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Science: Gene-for-Gene Resistance in Striga-Cowpea Associations (2009)

Science: Gene-for-Gene Resistance in Striga-Cowpea Associations (2009) | Plants and Microbes | Scoop.it

Seven races of Striga gesnerioides parasitic on cowpea, a major food and forage legume in sub-Saharan Africa, have been identified. Race-specific resistance of cowpea to Striga involves a coiled-coil nucleotide binding site leucine-rich repeat domain resistance protein encoded by the RSG3-301 gene. Knockdown of RSG3-301 expression by virus-induced gene silencing in the multirace-resistant cowpea cultivar B301 results in the failure of RSG3-301-silenced plants to mount a hypersensitive response and promotes parasite necrosis when challenged with Striga race SG3, whereas the resistance response to races SG2 and SG5 is unaltered. Our findings indicate that a gene-for-gene resistance mechanism is operating in these unique plant-plant associations.

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Phytopathology: Evolution, Diversity, and Taxonomy of the Peronosporaceae, with Focus on the Genus Peronospora (2016)

Phytopathology: Evolution, Diversity, and Taxonomy of the Peronosporaceae, with Focus on the Genus Peronospora (2016) | Plants and Microbes | Scoop.it

Downy mildews are a notorious group of oomycete plant pathogens, causing high economic losses in various crops and ornamentals. The most species-rich genus of oomycetes is the genus Peronospora. This review provides a wide overview of these pathogens, ranging from macro- and micro-evolutionary patterns, their biodiversity and ecology to short overviews for the currently economically most important pathogens and potential emerging diseases. In this overview, the taxonomy of economically relevant species is also discussed, as the application of the correct names and species concepts is a prerequisite for effective quarantine regulations and phytosanitary measures.

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Phytopathological Society of Japan: Cell physiological studies on the resistance of potato plant to Phytophthora infestans (1956)

Phytopathological Society of Japan: Cell physiological studies on the resistance of potato plant to Phytophthora infestans (1956) | Plants and Microbes | Scoop.it

Classic by Kohei Tomiyama. Part IV. On the movements of cytoplasm of the host cell induced by the invasion of Phytophthora infestans.

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bioRxiv: Cell re-entry assays do not support models of pathogen- independent translocation of AvrM and AVR3a effectors into plant cells (2016)

bioRxiv: Cell re-entry assays do not support models of pathogen- independent translocation of AvrM and AVR3a effectors into plant cells (2016) | Plants and Microbes | Scoop.it

The cell re-entry assay is widely used to evaluate pathogen effector protein uptake into plant cells. The assay is based on the premise that effector proteins secreted out of a leaf cell would translocate back into the cytosol of the same cell via a yet unknown host-derived uptake mechanism. Here, we critically assess this assay by expressing domains of the effector proteins AvrM-A of Melampsora lini and AVR3a of Phytophthora infestans fused to a signal peptide and fluorescent proteins in Nicotiana benthamiana. We found that the secreted fusion proteins do not re-enter plant cells from the apoplast and that the assay is prone to false-positives. We therefore emit a cautionary note on the use of the cell re-entry assay for protein trafficking studies.

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Nature Comms: A Phytophthora infestans RXLR effector targets plant PP1c isoforms that promote late blight disease (2016)

Nature Comms: A Phytophthora infestans RXLR effector targets plant PP1c isoforms that promote late blight disease (2016) | Plants and Microbes | Scoop.it

Plant pathogens deliver effectors to alter host processes. Knowledge of how effectors target and manipulate host proteins is critical to understand crop disease. Here, we show that in plantaexpression of the RXLR effector Pi04314 enhances leaf colonization by Phytophthora infestans via activity in the host nucleus and attenuates induction of jasmonic and salicylic acid-responsive genes. Pi04314 interacts with three host protein phosphatase 1 catalytic (PP1c) isoforms, causing their re-localization from the nucleolus to the nucleoplasm. Re-localization of PP1c-1 also occurs during infection and is dependent on an R/KVxF motif in the effector. Silencing the PP1c isoforms or overexpression of a phosphatase-dead PP1c-1 mutant attenuates infection, demonstrating that host PP1c activity is required for disease. Moreover, expression of PP1c–1mut abolishes enhanced leaf colonization mediated by in planta Pi04314 expression. We argue that PP1c isoforms are susceptibility factors forming holoenzymes with Pi04314 to promote late blight disease.

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Science Signaling: 2015: Signaling Breakthroughs of the Year

Science Signaling: 2015: Signaling Breakthroughs of the Year | Plants and Microbes | Scoop.it

Plants are subject to attack by pathogens, and, like animals, the plant innate immune response involves both surface and cytoplasmic receptors. Intracellular nucleotide-binding leucine-rich repeat receptors involved in the plant innate immune response are structurally and functionally similar to animal Nod-like receptors (NLRs), which play a key role in inflammasome activation. Plant NLRs, which detect pathogen-derived virulence factors (effectors) frequently directed against plant defenses triggered by the plasma membrane-localized immune receptors, can function in pairs, with both partners required for activation of an immune response. In work that he described as representing “a paradigmatic shift in our understanding of how immune receptors work,” Cyril Zipfel nominated three papers (24–26) describing an intriguing twist on effector detection. Le Roux et al. (24) and Sarris et al. (25) showed how integration of a “decoy” or “sensor” domain that mimics host targets baits pathogenic virulence factors to one member of a plant NLR pair, thereby activating the partner NLR to initiate defense signaling. In a third breakthrough paper on this theme, Maqbool et al. (26) determined the structural basis for effector interaction with a different class of integrated domain and demonstrated that a high binding affinity between the NLR domain and the effector is required to activate immunity. The emerging theme from these papers is that the very mechanisms that enable pathogen virulence factors to cripple the initial wave of the immune response have been turned to their own destruction.

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Tweet from @kseniakrasileva

Tweet from @kseniakrasileva | Plants and Microbes | Scoop.it

Coming soon to a PDF near you @PanosSarris @Turkish_Rambo @GulayGokD @jonathandgjones @kseniakrasileva #sneakpreview pic.twitter.com/I8afhkZVwH

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Cell Host & Microbe: A Bacterial Effector Co-opts Calmodulin to Target the Plant Microtubule Network (2016)

Cell Host & Microbe: A Bacterial Effector Co-opts Calmodulin to Target the Plant Microtubule Network (2016) | Plants and Microbes | Scoop.it

The bacterial pathogen Pseudomonas syringae depends on effector proteins secreted by its type III secretion system for the pathogenesis of plants. The majority of these effector proteins are known suppressors of immunity, but their plant targets remain elusive. Using Arabidopsis thaliana as a model host, we report that the HopE1 effector uses the host calcium sensor, calmodulin (CaM), as a co-factor to target the microtubule-associated protein 65 (MAP65), an important component of the microtubule network. HopE1 interacted with MAP65 in a CaM-dependent manner, resulting in MAP65-GFP dissociation from microtubules. Transgenic Arabidopsis expressing HopE1 had reduced secretion of the immunity protein PR-1 compared to wild–type plants. Additionally, Arabidopsis map65-1 mutants were immune deficient and were more susceptible to P. syringae. Our results suggest a virulence strategy in which a pathogen effector is activated by host calmodulin to target MAP65 and the microtubule network, thereby inhibiting cell wall-based extracellular immunity.


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Jim Alfano's curator insight, January 13, 1:03 PM

Real proud of my research team for bringing this paper together. Ming Guo, in particular, for leading the effort.

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eLife: An effector of the Irish potato famine pathogen antagonizes a host autophagy cargo receptor (2016)

eLife: An effector of the Irish potato famine pathogen antagonizes a host autophagy cargo receptor (2016) | Plants and Microbes | Scoop.it

Plants use autophagy to safeguard against infectious diseases. However, how plant pathogens interfere with autophagy related processes is unknown. Here we show that PexRD54, an effector from the Irish potato famine pathogen Phytophthora infestans, binds host autophagy protein ATG8CL to stimulate autophagosome formation. PexRD54 depletes the autophagy cargo receptor Joka2 out of ATG8CL complexes and interferes with Joka2's positive effect on pathogen defense. Thus a plant pathogen effector has evolved to antagonize a host autophagy cargo receptor in order to counteract host defenses.

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bioRxiv: Arabidopsis late blight: Infection of a nonhost plant by Albugo laibachii enables full colonization by Phytophthora infestans (2015)

bioRxiv: Arabidopsis late blight: Infection of a nonhost plant by Albugo laibachii enables full colonization by Phytophthora infestans (2015) | Plants and Microbes | Scoop.it

The oomycete pathogen Phytophthora infestans causes potato late blight, and as a potato and tomato specialist pathogen, is seemingly poorly adapted to infect plants outside the Solanaceae. Here, we report the unexpected finding that P. infestans can infect Arabidopsis thaliana when another oomycete pathogen, Albugo laibachii, has colonized the host plant. The behaviour and speed of P. infestans infection in Arabidopsis pre-infected with A. laibachii resemble P. infestans infection of susceptible potato plants. Transcriptional profiling of P. infestans genes during infection revealed a significant overlap in the sets of secreted-protein genes that are induced in P. infestans upon colonisation of potato and susceptible Arabidopsis, suggesting major similarities in P. infestans gene expression dynamics on the two plant species. Furthermore, we found haustoria of A. laibachii and P. infestanswithin in the same Arabidopsis cells. This Arabidopsis - A. laibachii - P. infestanstripartite interaction opens up various possibilities to dissect the molecular mechanisms of P. infestans infection and the processes occurring in co-infected Arabidopsis cells.

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Nature Genetics: A recently evolved hexose transporter variant confers resistance to multiple pathogens in wheat (2015)

Nature Genetics: A recently evolved hexose transporter variant confers resistance to multiple pathogens in wheat (2015) | Plants and Microbes | Scoop.it

As there are numerous pathogen species that cause disease and limit yields of crops, such as wheat (Triticum aestivum), single genes that provide resistance to multiple pathogens are valuable in crop improvement12. The mechanistic basis of multi-pathogen resistance is largely unknown. Here we use comparative genomics, mutagenesis and transformation to isolate the wheat Lr67 gene, which confers partial resistance to all three wheat rust pathogen species and powdery mildew. The Lr67 resistance gene encodes a predicted hexose transporter (LR67res) that differs from the susceptible form of the same protein (LR67sus) by two amino acids that are conserved in orthologous hexose transporters. Sugar uptake assays show that LR67sus, and related proteins encoded by homeoalleles, function as high-affinity glucose transporters. LR67res exerts a dominant-negative effect through heterodimerization with these functional transporters to reduce glucose uptake. Alterations in hexose transport in infected leaves may explain its ability to reduce the growth of multiple biotrophic pathogen species.


News & Views at http://www.nature.com/ng/journal/v47/n12/full/ng.3456.html

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Science: Rice perception of symbiotic arbuscular mycorrhizal fungi requires the karrikin receptor complex (2015)

Science: Rice perception of symbiotic arbuscular mycorrhizal fungi requires the karrikin receptor complex (2015) | Plants and Microbes | Scoop.it

In terrestrial ecosystems, plants take up phosphate predominantly via association with arbuscular mycorrhizal fungi (AMF). We identified loss of responsiveness to AMF in the rice (Oryza sativa) mutant hebiba, reflected by the absence of physical contact and of characteristic transcriptional responses to fungal signals. Among the 26 genes deleted in hebibaDWARF 14 LIKE is, the one responsible for loss of symbiosis . It encodes an alpha/beta-fold hydrolase, that is a component of an intracellular receptor complex involved in the detection of the smoke compound karrikin. Our finding reveals an unexpected plant recognition strategy for AMF and a previously unknown signaling link between symbiosis and plant development.

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PNAS: Rhizobium–legume symbiosis shares an exocytotic pathway required for arbuscule formation (2012)

PNAS: Rhizobium–legume symbiosis shares an exocytotic pathway required for arbuscule formation (2012) | Plants and Microbes | Scoop.it

Endosymbiotic interactions are characterized by the formation of specialized membrane compartments, by the host in which the microbes are hosted, in an intracellular manner. Two well-studied examples, which are of major agricultural and ecological importance, are the widespread arbuscular mycorrhizal symbiosis and the Rhizobium–legume symbiosis. In both symbioses, the specialized host membrane that surrounds the microbes forms a symbiotic interface, which facilitates the exchange of, for example, nutrients in a controlled manner and, therefore, forms the heart of endosymbiosis. Despite their key importance, the molecular and cellular mechanisms underlying the formation of these membrane interfaces are largely unknown. Recent studies strongly suggest that the Rhizobium–legume symbiosis coopted a signaling pathway, including receptor, from the more ancient arbuscular mycorrhizal symbiosis to form a symbiotic interface. Here, we show that two highly homologous exocytotic vesicle-associated membrane proteins (VAMPs) are required for formation of the symbiotic membrane interface in both interactions. Silencing of these Medicago VAMP72genes has a minor effect on nonsymbiotic plant development and nodule formation. However, it blocks symbiosome as well as arbuscule formation, whereas root colonization by the microbes is not affected. Identification of these VAMP72s as common symbiotic regulators in exocytotic vesicle trafficking suggests that the ancient exocytotic pathway forming the periarbuscular membrane compartment has also been coopted in the Rhizobium–legume symbiosis.

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New Phytologist: VAMP721a and VAMP721d are important for pectin dynamics and release of bacteria in soybean nodules (2016)

New Phytologist: VAMP721a and VAMP721d are important for pectin dynamics and release of bacteria in soybean nodules (2016) | Plants and Microbes | Scoop.it
  • In root nodules rhizobia enter host cells via infection threads. The release of bacteria to a host cell is possible from cell wall-free regions of the infection thread. We hypothesized that the VAMP721d and VAMP721e exocytotic pathway, identified before in Medicago truncatula, has a role in the local modification of cell wall during the release of rhizobia.
  • To clarify the role of VAMP721d and VAMP721e we used Glycine max, a plant with a determinate type of nodule. The localization of the main polysaccharide compounds of primary cell walls was analysed in control vs nodules with partially silenced GmVAMP721d.
  • The silencing of GmVAMP721d blocked the release of rhizobia. Instead of rhizobia-containing membrane compartments – symbiosomes – the infected cells contained big clusters of bacteria embedded in a matrix of methyl-esterified and de-methyl-esterified pectin. These clusters were surrounded by a membrane. We found that GmVAMP721d-positive vesicles were not transporting methyl-esterified pectin. We hypothesized that they may deliver the enzymes involved in pectin turnover. Subsequently, we found that GmVAMP721d is partly co-localized with pectate lyase.
  • Therefore, the biological role of VAMP721d may be explained by its action in delivering pectin-modifying enzymes to the site of release.
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New Phytologist: Integration of decoy domains derived from protein targets of pathogen effectors into plant immune receptors is widespread (2016)

New Phytologist: Integration of decoy domains derived from protein targets of pathogen effectors into plant immune receptors is widespread (2016) | Plants and Microbes | Scoop.it
  • Plant immune receptors of the class of nucleotide-binding and leucine-rich repeat domain (NLR) proteins can contain additional domains besides canonical NB-ARC (nucleotide-binding adaptor shared by APAF-1, R proteins, and CED-4 (NB-ARC)) and leucine-rich repeat (LRR) domains. Recent research suggests that these additional domains act as integrated decoys recognizing effectors from pathogens. Proteins homologous to integrated decoys are suspected to be effector targets and involved in disease or resistance.
  • Here, we scrutinized 31 entire plant genomes to identify putative integrated decoy domains in NLR proteins using the Interpro search. The involvement of the Zinc Finger–BED type (ZBED) protein containing a putative decoy domain, called BED, in rice (Oryza sativa) resistance was investigated by evaluating susceptibility to the blast fungus Magnaporthe oryzae in rice over-expression and knock-out mutants.
  • This analysis showed that all plants tested had integrated various atypical protein domains into their NLR proteins (on average 3.5% of all NLR proteins). We also demonstrated that modifying the expression of the ZBED gene modified disease susceptibility.
  • This study suggests that integration of decoy domains in NLR immune receptors is widespread and frequent in plants. The integrated decoy model is therefore a powerful concept to identify new proteins involved in disease resistance. Further in-depth examination of additional domains in NLR proteins promises to unravel many new proteins of the plant immune system.
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The Scientist: Holding Their Ground (2016)

The Scientist: Holding Their Ground (2016) | Plants and Microbes | Scoop.it

To protect the global food supply, scientists want to understand—and enhance—plants’ natural resistance to pathogens.

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New Phytologist: Mycorrhizal symbioses: today and tomorrow (2016)

New Phytologist: Mycorrhizal symbioses: today and tomorrow (2016) | Plants and Microbes | Scoop.it
The 2nd International Molecular Mycorrhiza Meeting, Cambridge, UK, September 2015The 2nd International Molecular Mycorrhiza Meeting, Cambridge, UK, September 2015Symbiotic interactions between plants and mycorrhizal fungi have a major impact on plant growth, development and evolution. Among them, the ectomycorrhizal (ECM) symbiosis formed between a large variety of phylogenetically diverse fungi and trees, and the arbuscular mycorrhizal (AM) symbiosis involving almost all land plants and the monophyletic Glomeromycota, are critical players of most ecosystems. Beyond their ecological functions, these associations offer a unique opportunity to improve the productivity and sustainability of current forest and agricultural systems. Over the last two decades, genetics conducted in model legumes has allowed the identification of a first set of genes and molecular mechanisms required for the efficient establishment of the AM symbiosis but also highlighted how scarce and incomplete our understanding of this association is at the molecular level. The 2nd international Molecular Mycorrhiza Meeting (2nd iMMM) brought together researchers who work on the molecular characterization of AM and ECM symbioses in a variety of contexts including root colonization, cell dynamics, nutrient exchange and metabolism, molecular evolution, genomics, effectors, plant–fungal communication, hormonal regulation or signal transduction. During this year's meeting many presenters outlined novel discoveries, concepts and models that are likely to take the research on mycorrhizal associations into new realms.
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Science Signaling: Rosmarinic acid is a homoserine lactone mimic produced by plants that activates a bacterial quorum-sensing regulator (2016)

Science Signaling: Rosmarinic acid is a homoserine lactone mimic produced by plants that activates a bacterial quorum-sensing regulator (2016) | Plants and Microbes | Scoop.it

Quorum sensing is a bacterial communication mechanism that controls genes, enabling bacteria to live as communities, such as biofilms. Homoserine lactone (HSL) molecules function as quorum-sensing signals for Gram-negative bacteria. Plants also produce previously unidentified compounds that affect quorum sensing. We identified rosmarinic acid as a plant-derived compound that functioned as an HSL mimic. In vitro assays showed that rosmarinic acid bound to the quorum-sensing regulator RhlR of Pseudomonas aeruginosaPAO1 and competed with the bacterial ligand N-butanoyl-homoserine lactone (C4-HSL). Furthermore, rosmarinic acid stimulated a greater increase in RhlR-mediated transcription in vitro than that of C4-HSL. In P. aeruginosa, rosmarinic acid induced quorum sensing–dependent gene expression and increased biofilm formation and the production of the virulence factors pyocyanin and elastase. Because P. aeruginosa PAO1 infection induces rosmarinic acid secretion from plant roots, our results indicate that rosmarinic acid secretion is a plant defense mechanism to stimulate a premature quorum-sensing response. P. aeruginosa is a ubiquitous pathogen that infects plants and animals; therefore, identification of rosmarinic acid as an inducer of premature quorum-sensing responses may be useful in agriculture and inform human therapeutic strategies.

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Frontiers: The poplar Rust-Induced Secreted Protein (RISP) inhibits the growth of the leaf rust pathogen Melampsora larici-populina and triggers cell culture alkalinisation (2016)

Frontiers: The poplar Rust-Induced Secreted Protein (RISP) inhibits the growth of the leaf rust pathogen Melampsora larici-populina and triggers cell culture alkalinisation (2016) | Plants and Microbes | Scoop.it

Plant cells secrete a wide range of proteins in extracellular spaces in response to pathogen attack. The poplar Rust-Induced Secreted Protein (RISP) is a small cationic protein of unknown function that was identified as the most induced gene in poplar leaves during immune responses to the leaf rust pathogen Melampsora larici-populina, an obligate biotrophic parasite. Here, we combined in planta and in vitro molecular biology approaches to tackle the function of RISP. Using a RISP-mCherry fusion transiently expressed in Nicotiana benthamiana leaves, we demonstrated that RISP is secreted into the apoplast. A recombinant RISP specifically binds to M. larici-populina urediniospores and inhibits their germination. It also arrests the growth of the fungus in vitro and on poplar leaves. Interestingly, RISP also triggers poplar cell culture alkalinisation and is cleaved at the C-terminus by a plant-encoded mechanism. Altogether our results indicate that RISP is an antifungal protein that has the ability to trigger cellular responses.


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Plant cells secrete a wide range of proteins in extracellular spaces in response to pathogen attack. The poplar Rust-Induced Secreted Protein (RISP) is a small cationic protein of unknown function that was identified as the most induced gene in poplar leaves during immune responses to the leaf rust pathogen Melampsora larici-populina, an obligate biotrophic parasite. Here, we combined in planta and in vitro molecular biology approaches to tackle the function of RISP. Using a RISP-mCherry fusion transiently expressed in Nicotiana benthamiana leaves, we demonstrated that RISP is secreted into the apoplast. A recombinant RISP specifically binds to M. larici-populina urediniospores and inhibits their germination. It also arrests the growth of the fungus in vitro and on poplar leaves. Interestingly, RISP also triggers poplar cell culture alkalinisation and is cleaved at the C-terminus by a plant-encoded mechanism. Altogether our results indicate that RISP is an antifungal protein that has the ability to trigger cellular responses.

Jim Alfano's curator insight, January 27, 8:18 AM

Is it secreted when other types of pathogens attack? That is, is it a typical PR protein?

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PLOS Biology: Microbial Hub Taxa Link Host and Abiotic Factors to Plant Microbiome Variation (2016)

PLOS Biology: Microbial Hub Taxa Link Host and Abiotic Factors to Plant Microbiome Variation (2016) | Plants and Microbes | Scoop.it

Plant-associated microorganisms have been shown to critically affect host physiology and performance, suggesting that evolution and ecology of plants and animals can only be understood in a holobiont (host and its associated organisms) context. Host-associated microbial community structures are affected by abiotic and host factors, and increased attention is given to the role of the microbiome in interactions such as pathogen inhibition. However, little is known about how these factors act on the microbial community, and especially what role microbe–microbe interaction dynamics play. We have begun to address this knowledge gap for phyllosphere microbiomes of plants by simultaneously studying three major groups of Arabidopsis thaliana symbionts (bacteria, fungi and oomycetes) using a systems biology approach. We evaluated multiple potential factors of microbial community control: we sampled various wild Athaliana populations at different times, performed field plantings with different host genotypes, and implemented successive host colonization experiments under lab conditions where abiotic factors, host genotype, and pathogen colonization was manipulated. Our results indicate that both abiotic factors and host genotype interact to affect plant colonization by all three groups of microbes. Considering microbe–microbe interactions, however, uncovered a network of interkingdom interactions with significant contributions to community structure. As in other scale-free networks, a small number of taxa, which we call microbial “hubs,” are strongly interconnected and have a severe effect on communities. By documenting these microbe–microbe interactions, we uncover an important mechanism explaining how abiotic factors and host genotypic signatures control microbial communities. In short, they act directly on “hub” microbes, which, via microbe–microbe interactions, transmit the effects to the microbial community. We analyzed two “hub” microbes (the obligate biotrophic oomycete pathogen Albugo and the basidiomycete yeast fungus Dioszegia) more closely. Albugo had strong effects on epiphytic and endophytic bacterial colonization. Specifically, alpha diversity decreased and beta diversity stabilized in the presence of Albugo infection, whereas they otherwise varied between plants. Dioszegia, on the other hand, provided evidence for direct hub interaction with phyllosphere bacteria. The identification of microbial “hubs” and their importance in phyllosphere microbiome structuring has crucial implications for plant–pathogen and microbe–microbe research and opens new entry points for ecosystem management and future targeted biocontrol. The revelation that effects can cascade through communities via “hub” microbes is important to understand community structure perturbations in parallel fields including human microbiomes and bioprocesses. In particular, parallels to human microbiome “keystone” pathogens and microbes open new avenues of interdisciplinary research that promise to better our understanding of functions of host-associated microbiomes.

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bioRxiv: A bacterial parasite effector mediates insect vector attraction in host plants independently of developmental changes (2016)

bioRxiv: A bacterial parasite effector mediates insect vector attraction in host plants independently of developmental changes (2016) | Plants and Microbes | Scoop.it

Parasites can take over their hosts and trigger dramatic changes in host appearance and behaviour that are typically interpreted as extended phenotypes to promote parasite survival and fitness. For example, Toxoplasma gondii manipulates the behaviour of infected rodents to aid transmission to cats and parasitic trematodes of the genus Ribeiroia alter limb development in their amphibian hosts to facilitate predation by birds. Plant parasites and pathogens also reprogram host development and morphology. Phytoplasma parasites of plants induce extensive leaf-like flower phenotype (phyllody) in their host plants, presumably to attract insect vectors on which these bacteria depend for transmission. However, it remains debatable whether morphological phenotypes, such as phyllody, are directly beneficial to the parasites or are side-products of parasite infection. Previously, we found that phytoplasma virulence protein (effector) SAP54 binds and mediates degradation of host MADS-box transcription factors (MTFs), regulatory hubs of plant development and hormone physiology, to induce phyllody and promote insect vector colonisation. Here we show that plants heterologously expressing SAP54 are strongly attractive to insects, but surprisingly, insect attraction was independent of the presence of leaf-like flowers. Moreover, plants that produce leaf-like flowers in the absence of SAP54 did not attract insects. We conclude that the SAP54 effector mediates insect vector attraction in host plants by exploiting the role of its MTF targets in insect defence and that perturbation of floral development may be a secondary effect of the effector activity.

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New Phytologist: CRN13 candidate effectors from plant and animal eukaryotic pathogens are DNA-binding proteins which trigger host DNA damage response (2015)

New Phytologist: CRN13 candidate effectors from plant and animal eukaryotic pathogens are DNA-binding proteins which trigger host DNA damage response (2015) | Plants and Microbes | Scoop.it
  • To successfully colonize their host, pathogens produce effectors that can interfere with host cellular processes. Here we investigated the function of CRN13 candidate effectors produced by plant pathogenic oomycetes and detected in the genome of the amphibian pathogenic chytrid fungus Batrachochytrium dendrobatidis (BdCRN13).
  • When expressed in Nicotiana, AeCRN13, from the legume root pathogen Aphanomyces euteiches, increases the susceptibility of the leaves to the oomycete Phytophthora capsici. When transiently expressed in amphibians or plant cells, AeCRN13 and BdCRN13 localize to the cell nuclei, triggering aberrant cell development and eventually causing cell death.
  • Using Förster resonance energy transfer experiments in plant cells, we showed that both CRN13s interact with nuclear DNA and trigger plant DNA damage response (DDR). Mutating key amino acid residues in a predicted HNH-like endonuclease motif abolished the interaction of AeCRN13 with DNA, the induction of DDR and the enhancement of Nicotiana susceptibility to P. capsici. Finally, H2AX phosphorylation, a marker of DNA damage, and enhanced expression of genes involved in the DDR were observed in A. euteiches-infected Medicago truncatula roots.
  • These results show that CRN13 from plant and animal eukaryotic pathogens promotes host susceptibility by targeting nuclear DNA and inducing DDR.
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PLOS Biology: A Latex Metabolite Benefits Plant Fitness under Root Herbivore Attack (2015)

PLOS Biology: A Latex Metabolite Benefits Plant Fitness under Root Herbivore Attack (2015) | Plants and Microbes | Scoop.it

Dandelion plants protect their roots from the larva of the common cockchafer beetle by accumulating and releasing a sesquiterpene lactone deterrent in their exuded latex.


Plants produce large amounts of secondary metabolites in their shoots and roots and store them in specialized secretory structures. Although secondary metabolites and their secretory structures are commonly assumed to have a defensive function, evidence that they benefit plant fitness under herbivore attack is scarce, especially below ground. Here, we tested whether latex secondary metabolites produced by the common dandelion (Taraxacum officinaleagg.) decrease the performance of its major native insect root herbivore, the larvae of the common cockchafer (Melolontha melolontha), and benefit plant vegetative and reproductive fitness under Mmelolontha attack. Across 17 Tofficinale genotypes screened by gas and liquid chromatography, latex concentrations of the sesquiterpene lactone taraxinic acid β-D-glucopyranosyl ester (TA-G) were negatively associated with Mmelolontha larval growth. Adding purified TA-G to artificial diet at ecologically relevant concentrations reduced larval feeding. Silencing the germacrene A synthase ToGAS1, an enzyme that was identified to catalyze the first committed step of TA-G biosynthesis, resulted in a 90% reduction of TA-G levels and a pronounced increase in Mmelolontha feeding. Transgenic, TA-G-deficient lines were preferred by Mmelolontha and suffered three times more root biomass reduction than control lines. In a common garden experiment involving over 2,000 Tofficinale individuals belonging to 17 different genotypes, high TA-G concentrations were associated with the maintenance of high vegetative and reproductive fitness under Mmelolontha attack. Taken together, our study demonstrates that a latex secondary metabolite benefits plants under herbivore attack, a result that provides a mechanistic framework for root herbivore driven natural selection and evolution of plant defenses below ground.

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YouTube: Protecting our food crops from fungal attack (2015)

Find out how we can fight back against wheat yellow rust disease by discovering new genomics-based surveillance techniques to track plant disease around the globe.

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#36NPS New Phytologist Symposium: Cell biology at the plant–microbe interface, Munich, Germany, 29 November – 1 December 2015 (with images, tweets)

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