Microbiome and plant immunity
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Rescooped by Giannis Stringlis from Rhizobium Research
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Type IV Effector Proteins Involved in the Sinorhizobium-Medicago Symbiosis | Molecular Plant-Microbe Interactions

Type IV Effector Proteins Involved in the Sinorhizobium-Medicago Symbiosis | Molecular Plant-Microbe Interactions | Microbiome and plant immunity | Scoop.it
In this study, we investigated genetic elements of the type IV secretion system (T4SS) found in Sinorhizobium and the role they play in symbiosis. Sinorhizobium meliloti and S. medicae each contain a putative T4SS, similar to that used by Agrobacterium tumefaciens during pathogenesis. The Cre reporter assay for translocation (CRAfT) system was used to validate potential effector proteins. Both S. meliloti and S. medicae contained the effector protein TfeA, which was translocated into the host plant. Sequence analysis revealed the presence of a nod box, involved in transcriptional activation of symbiosis-related genes, upstream of the transcriptional regulator (virG) in the Sinorhizobium T4SS. Replicate qRT-PCR analyses indicated that luteolin, released by roots and seeds of Medicago truncatula, upregulated transcription of tfeA and virG. Mutations in the T4SS apparatus, or tfeA alone, resulted in reduced numbers of nodules formed on M. truncatula genotypes. In addition, S. meliloti strain KH46c, which contains a deletion in the T4SS, was less competitive for nodule formation when co-inoculated with an equal number of cells of the wild-type strain. To our knowledge, TfeA is the first T4SS effector protein identified in Sinorhizobium. Our results indicate that Sinorhizobium 1) uses a T4SS during initiation of symbiosis with Medicago, and 2) alters Medicago cells in planta during symbiosis. This study also offers additional bioinformatic evidence that several different rhizobial species may use the T4SS in symbiosis with other legumes.

Nelson MS, Chun CL, Sadowsky MJ (2016).Mol Plant Microbe Interact. 2016 Dec 5. [Epub ahead of print]

Via IvanOresnik
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Rescooped by Giannis Stringlis from microbial pathogenesis and plant immunity
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Intracellular innate immune surveillance devices in plants and animals

Intracellular innate immune surveillance devices in plants and animals | Microbiome and plant immunity | Scoop.it
Multicellular eukaryotes coevolve with microbial pathogens, which exert strong selective pressure on the immune systems of their hosts. Plants and animals use intracellular proteins of the nucleotide-binding domain, leucine-rich repeat (NLR) superfamily to detect many types of microbial pathogens. The NLR domain architecture likely evolved independently and convergently in each kingdom, and the molecular mechanisms of pathogen detection by plant and animal NLRs have long been considered to be distinct. However, microbial recognition mechanisms overlap, and it is now possible to discern important key trans-kingdom principles of NLR-dependent immune function. Here, we attempt to articulate these principles. We propose that the NLR architecture has evolved for pathogen-sensing in diverse organisms because of its utility as a tightly folded “hair trigger” device into which a virtually limitless number of microbial detection platforms can be integrated. Recent findings suggest means to rationally design novel recognition capabilities to counter disease.

Via Ryohei Thomas Nakano, Jim Alfano
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Rescooped by Giannis Stringlis from The Plant Microbiome
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Arabidopsis thaliana root colonization by the nematophagous fungus Pochonia chlamydosporia is modulated by jasmonate signaling and leads to accelerated flowering and improved yield

Arabidopsis thaliana root colonization by the nematophagous fungus Pochonia chlamydosporia is modulated by jasmonate signaling and leads to accelerated flowering and improved yield | Microbiome and plant immunity | Scoop.it
Pochonia chlamydosporia has been intensively studied in nematode control of different crops. We have investigated the interaction between P. chlamydosporia and the model system Arabidopsis thaliana under laboratory conditions in the absence of nematodes.
This study demonstrates that P. chlamydosporia colonizes A. thaliana. Root colonization monitored with green fluorescent protein-tagged P. chlamydosporia and quantitative PCR (qPCR) quantitation methods revealed root cell invasion. Fungal inoculation reduced flowering time and stimulated plant growth, as determined by total FW increase, faster development of inflorescences and siliques, and a higher yield in terms of seed production per plant.
Precocious flowering was associated with significant expression changes in key flowering-time genes. In addition, we also provided molecular and genetic evidence that point towards jasmonate signaling as an important factor to modulate progression of plant colonization by the fungus.
Our results indicate that P. chlamydosporia provides benefits to the plant in addition to its nematophagous activity. This report highlights the potential of P. chlamydosporia to improve yield in economically important crops.

Via Christophe Jacquet, Stéphane Hacquard
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Scooped by Giannis Stringlis
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Direct evidence for microbial-derived soil organic matter formation and its ecophysiological controls

Direct evidence for microbial-derived soil organic matter formation and its ecophysiological controls | Microbiome and plant immunity | Scoop.it

Soil organic matter (SOM) and the carbon and nutrients therein drive fundamental submicron- to global-scale biogeochemical processes and influence carbon-climate feedbacks. Consensus is emerging that microbial materials are an important constituent of stable SOM, and new conceptual and quantitative SOM models are rapidly incorporating this view. However, direct evidence demonstrating that microbial residues account for the chemistry, stability and abundance of SOM is still lacking. Further, emerging models emphasize the stabilization of microbial-derived SOM by abiotic mechanisms, while the effects of microbial physiology on microbial residue production remain unclear. Here we provide the first direct evidence that soil microbes produce chemically diverse, stable SOM. We show that SOM accumulation is driven by distinct microbial communities more so than clay mineralogy, where microbial-derived SOM accumulation is greatest in soils with higher fungal abundances and more efficient microbial biomass production.

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Chitin receptor CERK1 links salt stress and chitin‐triggered innate immunity in Arabidopsis

Chitin receptor CERK1 links salt stress and chitin‐triggered innate immunity in Arabidopsis | Microbiome and plant immunity | Scoop.it
In nature, plants need to respond to multiple environmental stresses that require involvement and fine-tuning of different stress signaling pathways. Cross-tolerance in which plants pre-treated with chitin (a fungal microbe-associated molecular pattern) have improved salt tolerance was observed in Arabidopsis but is not well understood. Here, we show a unique link between chitin and salt signaling mediated by the chitin receptor CHITIN ELICITOR RECEPTOR KINASE 1 (CERK1). Transcriptome analysis revealed that salt stress-induced genes are highly correlated with chitin-induced genes, while this was not observed with other microbe-associated molecular patterns (MAMP) or with other abiotic stresses. The cerk1 mutant was more susceptible to NaCl than wild type. cerk1 plants had an irregular increase of cytosolic calcium ([Ca2+]cyt) after NaCl treatment. Bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation experiments indicated that CERK1 physically interacts with ANNEXIN 1 (ANN1), which was reported to form a calcium-permeable channel that contributes to the NaCl-induced [Ca2+]cyt signal. In turn, ann1 mutants showed elevated chitin-induced rapid responses. In short, molecular components previously shown to function in chitin or salt signaling physically interact and intimately link the downstream responses to fungal attack and salt stress.
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Rescooped by Giannis Stringlis from microbial pathogenesis and plant immunity
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Science: Regulation of sugar transporter activity for antibacterial defense in Arabidopsis (2016)

Science: Regulation of sugar transporter activity for antibacterial defense in Arabidopsis (2016) | Microbiome and plant immunity | Scoop.it

Microbial pathogens strategically acquire metabolites from their hosts during infection. Here we show that the host can intervene to prevent such metabolite loss to pathogens. Phosphorylation-dependent regulation of sugar transporter 13 (STP13) is required for antibacterial defense in the plant Arabidopsis thaliana. STP13 physically associates with the flagellin receptor flagellin-sensitive 2 (FLS2) and its co-receptor BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 (BAK1). BAK1 phosphorylates STP13 at threonine 485, which enhances its monosaccharide uptake activity to compete with bacteria for extracellular sugars. Limiting the availability of extracellular sugar deprives bacteria of an energy source and restricts virulence factor delivery. Our results reveal that control of sugar uptake, managed by regulation of a host sugar transporter, is a defense strategy deployed against microbial infection. Competition for sugar thus shapes host-pathogen interactions.


Via Kamoun Lab @ TSL, Suayib Üstün, Jim Alfano
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Rescooped by Giannis Stringlis from Plant immunity and legume symbiosis
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Sinorhizobium fredii HH103 invades Lotus burttii by crack entry in a Nod-factor and surface polysaccharides dependent manner

Sinorhizobium fredii HH103 invades Lotus burttii by crack entry in a Nod-factor and surface polysaccharides dependent manner | Microbiome and plant immunity | Scoop.it

Sinorhizobium fredii HH103-Rifr, a broad host-range rhizobial strain, induces nitrogen-fixing nodules in Lotus burttii but ineffective nodules in L. japonicus. Confocal microscopy studies showed that Mesorhizobium loti MAFF303099 and S. fredii HH103-Rifr invade L. burttii roots through infection threads or epidermal cracks, respectively. Infection threads in root hairs were not observed in L. burttii plants inoculated with S. fredii HH103-Rifr. A S. fredii HH103-Rifr nodA mutant failed to nodulate L. burttii, demonstrating that Nod-factors are strictly necessary for this crack-entry mode and a noeL mutant was also severely impaired in L. burttii nodulation, indicating that the presence of fucosyl residues in the Nod-factor is symbiotically relevant. However, significant symbiotic impacts due to the absence of methylation or to acetylation of the fucosyl residue were not detected. In contrast S. fredii HH103-Rifr mutants showing lipopolysaccharide alterations had reduced symbiotic capacity while mutants affected in production of exopolysaccharides and/or capsular polysaccharides were not impaired in nodulation. Mutants unable to produce cyclic glucans and purine or pyrimidine auxotrophic mutants formed ineffective nodules with L. burttii. Flagellin-dependent bacterial mobility was not required for crack infection, since HH103-Rifr fla mutants nodulated L. burttii. None of the S. fredii HH103-Rifr surface-polysaccharide mutants gained effective nodulation with L. japonicas. 


Acosta-Jurado S, Rodríguez-Navarro DN, Kawaharada Y, Fernández-Perea J, Gil-Serrano A, Jin H, An Q, Rodriguez-Carvajal MA, Andersen SU, Sandal N, Stougaard J, Vinardell JM, Ruiz-Sainz JE (2016). Mol Plant Microbe Interact. Nov 9. [Epub ahead of print]


Via IvanOresnik, Christophe Jacquet
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Root nodule symbiosis in Lotus japonicus drives the establishment of distinctive rhizosphere, root, and nodule bacterial communities

Root nodule symbiosis in Lotus japonicus drives the establishment of distinctive rhizosphere, root, and nodule bacterial communities | Microbiome and plant immunity | Scoop.it

Lotus japonicus has been used for decades as a model legume to study the establishment of binary symbiotic relationships with nitrogen-fixing rhizobia that trigger root nodule organogenesis for bacterial accommodation. Using community profiling of 16S rRNA gene amplicons, we reveal that in Lotus, distinctive nodule- and root-inhabiting communities are established by parallel, rather than consecutive, selection of bacteria from the rhizosphere and root compartments. Comparative analyses of wild-type (WT) and symbiotic mutants in Nod factor receptor5 (nfr5), Nodule inception (nin) and Lotus histidine kinase1 (lhk1) genes identified a previously unsuspected role of the nodulation pathway in the establishment of different bacterial assemblages in the root and rhizosphere. We found that the loss of nitrogen-fixing symbiosis dramatically alters community structure in the latter two compartments, affecting at least 14 bacterial orders. The differential plant growth phenotypes seen between WT and the symbiotic mutants in nonsupplemented soil were retained under nitrogen-supplemented conditions that blocked the formation of functional nodules in WT, whereas the symbiosis-impaired mutants maintain an altered community structure in the nitrogen-supplemented soil. This finding provides strong evidence that the root-associated community shift in the symbiotic mutants is a direct consequence of the disabled symbiosis pathway rather than an indirect effect resulting from abolished symbiotic nitrogen fixation. Our findings imply a role of the legume host in selecting a broad taxonomic range of root-associated bacteria that, in addition to rhizobia, likely contribute to plant growth and ecological performance.

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Not without my microbiome

Not without my microbiome | Microbiome and plant immunity | Scoop.it
When nodule bacteria supply plants with atmospheric nitrogen, characteristic microbial communities that drive plant growth become established in the root.
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Rescooped by Giannis Stringlis from The Plant Microbiome
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Measurement of bacterial replication rates in microbial communities

Measurement of bacterial replication rates in microbial communities | Microbiome and plant immunity | Scoop.it
Culture-independent microbiome studies have increased our understanding of the complexity and metabolic potential of microbial communities. However, to understand the contribution of individual microbiome members to community functions, it is important to determine which bacteria are actively replicating. We developed an algorithm, iRep, that uses draft-quality genome sequences and single time-point metagenome sequencing to infer microbial population replication rates. The algorithm calculates an index of replication (iRep) based on the sequencing coverage trend that results from bi-directional genome replication from a single origin of replication. We apply this method to show that microbial replication rates increase after antibiotic administration in human infants. We also show that uncultivated, groundwater-associated, Candidate Phyla Radiation bacteria only rarely replicate quickly in subsurface communities undergoing substantial changes in geochemistry. Our method can be applied to any genome-resolved microbiome study to track organism responses to varying conditions, identify actively growing populations and measure replication rates for use in modeling studies.

Via Stéphane Hacquard
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Stem-piped light activates phytochrome B to trigger light responses in Arabidopsis thaliana roots

Stem-piped light activates phytochrome B to trigger light responses in Arabidopsis thaliana roots | Microbiome and plant immunity | Scoop.it
Light affects not only the development and physiology of the shoots (stems, leaves, and flowers) of plants but also the underground root system. Light triggers shoot cells to release signals that travel to the root and affect the development and physiology of the root system. Like shoot cells, root cells also have photoreceptors that can be activated by light, leading Lee et al . to investigate if light actually reaches these underground parts of the plant. Exposing Arabidopsis thaliana shoots to light while protecting the roots from light activated the photoreceptor phyB in the roots. In the root, phyB activated Hy5, a transcription factor that mediates cellular responses to light and was important for growth of the primary root and for root gravitropism, the proper downward orientation of roots. Arabidopsis stems efficiently conducted only certain wavelengths of light to the root tissues, and these conducted wavelengths activated phyB directly in the roots. These findings demonstrate that roots not only receive information about light conditions through signaling molecules that travel from the shoot to the root in response to light but also directly perceive light that is conducted through the plant tissues.
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Rescooped by Giannis Stringlis from MycorWeb Plant-Microbe Interactions
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Unearthing the roots of ectomycorrhizal symbioses : Nature Reviews Microbiology

Unearthing the roots of ectomycorrhizal symbioses : Nature Reviews Microbiology | Microbiome and plant immunity | Scoop.it
During the diversification of Fungi and the rise of conifer-dominated and angiosperm- dominated forests, mutualistic symbioses developed between certain trees and ectomycorrhizal fungi that enabled these trees to colonize boreal and temperate regions. The evolutionary success of these symbioses is evident from phylogenomic analyses that suggest that ectomycorrhizal fungi have arisen in approximately 60 independent saprotrophic lineages, which has led to the wide range of ectomycorrhizal associations that exist today. In this Review, we discuss recent genomic studies that have revealed the adaptations that seem to be fundamental to the convergent evolution of ectomycorrhizal fungi, including the loss of some metabolic functions and the acquisition of effectors that facilitate mutualistic interactions with host plants. Finally, we consider how these insights can be integrated into a model of the development of ectomycorrhizal symbioses.

Via Francis Martin
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Bob Reeves's curator insight, November 5, 8:05 PM
Ectomycorrhizal fungi evolved after the primordial plant symbionts: endomycorrhizae. And their arrival paved the way for the dominance of the conifers and hardwood trees in today's temperate forests. They remain a linchpin mutualist organism supporting these ecosystems today.  
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The hijacking of a receptor kinase–driven pathway by a wheat fungal pathogen leads to disease

The hijacking of a receptor kinase–driven pathway by a wheat fungal pathogen leads to disease | Microbiome and plant immunity | Scoop.it
Necrotrophic pathogens live and feed on dying tissue, but their interactions with plants are not well understood compared to biotrophic pathogens. The wheat Snn1 gene confers susceptibility to strains of the necrotrophic pathogen Parastagonospora nodorum that produce the SnTox1 protein. We report the positional cloning of Snn1 , a member of the wall-associated kinase class of receptors, which are known to drive pathways for biotrophic pathogen resistance. Recognition of SnTox1 by Snn1 activates programmed cell death, which allows this necrotroph to gain nutrients and sporulate. These results demonstrate that necrotrophic pathogens such as P. nodorum hijack host molecular pathways that are typically involved in resistance to biotrophic pathogens, revealing the complex nature of susceptibility and resistance in necrotrophic and biotrophic pathogen interactions with plants.
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Shared and host‐specific microbiome diversity and functioning of grapevine and accompanying weed plants

Shared and host‐specific microbiome diversity and functioning of grapevine and accompanying weed plants | Microbiome and plant immunity | Scoop.it
Weeds and crop plants select their microbiota from the same pool of soil microorganisms, however, the ecology of weed microbiomes is poorly understood. We analyzed the microbiomes associated with roots and rhizospheres of grapevine and four weed species (Lamium amplexicaule L., Veronica arvensis L., Lepidium draba L. and Stellaria media L.) growing in proximity in the same vineyard using 16S rRNA gene sequencing. We also isolated and characterized 500 rhizobacteria and root endophytes from L. draba and grapevine. Microbiome data analysis revealed that all plants hosted significantly different microbiomes in the rhizosphere as well as in root compartment, however, differences were more pronounced in the root compartment. The shared microbiome of grapevine and the four weed species contained 145 OTUs (54.2%) in the rhizosphere, but only nine OTUs (13.2%) in the root compartment. Seven OTUs (12.3%) were shared in all plants and compartments. Approximately 56% of the major OTUs (>1%) showed more than 98% identity to bacteria isolated in this study. Moreover, weed-associated bacteria generally showed a higher species richness in the rhizosphere, whereas the root-associated bacteria were more diverse in the perennial plants grapevine and L. draba. Overall, weed isolates showed more plant growth-promoting characteristics compared to grapevine isolates. This article is protected by copyright. All rights reserved.
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The Plant Microbiota: Systems-Level Insights and Perspectives - Annual Review of Genetics, 50(1):211

The Plant Microbiota: Systems-Level Insights and Perspectives - Annual Review of Genetics, 50(1):211 | Microbiome and plant immunity | Scoop.it
Plants do not grow as axenic organisms in nature, but host a diverse community of microorganisms, termed the plant microbiota. There is an increasing awareness that the plant microbiota plays a role in plant growth and can provide protection from invading pathogens. Apart from intense research on crop plants, Arabidopsis is emerging as a valuable model system to investigate the drivers shaping stable bacterial communities on leaves and roots and as a tool to decipher the intricate relationship among the host and its colonizing microorganisms. Gnotobiotic experimental systems help establish causal relationships between plant and microbiota genotypes and phenotypes and test hypotheses on biotic and abiotic perturbations in a systematic way. We highlight major recent findings in plant microbiota research using comparative community profiling and omics analyses, and discuss these approaches in light of community establishment and beneficial traits like nutrient acquisition and plant health.
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The pattern-recognition receptor CORE of Solanaceae detects bacterial cold-shock protein

The pattern-recognition receptor CORE of Solanaceae detects bacterial cold-shock protein | Microbiome and plant immunity | Scoop.it
Plants and animals recognize microbial invaders by detecting microbe-associated molecular patterns (MAMPs) by cell surface receptors. Many plant species of the Solanaceae family detect the highly conserved nucleic acid binding motif RNP-1 of bacterial cold-shock proteins (CSPs), represented by the peptide csp22, as a MAMP. Here, we exploited the natural variation in csp22 perception observed between cultivated tomato (Solanum lycopersicum) and Solanum pennellii to map and identify the leucine-rich repeat (LRR) receptor kinase CORE (cold shock protein receptor) of tomato as the specific, high-affinity receptor site for csp22. Corroborating its function as a genuine receptor, heterologous expression of CORE in Arabidopsis thaliana conferred full sensitivity to csp22 and, importantly, it also rendered these plants more resistant to infection by the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. Our study also confirms the biotechnological potential of enhancing plant immunity by interspecies transfer of highly effective pattern-recognition receptors such as CORE to different plant families.
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Rescooped by Giannis Stringlis from Plant-Microbe Symbiosis
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The nutrient preference of plants influences their rhizosphere microbiome

The nutrient preference of plants influences their rhizosphere microbiome | Microbiome and plant immunity | Scoop.it
Many studies in recent decades have shown the signature effect of the host plant in determining the plant-associated microbiome in the soil. However, the important question as to the factors contributing to the selective enrichment of microorganisms in the plant rhizosphere has not been fully addressed. In this study, the role of the nutrient preferences of two plant species, tomato and cucumber, in variations in the soil microbiome were investigated using a five-season continuous pot experiment. The results of MiSeq sequencing showed that these two plants assembled specific bacterial and fungal communities in their rhizospheres, and the soil nutrient status resulting from the plant nutrient preference was identified as a key driver in the development of a plant-specific microbiome.


Via Jean-Michel Ané
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Plant domestication and the assembly of bacterial and fungal communities associated with strains of the common sunflower, Helianthus annuus

Plant domestication and the assembly of bacterial and fungal communities associated with strains of the common sunflower, Helianthus annuus | Microbiome and plant immunity | Scoop.it
Root and rhizosphere microbial communities can affect plant health, but it remains undetermined how plant domestication may influence these bacterial and fungal communities. We grew 33 sunflower (Helianthus annuus) strains (n = 5) that varied in their extent of domestication and assessed rhizosphere and root endosphere bacterial and fungal communities. We also assessed fungal communities in the sunflower seeds to investigate the degree to which root and rhizosphere communities were influenced by vertical transmission of the microbiome through seeds. Neither root nor rhizosphere bacterial communities were affected by the extent of sunflower domestication, but domestication did affect the composition of rhizosphere fungal communities. In particular, more modern sunflower strains had lower relative abundances of putative fungal pathogens. Seed-associated fungal communities strongly differed across strains, but several lines of evidence suggest that there is minimal vertical transmission of fungi from seeds to the adult plants. Our results indicate that plant-associated fungal communities are more strongly influenced by host genetic factors and plant breeding than bacterial communities, a finding that could influence strategies for optimizing microbial communities to improve crop yields.

Via Stéphane Hacquard, Jim Alfano, Francis Martin
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Back to the Roots 's curator insight, November 28, 6:12 AM
Impact of domestication in Helianthus annuus.
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Bacteria establish an aqueous living space in plants crucial for virulence

Bacteria establish an aqueous living space in plants crucial for virulence | Microbiome and plant immunity | Scoop.it
High humidity has a strong influence on the development of numerous diseases affecting the above-ground parts of plants (the phyllosphere) in crop fields and natural ecosystems, but the molecular basis of this humidity effect is not understood. Previous studies have emphasized immune suppression as a key step in bacterial pathogenesis. Here we show that humidity-dependent, pathogen-driven establishment of an aqueous intercellular space (apoplast) is another important step in bacterial infection of the phyllosphere. Bacterial effectors, such as Pseudomonas syringae HopM1, induce establishment of the aqueous apoplast and are sufficient to transform non-pathogenic P. syringae strains into virulent pathogens in immunodeficient Arabidopsis thaliana under high humidity. Arabidopsis quadruple mutants simultaneously defective in a host target (AtMIN7) of HopM1 and in pattern-triggered immunity could not only be used to reconstitute the basic features of bacterial infection, but also exhibited humidity-dependent dyshomeostasis of the endophytic commensal bacterial community in the phyllosphere. These results highlight a new conceptual framework for understanding diverse phyllosphere–bacterial interactions.
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Fast and sensitive taxonomic classification for metagenomics with Kaiju

Fast and sensitive taxonomic classification for metagenomics with Kaiju | Microbiome and plant immunity | Scoop.it

Metagenomics emerged as an important field of research not only in microbial ecology but also for human health and disease, and metagenomic studies are performed on increasingly larger scales. While recent taxonomic classification programs achieve high speed by comparing genomic k-mers, they often lack sensitivity for overcoming evolutionary divergence, so that large fractions of the metagenomic reads remain unclassified. Here we present the novel metagenome classifier Kaiju, which finds maximum (in-)exact matches on the protein-level using the Burrows–Wheeler transform. We show in a genome exclusion benchmark that Kaiju classifies reads with higher sensitivity and similar precision compared with current k-mer-based classifiers, especially in genera that are underrepresented in reference databases. We also demonstrate that Kaiju classifies up to 10 times more reads in real metagenomes. Kaiju can process millions of reads per minute and can run on a standard PC. Source code and web server are available at http://kaiju.binf.ku.dk.

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Volatile compounds emitted by diverse phytopathogenic microorganisms promote plant growth and flowering through cytokinin action

Volatile compounds emitted by diverse phytopathogenic microorganisms promote plant growth and flowering through cytokinin action | Microbiome and plant immunity | Scoop.it
It is known that volatile emissions from some beneficial rhizosphere microorganisms promote plant growth. Here we show that volatile compounds (VCs) emitted by phylogenetically diverse rhizosphere and non-rhizhosphere bacteria and fungi (including plant pathogens and microbes that do not normally interact mutualistically with plants) promote growth and flowering of various plant species, including crops. In Arabidopsis plants exposed to VCs emitted by the phytopathogen Alternaria alternata, changes included enhancement of photosynthesis and accumulation of high levels of cytokinins (CKs) and sugars. Evidence obtained using transgenic Arabidopsis plants with altered CK status show that CKs play essential roles in this phenomenon, because growth and flowering responses to the VCs were reduced in mutants with CK-deficiency (35S:AtCKX1) or low receptor sensitivity (ahk2/3). Further, we demonstrate that the plant responses to fungal VCs are light-dependent. Transcriptomic analyses of Arabidopsis leaves exposed to A. alternata VCs revealed changes in the expression of light- and CK-responsive genes involved in photosynthesis, growth and flowering. Notably, many genes differentially expressed in plants treated with fungal VCs were also differentially expressed in plants exposed to VCs emitted by the plant growth promoting rhizobacterium Bacillus subtilis GB03, suggesting that plants react to microbial VCs through highly conserved regulatory mechanisms.

Via Francis Martin
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Pampered inside, pestered outside? Differences and similarities between plants growing in controlled conditions and in the field - Poorter - 2016 - New Phytologist - Wiley Online Library

Pampered inside, pestered outside? Differences and similarities between plants growing in controlled conditions and in the field - Poorter - 2016 - New Phytologist - Wiley Online Library | Microbiome and plant immunity | Scoop.it
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Rescooped by Giannis Stringlis from of Plants & Bacteria (and sometimes other fellows too)
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Pseudomonas syringae Differentiates into Phenotypically Distinct Subpopulations During Colonization of a Plant Host

Pseudomonas syringae Differentiates into Phenotypically Distinct Subpopulations During Colonization of a Plant Host | Microbiome and plant immunity | Scoop.it
Authors: José S. Rufián, María-Antonia Sánchez-Romero, Diego López-Márquez, Alberto P. Macho, John W. Mansfield, Dawn L. Arnold, Javier Ruiz-Albert, Josep Casadesús and Carmen R. Beuzón.
Journal: Environmental Microbiology

Summary: 
Bacterial microcolonies with heterogeneous sizes are formed during colonization of Phaseolus vulgaris by Pseudomonas syringae. Heterogeneous expression of structural and regulatory components of the P. syringae type III secretion system (T3SS), essential for colonization of the host apoplast and disease development, is likewise detected within the plant apoplast. T3SS expression is bistable in the homogeneous environment of nutrient-limited T3SS-inducing medium, suggesting that subpopulation formation is not a response to different environmental cues. T3SS bistability is reversible, indicating a non-genetic origin, and the T3SSHIGH and T3SSLOW subpopulations show differences in virulence. T3SS bistability requires the transcriptional activator HrpL, the double negative regulatory loop established by HrpV and HrpG, and may be enhanced through a positive feedback loop involving HrpA, the main component of the T3SS pilus. To our knowledge, this is the first example of phenotypic heterogeneity in the expression of virulence determinants during colonization of a non-mammalian host. 

Via Freddy Monteiro
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Freddy Monteiro's curator insight, November 3, 4:53 PM
Take note of this phenomenon. Findings described here will be validated in other plant pathogens.
Rescooped by Giannis Stringlis from Plant pathogenic fungi
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The WEIZMASS spectral library for high-confidence metabolite identification

The WEIZMASS spectral library for high-confidence metabolite identification | Microbiome and plant immunity | Scoop.it
Annotation of metabolites is an essential, yet problematic, aspect of mass spectrometry (MS)-based metabolomics assays. The current repertoire of definitive annotations of metabolite spectra in public MS databases is limited and suffers from lack of chemical and taxonomic diversity. Furthermore, the heterogeneity of the data prevents the development of universally applicable metabolite annotation tools. Here we present a combined experimental and computational platform to advance this key issue in metabolomics. WEIZMASS is a unique reference metabolite spectral library developed from high-resolution MS data acquired from a structurally diverse set of 3,540 plant metabolites. We also present MatchWeiz, a multi-module strategy using a probabilistic approach to match library and experimental data. This strategy allows efficient and high-confidence identification of dozens of metabolites in model and exotic plants, including metabolites not previously reported in plants or found in few plant species to date.


Via Steve Marek
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The fungal-specific β-glucan-binding lectin FGB1 alters cell-wall composition and suppresses glucan-triggered immunity in plants

The fungal-specific β-glucan-binding lectin FGB1 alters cell-wall composition and suppresses glucan-triggered immunity in plants | Microbiome and plant immunity | Scoop.it

β-glucans are well-known modulators of the immune system in mammals but little is known about β-glucan triggered immunity in planta. Here we show by isothermal titration calorimetry, circular dichroism spectroscopy and nuclear magnetic resonance spectroscopy that the FGB1 gene from the root endophyte Piriformospora indica encodes for a secreted fungal-specific β-glucan-binding lectin with dual function. This lectin has the potential to both alter fungal cell wall composition and properties, and to efficiently suppress β-glucan-triggered immunity in different plant hosts, such as Arabidopsis, barley and Nicotiana benthamiana. Our results hint at the existence of fungal effectors that deregulate innate sensing of β-glucan in plants.


Via Pierre-Marc Delaux, Stéphane Hacquard, Francis Martin
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