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Peak District National Park Authority: Rare disease causing death of bilberry on the Roaches (2013)

Peak District National Park Authority: Rare disease causing death of bilberry on the Roaches (2013) | Plants and Microbes | Scoop.it

A fungal [sic] plant disease was identified on the Roaches, a beauty spot in the Staffordshire area of the national park, in 2011 that killed bilberry in some areas. The disease – called Phytophthora pseudosyringae – is harmless to humans and animals but can be spread to other plants on human clothing and the coats of animals. The Roaches remains open to the public but people are asked to avoid contact with bilberry by staying on the footpaths when walking and accessing climbing crags and boulders, and to keep dogs on a short lead. This will help reduce the risk of the disease spreading further. Monitoring in 2011 and 2012 indicated some spread of the disease on the estate but the majority of bilberry plants have remained healthy. Bilberry is one of the main moorland shrubs on the estate and there were concerns the infection could spread to other moorland sites.

 

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Anne-Sophie Roy's curator insight, January 30, 2013 10:08 AM

Phytophthora pseudosyringae is causing a severe disease on billerries in some parts of the Peak District National Park (Staffordshire, UK).

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Journal of Experimental Botany: Modulation of plant autophagy during pathogen attack (2017)

Journal of Experimental Botany: Modulation of plant autophagy during pathogen attack (2017) | Plants and Microbes | Scoop.it

In plants, the highly conserved catabolic process of autophagy has long been known as a means of maintaining cellular homeostasis and coping with abiotic stress conditions. Accumulating evidence has linked autophagy to immunity against invading pathogens, regulating plant cell death, and antimicrobial defences. In turn, it appears that phytopathogens have evolved ways not only to evade autophagic clearance but also to modulate and co-opt autophagy for their own benefit. In this review, we summarize and discuss the emerging discoveries concerning how pathogens modulate both host and self-autophagy machineries to colonize their host plants, delving into the arms race that determines the fate of interorganismal interaction.

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Science: Eudicot plant-specific sphingolipids determine host selectivity of microbial NLP cytolysins (2017)

Science: Eudicot plant-specific sphingolipids determine host selectivity of microbial NLP cytolysins (2017) | Plants and Microbes | Scoop.it

Necrosis and ethylene-inducing peptide 1–like (NLP) proteins constitute a superfamily of proteins produced by plant pathogenic bacteria, fungi, and oomycetes. Many NLPs are cytotoxins that facilitate microbial infection of eudicot, but not of monocot plants. Here, we report glycosylinositol phosphorylceramide (GIPC) sphingolipids as NLP toxin receptors. Plant mutants with altered GIPC composition were more resistant to NLP toxins. Binding studies and x-ray crystallography showed that NLPs form complexes with terminal monomeric hexose moieties of GIPCs that result in conformational changes within the toxin. Insensitivity to NLP cytolysins of monocot plants may be explained by the length of the GIPC head group and the architecture of the NLP sugar-binding site. We unveil early steps in NLP cytolysin action that determine plant clade-specific toxin selectivity.

 

See also commentary by Guido Van den Ackerveken "How plants differ in toxin-sensitivity".

 

Bailey et al. 1995. on Fusarioum Nep1.

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MPMI Special Issue: Focus on Effector-Triggered Susceptibility (2017)

MPMI Special Issue: Focus on Effector-Triggered Susceptibility (2017) | Plants and Microbes | Scoop.it

Focus on Effector-Triggered Susceptibility

Wenbo Ma, Yuanchao Wang, and John McDowell

 

Trick or Treat: Microbial Pathogens Evolved Apoplastic Effectors Modulating Plant Susceptibility to Infection

Yan Wang and Yuanchao Wang

 

Altering Plant Defenses: Herbivore-Associated Molecular Patterns and Effector Arsenal of Chewing Herbivores

Saumik Basu, Suresh Varsani, and Joe Louis

 

Effector Biology in Focus: A Primer for Computational Prediction and Functional Characterization

Ronaldo J. D. Dalio, John Herlihy, Tiago S. Oliveira, John M. McDowell, and Marcos Machado

 

Lessons in Effector and NLR Biology of Plant-Microbe Systems

Aleksandra Białas, Erin K. Zess, Juan Carlos De la Concepcion, Marina Franceschetti, Helen G. Pennington, Kentaro Yoshida, Jessica L. Upson, Emilie Chanclud, Chih-Hang Wu, Thorsten Langner, Abbas Maqbool, Freya A. Varden, Lida Derevnina, Khaoula Belhaj, Koki Fujisaki, Hiromasa Saitoh, Ryohei Terauchi, Mark J. Banfield, and Sophien Kamoun

 

The Elicitor Protein AsES Induces a Systemic Acquired Resistance Response Accompanied by Systemic Microbursts and Micro–Hypersensitive Responses in Fragaria ananassa

Verónica Hael-Conrad, Silvia Marisa Perato, Marta Eugenia Arias, Martín Gustavo Martínez-Zamora, Pía de los Ángeles Di Peto, Gustavo Gabriel Martos, Atilio Pedro Castagnaro, Juan Carlos Díaz-Ricci, and Nadia Regina Chalfoun

 

The Type III Secretion Chaperone HpaB Controls the Translocation of Effector and Noneffector Proteins From Xanthomonas campestris pv. vesicatoria

Felix Scheibner, Nadine Hartmann, Jens Hausner, Christian Lorenz, Anne-Katrin Hoffmeister, and Daniela Büttner

 

The Bacterial Effector AvrPto Targets the Regulatory Coreceptor SOBIR1 and Suppresses Defense Signaling Mediated by the Receptor-Like Protein Cf-4

Jinbin Wu, Aranka M. van der Burgh, Guozhi Bi, Lisha Zhang, James R. Alfano, Gregory B. Martin, and Matthieu H. A. J. Joosten

 

Potyviral Gene-Silencing Suppressor HCPro Interacts with Salicylic Acid (SA)-Binding Protein 3 to Weaken SA-Mediated Defense Responses

Sylvain Poque, Hui-Wen Wu, Chung-Hao Huang, Hao-Wen Cheng, Wen-Chi Hu, Jun-Yi Yang, David Wang, and Shyi-Dong Yeh

 

Inappropriate Expression of an NLP Effector in Colletotrichum orbiculare Impairs Infection on Cucurbitaceae Cultivars via Plant Recognition of the C-Terminal Region

Nur Sabrina Ahmad Azmi, Suthitar Singkaravanit-Ogawa, Kyoko Ikeda, Saeko Kitakura, Yoshihiro Inoue, Yoshihiro Narusaka, Ken Shirasu, Masanori Kaido, Kazuyuki Mise, and Yoshitaka Takano

 

A Gene Family Coding for Salivary Proteins (SHOT) of the Polyphagous Spider Mite Tetranychus urticae Exhibits Fast Host-Dependent Transcriptional Plasticity

Wim Jonckheere, Wannes Dermauw, Mousaalreza Khalighi, Nena Pavlidi, Wim Reubens, Geert Baggerman, Luc Tirry, Gerben Menschaert, Merijn R. Kant, Bartel Vanholme, and Thomas Van Leeuwen

 

Revisiting the Roles of Tobamovirus Replicase Complex Proteins in Viral Replication and Silencing Suppression

Nachelli Malpica-López, Rajendran Rajeswaran, Daria Beknazariants, Jonathan Seguin, Victor Golyaev, Laurent Farinelli, and Mikhail M. Pooggin

 

Specific Hypersensitive Response–Associated Recognition of New Apoplastic Effectors from Cladosporium fulvum in Wild Tomato

Carl H. Mesarich, Bilal Ӧkmen, Hanna Rovenich, Scott A. Griffiths, Changchun Wang, Mansoor Karimi Jashni, Aleksandar Mihajlovski, Jérôme Collemare, Lukas Hunziker, Cecilia H. Deng, Ate van der Burgt, Henriek G. Beenen, Matthew D. Templeton, Rosie E. Bradshaw, and Pierre J. G. M. de Wit

 

Suppression or Activation of Immune Responses by Predicted Secreted Proteins of the Soybean Rust Pathogen Phakopsora pachyrhizi

Mingsheng Qi, James P. Grayczyk, Janina M. Seitz, Youngsill Lee, Tobias I. Link, Doil Choi, Kerry F. Pedley, Ralf T. Voegele, Thomas J. Baum, and Steven A. Whitham

 

Type III Secretion–Dependent and –Independent Phenotypes Caused by Ralstonia solanacearum in Arabidopsis Roots

Haibin Lu, Saul Lema A, Marc Planas-Marquès, Alejandro Alonso-Díaz, Marc Valls, and Núria S. Coll

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New Phytologist: Sugar flux and signaling in plant‐microbe interactions (2017)

New Phytologist: Sugar flux and signaling in plant‐microbe interactions (2017) | Plants and Microbes | Scoop.it

Plant breeders have developed crop plants that are resistant to pests, but the continual evolution of pathogens creates the need to iteratively develop new control strategies. Molecular tools have allowed us to gain deep insights into disease responses, allowing for more efficient, rational engineering of crops that are more robust or resistant to a greater number of pathogen variants. Here we describe the roles in disease progress of SWEET and STP transporters, which are membrane proteins that mediate transport of sugars across the plasma membrane. We discuss how these transporters may enhance or restrict disease through controlling the level of nutrients provided to pathogens and if the transporters play a role in sugar signaling for disease resistance. This review indicates open questions that require further research and proposes the use of genome editing technologies for engineering disease resistance.


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MPMI: Lessons in Effector and NLR Biology of Plant-Microbe Systems (2017)

MPMI: Lessons in Effector and NLR Biology of Plant-Microbe Systems (2017) | Plants and Microbes | Scoop.it

A diversity of plant-associated organisms secrete effectors—proteins and metabolites that modulate plant physiology to favor host infection and colonization. However, effectors can also activate plant immune receptors, notably nucleotide-binding domain and leucine-rich repeat region (NLR)-containing proteins, enabling plants to fight off invading organisms. This interplay between effectors, their host targets, and the matching immune receptors is shaped by intricate molecular mechanisms and exceptionally dynamic coevolution. In this article, we focus on three effectors, AVR-Pik, AVR-Pia, and AVR-Pii, from the rice blast fungus Magnaporthe oryzae (syn. Pyricularia oryzae), and their corresponding rice NLR immune receptors, Pik, Pia, and Pii, to highlight general concepts of plant-microbe interactions. We draw 12 lessons in effector and NLR biology that have emerged from studying these three little effectors and are broadly applicable to other plant-microbe systems.

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New Phytologist: Multiple strategies for pathogen perception by plant immune receptors (2017)

New Phytologist: Multiple strategies for pathogen perception by plant immune receptors (2017) | Plants and Microbes | Scoop.it

Plants have evolved a complex immune system to protect themselves against phytopathogens. A major class of plant immune receptors called nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs) is ubiquitous in plants and is widely used for crop disease protection, making these proteins critical contributors to global food security. Until recently, NLRs were thought to be conserved in their modular architecture and functional features. Investigation of their biochemical, functional and structural properties has revealed fascinating mechanisms that enable these proteins to perceive a wide range of pathogens. Here, I review recent insights demonstrating that NLRs are more mechanistically and structurally diverse than previously thought. I also discuss how these findings provide exciting future prospects to improve plant disease resistance.

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Bridget Barker's curator insight, November 21, 2017 9:22 AM
Always thinking about links between animal and plant pathogens
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bioRxiv: Arabidopsis HIPP27 is a host susceptibility gene for the beet cyst nematode Heterodera schachtii (2017)

bioRxiv: Arabidopsis HIPP27 is a host susceptibility gene for the beet cyst nematode Heterodera schachtii (2017) | Plants and Microbes | Scoop.it

Sedentary plant-parasitic cyst nematodes are obligate biotrophs that infect the roots of their host plant. Their parasitism is based on modification of infected root cells to form a hypermetabolic syncytium from which the nematodes draw their nutrients. The aim of this study was to identify nematode susceptibility genes in Arabidopsis thaliana and to characterize their roles in supporting the parasitism of Heterodera schachtii. By selecting genes that were most strongly upregulated in response to cyst nematode infection, we identified HIPP27 (HEAVY METAL-ASSOCIATED ISOPRENYLATED PLANT PROTEIN 27) as a host susceptibility factor required for beet cyst nematode infection and development. Detailed expression analysis revealed that HIPP27 is a cytoplasmic protein and that HIPP27 is strongly expressed in leaves, young roots and nematode-induced syncytia. Loss-of-function Arabidopsis hipp27 mutants exhibited severely reduced susceptibility to Heterodera schachtii and abnormal starch accumulation in syncytial and peridermal plastids. Our results suggest that HIPP27 is a susceptibility gene in Arabidopsis whose loss-of-function reduces plant susceptibility to cyst nematode infection without increasing susceptibility to other pathogens or negatively affecting plant phenotype.

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Current Opinion in Plant Biology: Autophagy as a mediator of life and death in plants (2017)

Current Opinion in Plant Biology: Autophagy as a mediator of life and death in plants (2017) | Plants and Microbes | Scoop.it
Autophagy is a major pathway for degradation and recycling of cytoplasmic material, including individual proteins, aggregates, and entire organelles. Autophagic processes serve mainly survival functions in cellular homeostasis, stress adaptation and immune responses but can also have death-promoting activities in different eukaryotic organisms. In plants, the role of autophagy in the regulation of programmed cell death (PCD) remained elusive and a subject of debate. More recent evidence, however, has resulted in the consensus that autophagy can either promote or restrict different forms of PCD. Here, we present latest advances in understanding the molecular mechanisms and functions of plant autophagy and discuss their implications for life and death decisions in the context of developmental and pathogen-induced PCD.

Via Suayib Üstün
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Trends in Plant Science: Balancing Immunity and Yield in Crop Plants (2017)

Trends in Plant Science: Balancing Immunity and Yield in Crop Plants (2017) | Plants and Microbes | Scoop.it

Crop diseases cause enormous yield losses and threaten global food[ED1] security. The use of highly resistant cultivars can effectively control plant diseases, but in crops, genetic immunity to disease often comes with an unintended reduction in growth and yield. Here, we review recent advances in understanding how nucleotide-binding domain, leucine-rich repeat (NLR) receptors and cell wall-associated kinase (WAK) proteins function in balancing immunity and yield. We also discuss the role of plant hormones and transcription factors in regulating the trade-offs between plant growth and immunity. Finally, we describe how a novel mechanism of translational control of defense proteins can enhance immunity without the reduction in fitness.

 

  • High yield and immunity to pathogens are important objectives in plant breeding. However, plant growth and immunity pathways are intertwined and usually antagonistic.
  • Hormones are important for plant growth; however, activation of immunity redirects and initiates hormone signaling that can impair plant growth.
  • Transcription factors act as molecular integrators to regulate the trade-offs between immunity and growth. NLR and WAK immune receptors play dual roles in immunity and yield.
  • Pathogen-inducible translational control strategies can enhance plant immunity without fitness costs.
  • New breeding strategies should be developed to enhance immunity without sacrificing fitness and yield.
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bioRxiv: Phytophthora palmivora establishes tissue-specific intracellular infection structures in the earliest divergent land plant lineage (2017)

bioRxiv: Phytophthora palmivora establishes tissue-specific intracellular infection structures in the earliest divergent land plant lineage (2017) | Plants and Microbes | Scoop.it

The expansion of plants onto land was a formative event that brought forth profound changes to the Earth's geochemistry and biota. Filamentous eukaryotic microbes developed the ability to colonize plant tissues early during the evolution of land plants, as demonstrated by intimate symbiosis-like associations in >400 million-year-old fossils. However, the degree to which filamentous microbes establish pathogenic interactions with early divergent land plants is unclear. Here, we demonstrate that the broad host-range oomycete pathogen Phytophthora palmivora colonizes liverworts, the earliest divergent land plant lineage. We show that P. palmivora establishes a complex tissue-specific interaction with Marchantia polymorpha, where it completes a full infection cycle within air chambers of the dorsal photosynthetic layer. Remarkably, P. palmivora invaginates M. polymorpha cells with haustoria-like structures that accumulate host cellular trafficking machinery and the membrane-syntaxin MpSYP13B but not the related MpSYP13A. Our results indicate that the intracellular accommodation of filamentous microbes is an ancient plant trait that is successfully exploited by pathogens like P. palmivora.


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Philip Carella's curator insight, September 15, 2017 1:28 PM

Our new pre-print! Happy to receive any feedback. 

Philip Carella's curator insight, September 15, 2017 1:29 PM

Our new pre-print! Happy to receive any feedback

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Molecular Plant Pathology: Rmg8 and Rmg7, wheat genes for resistance to the wheat blast fungus, recognize the same avirulence gene AVR‐Rmg8 (2017)

Molecular Plant Pathology: Rmg8 and Rmg7, wheat genes for resistance to the wheat blast fungus, recognize the same avirulence gene AVR‐Rmg8 (2017) | Plants and Microbes | Scoop.it

Rmg8 and Rmg7 are genes for resistance to the wheat blast fungus (Pyricularia oryzae) located on 2B chromosome in hexaploid wheat and 2A chromosome in tetraploid wheat, respectively. AVR-Rmg8, an avirulence gene corresponding to Rmg8, was isolated from a wheat blast isolate through map-based strategy. The cloned fragment encoded a small protein containing a putative signal peptide. AVR-Rmg8 was recognized not only by Rmg8 but also by Rmg7, suggesting that these two resistance genes are equivalent to a single gene from the viewpoint of resistance breeding. This article is protected by copyright. All rights reserved.

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bioRxiv: MicroRNAs from the parasitic plant Cuscuta campestris target host messenger RNAs (2017)

bioRxiv: MicroRNAs from the parasitic plant Cuscuta campestris target host messenger RNAs (2017) | Plants and Microbes | Scoop.it

Dodders (Cuscuta spp.) are obligate parasitic plants that obtain water and nutrients from the stems of host plants via specialized feeding structures called haustoria. Dodder haustoria facilitate bi-directional movement of viruses, proteins, and mRNAs between host and parasite, but the functional effects of these movements are not clear. Here we show that C. campestris haustoria accumulate high levels of many novel microRNAs (miRNAs) while parasitizing Arabidopsis thaliana hosts. Many of these miRNAs are 22 nts long, a usually rare size of plant miRNA associated with amplification of target silencing through secondary small interfering RNA (siRNA) production. Several A. thaliana mRNAs are targeted by C. campestris 22 nt miRNAs during parasitism, resulting in mRNA cleavage, high levels of secondary siRNA production, and decreased mRNA accumulation levels. Hosts with a mutation in the target SIEVE ELEMENT OCCLUSION RELATED 1 (SEOR1) supported significantly higher growth of C. campestris. Homologs of target mRNAs from diverse plants also have predicted target sites to induced C. campestris miRNAs, and several of the same miRNAs are expressed when C. campestris parasitizes a second host, Nicotiana benthamiana. These data show that C. campestris miRNAs act as trans-species regulators of host gene expression, and suggest that they may act as virulence factors during parasitism.

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Genome Biology: RNA virus interference via CRISPR/Cas13a system in plants (2018)

Genome Biology: RNA virus interference via CRISPR/Cas13a system in plants (2018) | Plants and Microbes | Scoop.it

Background. CRISPR/Cas systems confer immunity against invading nucleic acids and phages in bacteria and archaea. CRISPR/Cas13a (known previously as C2c2) is a class 2 type VI-A ribonuclease capable of targeting and cleaving single-stranded RNA (ssRNA) molecules of the phage genome. Here, we employ CRISPR/Cas13a to engineer interference with an RNA virus, Turnip Mosaic Virus (TuMV), in plants.

 

Results. CRISPR/Cas13a produces interference against green fluorescent protein (GFP)-expressing TuMV in transient assays and stable overexpression lines of Nicotiana benthamiana. CRISPR RNA (crRNAs) targeting the HC-Pro and GFP sequences exhibit better interference than those targeting other regions such as coat protein (CP) sequence. Cas13a can also process pre-crRNAs into functional crRNAs.

 

Conclusions. Our data indicate that CRISPR/Cas13a can be used for engineering interference against RNA viruses, providing a potential novel mechanism for RNA-guided immunity against RNA viruses and for other RNA manipulations in plants.

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New Phytologist: Structure–function analysis of the Fusarium oxysporum Avr2 effector allows uncoupling of its immune‐suppressing activity from recognition (2017)

New Phytologist: Structure–function analysis of the Fusarium oxysporum Avr2 effector allows uncoupling of its immune‐suppressing activity from recognition (2017) | Plants and Microbes | Scoop.it

 

  • Plant pathogens employ effector proteins to manipulate their hosts. Fusarium oxysporumf. sp. lycopersici (Fol), the causal agent of tomato wilt disease, produces effector protein Avr2. Besides being a virulence factor, Avr2 triggers immunity in I-2 carrying tomato (Solanum lycopersicum). Fol strains that evade I-2 recognition carry point mutations in Avr2 (e.g. Avr2R45H), but retain full virulence.
  • Here we investigate the virulence function of Avr2 and determine its crystal structure. Transgenic tomato and Arabidopsis expressing either wild-type ΔspAvr2 (deleted signal-peptide) or the ΔspAvr2R45H variant become hypersusceptible to fungal, and even bacterial infections, suggesting that Avr2 targets a conserved defense mechanism. Indeed, Avr2 transgenic plants are attenuated in immunity-related readouts, including flg22-induced growth inhibition, ROS production and callose deposition.
  • The crystal structure of Avr2 reveals that the protein shares intriguing structural similarity to ToxA from the wheat pathogen Pyrenophora tritici-repentis and to TRAF proteins. The I-2 resistance-breaking Avr2V41M, Avr2R45H and Avr2R46P variants cluster on a surface-presented loop. Structure-guided mutagenesis enabled uncoupling of virulence from I-2-mediated recognition.
  • We conclude that I-2-mediated recognition is not based on monitoring Avr2 virulence activity, which includes suppression of immune responses via an evolutionarily conserved effector target, but by recognition of a distinct epitope.

 

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New Phytologist: Characterization of an antimicrobial and phytotoxic ribonuclease secreted by the fungal wheat pathogen Zymoseptoria tritici (2017)

New Phytologist: Characterization of an antimicrobial and phytotoxic ribonuclease secreted by the fungal wheat pathogen Zymoseptoria tritici (2017) | Plants and Microbes | Scoop.it
  •  The fungus Zymoseptoria tritici is the causal agent of Septoria Tritici Blotch (STB) disease of wheat leaves. Zymoseptoria tritici secretes many functionally uncharacterized effector proteins during infection. Here, we characterized a secreted ribonuclease (Zt6) with an unusual biphasic expression pattern.
  • Transient expression systems were used to characterize Zt6, and mutants thereof, in both host and non-host plants. Cell-free protein expression systems monitored the impact of Zt6 protein on functional ribosomes, and in vitroassays of cells treated with recombinant Zt6 determined toxicity against bacteria, yeasts and filamentous fungi.
  • We demonstrated that Zt6 is a functional ribonuclease and that phytotoxicity is dependent on both the presence of a 22-amino-acid N-terminal ‘loop’ region and its catalytic activity. Zt6 selectively cleaves both plant and animal rRNA species, and is toxic to wheat, tobacco, bacterial and yeast cells, but not to Z. tritici itself.
  • Zt6 is the first Z. tritici effector demonstrated to have a likely dual functionality. The expression pattern of Zt6 and potent toxicity towards microorganisms suggest that, although it may contribute to the execution of wheat cell death, it is also likely to have an important secondary function in antimicrobial competition and niche protection.
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Journal of Experimental Botany: Exchanging missives and missiles: the roles of extracellular vesicles in plant–pathogen interactions (2017)

Journal of Experimental Botany: Exchanging missives and missiles: the roles of extracellular vesicles in plant–pathogen interactions (2017) | Plants and Microbes | Scoop.it

This article comments on: Regente M, Pinedo M, San Clemente H, Balliau T, Jamet E, de la Canal L. 2017. Plant extracellular vesicles are incorporated by a fungal

 

Extracellular vesicles (EVs) are secreted by organisms from all forms of life. In the mammalian field they are intensively studied due to their importance in disease and potential for therapeutic use. However, there has been little research in plants and thus the paper byRegente et al. (2017) is a valuable addition to a small but hopefully growing body of data. The authors conducted proteomic analysis on purified sunflower EVs and demonstrated that they are enriched in defence-related proteins. They found that fungal spores treated with fresh EV preparations are damaged and show reduced growth.


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Bridget Barker's curator insight, November 30, 2017 11:12 AM
Curious about EVs in human fungal pathogens...
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MPMI: Phytophthora parasitica effector PpRxLR2 suppresses Nicotiana benthamiana immunity (2017)

MPMI: Phytophthora parasitica effector PpRxLR2 suppresses Nicotiana benthamiana immunity (2017) | Plants and Microbes | Scoop.it

Phytophthora species secrete several classes of effector proteins during interaction with their hosts. These proteins can have multiple functions including modulation of host physiology and immunity. The RxLR effectors have the ability to enter plant cells using the plant machinery. Some of these effectors have been characterized as immunity suppressors; however, very little is known about their functions in the interaction between Phytophthora parasitica and its hosts. Using a bioinformatics pipeline, we have identified 172 candidate RxLR effectors (CREs) in the isolate IAC 01_95 of P. parasitica. Out of these 172 CREs, 93 were found to be also present in other eight genomes of P. parasitica isolated from different hosts and continents. After transcriptomics and gene expression analysis we have found five CREs to be up-regulated in in vitro and in planta samples. Subsequently, we selected three CREs for functional characterization in the model plant Nicotiana benthamiana. We show that PpRxLR2 is able to completely suppress INF-1 induced cell death, whereas PpRxLR3 and PpRxLR5 moderately suppressed N. benthamiana immunity, in a lesser extent manner. Moreover, we confirmed the effector-triggered susceptibility activity of these proteins after transient transformation and infection of N. benthamiana plants. All three CREs enhanced virulence of P. parasitica during the interaction with N. benthamiana. These effectors, in particular PpRxLR2, can be targeted for the development of biotechnology-based control strategies of P. parasitica diseases.


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New Phytologist: Plasmodesmal regulation during plant–pathogen interactions (2017)

New Phytologist: Plasmodesmal regulation during plant–pathogen interactions (2017) | Plants and Microbes | Scoop.it

Plasmodesmata (PD) are plasma membrane-lined pores that connect neighbouring plant cells, bridging the cell wall and establishing cytoplasmic and membrane continuity between cells. PD are dynamic structures regulated by callose deposition in a variety of stress and developmental contexts. This process crudely controls the aperture of the pore and thus the flux of molecules between cells. During pathogen infection, plant cells initiate a range of immune responses and it was recently identified that, following perception of fungal and bacterial pathogens, plant cells initially close their PD. Systemic defence responses depend on the spread of signals between cells, raising questions about whether PD are in different functional states during different immune responses. It is well established that viral pathogens exploit PD to spread between cells, but it has more recently been identified that protein effectors secreted by fungal pathogens can spread between host cells via PD. It is possible that many classes of pathogens specifically target PD to aid infection, which would infer antagonistic regulation of PD by host and pathogen. How PD regulation benefits both host immune responses and pathogen infection is an important question and demands that we examine the multicellular nature of plant–pathogen interactions.

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New Phytologist: Effectors involved in fungal–fungal interaction lead to a rare phenomenon of hyperbiotrophy in the tritrophic system biocontrol agent–powdery mildew–plant (2017)

New Phytologist: Effectors involved in fungal–fungal interaction lead to a rare phenomenon of hyperbiotrophy in the tritrophic system biocontrol agent–powdery mildew–plant (2017) | Plants and Microbes | Scoop.it
  • Tritrophic interactions involving a biocontrol agent, a pathogen and a plant have been analyzed predominantly from the perspective of the biocontrol agent. We have conducted the first comprehensive transcriptomic analysis of all three organisms in an effort to understand the elusive properties of Pseudozyma flocculosa in the context of its biocontrol activity against Blumeria graminis f.sp. hordei as it parasitizes Hordeum vulgare.
  • After inoculation of P. flocculosa, the tripartite interaction was monitored over time and samples collected for scanning electron microscopy and RNA sequencing.
  • Based on our observations, P. flocculosa indirectly parasitizes barley, albeit transiently, by diverting nutrients extracted by B. graminis from barley leaves through a process involving unique effectors. This brings novel evidence that such molecules can also influence fungal–fungal interactions. Their release is synchronized with a higher expression of powdery mildew haustorial effectors, a sharp decline in the photosynthetic machinery of barley and a developmental peak in P. flocculosa. The interaction culminates with a collapse of B. graminis haustoria, thereby stopping P. flocculosa growth, as barley plants show higher metabolic activity.
  • To conclude, our study has uncovered a complex and intricate phenomenon, described here as hyperbiotrophy, only achievable through the conjugated action of the three protagonists.
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New Phytologist: Salicylic acid‐dependent immunity contributes to resistance against Rhizoctonia solani, a necrotrophic fungal agent of sheath blight, in rice and Brachypodium distachyon (2017)

New Phytologist: Salicylic acid‐dependent immunity contributes to resistance against Rhizoctonia solani, a necrotrophic fungal agent of sheath blight, in rice and Brachypodium distachyon (2017) | Plants and Microbes | Scoop.it

 

  • Rhizoctonia solani is a soil-borne fungus causing sheath blight. In consistent with its necrotrophic life style, no rice cultivars fully resistant to R. solani are known, and agrochemical plant defense activators used for rice blast, which upregulate a phytohormonal salicylic acid (SA)-dependent pathway, are ineffective towards this pathogen. As a result of the unavailability of genetics, the infection process of R. solaniremains unclear.
  • We used the model monocotyledonous plants Brachypodium distachyon and rice, and evaluated the effects of phytohormone-induced resistance to R. solani by pharmacological, genetic and microscopic approaches to understand fungal pathogenicity.
  • Pretreatment with SA, but not with plant defense activators used in agriculture, can unexpectedly induce sheath blight resistance in plants. SA treatment inhibits the advancement of R. solani to the point in the infection process in which fungal biomass shows remarkable expansion and specific infection machinery is developed. The involvement of SA in R. solani resistance is demonstrated by SA-deficient NahGtransgenic rice and the sheath blight-resistant B. distachyon accessions, Bd3-1 and Gaz-4, which activate SA-dependent signaling on inoculation.
  • Our findings suggest a hemi-biotrophic nature of R. solani, which can be targeted by SA-dependent plant immunity. Furthermore, B. distachyon provides a genetic resource that can confer disease resistance against R. solani to plants.

 

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bioRxiv: The plant calcium-dependent protein kinase CPK3 phosphorylates REM1.3 to restrict viral infection (2017)

bioRxiv: The plant calcium-dependent protein kinase CPK3 phosphorylates REM1.3 to restrict viral infection (2017) | Plants and Microbes | Scoop.it

Plants respond to pathogens through dynamic regulation of plasma membrane-bound signaling pathways. To date, how the plant plasma membrane is involved in responses to viruses is mostly unknown. Here, we show that plant cells sense the Potato virus X (PVX) COAT PROTEIN and TRIPLE GENE BLOCK 1 proteins and subsequently trigger the activation of a membrane-bound calcium-dependent kinase. We show that the Arabidopsis thaliana CALCIUM-DEPENDENT PROTEIN KINASE 3-interacts with group 1 REMORINs in vivo, phosphorylates the intrinsically disordered N-terminal domain of the Group 1 REMORIN REM1.3, and restricts PVX cell-to-cell movement. REM1.3's phospho-status defines its plasma membrane nanodomain organization and is crucial for REM1.3-dependent restriction of PVX cell-to-cell movement by regulation of callose deposition at plasmodesmata. This study unveils plasma membrane nanodomain-associated molecular events underlying the plant immune response to viruses.


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The Sainsbury Lab's curator insight, October 23, 2017 5:16 AM
Plants respond to pathogens through dynamic regulation of plasma membrane-bound signaling pathways. To date, how the plant plasma membrane is involved in responses to viruses is mostly unknown. Here, we show that plant cells sense the Potato virus X (PVX) COAT PROTEIN and TRIPLE GENE BLOCK 1 proteins and subsequently trigger the activation of a membrane-bound calcium-dependent kinase. We show that the Arabidopsis thaliana CALCIUM-DEPENDENT PROTEIN KINASE 3-interacts with group 1 REMORINs in vivo, phosphorylates the intrinsically disordered N-terminal domain of the Group 1 REMORIN REM1.3, and restricts PVX cell-to-cell movement. REM1.3's phospho-status defines its plasma membrane nanodomain organization and is crucial for REM1.3-dependent restriction of PVX cell-to-cell movement by regulation of callose deposition at plasmodesmata. This study unveils plasma membrane nanodomain-associated molecular events underlying the plant immune response to viruses.
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Trends in Plant Science: Dancing with the Stars: An Asterid NLR Family (2017)

Trends in Plant Science: Dancing with the Stars: An Asterid NLR Family (2017) | Plants and Microbes | Scoop.it

Wu and co-workers show how a network of sensor and helper NOD-like receptor proteins (NLRs) act together to confer robust resistance to diverse plant pathogens.

Plants engage with a plethora of potential pathogens but only some of these microbial overtures lead to disease. This is due to a highly successful system of innate immune receptors that quickly identify the invader and halt its progress. Wu et al. [1] now describe new insights into the molecular choreography of plant immune receptors.

 

Our understanding of these dances began with a simple two-step. There are two partners involved: a Resistance (R) gene in the host and an Avirulence (Avr) gene in the pathogen. They dance a dance according to the gene-for-gene model and resistance is manifest only if both partners are present [2]. The simplest interpretation of the gene-for-gene model is that the R gene encodes a receptor for the product of the Avr gene [3]. In fact, most R genes encode NOD-like receptors (NLRs) that pair a central nucleotide binding domain with C-terminal leucine rich repeats (NB-LRR proteins) [4]. On the other side, most Avr genes encode effectors that are secreted by pathogens to maintain virulence by strategic manipulation of host targets. As LRRs are receptor moieties in other proteins, early models posited them as receptor domains for effectors in a direct interaction, and this simple model holds true for some resistances [5].

 

Along the way, it transpired that more sophisticated models groove to a different beat. For instance, many NLRs recognise changes induced in another host target protein that is modified enzymatically by pathogen effector (Avr) proteins [6]. Examples are also known in which decoy proteins mimic such host target proteins and facilitate recognition by NLRs [7]. Effector decoys can also be provided in cis as a fusion with the NB-LRR moieties [8]. Some NLRs dance solo, but others need two to tango. In this molecular pas-de-deux, one NLR partner is the sensor that interacts with an effector, and the other is a helper that stimulates downstream signal transduction events. These pairs interact physically, and strikingly, are typically co-located genomically in a tail-to-tail arrangement (Figure 1) [9].
 
Sensor-helper relationships also occur between non-linked NLR genes. A widespread class of NLRs called CCR proteins typified by the Nicotiana benthamiana N-required gene 1 (NRG1) and Arabidopsis activated disease resistance gene 1 (ADR1) proteins are needed for a number of sensor NLRs that recognise diverse pathogens [10]. However in this case no contact between sensor and helper has been reported. An analogous situation exists in the Solanaceae, the nightshade family, which includes tomato, eggplant and tobacco. Here a family of NLRs called NRCs (NLR required for cell death), are essential for the function of a range of sensor NLRs [11, 12]. Wu and colleagues now flesh out the details of a network of sensors and helpers in Solanaceae that may enhance the robustness of immunity signalling pathways [1].

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Molecular Plant Pathology: Plum pox virus capsid protein suppresses plant pathogen-associated molecular pattern (PAMP)-triggered immunity (2016)

Molecular Plant Pathology: Plum pox virus capsid protein suppresses plant pathogen-associated molecular pattern (PAMP)-triggered immunity (2016) | Plants and Microbes | Scoop.it

The perception of pathogen-associated molecular patterns (PAMPs) by immune receptors launches defence mechanisms referred to as PAMP-triggered immunity (PTI). Successful pathogens must suppress PTI pathways via the action of effectors to efficiently colonize their hosts. So far, plant PTI has been reported to be active against most classes of pathogens, except viruses, although this defence layer has been hypothesized recently as an active part of antiviral immunity which needs to be suppressed by viruses for infection success. Here, we report that Arabidopsis PTI genes are regulated upon infection by viruses and contribute to plant resistance to Plum pox virus (PPV). Our experiments further show that PPV suppresses two early PTI responses, the oxidative burst and marker gene expression, during Arabidopsis infection. In planta expression of PPV capsid protein (CP) was found to strongly impair these responses in Nicotiana benthamiana and Arabidopsis, revealing its PTI suppressor activity. In summary, we provide the first clear evidence that plant viruses acquired the ability to suppress PTI mechanisms via the action of effectors, highlighting a novel strategy employed by viruses to escape plant defences.

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bioRxiv: Chemosensory proteins in the CSP4 clade evolved as plant immunity suppressors before two suborders of plant-feeding hemipteran insects diverged (2017)

bioRxiv: Chemosensory proteins in the CSP4 clade evolved as plant immunity suppressors before two suborders of plant-feeding hemipteran insects diverged (2017) | Plants and Microbes | Scoop.it

Chemosensory proteins (CSPs) are small globular proteins with hydrophobic binding pockets that have a role in detection of chemicals, regulation of development and growth and host seeking behaviour and feeding of arthropods. Here, we show that a CSP has evolved to modulate plant immune responses. Firstly, we found that the green peach aphid Myzus persicae CSP Mp10, which is delivered into the cytoplasm of plant cells, suppresses the reactive oxygen species (ROS) bursts to both aphid and bacterial elicitors in Arabidopsis thaliana and Nicotiana benthamiana. In contrast, other CSPs, including MpOS-D1, do not have this ROS suppression activity. Aphid RNA interference studies demonstrated that Mp10 modulates the first layer of the plant defence response, specifically the BAK1 pathway. Alignment of CSPs from multiple aphid species showed that Mp10 homologues uniquely have tyrosine (Y40) and tryptophan (W120) flanking the central binding region. Exchange of aromatic residues between Mp10 and MpOS-D1 showed a gain of ROS activity of MpOS-D1 and loss of this activity of Mp10. We identified Mp10 homologs in diverse plant-sucking insect species, including aphids, whiteflies, psyllids and leafhoppers, but not in other insect species, including blood-feeding hemipteran insects. Moreover, the positions of Y and W residues are conserved among these Mp10 homologs, which we found also suppress plant ROS. Together, these data and phylogenetic analyses provides evidence that an ancestral Mp10-like sequence acquired plant ROS suppression activity via gain-of-function mutations before the divergence of plant-sucking insect species over 250 million years ago.

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