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Telegraph: British scientists appeal to world for Ash dieback help (2012)

Telegraph: British scientists appeal to world for Ash dieback help (2012) | Plants and Microbes | Scoop.it
British scientists have made a global appeal for help finding weaknesses in the fungus causing ash dieback after publishing the first molecular sequencing data on the disease.

Using information on the fungus's RNA – the sister molecule of DNA which helps regulate the behaviour of genes – researchers hope to discover how the fungus causes disease, and how it can be stopped. Scientists from the Sainsbury Laboratory and the John Innes Centre examined a sample of pith from a twig of an infected Ash tree in Ashwellthorpe wood in Norfolk, the first natural environment where the fungus was found in the UK. From the sample they extracted RNA and sequenced it to help them identify which genes are most influential in allowing the fungus to spread between trees so quickly. In normal circumstances, scientists would analyse the sample thoroughly and have their findings peer-reviewed before publishing them in a journal. But because of the urgency of the situation, the researchers took the unusual step of publishing their data online and asking experts from around the world to help them produce accurate results more quickly through "crowdsourcing".
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Molecular Plant Pathology: The Top 10 oomycete pathogens in molecular plant pathology (2014)

Molecular Plant Pathology: The Top 10 oomycete pathogens in molecular plant pathology (2014) | Plants and Microbes | Scoop.it

Oomycetes form a deep lineage of eukaryotic organisms that includes a large number of plant pathogens that threaten natural and managed ecosystems. We undertook a survey to query the community for their ranking of plant pathogenic oomycete species based on scientific and economic importance. In total, we received 263 votes from 62 scientists in 15 countries for a total of 33 species. The Top 10 species and their ranking are: (1) Phytophthora infestans; (2, tied) Hyaloperonospora arabidopsidis; (2, tied) Phytophthora ramorum; (4) Phytophthora sojae; (5) Phytophthora capsici; (6) Plasmopara viticola; (7) Phytophthora cinnamomi; (8, tied) Phytophthora parasitica; (8, tied) Pythium ultimum; and (10) Albugo candida. The article provides an introduction to these 10 taxa and a snapshot of current research. We hope that the list will serve as a benchmark for future trends in oomycete research.


See also [link below]:


Top 10 plant-parasitic nematodes in molecular plant pathology
Top 10 plant viruses in molecular plant pathology
Top 10 plant pathogenic bacteria in molecular plant pathology
The Top 10 fungal pathogens in molecular plant pathology


http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1364-3703/homepage/free_poster.htm

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Keystone Symposia Conference: Plant Receptor Kinases: From Molecules to Environment, February 8—13, 2015, Taos, New Mexico

Keystone Symposia Conference: Plant Receptor Kinases: From Molecules to Environment, February 8—13, 2015, Taos, New Mexico | Plants and Microbes | Scoop.it
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MPMI: The HC-Pro and P3 Cistrons of an Avirulent Soybean mosaic virus Are Recognized by Different Resistance Genes at the Complex Rsv1 Locus (2014)

MPMI: The HC-Pro and P3 Cistrons of an Avirulent Soybean mosaic virus Are Recognized by Different Resistance Genes at the Complex Rsv1 Locus (2014) | Plants and Microbes | Scoop.it

The complex Rsv1 locus in soybean plant introduction (PI) ‘PI96983’ confers extreme resistance (ER) against Soybean mosaic virus (SMV) strain N but not SMV-G7 and SMV-G7d. Both the SMV helper-component proteinase (HC-Pro) and P3 cistrons can serve as avirulence factors recognized by Rsv1. To understand the genetics underlying recognition of the two cistrons, we have utilized two soybean lines (L800 and L943) derived from crosses between PI96983 (Rsv1) and Lee68 (rsv1) with distinct recombination events within the Rsv1 locus. L800 contains a single PI96983-derived member (3gG2) of an Rsv1-associated subfamily of nucleotide-binding leucine-rich repeat (NB-LRR) genes. In contrast, although L943 lacks 3gG2, it contains a suite of five other NB-LRR genes belonging to the same family. L800 confers ER against SMV-N whereas L943 allows limited replication at the inoculation site. SMV-N-derived chimeras containing HC-Pro from SMV-G7 or SMV-G7d gained virulence on L943 but not on L800 whereas those with P3 replacement gained virulence on L800 but not on L943. In reciprocal experiments, SMV-G7- and SMV-G7d-derived chimeras with HC-Pro replacement from SMV-N lost virulence on L943 but retained virulence on L800 whereas those with P3 replacement lost virulence on L800 while remaining virulent on L943. These data demonstrate that distinct resistance genes at the Rsv1 locus, likely belonging to the NB-LRR class, mediate recognition of HC-Pro and P3.

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Planta: The phytotoxin coronatine is a multifunctional component of the virulence armament of Pseudomonas syringae (2014)

Planta: The phytotoxin coronatine is a multifunctional component of the virulence armament of Pseudomonas syringae (2014) | Plants and Microbes | Scoop.it

Plant pathogens deploy an array of virulence factors to suppress host defense and promote pathogenicity. Numerous strains of Pseudomonas syringae produce the phytotoxin coronatine (COR). A major aspect of COR function is its ability to mimic a bioactive jasmonic acid (JA) conjugate and thus target the JA-receptor COR-insensitive 1 (COI1). Biological activities of COR include stimulation of JA-signaling and consequent suppression of SA-dependent defense through antagonistic crosstalk, antagonism of stomatal closure to allow bacterial entry into the interior of plant leaves, contribution to chlorotic symptoms in infected plants, and suppression of plant cell wall defense through perturbation of secondary metabolism. Here, we review the virulence function of COR, including updates on these established activities as well as more recent findings revealing COI1-independent activity of COR and shedding light on cooperative or redundant defense suppression between COR and type III effector proteins.

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David Kuykendall's curator insight, August 27, 8:41 AM

This phytotoxin produced by a plant pathogen

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News: Hazelnut harvest — and the world's Nutella stock — threatened by blight (2014)

News: Hazelnut harvest — and the world's Nutella stock — threatened by blight (2014) | Plants and Microbes | Scoop.it

A hazelnut farm in Agassiz is determined not to let a rampant fungus hinder its ability to provide locally-grown nuts, even as damaged Turkish crops drive up prices and fears of a Nutella shortage around the world.


General manager Shelley Krahn of Agassiz’s Canadian Hazelnut Inc. said the Eastern Filbert Blight (EFB) has ravaged a number of the farm’s trees, shrinking the size of this year’s hazelnut harvest and jeopardizing the future of B.C.-grown hazelnuts.


“It’s become very rampant in the last two years,” Krahn said. “Back in the early 2000s, it only affected a tree here or there and now it’s widespread throughout B.C. in every single orchard.”


According to the Ministry of Agriculture, the EFB was first discovered in 2001 at several non-commercial sites in Abbotsford. Since then, it has also been detected at orchards in Langley, and most recently, in 2008 at a commercial orchard in Yarrow.

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PLOS Pathogens: NLR-Associating Transcription Factor bHLH84 and Its Paralogs Function Redundantly in Plant Immunity (2014)

PLOS Pathogens: NLR-Associating Transcription Factor bHLH84 and Its Paralogs Function Redundantly in Plant Immunity (2014) | Plants and Microbes | Scoop.it

In plants and animals, nucleotide-binding and leucine-rich repeat domain containing (NLR) immune receptors are utilized to detect the presence or activities of pathogen-derived molecules. However, the mechanisms by which NLR proteins induce defense responses remain unclear. Here, we report the characterization of one basic Helix-loop-Helix (bHLH) type transcription factor (TF), bHLH84, identified from a reverse genetic screen. It functions as a transcriptional activator that enhances the autoimmunity of NLR mutant snc1 (suppressor of npr1-1, constitutive 1) and confers enhanced immunity in wild-type backgrounds when overexpressed. Simultaneously knocking out three closely related bHLH paralogs attenuates RPS4-mediated immunity and partially suppresses the autoimmune phenotypes of snc1, while overexpression of the other two close paralogs also renders strong autoimmunity, suggesting functional redundancy in the gene family. Intriguingly, the autoimmunity conferred by bHLH84overexpression can be largely suppressed by the loss-of-function snc1-r1 mutation, suggesting that SNC1 is required for its proper function. In planta co-immunoprecipitation revealed interactions between not only bHLH84 and SNC1, but also bHLH84 and RPS4, indicating that bHLH84 associates with these NLRs. Together with previous finding that SNC1 associates with repressor TPR1 to repress negative regulators, we hypothesize that nuclear NLR proteins may interact with both transcriptional repressors and activators during immune responses, enabling potentially faster and more robust transcriptional reprogramming upon pathogen recognition.

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Science: Genomic-scale exchange of mRNA between a parasitic plant and its hosts (2014)

Science: Genomic-scale exchange of mRNA between a parasitic plant and its hosts (2014) | Plants and Microbes | Scoop.it

Movement of RNAs between cells of a single plant is well documented, but cross-species RNA transfer is largely unexplored. Cuscuta pentagona (dodder) is a parasitic plant that forms symplastic connections with its hosts and takes up host messenger RNAs (mRNAs). We sequenced transcriptomes of Cuscuta growing on Arabidopsis and tomato hosts to characterize mRNA transfer between species and found that mRNAs move in high numbers and in a bidirectional manner. The mobile transcripts represented thousands of different genes, and nearly half the expressed transcriptome of Arabidopsis was identified in Cuscuta. These findings demonstrate that parasitic plants can exchange large proportions of their transcriptomes with hosts, providing potential mechanisms for RNA-based interactions between species and horizontal gene transfer.

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Popular Science: Has The End Of The Banana Arrived? (2014)

Popular Science: Has The End Of The Banana Arrived? (2014) | Plants and Microbes | Scoop.it

Two weeks ago, at a conference in South Africa, scientists met to discuss how to contain a deadly banana disease outbreak in nearby Mozambique, Africa. At fault was a fungus that continues its march around the planet. In recent years, it has spread across Asia and Australia, devastating plants there that bear the signature yellow supermarket fruit.


The international delegation of researchers shared their own approaches to the malady, hoping to arrive at some strategy to insulate Mozambique and the rest of Africa: a continent where bananas are essential to the lives of millions. They left the Cape Town-based meeting with an air of optimism.


Only days after the meeting, however, a devastating new survey of the stricken Mozambique farm was released. Scientists at the conference assumed that the fungus was limited to a single plot. The new report suggested the entire plantation was infested, expanding 125 diseased acres to more than 3,500. All told, 7 million banana plants were doomed to wilt and rot.


“The future looks bleak,” says Altus Viljoen, the South African plant pathologist who organized the conference. "There’s no way they’ll be able to stop any further spread if they continue to farm.” Worse, he says, the disease's rapid spread endangers banana crops beyond Mozambique’s borders.


The story of the African farm is the story of a threat to the world’s largest fruit crop. Commercially, bananas generate $8 billion annually and, according to the United Nations Conference on Trade and Development, more than 400 million people rely on the fruit as their primary source of calories. Though more bananas are grown in Asia, Africans depend heavily on the crop; in countries like Rwanda and Uganda, for example, average banana consumption is about 500 pounds per person annually, or 20 times that of the typical American. If the bananas vanish, people starve.

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Harri Kokko's curator insight, August 11, 2:10 AM

Saattaako tuhoisa ja ikävä . Fusarium  sieni banaanin tuottajat ahdinkoon, kuten teki aikanaan perunarutto?

Vaikka nyt EI ole kyseessä  rapuruton kaltainen munasieni. ko.Fusarium suvun sienet aiheuttavat ongelmia ravulle nakertavat ravun kitiinikuorta.

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1000 Fungal Genome (1KFG) project: Graduate Student-Postdoc Challenge (2014)

1000 Fungal Genome (1KFG) project: Graduate Student-Postdoc Challenge (2014) | Plants and Microbes | Scoop.it

The 1000 Fungal Genome (1KFG) project is a large-scale community sequencing project supported by the Joint Genome Institute (JGI).  The goal of 1KFG is to facilitate the sequencing of fungal genomes across the Kingdom Fungi with the objective to significantly advance genome-enabled mycology.  The sampling guideline is to sequence two species of fungi for every family-level clade of Fungi so that genomic data is representative of phylogenetic diversity of Fungi. In support of this endeavor, 1KFG is pleased to announce the Graduate Student/Postdoc Challenge.  From July 2014-June 30 2015 we will accept nominations to sequence up to 100 species of fungi in support of graduate student and postdoctoral research projects.  Students and postdocs are encouraged to nominate species and submit DNA and RNA samples for genomic sequencing.


Follow the link to find out how to nominate species.

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PLOS Genetics: Comparative Phylogenomics Uncovers the Impact of Symbiotic Associations on Host Genome Evolution (2014)

PLOS Genetics: Comparative Phylogenomics Uncovers the Impact of Symbiotic Associations on Host Genome Evolution (2014) | Plants and Microbes | Scoop.it

Mutualistic symbioses between eukaryotes and beneficial microorganisms of their microbiome play an essential role in nutrition, protection against disease, and development of the host. However, the impact of beneficial symbionts on the evolution of host genomes remains poorly characterized. Here we used the independent loss of the most widespread plant–microbe symbiosis, arbuscular mycorrhization (AM), as a model to address this question. Using a large phenotypic approach and phylogenetic analyses, we present evidence that loss of AM symbiosis correlates with the loss of many symbiotic genes in the Arabidopsis lineage (Brassicales). Then, by analyzing the genome and/or transcriptomes of nine other phylogenetically divergent non-host plants, we show that this correlation occurred in a convergent manner in four additional plant lineages, demonstrating the existence of an evolutionary pattern specific to symbiotic genes. Finally, we use a global comparative phylogenomic approach to track this evolutionary pattern among land plants. Based on this approach, we identify a set of 174 highly conserved genes and demonstrate enrichment in symbiosis-related genes. Our findings are consistent with the hypothesis that beneficial symbionts maintain purifying selection on host gene networks during the evolution of entire lineages.

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New Phytologist: Hitchhiker's guide to multi-dimensional plant pathology (2014)

New Phytologist: Hitchhiker's guide to multi-dimensional plant pathology (2014) | Plants and Microbes | Scoop.it

Filamentous pathogens pose a substantial threat to global food security. One central question in plant pathology is how pathogens cause infection and manage to evade or suppress plant immunity to promote disease. With many technological advances over the past decade, including DNA sequencing technology, an array of new tools has become embedded within the toolbox of next-generation plant pathologists. By employing a multidisciplinary approach plant pathologists can fully leverage these technical advances to answer key questions in plant pathology, aimed at achieving global food security. This review discusses the impact of: cell biology and genetics on progressing our understanding of infection structure formation on the leaf surface; biochemical and molecular analysis to study how pathogens subdue plant immunity and manipulate plant processes through effectors; genomics and DNA sequencing technologies on all areas of plant pathology; and new forms of collaboration on accelerating exploitation of big data. As we embark on the next phase in plant pathology, the integration of systems biology promises to provide a holistic perspective of plant–pathogen interactions from big data and only once we fully appreciate these complexities can we design truly sustainable solutions to preserve our resources.

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Marie Zen Attitude's curator insight, July 26, 8:21 AM

Un petit lien spécial pour Emeric ;)

 

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Nature: The long-term maintenance of a resistance polymorphism through diffuse interactions (2014)

Nature: The long-term maintenance of a resistance polymorphism through diffuse interactions (2014) | Plants and Microbes | Scoop.it

Plant resistance (R) genes are a crucial component in plant defence against pathogens1. Although R genes often fail to provide durable resistance in an agricultural context, they frequently persist as long-lived balanced polymorphisms in nature234. Standard theory explains the maintenance of such polymorphisms through a balance of the costs and benefits of resistance and virulence in a tightly coevolving host–pathogen pair56. However, many plant–pathogen interactions lack such specificity7. Whether, and how, balanced polymorphisms are maintained in diffusely interacting species8 is unknown. Here we identify a naturally interacting R gene and effector pair in Arabidopsis thaliana and its facultative plant pathogen, Pseudomonas syringae. The protein encoded by the R gene RPS5 recognizes an AvrPphB homologue (AvrPphB2) and exhibits a balanced polymorphism that has been maintained for over 2 million years (ref. 3). Consistent with the presence of an ancient balanced polymorphism, the R gene confers a benefit when plants are infected with P. syringae carrying avrPphB2 but also incurs a large cost in the absence of infection. RPS5alleles are maintained at intermediate frequencies in populations globally, suggesting ubiquitous selection for resistance. However, the presence of P. syringae carrying avrPphB is probably insufficient to explain the RPS5 polymorphism. First, avrPphB homologues occur at very low frequencies in P. syringae populations on A. thaliana. Second, AvrPphB only rarely confers a virulence benefit to P. syringae on A. thaliana. Instead, we find evidence that selection for RPS5 involves multiple non-homologous effectors and multiple pathogen species. These results and an associated model suggest that the R gene polymorphism in A. thaliana may not be maintained through a tightly coupled interaction involving a single coevolved R gene and effector pair. More likely, the stable polymorphism is maintained through complex and diffuse community-wide interactions.

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Nature Biotechnology: Simultaneous editing of three homoeoalleles in hexaploid bread wheat confers heritable resistance to powdery mildew (2014)

Nature Biotechnology: Simultaneous editing of three homoeoalleles in hexaploid bread wheat confers heritable resistance to powdery mildew (2014) | Plants and Microbes | Scoop.it

Sequence-specific nucleases have been applied toengineer targeted modifications in polyploid genomes, but simultaneous modification of multiple homoeoalleles has not been reported. Here we use transcription activator–like effector nuclease (TALEN) and clustered, regularly interspaced, short palindromic repeats (CRISPR)-Cas9 technologies in hexaploid bread wheat to introduce targeted mutations in the three homoeoalleles that encode MILDEW- RESISTANCE LOCUS (MLO) proteins. Genetic redundancy has prevented evaluation of whether mutation of all three MLO alleles in bread wheat might confer resistance to powdery mildew, a trait not found in natural populations. We show that TALEN-induced mutation of all three TaMLO homoeologs in the same plant confers heritable broad-spectrum resistanceto powdery mildew. We further use CRISPR-Cas9 technologyto generate transgenic wheat plants that carry mutations inthe TaMLO-A1 allele. We also demonstrate the feasibility of engineering targeted DNA insertion in bread wheat through nonhomologous end joining of the double-strand breaks caused by TALENs. Our findings provide a methodological framework to improve polyploid crops.



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Fesquet didier's curator insight, July 22, 5:22 AM

this open the way for developping non toxic wheat species...good for celiac people...maybe one day...hopes for a slice of pizza :-)

 

Mary Williams's curator insight, July 31, 6:33 AM

I'm trying to catch up with what I missed while traveling. I think this is one of the more exciting papers that came out in the past few weeks, and I'm a bit surprised that it didn't get more press coverage.

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New Phytologist: A novel Arabidopsis CHITIN ELICITOR RECEPTOR KINASE 1 (CERK1) mutant with enhanced pathogen-induced cell death and altered receptor processing (2014)

New Phytologist: A novel Arabidopsis CHITIN ELICITOR RECEPTOR KINASE 1 (CERK1) mutant with enhanced pathogen-induced cell death and altered receptor processing (2014) | Plants and Microbes | Scoop.it
  • Plants detect pathogens by sensing microbe-associated molecular patterns (MAMPs) through pattern recognition receptors. Pattern recognition receptor complexes also have roles in cell death control, but the underlying mechanisms are poorly understood. Here, we report isolation of cerk1-4, a novel mutant allele of the Arabidopsis chitin receptor CERK1 with enhanced defense responses.
  • We identified cerk1-4 in a forward genetic screen with barley powdery mildew and consequently characterized it by pathogen assays, mutant crosses and analysis of defense pathways. CERK1 and CERK1-4 proteins were analyzed biochemically.
  • The cerk1-4 mutation causes an amino acid exchange in the CERK1 ectodomain. Mutant plants maintain chitin signaling capacity but exhibit hyper-inducible salicylic acid concentrations and deregulated cell death upon pathogen challenge. In contrast to chitin signaling, the cerk1-4 phenotype does not require kinase activity and is conferred by the N-terminal part of the receptor. CERK1 undergoes ectodomain shedding, a well-known process in animal cell surface proteins. Wild-type plants contain the full-length CERK1 receptor protein as well as a soluble form of the CERK1 ectodomain, whereas cerk1-4 plants lack the N-terminal shedding product.
  • Our work suggests that CERK1 may have a chitin-independent role in cell death control and is the first report of ectodomain shedding in plants.
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The Independent: Potatoes could be off the menu as crop pests threaten UK (2014)

The Independent: Potatoes could be off the menu as crop pests threaten UK (2014) | Plants and Microbes | Scoop.it

Britain has “significantly underestimated” the risk that crop pests pose to its food supply. Fungi and viruses present so great a danger to staples such as wheat and potatoes that they may force the nation to change its diet, an academic has warned. The rise of deadly pests poses a threat to the world’s entire food system, but the UK is among the most vulnerable countries, according to a new study from the University of Exeter. It forecasts that food-growing nations, including the UK, will be “overwhelmed” by pests within the next 30 years as climate change, inadequate biosecurity measures and new variants help them spread. “The UK has significantly underestimated the scale of the threat. This is a huge problem that is lacking in public and political awareness. People are absolutely paralysed with fear of diseases like Ebola, but while they are extremely dangerous, the need to tackle crop diseases is just as pressing,” said Professor Sarah Gurr, of the University of Exeter and Rothamsted Research. “We are not spending enough on research, on training, on surveillance and on biosecurity. Unless we significantly step up our efforts we could be forced to change our diets in the future as crops come and go,” she added. Crop pests include fungi, bacteria, viruses, insects, nematodes (worms) and viroids (plant viruses).

Fungi pose the biggest threat globally and in the UK, where they threaten the country’s wheat and potato harvests. Zymoseptoria tritici – or Septoria leaf blotch – and Blumeria graminis, a powdery mildew, are a danger to wheat, while the potato cyst nematode and new variants of Phytophthora infestans threaten the potato. The report warns that if crop pests continue to spread at their current rate a significant portion of the world’s biggest food-producing countries will be “saturated” with pests – the crops simply wouldn’t be able to accommodate any more.

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Nature Communications: Unconventionally secreted effectors of two filamentous pathogens target plant salicylate biosynthesis (2014)

Nature Communications: Unconventionally secreted effectors of two filamentous pathogens target plant salicylate biosynthesis (2014) | Plants and Microbes | Scoop.it

Plant diseases caused by fungi and oomycetes pose an increasing threat to food security and ecosystem health worldwide. These filamentous pathogens, while taxonomically distinct, modulate host defense responses by secreting effectors, which are typically identified based on the presence of signal peptides. Here we show that Phytophthora sojae and Verticillium dahliaesecrete isochorismatases (PsIsc1 and VdIsc1, respectively) that are required for full pathogenesis. PsIsc1 and VdIsc1 can suppress salicylate-mediated innate immunity in plantaand hydrolyse isochorismate in vitro. A conserved triad of catalytic residues is essential for both functions. Thus, the two proteins are isochorismatase effectors that disrupt the plant salicylate metabolism pathway by suppressing its precursor. Furthermore, these proteins lack signal peptides, but exhibit characteristics that lead to unconventional secretion. Therefore, this secretion pathway is a novel mechanism for delivering effectors and might play an important role in host–pathogen interactions.

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New Phytologist: TAL effectors – pathogen strategies and plant resistance engineering (2014)

New Phytologist: TAL effectors – pathogen strategies and plant resistance engineering (2014) | Plants and Microbes | Scoop.it

Transcription activator-like effectors (TALEs) from plant pathogenic Xanthomonas spp. and the related RipTALs from Ralstonia solanacearum are DNA-binding proteins with a modular DNA-binding domain. This domain is both predictable and programmable, which simplifies elucidation of TALE function in planta and facilitates generation of DNA-binding modules with desired specificity for biotechnological approaches. Recently identified TALE host target genes that either promote or stop bacterial disease provide new insights into how expression of TALE genes affects the plant–pathogen interaction. Since its elucidation the TALE code has been continuously refined and now provides a mature tool that, in combination with transcriptome profiling, allows rapid isolation of novel TALE target genes. The TALE code is also the basis for synthetic promoter-traps that mediate recognition of TALE or RipTAL proteins in engineered plants. In this review, we will summarize recent findings in plant-focused TALE research. In addition, we will provide an outline of the newly established gene isolation approach for TALE or RipTAL host target genes with an emphasis on potential pitfalls.


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BMC Plant Biology: The necrotrophic effector protein SnTox3 re-programs metabolism and elicits a strong defence response in susceptible wheat leaves (2014)

BMC Plant Biology: The necrotrophic effector protein SnTox3 re-programs metabolism and elicits a strong defence response in susceptible wheat leaves (2014) | Plants and Microbes | Scoop.it

BackgroundThe fungus Stagonospora nodorum is a necrotrophic pathogen of wheat. It causes disease by secreting proteinaceous effectors which interact with proteins encoded by dominant susceptibility genes in the host. The outcome of these interactions results in necrosis, allowing the fungus to thrive on dead plant material. The mechanisms of these effectors though are poorly understood. In this study, we undertake a comprehensive transcriptomics, proteomic and metabolomic approach to understand how a susceptible wheat cultivar responds to exposure to the Stagonospora nodorum effector protein SnTox3.ResultsMicroarray and proteomic studies revealed that SnTox3 strongly induced responses consistent with those previously associated with classical host defence pathways including the expression of pathogenicity-related proteins and the induction of cell death. Collapse of the photosynthetic machinery was also apparent at the transcriptional and translational level. SnTox3-infiltrated wheat leaves also showed a strong induction of enzymes involved in primary metabolism consistent with increases in hexoses, amino acids and organic acids as determined by primary metabolite profiling. Methionine and homocysteine metabolism was strongly induced upon exposure to SnTox3. Pathogenicity in the presence of homocysteine was inhibited confirming that the compound has a role in plant defence. Consistent with the strong defence responses observed, secondary metabolite profiling revealed the induction of several compounds associated with plant defence, including the phenylpropanoids chlorogenic acid and feruloylquinic acid, and the cyanogenic glucoside dhurrin. Serotonin did not accumulate subsequent to SnTox3 infiltration.ConclusionsThese data support the theory that the SnTox3 effector protein elicits a host cell death response to facilitate the pathogen?s necrotrophic infection cycle. Our data also demonstrate that the mechanism of SnTox3 appears distinct from the previously characterised Stagonospora nodorum effector SnToxA. Collectively, this comprehensive analysis has advanced our understanding of necrotrophic effector biology and highlighted the complexity of effector-triggered susceptibility.

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Frontiers: RNA trafficking in parasitic plant systems (2012)

Frontiers: RNA trafficking in parasitic plant systems (2012) | Plants and Microbes | Scoop.it

RNA trafficking in plants contributes to local and long-distance coordination of plant development and response to the environment. However, investigations of mobile RNA identity and function are hindered by the inherent difficulty of tracing a given molecule of RNA from its cell of origin to its destination. Several methods have been used to address this problem, but all are limited to some extent by constraints associated with accurately sampling phloem sap or detecting trafficked RNA. Certain parasitic plant species form symplastic connections to their hosts and thereby provide an additional system for studying RNA trafficking. The haustorial connections of Cuscuta andPhelipanche species are similar to graft junctions in that they are able to transmit mRNAs, viral RNAs, siRNAs, and proteins from the host plants to the parasite. In contrast to other graft systems, these parasites form connections with host species that span a wide phylogenetic range, such that a high degree of nucleotide sequence divergence may exist between host and parasites and allow confident identification of most host RNAs in the parasite system. The ability to identify host RNAs in parasites, and vice versa, will facilitate genomics approaches to understanding RNA trafficking. This review discusses the nature of host–parasite connections and the potential significance of host RNAs for the parasite. Additional research on host–parasite interactions is needed to interpret results of RNA trafficking studies, but parasitic plants may provide a fascinating new perspective on RNA trafficking.

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Annu Rev Phytopathology: Horizontal Gene Transfer in Eukaryotic Plant Pathogens (2014)

Annu Rev Phytopathology: Horizontal Gene Transfer in Eukaryotic Plant Pathogens (2014) | Plants and Microbes | Scoop.it

Gene transfer has been identified as a prevalent and pervasive phenomenon and an important source of genomic innovation in bacteria. The role of gene transfer in microbial eukaryotes seems to be of a reduced magnitude but in some cases can drive important evolutionary innovations, such as new functions that underpin the colonization of different niches. The aim of this review is to summarize published cases that support the hypothesis that horizontal gene transfer (HGT) has played a role in the evolution of phytopathogenic traits in fungi and oomycetes. Our survey of the literature identifies 46 proposed cases of transfer of genes that have a putative or experimentally demonstrable phytopathogenic function. When considering the life-cycle steps through which a pathogen must progress, the majority of the HGTs identified are associated with invading, degrading, and manipulating the host. Taken together, these data suggest HGT has played a role in shaping how fungi and oomycetes colonize plant hosts.


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Frontiers: Effector proteins of rust fungi (2014)

Frontiers: Effector proteins of rust fungi (2014) | Plants and Microbes | Scoop.it

Rust fungi include many species that are devastating crop pathogens. To develop resistant plants, a better understanding of rust virulence factors, or effector proteins, is needed. Thus far, only six rust effector proteins have been described: AvrP123, AvrP4, AvrL567, AvrM, RTP1 and PGTAUSPE-10-1. Although some are well established model proteins used to investigate mechanisms of immune receptor activation (avirulence activities) or entry into plant cells, how they work inside host tissues to promote fungal growth remains unknown. The genome sequences of four rust fungi (two Melampsoraceae and two Pucciniaceae) have been analyzed so far. Genome-wide analyses of these species, as well as transcriptomics performed on a broader range of rust fungi, revealed hundreds of small secreted proteins considered as rust candidate secreted effector proteins (CSEPs). The rust community now needs high-throughput approaches (effectoromics) to accelerate effector discovery/characterization and to better understand how they function in planta. However, this task is challenging due to the non-amenability of rust pathosystems (obligate biotrophs infecting crop plants) to traditional molecular genetic approaches mainly due to difficulties in culturing these species in vitro. The use of heterologous approaches should be promoted in the future.

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F1000Prime Recommended Article: Comparative Phylogenomics Uncovers the Impact of Symbiotic Associations on Host Genome Evolution (2014)

F1000Prime Recommended Article: Comparative Phylogenomics Uncovers the Impact of Symbiotic Associations on Host Genome Evolution (2014) | Plants and Microbes | Scoop.it

This paper is an excellent demonstration of the power of phylogenomics for the discovery of genes involved in traits of interest. 


The authors report a larger scale genome comparison between symbiotic (arbuscular mycorrhiza forming) and non-symbiotic plant groups. They identify gene loss in plant species that go back to a minimum of four independent loss-of-symbiosis events; one in the Brassicales, one in the Caryophyllales (Amaranthaceae), one in the Laminales (Orobanchaceae) and one in the Fabales (Lupinus). 

They performed an impressive phylogenomic analysis and identified a list of 300 Medicago genes that are present in most of the analyzed species but absent in all non-symbiotic Brassicaceae. Upon filtering the list further, by including paraphyletic non-symbiotic species, they arrived at a list of around 100 genes that were consistently absent in the non-mycorrhizal species. Lupinus as a plant that lost arbuscular mycorrhiza but maintained root nodule symbiosis was very informative because common symbiosis genes should be maintained in this genus. 

The results are consistent with an evolutionary scenario in which each of the independent loss-of-symbiosis events, for which the loss of a single gene function was sufficient, was followed by a subsequent larger scale gene erosion that consistently removed the same orthologous genes in the four different clades. 

This very interesting and largely unexpected observation reveals two opposing evolutionary forces that decide over the prevalence of this 'symbiosis-associated' gene set. On the one hand, the existing symbiosis leads to a successful maintenance of symbiosis genes. On the other hand, a yet unidentified force resulted in a consistent pattern of larger scale gene loss after each independent loss-of-symbiosis event. The forces behind this erosion must have acted either very quickly, before each of the non-symbiotic clades diversified from their respective common ancestor, or they independently led to consistent gene loss patterns after speciation. 

Because symbiosis-related genes are overrepresented in the eroded gene set, it is likely that a large proportion, if not all of them, are of specific functional relevance in arbuscular mycorrhization (AM). Therefore this study is of major importance not only from an evolutionary perspective, but also because it demonstrates a novel strategy to identify candidate genes involved in AM symbiosis.


By Martin Parniske, F1000 Plant Biology, Biocenter University of Munich (LMU), Martinsried, Germany.


Disclosures - Martin Parniske has published a joint paper with the corresponding author in 2012.
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Plant Cell: Interaction of the Arabidopsis GTPase RabA4c with Its Effector PMR4 Results in Complete Penetration Resistance to Powdery Mildew (2014)

Plant Cell: Interaction of the Arabidopsis GTPase RabA4c with Its Effector PMR4 Results in Complete Penetration Resistance to Powdery Mildew (2014) | Plants and Microbes | Scoop.it

The (1,3)-β-glucan callose is a major component of cell wall thickenings in response to pathogen attack in plants. GTPases have been suggested to regulate pathogen-induced callose biosynthesis. To elucidate the regulation of callose biosynthesis in Arabidopsis thaliana, we screened microarray data and identified transcriptional upregulation of the GTPase RabA4c after biotic stress. We studied the function of RabA4c in its native and dominant negative (dn) isoform inRabA4c overexpression lines. RabA4c overexpression caused complete penetration resistance to the virulent powdery mildew Golovinomyces cichoracearum due to enhanced callose deposition at early time points of infection, which prevented fungal ingress into epidermal cells. By contrast,RabA4c(dn) overexpression did not increase callose deposition or penetration resistance. A cross of the resistant line with the pmr4 disruption mutant lacking the stress-induced callose synthase PMR4 revealed that enhanced callose deposition and penetration resistance were PMR4-dependent. In live-cell imaging, tagged RabA4c was shown to localize at the plasma membrane prior to infection, which was broken in the pmr4 disruption mutant background, with callose deposits at the site of attempted fungal penetration. Together with our interactions studies including yeast two-hybrid, pull-down, and in planta fluorescence resonance energy transfer assays, we concluded that RabA4c directly interacts with PMR4, which can be seen as an effector of this GTPase.

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PLOS Pathogens: Pto Kinase Binds Two Domains of AvrPtoB and Its Proximity to the Effector E3 Ligase Determines if It Evades Degradation and Activates Plant Immunity (2014)

PLOS Pathogens: Pto Kinase Binds Two Domains of AvrPtoB and Its Proximity to the Effector E3 Ligase Determines if It Evades Degradation and Activates Plant Immunity (2014) | Plants and Microbes | Scoop.it

The tomato—Pseudomonas syringae pv. tomato (Pst)—pathosystem is one of the best understood models for plant-pathogen interactions. Certain wild relatives of tomato express two closely related members of the same kinase family, Pto and Fen, which recognize the Pstvirulence protein AvrPtoB and activate effector-triggered immunity (ETI). AvrPtoB, however, contains an E3 ubiquitin ligase domain in its carboxyl terminus which causes degradation of Fen and undermines its ability to activate ETI. In contrast, Pto evades AvrPtoB-mediated degradation and triggers ETI in response to the effector. It has been reported recently that Pto has higher kinase activity than Fen and that this difference allows Pto to inactivate the E3 ligase through phosphorylation of threonine-450 (T450) in AvrPtoB. Here we show that, in contrast to Fen which can only interact with a single domain proximal to the E3 ligase of AvrPtoB, Pto binds two distinct domains of the effector, the same site as Fen and another N-terminal domain. In the absence of E3 ligase activity Pto binds to either domain of AvrPtoB to activate ETI. However, the presence of an active E3 ligase domain causes ubiquitination of Pto that interacts with the domain proximal to the E3 ligase, identical to ubiquitination of Fen. Only when Pto binds its unique distal domain can it resist AvrPtoB-mediated degradation and activate ETI. We show that phosphorylation of T450 is not required for Pto-mediated resistance in vivo and that a kinase-inactive version of Pto is still capable of activating ETI in response to AvrPtoB. Our results demonstrate that the ability of Pto to interact with a second site distal to the E3 ligase domain in AvrPtoB, and not a higher kinase activity or T450 phosphorylation, allows Pto to evade ubiquitination and to confer immunity to Pst.

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Mashable: Chinese Researchers Create Disease-Resistant Wheat by Deleting Genes (2014)

Mashable: Chinese Researchers Create Disease-Resistant Wheat by Deleting Genes (2014) | Plants and Microbes | Scoop.it

Advanced genome-editing techniques have been used to create a strain of wheat resistant to a destructive fungal pathogen — called powdery mildew — that is a major bane to the world's top food source, according to scientists at one of China's leading centers for agricultural research.


To stop the mildew, researchers at the Chinese Academy of Sciences deleted genes that encode proteins that repress defenses against the mildew. The work promises to someday make wheat more resistant to the disease, which is typically controlled through the heavy use of fungicides. It also represents an important achievement in using genome editing tools to engineer food crops without inserting foreign genes — a flashpoint for opposition to genetically modified crops.


The gene-deletion trick is particularly tough to do in wheat because the plant has three genomes — with largely similar copies of the same genes — meaning all three must be deleted or the trait will not be changed. Using gene-editing tools known as TALENs and CRISPR, the researchers were able to do that without changing anything else or adding genes from other organisms.


"We now caught all three copies, and only by knocking out all three copies can we get this [mildew]-resistant phenotype," says Caixia Gao, who heads a gene-editing research group at the State Key Laboratory of Plant Cell and Chromosome Engineering at the Institute of Microbiology in Beijing.


A paper describing the results appears in Nature Biotechnology http://dx.doi.org/10.1038/nbt.2969.

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