MycorWeb Plant-Microbe Interactions
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The Structure, Distribution, and Biomass of the World's Forests

The Structure, Distribution, and Biomass of the World's Forests | MycorWeb Plant-Microbe Interactions | Scoop.it

Forests are the dominant terrestrial ecosystem on Earth. We review the environmental factors controlling their structure and global distribution and evaluate their current and future trajectory. Adaptations of trees to climate and resource gradients, coupled with disturbances and forest dynamics, create complex geographical patterns in forest assemblages and structures. These patterns are increasingly discernible through new satellite and airborne observation systems, improved forest inventories, and global ecosystem models. Forest biomass is a complex property affected by forest distribution, structure, and ecological processes. Since at least 1990, biomass density has consistently increased in global established forests, despite increasing mortality in some regions, suggesting that a global driver such as elevated CO2 may be enhancing biomass gains. Global forests have also apparently become more dynamic. Advanced information about the structure, distribution, and biomass of the world's forests provides critical ecological insights and opportunities for sustainable forest management and enhancing forest conservation and ecosystem services.

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The receptor kinase FER is a RALF-regulated scaffold controlling plant immune signaling

The receptor kinase FER is a RALF-regulated scaffold controlling plant immune signaling | MycorWeb Plant-Microbe Interactions | Scoop.it

RALFs (rapid alkalinization factors), a family of small peptides in plants, are produced in response to rapidly changing conditions. Stegmann et al. studied the agility and diversity built into this signaling network. Some RALFs, such as RALF23 and its relative RALF33, are activated by proteolytic cleavage. Others, such as RALF32, are not. RALF23 and RALF33 are called into play after a pathogen triggers immune responses. RALF32, on the other hand, regulates seedling growth. All three of these RALFs use the same receptor kinase, which can interact with other signaling components. Thus, plant responses can be fine-tuned by rapid release of peptides.

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Shift in fungal communities and associated enzyme activities along an age gradient of managed Pinus sylvestris stands

Shift in fungal communities and associated enzyme activities along an age gradient of managed Pinus sylvestris stands | MycorWeb Plant-Microbe Interactions | Scoop.it
Forestry reshapes ecosystems with respect to tree age structure, soil properties and vegetation composition. These changes are likely to be paralleled by shifts in microbial community composition with potential feedbacks on ecosystem functioning. Here, we assessed fungal communities across a chronosequence of managed Pinus sylvestris stands and investigated correlations between taxonomic composition and extracellular enzyme activities. Not surprisingly, clear-cutting had a negative effect on ectomycorrhizal fungal abundance and diversity. In contrast, clear-cutting favoured proliferation of saprotrophic fungi correlated with enzymes involved in holocellulose decomposition. During stand development, the re-establishing ectomycorrhizal fungal community shifted in composition from dominance by Atheliaceae in younger stands to Cortinarius and Russula species in older stands. Late successional ectomycorrhizal taxa correlated with enzymes involved in mobilisation of nutrients from organic matter, indicating intensified nutrient limitation. Our results suggest that maintenance of functional diversity in the ectomycorrhizal fungal community may sustain long-term forest production by retaining a capacity for symbiosis-driven recycling of organic nutrient pools.
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Tracing the peopling of the world through genomics

Tracing the peopling of the world through genomics | MycorWeb Plant-Microbe Interactions | Scoop.it


Advances in the sequencing and the analysis of the genomes of both modern and ancient peoples have facilitated a number of breakthroughs in our understanding of human evolutionary history. These include the discovery of interbreeding between anatomically modern humans and extinct hominins; the development of an increasingly detailed description of the complex dispersal of modern humans out of Africa and their population expansion worldwide; and the characterization of many of the genetic adaptions of humans to local environmental conditions. Our interpretation of the evolutionary history and adaptation of humans is being transformed by analyses of these new genomic data.
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Extensive recent secondary contacts between four European white oak species

Extensive recent secondary contacts between four European white oak species | MycorWeb Plant-Microbe Interactions | Scoop.it


Historical trajectories of tree species during the late Quaternary have been well reconstructed through genetic and palaeobotanical studies. However, many congeneric tree species are interfertile, and the timing and contribution of introgression to species divergence during their evolutionary history remains largely unknown. We quantified past and current gene flow events between four morphologically divergent oak species (Quercus petraea, Q. robur, Q. pyrenaica, Q. pubescens), by two independent inference methods: diffusion approximation to the joint frequency spectrum (∂a∂i) and approximate Bayesian computation (ABC). For each pair of species, alternative scenarios of speciation allowing gene flow over different timescales were evaluated. Analyses of 3524 single nucleotide polymorphisms (SNPs) randomly distributed in the genome, showed that these species evolved in complete isolation for most of their history, but recently came into secondary contact, probably facilitated by the most recent period of postglacial warming. We demonstrated that: there was sufficient genetic differentiation before secondary contact for the accumulation of barriers to gene flow; and current European white oak genomes are a mosaic of genes that have crossed species boundaries and genes impermeable to gene flow.
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Evolutionary genomics of the cold-adapted diatom Fragilariopsis cylindrus

Evolutionary genomics of the cold-adapted diatom Fragilariopsis cylindrus | MycorWeb Plant-Microbe Interactions | Scoop.it
The Southern Ocean houses a diverse and productive community of organisms1, 2. Unicellular eukaryotic diatoms are the main primary producers in this environment, where photosynthesis is limited by low concentrations of dissolved iron and large seasonal fluctuations in light, temperature and the extent of sea ice3, 4, 5, 6, 7. How diatoms have adapted to this extreme environment is largely unknown. Here we present insights into the genome evolution of a cold-adapted diatom from the Southern Ocean, Fragilariopsis cylindrus8, 9, based on a comparison with temperate diatoms. We find that approximately 24.7 per cent of the diploid F. cylindrus genome consists of genetic loci with alleles that are highly divergent (15.1 megabases of the total genome size of 61.1 megabases). These divergent alleles were differentially expressed across environmental conditions, including darkness, low iron, freezing, elevated temperature and increased CO2. Alleles with the largest ratio of non-synonymous to synonymous nucleotide substitutions also show the most pronounced condition-dependent expression, suggesting a correlation between diversifying selection and allelic differentiation. Divergent alleles may be involved in adaptation to environmental fluctuations in the Southern Ocean.
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Five big mysteries about CRISPR’s origins

Five big mysteries about CRISPR’s origins | MycorWeb Plant-Microbe Interactions | Scoop.it
Francisco Mojica was not the first to see CRISPR, but he was probably the first to be smitten by it. He remembers the day in 1992 when he got his first glimpse of the microbial immune system that would launch a biotechnology revolution. He was reviewing genome-sequence data from the salt-loving microbe Haloferax mediterranei and noticed 14 unusual DNA sequences, each 30 bases long. They read roughly the same backwards and forwards, and they repeated every 35 bases or so. Soon, he saw more of them. Mojica was entranced, and made the repeats a focus of his research at the University of Alicante in Spain.

It wasn't a popular decision. His lab went years without funding. At meetings, Mojica would grab the biggest bigwigs he could find and ask what they thought of the strange little repeats. “Don't care about repeats so much,” he says that they would warn him. “There are many repeats in many organisms — we've known about them for years and still don't know how many of them work.”

CRISPR: gene editing is just the beginning

Today, much more is known about the clustered, regularly interspaced short palindromic repeats that give CRISPR its name and help the CRISPR–Cas microbial immune system to destroy invading viruses. But although most in biomedicine have come to revere the mechanics of the system — particularly of a version called CRISPR–Cas9 — for the ways in which it can be harnessed to edit genes, Mojica and other microbiologists are still puzzling over some basic questions about the system and how it works. How did it evolve, and how did it shape microbial evolution? Why do some microbes use it, whereas others don't? And might it have other, yet-to-be-appreciated roles in their basic biology?
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Rescooped by Francis Martin from Plant & Evolution
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Strigolactone Signaling and Evolution

Strigolactones are a structurally diverse class of plant hormones that control many aspects of shoot and root growth. Strigolactones are also exuded by plants into the rhizosphere, where they promote symbiotic interactions with arbuscular mycorrhizal fungi and germination of root parasitic plants in the Orobanchaceae family. Therefore, understanding how strigolactones are made, transported, and perceived may lead to agricultural innovations as well as a deeper knowledge of how plants function. Substantial progress has been made in these areas over the past decade. In this review, we focus on the molecular mechanisms, core developmental roles, and evolutionary history of strigolactone signaling. We also propose potential translational applications of strigolactone research to agriculture.


Via Pierre-Marc Delaux
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Jasmonate signaling and manipulation by pathogens and insects

Jasmonate signaling and manipulation by pathogens and insects | MycorWeb Plant-Microbe Interactions | Scoop.it
Plants synthesize jasmonates (JAs) in response to developmental cues or environmental stresses, in order to coordinate plant growth, development or defense against pathogens and herbivores. Perception of pathogen or herbivore attack promotes synthesis of jasmonoyl-L-isoleucine (JA-Ile), which binds to the COI1-JAZ receptor, triggering the degradation of JAZ repressors and induction of transcriptional reprogramming associated with plant defense. Interestingly, some virulent pathogens have evolved various strategies to manipulate JA signaling to facilitate their exploitation of plant hosts. In this review, we focus on recent advances in understanding the mechanism underlying the enigmatic switch between transcriptional repression and hormone-dependent transcriptional activation of JA signaling. We also discuss various strategies used by pathogens and insects to manipulate JA signaling and how interfering with this could be used as a novel means of disease control.
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Microbiology: Bacterial explorers move fast

Microbiology: Bacterial explorers move fast | MycorWeb Plant-Microbe Interactions | Scoop.it

Bacteria that were long thought to be stationary are capable of rapid movement across surfaces when grown alongside yeast.


Streptomyces bacteria are common in soil and generate many antibiotics. Marie Elliot at McMaster University in Hamilton, Canada, and her colleagues cultured Streptomyces venezuelae along with baker's yeast (Saccharomyces cerevisiae) for 14 days. They found that the bacteria form non-branched filaments that spread over various surfaces (pictured) and obstacles. The 'explorer' cells released a volatile alkaline compound that stimulated physically separated Streptomyces to initiate exploration, and inhibited the growth of other bacteria.

This exploratory growth could be a way for the organisms to scavenge more nutrients, the authors say.

eLife 6, e21738 (2017)


Via Christophe Jacquet
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Plant-soil feedback and the maintenance of diversity in Mediterranean-climate shrublands

Plant-soil feedback and the maintenance of diversity in Mediterranean-climate shrublands | MycorWeb Plant-Microbe Interactions | Scoop.it

Soil biota, including symbionts such as mycorrhizal fungi and nitrogen-fixing bacteria, as well as fungal and bacterial pathogens, affect terrestrial plant diversity and growth patterns. Teste et al. monitored growth and survival in Australian shrubland plant species paired with soil biota from plants of the same species and from other plants that use different nutrient acquisition strategies. Plant-soil feedbacks appear to drive local plant diversity through interactions between the different types of plants and their associated soil biota. Bennett et al. studied plant-soil feedbacks in soil and seeds from 550 populations of 55 species of North American trees. Feedbacks ranged from positive to negative, depending on the type of mycorrhizal association, and were related to how densely the same species occurred in natural populations.

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A paralogous decoy protects Phytophthora sojae apoplastic effector PsXEG1 from a host inhibitor

The extracellular space (apoplast) of plant tissue represents a critical battleground between plants and attacking microbes. Here we show that a pathogen-secreted apoplastic Xyloglucan-specific EndoGlucanase PsXEG1 is a focus of this struggle in the Phytophthora sojae -soybean interaction. We show that soybean produces an apoplastic Glucanase Inhibitor Protein, (GmGIP1), that binds to PsXEG1 to block its contribution to virulence. P. sojae however, secretes a paralogous PsXEG1-Like Protein (PsXLP1) that has lost enzyme activity but binds to GmGIP1 more tightly than does PsXEG1, thus freeing PsXEG1 to support P. sojae infection. The PsXEG1 and PsXLP1gene pair is conserved in many Phytophthora species, and the P. parasitica orthologs PpXEG1 and PpXLP1 have similar functions. Thus this apoplastic decoy strategy maybe widely employed in Phytophthora pathosystems.
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Pampered inside, pestered outside?

Pampered inside, pestered outside? | MycorWeb Plant-Microbe Interactions | Scoop.it
I recently spoke to Hendrik Poorter, Senior Researcher at the Institute of Bio- and Geosciences, Jülich Forschungszentrum, about his Tansley review: Pampered inside, pestered outside? Differences and similarities between plants growing in controlled conditions and in the field. Read on for Hendrik’s experiences of being a plant scientist, his take on what makes plants grown indoors different to plants grown outside, and his advice for early career researchers.

How did you get into plant science?

When I started my biology study, I was fascinated by bird ecology. However, I was ‘led astray’ by a microbiologist at our university, who was developing chemostats, machines by which you can grow bacteria in a constant and specific environment, and analyse their physiology. No messing around with batch cultures or petri-dishes, hi-tech full control! Unfortunately, their course was overbooked and I had to find something else. The plant physiologists had a very good working atmosphere, a charming supervisor by the name of Hans Lambers and growth chambers that also allowed for good environmental control. That did it!
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Photoreceptors in the dark: a functional white collar-like complex and other putative light-sensing components encoded by the genome of the subterranean fungus Tuber melanosporum

Photoreceptors in the dark: a functional white collar-like complex and other putative light-sensing components encoded by the genome of the subterranean fungus Tuber melanosporum | MycorWeb Plant-Microbe Interactions | Scoop.it
Light is perceived and transduced by fungi, where it modulates processes as diverse as growth and morphogenesis, sexual development and secondary metabolism. A special case in point is that of fungi with a subterranean, light-shielded habitat such as Tuber spp. Using as reference the genome sequence of the black truffle Tuber melanosporum, we employed sequence prediction tools and expression data to gain insight on the photoreceptor systems expressed by this hypogeous ectomycorryzal fungus. These include a chromophore-less opsin preferentially expressed in fruiting bodies, a putative red light-sensing phytochrome that is not expressed at detectable levels in any of the examined developmental conditions, and a nearly canonical two-component (WC-1/WC-2) photoreceptor system similar to the Neurospora white collar complex. The latter is expressed at relatively high levels throughout the different developmental stages of T. melanosporum, except for sexual stage fruiting bodies where it is down-regulated. Various evidences, including the growth arrest phenotype elicited by blue light and the ability of a chimeric Tuber/Neurospora WC-1 protein to complement a N. crassa wc-1ko blind strain suggest that the Tuber white collar complex is likely functional and capable of responding to blue-light. The other putative photoreceptor components we have identified in the T. melanosporum genome, especially the chromophore-less opsin and the likely non-functional phytochrome, may represent the signatures of adaptation to a hypogeous (light-shielded) lifestyle.
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A peptide hormone required for Casparian strip diffusion barrier formation in Arabidopsis roots

A peptide hormone required for Casparian strip diffusion barrier formation in Arabidopsis roots | MycorWeb Plant-Microbe Interactions | Scoop.it

The Casparian strip provides a waterproofing function to plant roots, protecting them against unregulated influxes of water and minerals. The integrity of the Casparian strip depends on a receptor-like kinase. Doblas et al. and Nakayama et al. now identify the peptide ligands in the core of the root (the stele) that help regulate Casparian strip formation. The receptor is expressed on the outward-facing surface of the root endodermal cells that surround the stele. When the endodermal layer is sealed by the Casparian strip, the peptide ligands cannot reach their receptors. When the endodermal layer is breached, whether by damage or during development, the peptides reach their receptors and activate signaling that encourages lignin deposition, shoring up the strips.


Via Loïc Lepiniec
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Comparative genomics of Mortierella elongata and its bacterial endosymbiont Mycoavidus cysteinexigens

Comparative genomics of Mortierella elongata and its bacterial endosymbiont Mycoavidus cysteinexigens | MycorWeb Plant-Microbe Interactions | Scoop.it
Endosymbiosis of bacteria by eukaryotes is a defining feature of cellular evolution. In addition to well known bacterial origins for mitochondria and chloroplasts, multiple origins of bacterial endosymbiosis are known within the cells of diverse animals, plants, and fungi. Early-diverging lineages of terrestrial fungi harbor endosymbiotic bacteria belonging to the Burkholderiaceae. We sequenced the metagenome of the soil-inhabiting fungus Mortierella elongata and assembled the complete circular chromosome of its endosymbiont, Mycoavidus cysteinexigens, which we place within in a lineage of endofungal symbionts that are sister clade to Burkholderia. The M. elongata strain AG77 genome features a core set of primary metabolic pathways for degradation of simple carbohydrates and lipid biosynthesis, while the M. cysteinexigens (AG77) genome is reduced in size and function. Experiments using antibiotics to cure the endobacterium from the host demonstrate that the fungal host metabolism is highly modulated by presence/absence of M. cysteinexigens. Independent comparative phylogenomic analyses of fungal and bacterial genomes are consistent with an ancient origin for M. elongata – M. cysteinexigens symbiosis, most likely over 350 million years ago and concomitant with the terrestrialization and diversification of fungi and plants
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Comparative genomics and expression levels of hydrophobins from eight mycorrhizal genomes

Comparative genomics and expression levels of hydrophobins from eight mycorrhizal genomes | MycorWeb Plant-Microbe Interactions | Scoop.it
Hydrophobins are small secreted proteins that are present as several gene copies in most fungal genomes. Their properties are now well understood: they are amphiphilic and assemble at hydrophilic/hydrophobic interfaces. However, their physiological functions remain largely unexplored, especially within mycorrhizal fungi. In this study, we identified hydrophobin genes and analysed their distribution in eight mycorrhizal genomes. We then measured their expression levels in three different biological conditions (mycorrhizal tissue vs. free-living mycelium, organic vs. mineral growth medium and aerial vs. submerged growth). Results confirmed that the size of the hydrophobin repertoire increased in the terminal orders of the fungal evolutionary tree. Reconciliation analysis predicted that in 41% of the cases, hydrophobins evolved from duplication events. Whatever the treatment and the fungal species, the pattern of expression of hydrophobins followed a reciprocal function, with one gene much more expressed than others from the same repertoire. These most-expressed hydrophobin genes were also among the most expressed of the whole genome, which suggests that they play a role as structural proteins. The fine-tuning of the expression of hydrophobin genes in each condition appeared complex because it differed considerably between species, in a way that could not be explained by simple ecological traits. Hydrophobin gene regulation in mycorrhizal tissue as compared with free-living mycelium, however, was significantly associated with a calculated high exposure of hydrophilic residues.
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Life, death and rebirth of avirulence effectors in a fungal pathogen of Brassica crops, Leptosphaeria maculans

Life, death and rebirth of avirulence effectors in a fungal pathogen of Brassica crops, Leptosphaeria maculans | MycorWeb Plant-Microbe Interactions | Scoop.it


In agricultural systems, major (R) genes for resistance in plants exert strong selection pressure on cognate/corresponding avirulence effector genes of phytopathogens. However, a complex interplay often exists between trade-offs linked to effector function and the need to escape R gene recognition. Here, using the Leptosphaeria maculans–oilseed rape pathosystem we review evolution of effectors submitted to multiple resistance gene selection. Characteristics of this pathosystem include a crop in which resistance genes have been deployed intensively resulting in ‘boom and bust’ cycles; a fungal pathogen with a high adaptive potential in which seven avirulence genes are cloned and for which population surveys have been coupled with molecular analysis of events responsible for virulence. The mode of evolution of avirulence genes, all located in dispensable parts of the ‘two-speed’ genome, is a highly dynamic gene-specific process. In some instances, avirulence genes are readily deleted under selection. However, others, even when located in the most plastic genome regions, undergo only limited point mutations or their avirulence phenotype is ‘camouflaged’ by another avirulence gene. Thus, while hundreds of effector genes are present, some effectors are likely to have an important and nonredundant function, suggesting functional redundancy and dispensability of effectors might not be the rule.
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The life of diatoms in the world's oceans : Article : Nature

The life of diatoms in the world's oceans : Article : Nature | MycorWeb Plant-Microbe Interactions | Scoop.it
Marine diatoms rose to prominence about 100 million years ago and today generate most of the organic matter that serves as food for life in the sea. They exist in a dilute world where compounds essential for growth are recycled and shared, and they greatly influence global climate, atmospheric carbon dioxide concentration and marine ecosystem function. How these essential organisms will respond to the rapidly changing conditions in today's oceans is critical for the health of the environment and is being uncovered by studies of their genomes.
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Arabica Coffee Genome Sequenced

Arabica Coffee Genome Sequenced | MycorWeb Plant-Microbe Interactions | Scoop.it
he first public genome sequence for Coffea arabica, the species responsible for more than 70 percent of global coffee production, was released today by researchers at the University of California, Davis.

Funding for the sequencing was provided by Suntory group, an international food and beverage company based in Tokyo.

Now available for immediate use by scientists and plant breeders around the world, the new genome sequence has been posted to Phytozome.net, the public database for comparative plant genomics coordinated by the U.S. Department of Energy’s Joint Genome Institute.

Details of the sequence will be presented Sunday, Jan. 15, at the Plant and Animal Genome Conference in San Diego.

Sequencing of the C. arabica genome is particularly meaningful for California, where coffee plants are being grown commercially for the first time in the continental United States and a specialty-coffee industry is emerging.
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Biology, dynamics, and applications of transposable elements in basidiomycete fungi

Biology, dynamics, and applications of transposable elements in basidiomycete fungi | MycorWeb Plant-Microbe Interactions | Scoop.it
The phylum Basidiomycota includes filamentous fungi and yeast species with different ecological and genomic characteristics. Transposable elements (TEs) are abundant components of most eukaryotic genomes, and their transition from being genomic parasites to key drivers of genomic architecture, functionality, and evolution is a subject receiving much attention. In light of the abundant genomic information released during the last decade, the aims of this mini-review are to discuss the dynamics and impact of TEs in basidiomycete fungi. To do this, we surveyed and explored data from 75 genomes, which encompass the phylogenetic diversity of the phylum Basidiomycota. We describe annotation approaches and analyze TE distribution in the context of species phylogeny and genome size. Further, we review the most relevant literature about the role of TEs in species lifestyle, their impact on genome architecture and functionality, and the defense mechanisms evolved to control their proliferation. Finally, we discuss potential applications of TEs that can drive future innovations in fungal research
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Asgard archaea illuminate the origin of eukaryotic cellular complexity

Asgard archaea illuminate the origin of eukaryotic cellular complexity | MycorWeb Plant-Microbe Interactions | Scoop.it

The origin and cellular complexity of eukaryotes represent a major enigma in biology. Current data support scenarios in which an archaeal host cell and an alphaproteobacterial (mitochondrial) endosymbiont merged together, resulting in the first eukaryotic cell. The host cell is related to Lokiarchaeota, an archaeal phylum with many eukaryotic features. The emergence of the structural complexity that characterizes eukaryotic cells remains unclear. Here we describe the ‘Asgard’ superphylum, a group of uncultivated archaea that, as well as Lokiarchaeota, includes Thor-, Odin- and Heimdallarchaeota. Asgard archaea affiliate with eukaryotes in phylogenomic analyses, and their genomes are enriched for proteins formerly considered specific to eukaryotes. Notably, thorarchaeal genomes encode several homologues of eukaryotic membrane-trafficking machinery components, including Sec23/24 and TRAPP domains. Furthermore, we identify thorarchaeal proteins with similar features to eukaryotic coat proteins involved in vesicle biogenesis. Our results expand the known repertoire of ‘eukaryote-specific’ proteins in Archaea, indicating that the archaeal host cell already contained many key components that govern eukaryotic cellular complexity.


Via Pierre-Marc Delaux
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Belowground drivers of plant diversity

Belowground drivers of plant diversity | MycorWeb Plant-Microbe Interactions | Scoop.it
Long before Ernst Haeckel coined the term “ecology” in 1866, nature explorers, such as Alexander von Humboldt, observed that vegetation composition changes with climate. However, it still remains unclear what determines the local composition and species richness of vegetation. Understanding the roles of belowground invertebrates and microbes is particularly challenging. On pages 173 and 181 of this issue, respectively, Teste et al. ( 1 ) and Bennett et al. ( 2 ) report field studies that elucidate the role of soil microorganisms as drivers of plant community composition.
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Plant-soil feedbacks and mycorrhizal type influence temperate forest population dynamics

Plant-soil feedbacks and mycorrhizal type influence temperate forest population dynamics | MycorWeb Plant-Microbe Interactions | Scoop.it

Soil biota, including symbionts such as mycorrhizal fungi and nitrogen-fixing bacteria, as well as fungal and bacterial pathogens, affect terrestrial plant diversity and growth patterns. Teste et al. monitored growth and survival in Australian shrubland plant species paired with soil biota from plants of the same species and from other plants that use different nutrient acquisition strategies. Plant-soil feedbacks appear to drive local plant diversity through interactions between the different types of plants and their associated soil biota. Bennett et al. studied plant-soil feedbacks in soil and seeds from 550 populations of 55 species of North American trees. Feedbacks ranged from positive to negative, depending on the type of mycorrhizal association, and were related to how densely the same species occurred in natural populations.

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The ERF Required for Nodulation1 (ERN1) transcription factor is required for infection thread formation in Lotus japonicus

Several hundred genes are transcriptionally regulated during infection thread formation and development of nitrogen fixing root nodules. We have characterized a set of Lotus japonicus mutants impaired in root nodule formation and found that the causative gene, Ern1, encodes a protein with a characteristic APETALA2/Ethylene Responsive Factor (AP2/ERF) transcription factor domain. Phenotypic characterisation of four ern1 alleles shows that infection pockets are formed but root hair infection threads are absent. Formation of root nodule primordia is delayed and no normal trans-cellular infection threads are found in the infected nodules. Corroborating the role of ERN1 in nodule organogenesis, spontaneous nodulation induced by an autoactive CCaMK and cytokinin induced nodule primordia were not observed in ern1 mutants. Expression of Ern1 is induced in the susceptible zone by Nod factor treatment or rhizobial inoculation. At the cellular level, the pErn1:GUS reporter is highly expressed in root epidermal cells of the susceptible zone and in the cortical cells that form nodule primordia. The genetic regulation of this cellular expression pattern was further investigated in symbiotic mutants. Nod factor induction of Ern1 in epidermal cells was found to depend on Nfr1, Cyclops and Nsp2 but was independent of Nin and Nf-ya1. These results suggest that ERN1 functions as a transcriptional regulator involved in the formation of infection threads and development of nodule primordia, and may coordinate these two processes.

Via Pierre-Marc Delaux
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Fungal–algal association patterns in lichen symbiosis linked to macroclimate

Both macroclimate and evolutionary events may influence symbiont association and diversity patterns. Here we assess how climatic factors and evolutionary events shape fungal–algal association patterns in the widely distributed lichen-forming fungal genus Protoparmelia. Multilocus phylogenies of fungal and algal partners were generated using 174 specimens. Coalescent-based species delimitation analysis suggested that 23 fungal hosts are associating with 20 algal species. Principal component analysis (PCA) was performed to infer how fungal–algal association patterns varied with climate. Fungi associated with one to three algal partners whereas algae accepted one to five fungal partners. Both fungi and algae were more specific, associating with fewer partners, in the warmer climates. Interaction with more than one partner was more frequent in cooler climates for both the partners. Cophylogenetic analyses suggest congruent fungal–algal phylogenies. Host switch was a more common event in warm climates, whereas failure of the photobiont to diverge with its fungal host was more frequent in cooler climates. We conclude that both environmental factors and evolutionary events drive fungal and algal evolution in Protoparmelia. The processes leading to phylogenetic congruence of fungi and algae are different in different macrohabitats in our study system. Hence, closely related species inhabiting diverse habitats may follow different evolutionary pathways.
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