella
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A genomics-informed study of oxalate and cellulase regulation by brown rot wood-degrading fungi

A genomics-informed study of oxalate and cellulase regulation by brown rot wood-degrading fungi | MycorWeb Plant-Microbe Interactions | Scoop.it
Highlights 
• We grew brown rot fungi directionally in wood to map oxalate and cellulase regulation. 
• Oxalate was up-regulated before the onset of cellulases, then consistently stabilized. 
• Overlays provide gene-level insight on how and why brown rot fungi optimize oxalate. 

Abstract.  Wood-degrading fungi that selectively remove carbohydrates (brown rot) combine Fenton-based oxidation and enzymatic hydrolysis to degrade wood. These two steps are incompatible in close proximity. To explain this, brown rot fungi may stagger oxidative reactions ahead of hydrolysis, but the scale and environmental controls for such a mechanism have not been resolved in solid wood. Here, we focused on one reaction control parameter, oxalate. In coordination with Fe3+-reducing compounds (e.g., 2,5-dimethoxyhydroquinone), oxalate can either promote Fenton chemistry by mobilizing Fe3+ as mono-oxalates (facilitative) or inhibit Fenton chemistry (protective) by restricting reducibility and the formation of Fenton’s reagent as Fe3+/Fe2-(oxalate)2,3. Here, we sectioned wood wafers colonized directionally by Postia placenta and Gloeophyllum trabeum to map end-to-end the expression of oxalate synthesis genes and to overlay enzyme activities, metabolites, and wood modifications. Near advancing hyphal fronts, oxaloacetase expression was up upregulated for both fungi, while regulation patterns of paralogous of isocitrate lyases and glyoxylate dehydrogenases varied, suggesting different physiological roles. Oxalate decarboxylase (ODC) expression in G. trabeum was induced in more decayed wood behind the hyphal front, but was constitutively expressed in all P. placenta sections. Relative ODC activities increased and oxalate levels stabilized in more decayed wood behind the hyphal front. Endoglucanase (EG) activity, on the other hand, peaked for both fungi in later decay stages. These oxalate optimization patterns are in line with previous whole-block ‘spiking’ experiments tracking oxalate, but we provide here information on its genetic controls across a spatial gradient. As a complement, we also demonstrate in vitro the plausibility of a protective role for oxalate, to emphasize that these fungi might be optimizing oxalate at a given level to maximize Fenton reactions but to minimize oxidative damage.

Via Steve Marek
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Current Opinion Plant Biology: Extracellular vesicles as key mediators of plant–microbe interactions (2018)

Current Opinion Plant Biology: Extracellular vesicles as key mediators of plant–microbe interactions (2018) | MycorWeb Plant-Microbe Interactions | Scoop.it
• Plants produce extracellular vesicles (EVs) in response to infection.• Recent advances in EV purification are now revealing the contents of plant EVs.• Plant EVs are enriched in stress-response proteins and signaling lipids.• EVs contain transporters for antimicrobial compounds such as glucosinolates.• Indirect evidence suggests that EVs may mediate inter-kingdom RNA interference.

Extracellular vesicles (EVs) are lipid compartments capable of trafficking proteins, lipids, RNA and metabolites between cells. Plant cells have been shown to secrete EVs during immune responses, but virtually nothing is known about their formation, contents or ultimate function. Recently developed methods for isolating plant EVs have revealed that these EVs are enriched in stress response proteins and signaling lipids, and appear to display antifungal activity. Comparison to work on animal EVs, and the observation that host-derived small interfering RNAs and microRNAs can silence fungal genes, suggests that plant EVs may also mediate trans-kingdom RNA interference. Many fundamental questions remain, however, regarding how plant EVs are produced, how they move, and if and how they are taken up by target cells.


Via Kamoun Lab @ TSL
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Tracing the role of human civilization in the globalization of plant pathogens

Tracing the role of human civilization in the globalization of plant pathogens | MycorWeb Plant-Microbe Interactions | Scoop.it
Co-evolution between plants and parasites, including herbivores and pathogens, has arguably generated much of Earth’s biological diversity. Within an ecosystem, co-evolution of plants and pathogens is a stepwise reciprocal evolutionary interaction: epidemics result in intense selection pressures on both host and pathogen populations, ultimately allowing long-term persistence and ecosystem stability. Historically, plants, and pathogens evolved in unique regional assemblages, largely isolated from other assemblages by geographical barriers. When barriers are broken, non-indigenous pathogenic organisms are introduced into new environments, potentially finding suitable hosts lacking resistance genes and environments favouring pathogenic behavior; this process may result in epidemics of newly emerging diseases. Biological invasions are tightly linked to human activities and have been a constant feature throughout human history. Several pathways enable pathogens to enter new environments, the great majority being human mediated.
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The fungus that came in from the cold: dry rot’s pre-adapted ability to invade buildings

The fungus that came in from the cold: dry rot’s pre-adapted ability to invade buildings | MycorWeb Plant-Microbe Interactions | Scoop.it
Many organisms benefit from being pre-adapted to niches shaped by human activity, and have successfully invaded man-made habitats. One such species is the dry rot fungus Serpula lacrymans, which has a wide distribution in buildings in temperate and boreal regions, where it decomposes coniferous construction wood. Comparative genomic analyses and growth experiments using this species and its wild relatives revealed that S. lacrymans evolved a very effective brown rot decay compared to its wild relatives, enabling an extremely rapid decay in buildings under suitable conditions. Adaptations in intracellular transport machineries promoting hyphal growth, and nutrient and water transport may explain why it is has become a successful invader of timber in houses. Further, we demonstrate that S. lacrymans has poor combative ability in our experimental setup, compared to other brown rot fungi. In sheltered indoor conditions, the dry rot fungus may have limited encounters with other wood decay fungi compared to its wild relatives. Overall, our analyses indicate that the dry rot fungus is an ecological specialist with poor combative ability against other fungi.
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Highlighting patterns of fungal diversity and composition shaped by ocean currents using the East China Sea as a model

Highlighting patterns of fungal diversity and composition shaped by ocean currents using the East China Sea as a model | MycorWeb Plant-Microbe Interactions | Scoop.it
How ocean currents shape fungal transport, dispersal and more broadly fungal biogeography remains poorly understood. The East China Sea (ECS) is a complex and dynamic habitat with different water masses blending microbial communities. The internal transcribed spacer 2 region of fungal rDNA was analysed in water and sediment samples directly collected from the coastal (CWM), Kuroshio (KSWM), Taiwan warm (TWM) and the shelf mixed water mass (MWM), coupled with hydrographic properties measurements, to determine how ocean currents impact the fungal community composition. Almost 9k fungal operational taxonomic units (OTUs) spanning six phyla, 25 known classes, 102 orders and 694 genera were obtained. The typical terrestrial and freshwater fungal genus, Byssochlamys, was dominant in the CWM, while increasing abundance of a specific OTU affiliated with Aspergillus was revealed from coastal to open ocean water masses (TWM and KSWM). Compared with water samples, sediment harboured an increased diversity with distinct fungal communities. The proximity of the Yangtze and Qiantang estuaries homogenizes the surface water and sediment communities. A significant influence of ocean currents on community structure was found, which is believed to reduce proportionally the variation explained by environmental parameters at the scale of the total water masses. Dissolved oxygen and depth were identified as the major parameters structuring the fungal community. Our results indicate that passive fungal dispersal driven by ocean currents and river run‐off, in conjunction with the distinct hydrographic conditions of individual water masses, shapes the fungal community composition and distribution pattern in the ECS.
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Genomic changes associated with the evolutionary transitions of Nostoc to a plant symbiont

Genomic changes associated with the evolutionary transitions of Nostoc to a plant symbiont | MycorWeb Plant-Microbe Interactions | Scoop.it

The cyanobacteria belonging to the genus Nostoc comprise free-living strains but also facultative plant-symbionts. Symbiotic strains can enter into symbiosis with taxonomically diverse range of host plants. Little is known about genomic changes associated with evolutionary transition of Nostoc from free-living to plant symbiont. Here we compared the genomes derived from eleven symbiotic Nostoc strains isolated from different host plants and infer phylogenetic relationships between strains. Phylogenetic reconstructions of 89 Nostocales showed that symbiotic Nostoc strains with a broad host range, entering epiphytic and intracellular or extracellular endophytic interactions, form a monophyletic clade indicating a common evolutionary history. A polyphyletic origin was found for Nostoc strains which enter only extracellular symbioses, and inference of transfer events implied that this trait was likely acquired several times in the evolution of the Nostocales. Symbiotic Nostoc strains showed enriched functions in transport and metabolism of organic sulfur, chemotaxis and motility, as well as the uptake of phosphate, branched-chain amino acid, and ammonium. The genomes of the intracellular clade differ from that of other Nostoc strains, with a gain/enrichment of genes encoding proteins to generate L-methionine from sulfite and pathways for the degradation of the plant metabolites vanillin and vanillate, and of the macromolecule xylan present in plant cell-walls. These compounds could function as C sources for members of the intracellular clade. Molecular clock analysis indicated that the intracellular clade emerged ca. 600 million years ago, suggesting that intracellular Nostoc symbioses predate the origin of land plants and the emergence of their extant hosts.


Via Pierre-Marc Delaux, Steve Marek
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Analysis of Human Sequence Data Reveals Two Pulses of Archaic Denisovan Admixture

Analysis of Human Sequence Data Reveals Two Pulses of Archaic Denisovan Admixture | MycorWeb Plant-Microbe Interactions | Scoop.it

Anatomically modern humans interbred with Neanderthals and with a related archaic population known as Denisovans. Genomes of several Neanderthals and one Denisovan have been sequenced, and these reference genomes have been used to detect introgressed genetic material in present-day human genomes. Segments of introgression also can be detected without use of reference genomes, and doing so can be advantageous for finding introgressed segments that are less closely related to the sequenced archaic genomes. We apply a new reference-free method for detecting archaic introgression to 5,639 whole-genome sequences from Eurasia and Oceania. We find Denisovan ancestry in populations from East and South Asia and Papuans. Denisovan ancestry comprises two components with differing similarity to the sequenced Altai Denisovan individual. This indicates that at least two distinct instances of Denisovan admixture into modern humans occurred, involving Denisovan populations that had different levels of relatedness to the sequenced Altai Denisovan.


Via Pierre Gladieux, Niklaus Grunwald
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Intraspecific comparative genomics of isolates of the Norway spruce pathogen (Heterobasidion parviporum) and identification of its potential virulence factors 

Intraspecific comparative genomics of isolates of the Norway spruce pathogen (Heterobasidion parviporum) and identification of its potential virulence factors  | MycorWeb Plant-Microbe Interactions | Scoop.it
Heterobasidion parviporum is an economically most important fungal forest pathogen in northern Europe, causing root and butt rot disease of Norway spruce (Picea abies (L.) Karst.). The mechanisms underlying the pathogenesis and virulence of this species remain elusive. No reference genome to facilitate functional analysis is available for this species. To better understand the virulence factor at both phenotypic and genomic level, we characterized 15 H. parviporum isolates originating from different locations across Finland for virulence, vegetative growth, sporulation and saprotrophic wood decay. Wood decay capability and latitude of fungal origins exerted interactive effects on their virulence and appeared important for H. parviporum virulence. We sequenced the most virulent isolate, the first full genome sequences of H. parviporum as a reference genome, and re-sequenced the remaining 14 H. parviporum isolates. Genome-wide alignments and intrinsic polymorphism analysis showed that these isolates exhibited overall high genomic similarity with an average of at least 96% nucleotide identity when compared to the reference, yet had remarkable intra-specific level of polymorphism with a bias for CpG to TpG mutations. Reads mapping coverage analysis enabled the classification of all predicted genes into five groups and uncovered two genomic regions exclusively present in the reference with putative contribution to its higher virulence. Genes enriched for copy number variations (deletions and duplications) and nucleotide polymorphism were involved in oxidation-reduction processes and encoding domains relevant to transcription factors. Some secreted protein coding genes based on the genome-wide selection pressure, or the presence of variants were proposed as potential virulence candidates. Our study reported on the first reference genome sequence for this Norway spruce pathogen (H. parviporum). Comparative genomics analysis gave insight into the overall genomic variation among this fungal species and also facilitated the identification of several secreted protein coding genes as putative virulence factors for the further functional analysis. We also analyzed and identified phenotypic traits potentially linked to its virulence.
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Divergence of Funneliformis mosseae populations over 20 years of laboratory cultivation, as revealed by vegetative incompatibility and molecular analysis

Arbuscular mycorrhizal fungi (AMF) are widespread, important plant symbionts. They absorb and translocate mineral nutrients from the soil to host plants through an extensive extraradical mycelium, consisting of indefinitely large networks of nonseptate, multinucleated hyphae which may be interconnected by hyphal fusions (anastomoses). This work investigated whether different lineages of the same isolate may lose the ability to establish successful anastomoses, becoming vegetatively incompatible, when grown separately. The occurrence of hyphal incompatibility among five lineages of Funneliformis mosseae, originated from the same ancestor isolate and grown in vivo for more than 20 years in different European locations, was assessed by systematic detection of anastomosis frequency and cytological studies. Anastomosis frequencies ranged from 60 to 80% within the same lineage and from 17 to 44% among different lineages. The consistent detection of protoplasm continuity and nuclei in perfect fusions showed active protoplasm flow both within and between lineages. In pairings between different lineages, post-fusion incompatible reactions occurred in 6–48% of hyphal contacts and pre-fusion incompatibility in 2–17%. Molecular fingerprinting profiles showed genetic divergence among lineages, with overall Jaccard similarity indices ranging from 0.85 to 0.95. Here, phenotypic divergence among the five F. mosseae lineages was demonstrated by the reduction of their ability to form anastomosis and the detection of high levels of vegetative incompatibility. Our data suggest that potential genetic divergence may occur in AMF over only 20 years and represent the basis for detailed studies on the relationship between genes regulating anastomosis formation and hyphal compatibility in AMF.


Via Jean-Michel Ané
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Using Hierarchical Clustering of Secreted Protein Families to Classify and Rank Candidate Effectors of Rust Fungi

Using Hierarchical Clustering of Secreted Protein Families to Classify and Rank Candidate Effectors of Rust Fungi | MycorWeb Plant-Microbe Interactions | Scoop.it
Rust fungi are obligate biotrophic pathogens that cause considerable damage on crop plants. Puccinia graminis f. sp. tritici, the causal agent of wheat stem rust, and Melampsora larici-populina, the poplar leaf rust pathogen, have strong deleterious impacts on wheat and poplar wood production, respectively. Filamentous pathogens such as rust fungi secrete molecules called disease effectors that act as modulators of host cell physiology and can suppress or trigger host immunity. Current knowledge on effectors from other filamentous plant pathogens can be exploited for the characterisation of effectors in the genome of recently sequenced rust fungi. We designed a comprehensive in silico analysis pipeline to identify the putative effector repertoire from the genome of two plant pathogenic rust fungi. The pipeline is based on the observation that known effector proteins from filamentous pathogens have at least one of the following properties: (i) contain a secretion signal, (ii) are encoded by in planta induced genes, (iii) have similarity to haustorial proteins, (iv) are small and cysteine rich, (v) contain a known effector motif or a nuclear localization signal, (vi) are encoded by genes with long intergenic regions, (vii) contain internal repeats, and (viii) do not contain PFAM domains, except those associated with pathogenicity. We used Markov clustering and hierarchical clustering to classify protein families of rust pathogens and rank them according to their likelihood of being effectors. Using this approach, we identified eight families of candidate effectors that we consider of high value for functional characterization. This study revealed a diverse set of candidate effectors, including families of haustorial expressed secreted proteins and small cysteine-rich proteins. This comprehensive classification of candidate effectors from these devastating rust pathogens is an initial step towards probing plant germplasm for novel resistance components.
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Evidence of non-tandemly repeated rDNAs and their intragenomic heterogeneity in Rhizophagus irregularis

Arbuscular mycorrhizal fungus (AMF) species are one of the most widespread symbionts of land plants. Our substantially improved reference genome assembly of a model AMF, Rhizophagus irregularis DAOM-181602 (total contigs = 210), facilitated discovery of repetitive elements with unusual characteristics. R. irregularis has only ten or eleven copies of complete 45S rDNAs, whereas the general eukaryotic genome has tens to thousands of rDNA copies. R. irregularis rDNAs are highly heterogeneous and lack a tandem repeat structure. These findings provide evidence for the hypothesis that rDNA heterogeneity depends on the lack of tandem repeat structures. RNA-Seq analysis confirmed that all rDNA variants are actively transcribed. Observed rDNA/rRNA polymorphisms may modulate translation by using different ribosomes depending on biotic and abiotic interactions. The non-tandem repeat structure and intragenomic heterogeneity of AMF rDNA/rRNA may facilitate adaptation to a various environmental condition including the broad host range.


Via Pierre-Marc Delaux
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10KP: A phylodiverse genome sequencing plan | GigaScience | Oxford Academic

10KP: A phylodiverse genome sequencing plan | GigaScience | Oxford Academic | MycorWeb Plant-Microbe Interactions | Scoop.it
Understanding plant evolution and diversity in a phylogenomic context is an enormous challenge due, in part, to limited availability of genome-scale data across phylodiverse species. The 10KP (10,000 Plants) Genome Sequencing Project will sequence and characterize representative genomes from every major clade of embryophytes, green algae, and protists (excluding fungi) within the next 5 years. By implementing and continuously improving leading-edge sequencing technologies and bioinformatics tools, 10KP will catalogue the genome content of plant and protist diversity and make these data freely available as an enduring foundation for future scientific discoveries and applications. 10KP is structured as an international consortium, open to the global community, including botanical gardens, plant research institutes, universities, and private industry. Our immediate goal is to establish a policy framework for this endeavor, the principles of which are outlined here
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Effects of timber harvesting on the genetic potential for carbon and nitrogen cycling in five North American forest ecozones

Effects of timber harvesting on the genetic potential for carbon and nitrogen cycling in five North American forest ecozones | MycorWeb Plant-Microbe Interactions | Scoop.it

Forest ecosystems are critical to global biogeochemical cycles but under pressure from harvesting and climate change. We investigated the effects of organic matter (OM) removal during forest harvesting on the genetic potential of soil communities for biomass decomposition and nitrogen cycling in five ecozones across North America. We analyzed 107 samples, representing four treatments with varied levels of OM removal, at Long-Term Soil Productivity Study sites. Samples were collected more than ten years after harvesting and replanting and were analyzed via shotgun metagenomics. High-quality short reads totaling 1.2 Tbp were compared to the Carbohydrate Active Enzyme (CAZy) database and a custom database of nitrogen cycle genes. Gene profile variation was mostly explained by ecozone and soil layer. Eleven CAZy and nine nitrogen cycle gene families were associated with particular soil layers across all ecozones. Treatment effects on gene profiles were mainly due to harvesting, and only rarely to the extent of OM removal. Harvesting generally decreased the relative abundance of CAZy genes while increasing that of nitrogen cycle genes, although these effects varied among ecozones. Our results suggest that ecozone-specific nutrient availability modulates the sensitivity of the carbon and nitrogen cycles to harvesting with possible consequences for long-term forest sustainability.


Via Petr Baldrian
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The origin and evolution of mycorrhizal symbioses: from palaeomycology to phylogenomics

The origin and evolution of mycorrhizal symbioses: from palaeomycology to phylogenomics | MycorWeb Plant-Microbe Interactions | Scoop.it
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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Host‐ and stage‐dependent secretome of the arbuscular mycorrhizal fungus Rhizophagus irregularis 

Arbuscular mycorrhizal fungi form the most wide-spread endosymbiosis with plants. There is very little host-specificity in this interaction, however host preferences as well as varying symbiotic efficiencies have been observed. We hypothesize that secreted proteins (SPs) may act as fungal effectors to control symbiotic efficiency in a host-dependent manner. Therefore, we studied whether AM fungi adjust their secretome in a host- and stage-dependent manner to contribute to their extremely wide host-range. We investigated the expression of SP-encoding genes of Rhizophagus irregularis in three evolutionary distantly-related plant species, Medicago truncatula, Nicotiana benthamiana and Allium schoenoprasum. In addition we used laser microdissection in combination with RNAseq to study SP expression at different stages of the interaction in Medicago. Our data indicate that most expressed SPs show roughly equal expression levels in the interaction with all three host plants. In addition, a subset shows significant differential expression depending on the host plant. Furthermore, SP expression is controlled locally in the hyphal network in response to host dependent cues. Overall, this study presents a comprehensive analysis of the R. irregularis secretome, which now offers a solid basis to direct functional studies on the role of fungal SPs in AM symbiosis. This article is protected by copyright. All rights reserved.

Via Pierre-Marc Delaux
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A single fungal MAP kinase controls plant cell-to-cell invasion by the rice blast fungus

A single fungal MAP kinase controls plant cell-to-cell invasion by the rice blast fungus | MycorWeb Plant-Microbe Interactions | Scoop.it
Blast disease destroys up to 30% of the rice crop annually and threatens global food security. The blast fungus Magnaporthe oryzae invades plant tissue with hyphae that proliferate and grow from cell to cell, often through pit fields, where plasmodesmata cluster. We showed that chemical genetic inhibition of a single fungal mitogen-activated protein (MAP) kinase, Pmk1, prevents M. oryzae from infecting adjacent plant cells, leaving the fungus trapped within a single plant cell. Pmk1 regulates expression of secreted fungal effector proteins implicated in suppression of host immune defenses, preventing reactive oxygen species generation and excessive callose deposition at plasmodesmata. Furthermore, Pmk1 controls the hyphal constriction required for fungal growth from one rice cell to the neighboring cell, enabling host tissue colonization and blast disease.
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Rescooped by Francis Martin from Plant-Microbe Symbiosis
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Identification and Expression Analysis of Medicago truncatula Isopentenyl Transferase Genes (IPTs) Involved in Local and Systemic Control of Nodulation 

Identification and Expression Analysis of Medicago truncatula Isopentenyl Transferase Genes (IPTs) Involved in Local and Systemic Control of Nodulation  | MycorWeb Plant-Microbe Interactions | Scoop.it
Cytokinins are essential for legume plants to establish a nitrogen-fixing symbiosis with rhizobia. Recently, the expression level of cytokinin biosynthesis IPTs (ISOPENTENYLTRANSFERASES) genes was shown to be increased in response to rhizobial inoculation in Lotus japonicus, Medicago truncatula and Pisum sativum. In addition to its well-established positive role in nodule primordium initiation in root cortex, cytokinin negatively regulates infection processes in the epidermis. Moreover, it was reported that shoot-derived cytokinin inhibits the subsequent nodule formation through AON (autoregulation of nodulation) pathway. In L. japonicus, LjIPT3 gene was shown to be activated in the shoot phloem via the components of AON system, negatively affecting nodulation. However, in M. truncatula, the detailed analysis of MtIPTs expression, both in roots and shoots, in response to nodulation has not been performed yet, and the link between IPTs and AON has not been studied so far. In this study, we performed an extensive analysis of MtIPTs expression levels in different organs, focusing on the possible role of MtIPTs in nodule development. MtIPTs expression dynamics in inoculated roots suggest that besides its early established role in the nodule primordia development, cytokinin may be also important for later stages of nodulation. According to expression analysis, MtIPT3, MtIPT4, and MtIPT5 are activated in the shoots in response to inoculation. Among these genes, MtIPT3 is the only one the induction of which was not observed in leaves of the sunn-3 mutant defective in CLV1-like kinase, the key component of AON, suggesting that MtIPT3 is activated in the shoots in an AON-dependent manner. Taken together, our findings suggest that MtIPTs are involved in the nodule development at different stages, both locally in inoculated roots and systemically in shoots, where their expression can be activated in an AON-dependent manner.

Via Christophe Jacquet, Jean-Michel Ané
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Scaling up: A guide to high‐throughput genomic approaches for biodiversity analysis

Scaling up: A guide to high‐throughput genomic approaches for biodiversity analysis | MycorWeb Plant-Microbe Interactions | Scoop.it
The purpose of this review is to present the most common and emerging DNA‐based methods used to generate data for biodiversity and biomonitoring studies. As environmental assessment and monitoring programmes may require biodiversity information at multiple levels, we pay particular attention to the DNA metabarcoding method and discuss a number of bioinformatic tools and considerations for producing DNA‐based indicators using operational taxonomic units (OTUs), taxa at a variety of ranks and community composition. By developing the capacity to harness the advantages provided by the newest technologies, investigators can “scale up” by increasing the number of samples and replicates processed, the frequency of sampling over time and space, and even the depth of sampling such as by sequencing more reads per sample or more markers per sample. The ability to scale up is made possible by the reduced hands‐on time and cost per sample provided by the newest kits, platforms and software tools. Results gleaned from broad‐scale monitoring will provide opportunities to address key scientific questions linked to biodiversity and its dynamics across time and space as well as being more relevant for policymakers, enabling science‐based decision‐making, and provide a greater socio‐economic impact. As genomic approaches are continually evolving, we provide this guide to methods used in biodiversity genomics.
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Rescooped by Francis Martin from Plants & Evolution
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Out of Water: The Origin and Early Diversification of Plant R-Genes

Out of Water: The Origin and Early Diversification of Plant R-Genes | MycorWeb Plant-Microbe Interactions | Scoop.it
During plant-pathogen interactions, plants use intracellular proteins with nucleotide-binding site and leucine-rich repeat (NBS-LRR) domains to detect pathogens. NBS-LRR proteins represent a major class of plant disease resistance genes (R-genes). Whereas R-genes have been well characterized in angiosperms, little is known about their origin and early diversification. Here we perform comprehensive evolutionary analyses of R-genes in plants and report the identification of R-genes in basal-branching streptophytes, including charophytes, liverworts, and mosses. Phylogenetic analyses suggest that plant R-genes originated in charophytes and R-proteins diversified into TIR-NBS-LRR proteins (TNLs) and non-TIR-NBS-LRR proteins (nTNLs) in charophytes. Moreover, we show that plant R-proteins evolved in a modular fashion through frequent gain or loss of protein domains. Most of the R-genes in basal-branching streptophytes underwent adaptive evolution, indicating an ancient involvement of R-genes in plant-pathogen interactions. Our findings provide novel insights into the origin and evolution of R-genes and the mechanisms underlying colonization of terrestrial environments by plants.

Via Pierre-Marc Delaux
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