Plants and Microbes
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Evolution: Partial resistance in the Linum-Melampsora host-pathogen system: does partial resistance make the red queen run slower? (2010)

Five levels of disease expression were scored in a cross-inoculation study of 120 host and 60 pathogen lines of wild flax Linum marginale and its rust fungus Melampsora lini sampled from six natural populations. Patterns of partial resistance showed clear evidence of gene-for-gene interactions, with particular levels of partial resistance occurring in specific host–pathogen combinations. Sympatric and putatively more highly coevolved host–pathogen combinations had a lower frequency of partial resistance types relative to allopatric combinations. Sympatric host–pathogen combinations also showed a lower diversity of resistance responses, but there was a trend toward a greater fraction of this variance being determined by pathogen-genotype × host-genotype interactions. In this system, there was no evidence that partial resistances slow host–pathogen coevolution. The analyses show that if variation is generated by among population host or pathogen dispersal, then coevolution occurs largely by pathogens overcoming the partial resistances that are generated.
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The Guardian: This new disease could devastate our wildlife (2017)

The Guardian: This new disease could devastate our wildlife (2017) | Plants and Microbes | Scoop.it

The less you care, the better you will do. This has long been the promise of conservative politics on both sides of the Atlantic. People who couldn’t give a tinker’s cuss about the consequences of their actions are elevated to the highest levels of government. Their role is to trash what lesser mortals value.

 

This describes the position of almost everyone in Donald Trump’s cabinet. In the UK, I feel it applies, among others, to Jeremy Hunt at the Department of Health, Boris Johnson at the Foreign Office, Priti Patel at international development and now Michael Gove at the environment department: the worst possible candidates are given the most sensitive portfolios.

 

Let me give you an example of how dangerous this appointment – and the government’s wider agenda – could be. A plant disease called Xylella fastidiosa, which originated in South America, is leaping across the European continent. It has now reached Italy, the Balearic Islands, Germany and France. As well as crops, it threatens many forest trees, including oak, elm, ash, cherry, sycamore and plane. Urban trees seem to be especially susceptible, perhaps because of the stresses they suffer: in American cities, some streets have had to be clear-felled. There is no known cure.

 

Xylella has ripped through olive groves in Italy and vineyards and fruit farms in the Americas. It is impossible to say how many species it might affect, how much damage it might do, and whether it would thrive in our climate. But we should hope we never find out.

 

It is unlikely to stay within the current European infection sites. Once the disease arrives, in imported plants, it is spread by sap-sucking insects, which can quickly be blown beyond the exclusion zones the EU has established. One of the few places that could remain unaffected is the UK, whose islands, Shakespeare remarked, are a “fortress built by Nature for herself against infection”. This blessed plot could become a reserve for species hammered by invasive diseases elsewhere.

 

But the government won’t contemplate it. Ignoring the pleas of foresters, scientists and some tree nurseries, the only measure it will apply is a “plant passport”. This will certify that potential hosts of the disease are free from infection before they are imported. There are 55 plants on its list. But already, according to the European Food Safety Authority, 359 plant species are known to carry the disease, in many cases without showing symptoms. They range across wildly different plant families, from magnolias to meadow grass, hydrangeas to holly, asparagus to aubergines, broad beans to buttercups, nettles to nightshade and lilac to lemon trees. New hosts are being discovered all the time. The only safe assumption is that almost any species could be a potential carrier.

 

In other words, the entire live plant trade presents a threat. The freedom with which it can move plants and the soil in which they are rooted across borders is a classic example of regulatory failure that has over the years spread hundreds of invasive species around the world. Unless there is a radical change of policy, the UK appears likely to repeat its grim experience with Dutch elm disease and ash dieback, but in this case potentially affecting far more species.

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MPMI: The tomato kinase Pti1 contributes to production of reactive oxygen species in response to two flagellin-derived peptides and promotes resistance to Pseudomonas syringae infection (2017)

MPMI: The tomato kinase Pti1 contributes to production of reactive oxygen species in response to two flagellin-derived peptides and promotes resistance to Pseudomonas syringae infection (2017) | Plants and Microbes | Scoop.it

The Pti1 kinase was identified from a reverse genetic screen as contributing to pattern-triggered immunity (PTI) against Pseudomonas syringae pv. tomato (Pst). This was unexpected because Pti1 was originally identified as an interactor of the Pto kinase and was implicated in effector-triggered immunity. The tomato genome has two Pti1 genes, referred to as Pti1a and Pti1b. A hairpin-Pti1 (hpPti1) construct was developed and used to generate two independent stable transgenic tomato lines, which had reduced transcript abundance of both genes. In response to Pst inoculation, these hpPti1 plants developed more severe disease symptoms, supported higher bacterial populations, and had reduced transcript accumulation of PTI-associated genes compared to wild-type plants. In response to two flagellin-derived peptides the hpPti1 plants produced less reactive oxygen species (ROS), but showed no difference in mitogen-activated protein kinase (MAPK). Synthetic Pti1a and Pti1bgenes designed to avoid silencing were transiently expressed in the hpPti1 plants and restored the ability of the plants to produce wild-type levels of ROS. Our results identify a new component of PTI in tomato which, because it affects ROS production but not MAPK signaling, appears to act early in the immune response.

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Fourth Powdery Mildew School, Eger, Hungary, 9-13 September 2017

Fourth Powdery Mildew School, Eger, Hungary, 9-13 September 2017 | Plants and Microbes | Scoop.it

Eszterházy Károly University (Eger, Hungary), in collaboration with Plant Protection Institute, Centre for Agricultural Research, Hungarian Academy of Sciences (Budapest, Hungary) and Centre for Crop Health, University of Southern Queensland (Toowoomba, Australia), invites MSc and PhD students and postdoc researchers interested in the study of powdery mildew fungi (Erysiphales) to an exciting autumn school covering all the major aspects of powdery mildew research. The official language of the course is English. This is the fourth Powdery Mildew School; the previous ones were organized in 2014, 2015 and 2016. Participants of the earlier workshops are welcome again in Eger.


The programme includes:

 

lectures on the morphology, phylogeny, genomics, host range, invasive patterns, host-pathogen interactions, and control of powdery mildews;

 

practical training in the classical and molecular identification of powdery mildews, quantification of infection levels, ascospore viability tests, and so on; the training activities will consist of hands-on experiments using light microscopy, including fluorescence techniques, DNA extractions from fresh and herbarium samples, PCR and qPCR methods, etc.;

 

discussion seminars on a number of recent and important papers; these will be presented by those participants who volunteer in advance to present a paper from the list of papers to be discussed in Eger.

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Plant Cell: Interplay of Plasma Membrane and Vacuolar Ion Channels, Together with BAK1, Elicits Rapid Cytosolic Calcium Elevations in Arabidopsis during Aphid Feeding (2017)

Plant Cell: Interplay of Plasma Membrane and Vacuolar Ion Channels, Together with BAK1, Elicits Rapid Cytosolic Calcium Elevations in Arabidopsis during Aphid Feeding (2017) | Plants and Microbes | Scoop.it

A transient rise in cytosolic calcium ion concentration is one of the main signals used by plants in perception of their environment. The role of calcium in the detection of abiotic stress is well documented; however, its role during biotic interactions remains unclear. Here, we use a fluorescent calcium biosensor (GCaMP3) in combination with the green peach aphid (Myzus persicae) as a tool to study Arabidopsis thaliana calcium dynamics in vivo and in real time during a live biotic interaction. We demonstrate rapid and highly-localised plant calcium elevations around the feeding sites of M. persicae, and by monitoring aphid feeding behaviour electrophysiologically we demonstrate that these elevations correlate with aphid probing of epidermal and mesophyll cells. Furthermore, we dissect the molecular mechanisms involved, showing that interplay between the plant defence co-receptor BRASSINOSTEROID INSENSITIVE-ASSOCIATED KINASE 1 (BAK1), the plasma membrane ion channels GLUTAMATE RECEPTOR-LIKE 3.3 and 3.6 (GLR3.3 and GLR3.6) and the vacuolar ion channel TWO-PORE CHANNEL 1 (TPC1) mediate these calcium elevations. Consequently, we identify a link between plant perception of biotic threats by BAK1, cellular calcium entry mediated by GLRs, and intracellular calcium release by TPC1 during a biologically relevant interaction.

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Science: Ecological and evolutionary effects of fragmentation on infectious disease dynamics (2014)

Science: Ecological and evolutionary effects of fragmentation on infectious disease dynamics (2014) | Plants and Microbes | Scoop.it

Ecological theory predicts that disease incidence increases with increasing density of host networks, yet evolutionary theory suggests that host resistance increases accordingly. To test the combined effects of ecological and evolutionary forces on host-pathogen systems, we analyzed the spatiotemporal dynamics of a plant (Plantago lanceolata)–fungal pathogen (Podosphaera plantaginis)relationship for 12 years in over 4000 host populations. Disease prevalence at the metapopulation level was low, with high annual pathogen extinction rates balanced by frequent (re-)colonizations. Highly connected host populations experienced less pathogen colonization and higher pathogen extinction rates than expected; a laboratory assay confirmed that this phenomenon was caused by higher levels of disease resistance in highly connected host populations.


Via Niklaus Grunwald
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Plant Cell: The RxLR Motif of the Host Targeting Effector AVR3a of Phytophthora infestans Is Cleaved Before Secretion (2017)

Plant Cell: The RxLR Motif of the Host Targeting Effector AVR3a of Phytophthora infestans Is Cleaved Before Secretion (2017) | Plants and Microbes | Scoop.it

When plant-pathogenic oomycetes infect their hosts, they employ a large arsenal of effector proteins to establish a successful infection. Some effector proteins are secreted and are destined to be translocated and function inside host cells. The largest group of translocated proteins from oomycetes are the RxLR effectors, defined by their conserved N-terminal Arg-Xaa-Leu-Arg (RxLR) motif. However, the precise role of this motif in the host cell translocation process is unclear. Here detailed biochemical studies of the RxLR effector AVR3a from the potato pathogen Phytophthora infestans are presented. Mass spectrometric analysis revealed that the RxLR sequence of native AVR3a is cleaved off prior to secretion by the pathogen and the N-terminus of the mature effector was found likely to be acetylated. High-resolution NMR structure analysis of AVR3a indicates that the RxLR motif is well accessible to potential processing enzymes. Processing and modification of AVR3a is to some extent similar to events occurring with the export element (PEXEL) found in malaria effector proteins from Plasmodium falciparum. These findings imply a role for the RxLR motif in the secretion of AVR3a by the pathogen, rather than a direct role in the host cell entry process itself.

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bioRxiv: Organ-Specific NLR Resistance Gene Expression Varies With Plant Symbiotic Status (2017)

bioRxiv: Organ-Specific NLR Resistance Gene Expression Varies With Plant Symbiotic Status (2017) | Plants and Microbes | Scoop.it

Nucleotide-binding site leucine-rich repeat resistance genes (NLRs) allow plants to detect microbial effectors. We hypothesized that NLR expression patterns would reflect organ-specific differences in effector challenge and tested this by carrying out a meta-analysis of expression data for 1,235 NLRs from 9 plant species. We found stable NLR root/shoot expression ratios within species, suggesting organ-specific hardwiring of NLR expression patterns in anticipation of distinct challenges. Most monocot and dicot plant species preferentially expressed NLRs in roots. In contrast, Brassicaceae species, including oilseed rape and the model plant Arabidopsis thaliana, were unique in showing NLR expression skewed towards the shoot across multiple phylogenetically distinct groups of NLRs. The Brassicaceae NLR expression shift coincides with loss of the endomycorrhization pathway, which enables intracellular root infection by symbionts. We propose that its loss offer two likely explanations for the unusual Brassicaceae NLR expression pattern: loss of NLR-guarded symbiotic components and elimination of constraints on general root defences associated with exempting symbionts from targeting. This hypothesis is consistent with the existence of Brassicaceae-specific receptors for conserved microbial molecules and suggests that Brassicaceae species could be rich sources of unique antimicrobial root defence mechanisms.

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New Phytologist: A small secreted protein in Zymoseptoria tritici is responsible for avirulence on wheat cultivars carrying the Stb6 resistance gene (2016)

New Phytologist: A small secreted protein in Zymoseptoria tritici is responsible for avirulence on wheat cultivars carrying the Stb6 resistance gene (2016) | Plants and Microbes | Scoop.it
  • Zymoseptoria tritici is the causal agent of Septoria tritici blotch, a major pathogen of wheat globally and the most damaging pathogen of wheat in Europe. A gene-for-gene (GFG) interaction between Z. tritici and wheat cultivars carrying the Stb6resistance gene has been postulated for many years, but the genes have not been identified.
  • We identified AvrStb6 by combining quantitative trait locus mapping in a cross between two Swiss strains with a genome-wide association study using a natural population of c. 100 strains from France. We functionally validated AvrStb6 using ectopic transformations.
  • AvrStb6 encodes a small, cysteine-rich, secreted protein that produces an avirulence phenotype on wheat cultivars carrying the Stb6 resistance gene. We found 16 nonsynonymous single nucleotide polymorphisms among the tested strains, indicating that AvrStb6 is evolving very rapidly. AvrStb6 is located in a highly polymorphic subtelomeric region and is surrounded by transposable elements, which may facilitate its rapid evolution to overcome Stb6 resistance.
  • AvrStb6 is the first avirulence gene to be functionally validated in Z. tritici, contributing to our understanding of avirulence in apoplastic pathogens and the mechanisms underlying GFG interactions between Z. tritici and wheat.

 


Via Christophe Jacquet
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Molecular Plant: Effector–Decoy Pairs: Another Countermeasure Emerging during Host–Microbe Co-evolutionary Arms Races? (2017)

Molecular Plant: Effector–Decoy Pairs: Another Countermeasure Emerging during Host–Microbe Co-evolutionary Arms Races? (2017) | Plants and Microbes | Scoop.it
Plant pathogenic microbes pose a significant threat to food production, collectively affecting all cultivated crops. Given the impact of these pathogens on food security, there continues to be an urgent need to understand and exploit the biology of pathogenesis, plant susceptibility, and immunity in crop systems. Consequently, intense research efforts have helped define the molecular and evolutionary events that underpin plant-microbe interactions.

Via Nicolas Denancé
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PNAS: Interspecies hormonal control of host root morphology by parasitic plants (2017)

PNAS: Interspecies hormonal control of host root morphology by parasitic plants (2017) | Plants and Microbes | Scoop.it

Parasitic plants share a common anatomical feature, the haustorium. Haustoria enable both infection and nutrient transfer, which often leads to growth penalties for host plants and yield reduction in crop species. Haustoria also reciprocally transfer substances, such as RNA and proteins, from parasite to host, but the biological relevance for such movement remains unknown. Here, we studied such interspecies transport by using the hemiparasitic plant Phtheirospermum japonicum during infection of Arabidopsis thaliana. Tracer experiments revealed a rapid and efficient transfer of carboxyfluorescein diacetate (CFDA) from host to parasite upon formation of vascular connections. In addition, Phtheirospermum induced hypertrophy in host roots at the site of infection, a form of enhanced secondary growth that is commonly observed during various parasitic plant–host interactions. The plant hormone cytokinin is important for secondary growth, and we observed increases in cytokinin and its response during infection in both host and parasite. Phtheirospermum-induced host hypertrophy required cytokinin signaling genes (AHK3,4) but not cytokinin biosynthesis genes (IPT1,3,5,7) in the host. Furthermore, expression of a cytokinin-degrading enzyme in Phtheirospermum prevented host hypertrophy. Wild-type hosts with hypertrophy were smaller than ahk3,4 mutant hosts resistant to hypertrophy, suggesting hypertrophy improves the efficiency of parasitism. Taken together, these results demonstrate that the interspecies movement of a parasite-derived hormone modified both host root morphology and fitness. Several microbial and animal plant pathogens use cytokinins during infections, highlighting the central role of this growth hormone during the establishment of plant diseases and revealing a common strategy for parasite infections of plants.


Via Pierre-Marc Delaux
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Book: Fortress Plant- How to survive when everything wants to eat you (2017)

Book: Fortress Plant- How to survive when everything wants to eat you (2017) | Plants and Microbes | Scoop.it

The survival of plants on our planet is nothing short of miraculous. They are virtually stationary packages of food, providing sustenance for a vast array of organisms, ranging from bacteria and fungi, through to insects, and even other plants. But plants are master survivors, having coped with changing environments and evolving predators over much of the history of life on earth.

 

  • Looks at how plants defend themselves against a wide variety of attackers, such as big animals, tiny insects, fungi, and bacteria, using an arsenal of weapons
  • Explores the evolution of plant defences, showing how they have resulted from an arms race with attackers that has been raging for millions of years
  • Describes the approaches by which scientists learn about plant defences
  • Considers how we can use our knowledge of plant defences to help protect our food crops and forests
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Cell Host & Microbe: Matching NLR Immune Receptors to Autoimmunity in camta3 Mutants Using Antimorphic NLR Alleles (2017)

Cell Host & Microbe: Matching NLR Immune Receptors to Autoimmunity in camta3 Mutants Using Antimorphic NLR Alleles (2017) | Plants and Microbes | Scoop.it

Highlights
• Dominant-negative NLR forms (DN-NLR) disrupt the function of wild-type NLR alleles
• DN-NLRs can be used to screen for suppression of autoimmunity in autoimmune mutants
• Two NLRs (DSC1 and DSC2) are responsible for autoimmunity in Arabidopsis camta3 mutants
• Immunity triggered by DSC1 or DSC2 in tobacco is suppressed by CAMTA3 co-expression
 
Summary

To establish infection, pathogens deploy effectors to modify or remove host proteins. Plant immune receptors with nucleotide-binding, leucine-rich repeat domains (NLRs) detect these modifications and trigger immunity. Plant NLRs thus guard host “guardees.” A corollary is that autoimmunity may result from inappropriate NLR activation because mutations in plant guardees could trigger corresponding NLR guards. To explore these hypotheses, we expressed 108 dominant-negative (DN) Arabidopsis NLRs in various lesion mimic mutants, including camta3, which exhibits autoimmunity. CAMTA3 was previously described as a negative regulator of immunity, and we find that autoimmunity in camta3 is fully suppressed by expressing DNs of two NLRs, DSC1 and DSC2. Additionally, expression of either NLR triggers cell death that can be suppressed by CAMTA3 expression. These findings support a model in which DSC1 and DSC2 guard CAMTA3, and they suggest that other negative regulators of immunity may similarly represent guardees. 

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Trends in Plant Sciences: Strigolactones in Plant Interactions with Beneficial and Detrimental Organisms: The Yin and Yang (2017)

Trends in Plant Sciences: Strigolactones in Plant Interactions with Beneficial and Detrimental Organisms: The Yin and Yang (2017) | Plants and Microbes | Scoop.it

Strigolactones (SLs) are plant hormones that have important roles as modulators of plant development. They were originally described as ex planta signaling molecules in the rhizosphere that induce the germination of parasitic plants, a role that was later linked to encouraging the beneficial symbiosis with arbuscular mycorrhizal (AM) fungi. Recently, the focus has shifted to examining the role of SLs in plant–microbe interactions, and has revealed roles for SLs in the association of legumes with nitrogen-fixing rhizobacteria and in interactions with disease-causing pathogens.


Via Pierre-Marc Delaux, Jean-Michel Ané, Jim Alfano
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Vimeo: Soil Life in Action: Tomato Plants with fungal infection (2017)

Time-lapse of a healthy tomato plant (left) and a tomato plant that was inoculated with the fungus Verticillium dahliae (right).The effect on the root and stem development is visible.

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Plantae: In Brief: An Emerging Paradigm? RxLR Cleavage Before Effector Secretion (2017)

Plantae: In Brief: An Emerging Paradigm? RxLR Cleavage Before Effector Secretion (2017) | Plants and Microbes | Scoop.it

Eukaryotic pathogens are responsible for devastating plant diseases that threaten food supplies globally – think potato blight caused by the oomycete Phytophora infestans, rice blast caused by the fungus Magnaporthe oryzae, and wheat stem rust caused by the fungus Puccinia graminis f. sp. tritici. These pathogens secrete effector proteins that condition the host cells for successful infection, some by acting in the apoplast and others after entering into the host cells. Many oomycete effectors have an RxLR sequence motif in their N-terminal region that seems to function in host cell targeting, although the mechanisms are a matter of debate (reviewed in Wawra et al., 2012 and Petre and Kamoun, 2014). It is notoriously difficult to study the secretion and targeting of effectors, as these processes occur only at the interface of the pathogen with the host and only during infection. In fact, there are mounting indications that some alternative approaches often used to assess pathogen effector secretion and entry in the host plant could be flawed (see, for example, Petre et al., http://dx.doi.org/10.1101/038232). In a new Breakthrough Report, Wawra & Trusch et al. (2017) provide evidence that the RxLR motif is important for effector secretion from the pathogen, rather than for direct interaction with the host cells.

 

Plasmodium parasites, which cause malaria, are distantly related to oomycete plant pathogens and similarly have RxLR-like N-terminal sequences that are responsible for targeting to host cells. For many Plasmodium effectors, this so-called PEXEL motif is cleaved in the ER, after which the newly exposed N-terminus is acetylated and the effector is secreted. Another motif, called the TEXEL motif, is important for effector processing in Toxoplasma gondii. The similarity of the RxLR motif to the PEXEL and TEXEL motifs prompted Wawra and coworkers to explore whether RxLR cleavage is involved in effector secretion from P. infestans.

 

Wawra & Trusch et al. isolated the native (untagged) form of the AVR3a effector secreted into the culture medium by P. infestans. LC-MS/MS analysis did not reveal a peptide representing any sequence more N-terminal than the RxLR motif, but did find a peptide that started immediately downstream of the motif. In addition, the MS data showed likely acetylation. To further characterize the secreted form of the effector, the authors performed reverse-phase chromatography followed by MALDI-TOF analysis. After deglycosylation, the mass of the main product indicated that the AVR3a protein from the medium lacked the first 47 amino acids (i.e., the region up to and including the RxLR motif) with an additional mass for a possible acetylation.

 

Wawra and coworkers followed up on the possibility of N-terminal acetylation using Edman degradation, which can cleave an N-terminal peptide bond when it is accessible. They observed no cleavage of the AVR3a peptide from the medium, indicating that the N-terminus was not accessible, consistent with it being acetylated. The likely N-acetylation of AVR3a is particularly intriguing as the acetyltransferases that carry out such N-acetylation are found only inside the cell.

 

Overall, these results are consistent with cleavage of the RxLR motif of AVR3a, followed by acetylation of the new N-terminal amino acid before secretion from P. infestans. It is not clear what protease might be responsible for the cleavage, because none of the 11 P. infestans aspartic proteases homologous to the protease that cleaves the PEXEL motif in Plasmodium could cleave AVR3a in assays using recombinant bacterially expressed proteins. Nevertheless, the potential similarity of this process to the processing and secretion of effectors from other species containing the PEXEL and TEXEL motifs points to its biological relevance and a possible conserved mechanism for effector secretion.

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bioRxiv: Lipid transfer from plants to arbuscular mycorrhiza fungi (2017)

bioRxiv: Lipid transfer from plants to arbuscular mycorrhiza fungi (2017) | Plants and Microbes | Scoop.it

Arbuscular mycorrhiza (AM) symbioses contribute to global carbon cycles as plant hosts divert up to 20% of photosynthate to the obligate biotrophic fungi. Previous studies suggested carbohydrates as the only form of carbon transferred to the fungi. However, de novo fatty acid (FA) synthesis has not been observed in AM fungi in absence of the plant. In a forward genetic approach, we identified two Lotus japonicus mutants defective in AM-specific paralogs of lipid biosynthesis genes (KASI and GPAT6). These mutants perturb fungal development and accumulation of emblematic fungal 16:1ω5 FAs. Using isotopolog profiling we demonstrate that 13C patterns of fungal FAs recapitulate those of wild-type hosts, indicating cross-kingdom lipid transfer from plants to fungi. This transfer of labelled FAs was not observed for the AM-specific lipid biosynthesis mutants. Thus, growth and development of beneficial AM fungi is not only fueled by sugars but depends on lipid transfer from plant hosts.

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Biological Control: Ampelomyces quisqualis—a parasite of powdery mildews

Biological Control: Ampelomyces quisqualis—a parasite of powdery mildews | Plants and Microbes | Scoop.it

The fungus Ampelomyces quisqualis is a naturally occurring hyperparasite of powdery mildews. It infects and forms pycnidia (fruiting bodies) within powdery mildew hyphae, conidiophores (specialized spore-producing hyphae), and cleistothecia (the closed fruiting bodies of powdery mildews). This parasitism reduces growth and may eventually kill the mildew colony. A. quisqualis has been the subject of numerous investigations on biological control of powdery mildews for over 50 years.

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New Phytologist: A new proteinaceous pathogen‐associated molecular pattern (PAMP) identified in Ascomycete fungi induces cell death in Solanaceae (2017)

New Phytologist: A new proteinaceous pathogen‐associated molecular pattern (PAMP) identified in Ascomycete fungi induces cell death in Solanaceae (2017) | Plants and Microbes | Scoop.it

Pathogen-associated molecular patterns (PAMPs) are detected by plant pattern recognition receptors (PRRs), which gives rise to PAMP-triggered immunity (PTI). We characterized a novel fungal PAMP, Cell Death Inducing 1 (RcCDI1), identified in the Rhynchosporium commune transcriptome sampled at an early stage of barley (Hordeum vulgare) infection. The ability of RcCDI1 and its homologues from different fungal species to induce cell death in Nicotiana benthamiana was tested following agroinfiltration or infiltration of recombinant proteins produced by Pichia pastoris. Virus-induced gene silencing (VIGS) and transient expression of Phytophthora infestans effectors PiAVR3a and PexRD2 were used to assess the involvement of known components of PTI in N. benthamiana responses to RcCDI1. RcCDI1 was highly upregulated early during barley colonization with R. commune. RcCDI1 and its homologues from different fungal species, including Zymoseptoria tritici, Magnaporthe oryzae and Neurospora crassa, exhibited PAMP activity, inducing cell death in Solanaceae but not in other families of dicots or monocots. RcCDI1-triggered cell death was shown to require N. benthamiana Brassinosteroid insensitive 1-Associated Kinase 1 (NbBAK1), N. benthamiana suppressor of BIR1-1 (NbSOBIR1) and N. benthamiana SGT1 (NbSGT1), but was not suppressed by PiAVR3a or PexRD2. We report the identification of a novel Ascomycete PAMP, RcCDI1, recognized by Solanaceae but not by monocots, which activates cell death through a pathway that is distinct from that triggered by the oomycete PAMP INF1.


Via Elsa Ballini
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International Symposium on Potato Late Blight Resistance, Huazhong Agricultural University, 10-14 October 2017

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bioRxiv: Specific hypersensitive response-associated recognition of new apoplastic effectors from Cladosporium fulvum in wild tomato (2017)

bioRxiv: Specific hypersensitive response-associated recognition of new apoplastic effectors from Cladosporium fulvum in wild tomato (2017) | Plants and Microbes | Scoop.it

Tomato leaf mould disease is caused by the biotrophic fungus Cladosporium fulvum. During infection, C. fulvum produces extracellular small secreted protein (SSP) effectors that function to promote colonization of the leaf apoplast. Resistance to the disease is governed by Cf immune receptor genes that encode receptor-like proteins (RLPs). These RLPs recognize specific SSP effectors to initiate a hypersensitive response (HR) that renders the pathogen avirulent. C. fulvum strains capable of overcoming one or more of all cloned Cf genes have now emerged. To combat these strains, new Cf genes are required. An effectoromics approach was employed to identify wild tomato accessions carrying new Cf genes. Proteomics and transcriptome sequencing were first used to identify 70 apoplastic in planta-induced C. fulvum SSPs. Based on sequence homology, 61 of these SSPs were novel or lacked known functional domains. Seven, however, had predicted structural homology to antimicrobial proteins, suggesting a possible role in mediating antagonistic microbe-microbe interactions in planta. Wild tomato accessions were then screened for HR-associated recognition of 41 SSPs using the Potato virus X-based transient expression system. Nine SSPs were recognized by one or more accessions, suggesting that these plants carry new Cf genes available for incorporation into cultivated tomato.

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Current Biology: Plant Autoimmunity: When Good Things Go Bad (2017)

Current Biology: Plant Autoimmunity: When Good Things Go Bad (2017) | Plants and Microbes | Scoop.it

A recent study finds that the Arabidopsis DM1 and DM2d proteins physically interact and trigger autoimmunity in plants. The DM1–DM2d interaction pattern differs from that of known immune receptor pairs, portraying the versatility in NLR functioning.

 

See Tran et al. Activation of a Plant NLR Complex through Heteromeric Association with an Autoimmune Risk Variant of Another NLR http://www.cell.com/current-biology/abstract/S0960-9822(17)30287-7

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Current Opinion in Plant Biology: Taking the stage: effectors in the spotlight (2017)

Current Opinion in Plant Biology: Taking the stage: effectors in the spotlight (2017) | Plants and Microbes | Scoop.it

• Plant pathogens deploy host-translocated effectors to promote disease.
• Hundreds of putative effectors have been identified, but few have been studied.
• Knowledge of host targets, and/or effector activity, allows insight into function.
• Understanding effector function offers opportunities for improving agriculture.

Plant pathogens are a serious threat to agriculture and to global food security, causing diverse crop diseases which lead to extensive annual yield losses. Production of effector proteins by pathogens, to manipulate host cellular processes, is central to their success. An understanding of fundamental effector biology is key to addressing the threat posed by these pathogens. Recent advances in ‘omics’ technologies have facilitated high-throughput identification of putative effector proteins, while evolving cellular, structural and biochemical approaches have assisted in characterising their function. Furthermore, structures of effectors in complex with host factors now provide opportunities for applying our knowledge of effector biology to influence disease outcomes. In this review, we highlight recent advances in the field and suggest avenues for future research.

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Colloque: Académie des sciences "Symbiose et cohabitation", Paris, 25 avril 2017

Colloque: Académie des sciences "Symbiose et cohabitation", Paris, 25 avril 2017 | Plants and Microbes | Scoop.it
Les interactions symbiotiques sont beaucoup plus répandues que ce que l’on pensait jusqu'à récemment. Ce qui était souvent considéré comme une simple cohabitation avec des microorganismes commensaux se trouve être une véritable association à bénéfices réciproques, avec échanges multiples de signaux entre partenaires. L’essor de la métagénomique et de la biologie cellulaire permet maintenant une analyse beaucoup plus détaillée de ces interactions. Le principal modèle de symbiose étudié au niveau moléculaire a été l’interaction entre légumineuses et la bactérie Sinorhizobium qui aide la plante à fixer l’azote atmosphérique. De nombreuses autres symbioses sont maintenant à l’étude. L’objectif de ce colloque est de faire le point de nos connaissances, notamment sur ces nouveaux modèles d’interaction et d’en comprendre les mécanismes et la signalisation.

-> Mardi 25 avril 2017 de 9h30 à 17h, en Grande salle des séances de l'Institut de France.
 

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New Phytologist: Arbuscular mycorrhiza‐specific enzymes FatM and RAM2 fine‐tune lipid biosynthesis to promote development of arbuscular mycorrhiza (2017)

New Phytologist: Arbuscular mycorrhiza‐specific enzymes FatM and RAM2 fine‐tune lipid biosynthesis to promote development of arbuscular mycorrhiza (2017) | Plants and Microbes | Scoop.it
  • During arbuscular mycorrhizal symbiosis (AMS), considerable amounts of lipids are generated, modified and moved within the cell to accommodate the fungus in the root, and it has also been suggested that lipids are delivered to the fungus. To determine the mechanisms by which root cells redirect lipid biosynthesis during AMS we analyzed the roles of two lipid biosynthetic enzymes (FatM and RAM2) and an ABC transporter (STR) that are required for symbiosis and conserved uniquely in plants that engage in AMS.
  • Complementation analyses indicated that the biochemical function of FatM overlaps with that of other Fat thioesterases, in particular FatB. The essential role of FatM in AMS was a consequence of timing and magnitude of its expression.
  • Lipid profiles of fatm and ram2 suggested that FatM increases the outflow of 16:0 fatty acids from the plastid, for subsequent use by RAM2 to produce 16:0 β-monoacylglycerol.
  • Thus, during AMS, high-level, specific expression of key lipid biosynthetic enzymes located in the plastid and the endoplasmic reticulum enables the root cell to fine-tune lipid biosynthesis to increase the production of β-monoacylglycerols. We propose a model in which β-monoacylglycerols, or a derivative thereof, are exported out of the root cell across the periarbuscular membrane for ultimate use by the fungus.

 

 

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MPMI: Foundational and translational research opportunities to improve plant health (2017)

MPMI: Foundational and translational research opportunities to improve plant health (2017) | Plants and Microbes | Scoop.it

This whitepaper reports the deliberations of a workshop focused on biotic challenges to plant health held in Washington, D.C. in September 2016. Ensuring health of food plants is critical to maintaining the quality and productivity of crops and for sustenance of the rapidly growing human population. There is a close linkage between food security and societal stability; however, global food security is threatened by the vulnerability of our agricultural systems to numerous pests, pathogens, weeds, and environmental stresses. These threats are aggravated by climate change, the globalization of agriculture, and an over-reliance on non-sustainable inputs. New analytical and computational technologies are providing unprecedented resolution at a variety of molecular, cellular, organismal, and population scales for crop plants as well as pathogens, pests, beneficial microbes, and weeds. It is now possible to both characterize useful or deleterious variation as well as precisely manipulate it. Data-driven, informed decisions based on knowledge of the variation of biotic challenges and of natural and synthetic variation in crop plants will enable deployment of durable interventions throughout the world. These should be integral, dynamic components of agricultural strategies for sustainable agriculture. Specific findings: ● Genetic improvement of crops is the most reliable, least expensive management strategy when suitable genetic variation is available. Nonetheless, some interventions have not proved durable due to the evolution and global dispersal of virulent pathogens and pests as well as herbicide-resistant weeds. ● Additional strategies are becoming essential as multiple fungicides, nematicides, and herbicides become ineffective due to the evolution of resistance and/or are phased out due to registration withdrawals. ● Strategies are needed that maximize the evolutionary hurdles for pathogens, pests, and weeds to overcome control measures. Interventions need to evolve as fast as the biotic challenges. Moreover, deployments of interventions must be driven by knowledge of the evolutionary capacity of the biotic challenge. ● Considerable knowledge exists but more research into the mechanisms of plant immunity and other forms of resistance is needed as the foundation for translational applications. ● Several new technologies are increasing foundational knowledge and providing numerous opportunities for generating crops with durable resistance to pests and diseases as well as control of weeds and reduction of the environmental impact of agriculture. ● There are multiple strategies for counteracting biotic challenges involving canonical and non-canonical disease resistance genes, genes encoding susceptibility factors, small RNAs, or immunomodulators. Simultaneous deployment of disease resistance strategies with different modes of action, as well as the judicious use of fungicides, will enhance durability of control measures. ● Pathogen effectors provide tools for discovering resistance genes and susceptibility factors as well as for dissecting/manipulating plant biology and breeding plants for durable disease resistance. ● There are several, as yet little exploited, opportunities for leveraging beneficial interactions among plants, microbes, insects and other organisms in the phytobiome to enhance plant health and productivity as well as breeding plants to promote beneficial phytobiome communities. ● Global monitoring of plant health is feasible and desirable in order to anticipate and counter threats. ● Climate change increases the need for continual global monitoring of pathogens, pests, and weeds and adjusting of control strategies. ● There are numerous current and future opportunities for knowledge exchange and partnerships between developed and developing countries to foster improved local and global food security. ● Both genetically modified (GM) and non-GM strategies are needed to maximize plant health and food security. ● Significant, sustained financial support is required if the beneficial impacts of foundational and translational research on global food security are to be realized. The needs, opportunities, approaches, and deliverables for addressing biotic challenges to plant health are detailed in Table 1. These can be broadly classified as assessing variation, characterizing it in detail at a variety of scales, and deploying beneficial interventions. Immediate investments in global monitoring of pathogens/pests and in situ and ex-situ determination of what natural variation exists in crop plants for countering challenges and threats should be a high priority. Detailed investigations of the molecular basis of the various types of plant resistance and of the basis of pathogen/pest virulence are critical for providing the foundation for novel intervention strategies; these will be facilitated by development of high resolution structural and functional analytical techniques. Optimization of protocols for delivery of reagents for allele replacement and gene insertions into diverse major and minor crop plants should be a high priority. Monitoring and deployment should be a global endeavor involving multinational partnerships and knowledge exchanges in order to ensure that interventions are locally relevant and globally durable.

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