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Effectors and Plant Immunity
Strategies of plant defense and microbe attacks
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Nature Commun.: CRT1 is a nuclear-translocated MORC endonuclease that participates in multiple levels of plant immunity (2012)

Nature Commun.: CRT1 is a nuclear-translocated MORC endonuclease that participates in multiple levels of plant immunity (2012) | Effectors and Plant Immunity | Scoop.it
Arabidopsis thaliana CRT1 (compromised for recognition of Turnip Crinkle Virus) was previously shown to be required for effector-triggered immunity. Sequence analyses previously revealed that CRT1 contains the ATPase and S5 domains characteristic of Microchidia (MORC) proteins; these proteins are associated with DNA modification and repair. Here we show that CRT1 and its closest homologue, CRH1, are also required for pathogen-associated molecular pattern (PAMP)-triggered immunity, basal resistance, non-host resistance and systemic acquired resistance. Consistent with its role in PAMP-triggered immunity, CRT1 interacted with the PAMP recognition receptor FLS2. Subcellular fractionation and transmission electron microscopy detected a subpopulation of CRT1 in the nucleus, whose levels increased following PAMP treatment or infection with an avirulent pathogen. These results, combined with the demonstration that CRT1 binds DNA, exhibits endonuclease activity, and affects tolerance to the DNA-damaging agent mitomycin C, argue that this prototypic eukaryotic member of the MORC superfamily has important nuclear functions during immune response activation.


Hong-Gu Kang, Hyong Woo Choi, Sabrina von Einem, Patricia Manosalva, Katrin Ehlers, Po-Pu Liu, Stefanie V. Buxa, Magali Moreau, Hyong-Gon Mang, Pradeep Kachroo, Karl-Heinz Kogel and Daniel F. Klessig
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PLOS ONE: Regulation of Cell Wall-Bound Invertase in Pepper Leaves by Xanthomonas campestris pv. vesicatoria Type Three Effectors (2012)

PLOS ONE: Regulation of Cell Wall-Bound Invertase in Pepper Leaves by Xanthomonas campestris pv. vesicatoria Type Three Effectors (2012) | Effectors and Plant Immunity | Scoop.it
Xanthomonas campestris pv. vesicatoria (Xcv) possess a type 3 secretion system (T3SS) to deliver effector proteins into its Solanaceous host plants. These proteins are involved in suppression of plant defense and in reprogramming of plant metabolism to favour bacterial propagation. There is increasing evidence that hexoses contribute to defense responses. They act as substrates for metabolic processes and as metabolic semaphores to regulate gene expression. Especially an increase in the apoplastic hexose-to-sucrose ratio has been suggested to strengthen plant defense. This shift is brought about by the activity of cell wall-bound invertase (cw-Inv). We examined the possibility that Xcv may employ type 3 effector (T3E) proteins to suppress cw-Inv activity during infection. Indeed, pepper leaves infected with a T3SS-deficient Xcv strain showed a higher level of cw-Inv mRNA and enzyme activity relative to Xcv wild type infected leaves. Higher cw-Inv activity was paralleled by an increase in hexoses and mRNA abundance for the pathogenesis-related gene PRQ. These results suggest that Xcv suppresses cw-Inv activity in a T3SS-dependent manner, most likely to prevent sugar-mediated defense signals. To identify Xcv T3Es that regulate cw-Inv activity, a screen was performed with eighteen Xcv strains, each deficient in an individual T3E. Seven Xcv T3E deletion strains caused a significant change in cw-Inv activity compared to Xcv wild type. Among them, Xcv lacking the xopB gene (Xcv ΔxopB) caused the most prominent increase in cw-Inv activity. Deletion of xopB increased the mRNA abundance of PRQ in Xcv ΔxopB-infected pepper leaves, but not of Pti5 and Acre31, two PAMP-triggered immunity markers. Inducible expression of XopB in transgenic tobacco inhibited Xcv-mediated induction of cw-Inv activity observed in wild type plants and resulted in severe developmental phenotypes. Together, these data suggest that XopB interferes with cw-Inv activity in planta to suppress sugar-enhanced defense responses during Xcv infection.

Sophia Sonnewald, Johannes P. R. Priller, Julia Schuster, Eric Glickmann, Mohammed-Reza Hajirezaei, Stefan Siebig, Mary Beth Mudgett, Uwe Sonnewald
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PLOS Pathogens: Parallels in Intercellular Communication in Oomycete and Fungal Pathogens of Plants and Humans (2012)

PLOS Pathogens: Parallels in Intercellular Communication in Oomycete and Fungal Pathogens of Plants and Humans (2012) | Effectors and Plant Immunity | Scoop.it
Sexual reproduction is one of the most fascinating evolutionary outcomes in nature. Sexual development is paradoxical, conferring both benefits and costs, which makes sex an attractive subject in evolutionary biology. In pathogenic microbes, sexual development generates progeny with diverse genetic repertoires and can contribute to create more virulent genotypes. Sexual reproduction is ubiquitous in eukaryotic organisms, from single-celled yeasts to humans. Mating systems are highly adapted in each group and vary from species to species, which results in extremely diverse sexual modes throughout nature. However, in some cases, quite divergent groups share similar mechanisms. This review describes a similarity in pheromone synthesis routes in two group of microbial pathogens of historic importance that are evolutionarily quite distinct: zygomycete pathogenic fungi that belong to the kingdom Fungi in the opisthokonts clade, and Phytophthora oomycete species that belong to the stramenopile supergroup.

Soo Chan Lee, Jean B. Ristaino, Joseph Heitman
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Plant Cell: Relocalization of Late Blight Resistance Protein R3a to Endosomal Compartments Is Associated with Effector Recognition and Required for the Immune Response (2012)

Plant Cell: Relocalization of Late Blight Resistance Protein R3a to Endosomal Compartments Is Associated with Effector Recognition and Required for the Immune Response (2012) | Effectors and Plant Immunity | Scoop.it
An important objective of plant–pathogen interactions research is to determine where resistance proteins detect pathogen effectors to mount an immune response. Many nucleotide binding–Leu-rich repeat (NB-LRR) resistance proteins accumulate in the plant nucleus following effector recognition, where they initiate the hypersensitive response (HR). Here, we show that potato (Solanum tuberosum) resistance protein R3a relocates from the cytoplasm to endosomal compartments only when coexpressed with recognized Phytophthora infestans effector form AVR3aKI and not unrecognized form AVR3aEM. Moreover, AVR3aKI, but not AVR3aEM, is also relocalized to endosomes in the presence of R3a. Both R3a and AVR3aKI colocalized in close physical proximity at endosomes in planta. Treatment with brefeldin A (BFA) or wortmannin, inhibitors of the endocytic cycle, attenuated both the relocalization of R3a to endosomes and the R3a-mediated HR. No such effect of these inhibitors was observed on HRs triggered by the gene-for-gene pairs Rx1/PVX-CP and Sto1/IpiO1. An R3a(D501V) autoactive MHD mutant, which triggered HR in the absence of AVR3aKI, failed to localize to endosomes. Moreover, BFA and wortmannin did not alter cell death triggered by this mutant. We conclude that effector recognition and consequent HR signaling by NB-LRR resistance protein R3a require its relocalization to vesicles in the endocytic pathway.

Stefan Engelhardt, Petra C. Boevink, Miles R. Armstrong, Maria Brisa Ramos, Ingo Hein, and Paul R.J. Birch
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Mol. Mic.: A translocator-specific export signal establishes the translocator–effector secretion hierarchy that is important for type III secretion system function (2012)

Mol. Mic.: A translocator-specific export signal establishes the translocator–effector secretion hierarchy that is important for type III secretion system function (2012) | Effectors and Plant Immunity | Scoop.it
Type III secretion systems are used by many Gram-negative pathogens to directly deliver effector proteins into the cytoplasm of host cells. To accomplish this, bacteria secrete translocator proteins that form a pore in the host-cell membrane through which the effector proteins are then introduced into the host cell. Evidence from multiple systems indicates that the pore-forming translocator proteins are exported before effectors, but how this secretion hierarchy is established is unclear. Here we used the Pseudomonas aeruginosa translocator protein PopD as a model to identify its export signals. The N-terminal secretion signal and chaperone, PcrH, are required for export under all conditions. Two novel signals in PopD, one proximal to the chaperone binding site and one at the very C-terminus of the protein, are required for export of PopD before effector proteins. These novel export signals establish the translocator–effector secretion hierarchy, which in turn, is critical for the delivery of effectors into host cells.

Amanda G. Tomalka, Charles M. Stopford, Pei-Chung Lee, Arne Rietsch
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Science: The Tale of the TALEs (2012)

Science: The Tale of the TALEs (2012) | Effectors and Plant Immunity | Scoop.it
Some of biology's best technologies come from unexpected places. Now, proteins from a feared plant pest are poised to make genome engineering, the large-scale, directed manipulation of genes, routine for researchers. These proteins, called transcription activator–like effectors (TALEs), can be programmed to home in on specific DNA sequences and carry out an action once there. When attached to enzymes called nucleases that cut DNA, for example, they can knock out a gene or change its sequence. Engineered TALEs have now targeted a wide range of genes in a variety of organisms

Elizabeth Pennisi
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Plant J: The XA21 binding protein XB25 is required for maintaining XA21-mediated Disease Resistance (2012)

Plant J: The XA21 binding protein XB25 is required for maintaining XA21-mediated Disease Resistance (2012) | Effectors and Plant Immunity | Scoop.it
Plant genomes encode a large number of proteins that potentially function as immune receptors to defend against pathogen invasion. As a well-characterized receptor kinase consisting of 23 tandem leucine-rich repeats, a transmembrane domain, and a serine/threonine kinase, the rice (Oryza sativa) protein XA21 confers resistance to a broad-spectrum of Xanthomonas oryzae pv. oryzae (Xoo) races that cause bacterial blight disease. We report here that XA21 binding protein 25 (XB25) belongs to the Plant-specific Ankyrin-repeat (PANK) family. XB25 physically interacts, in vitro, with the transmembrane domain of XA21 through its N-terminal binding to transmembrane and positive charged domain (BTMP) repeats. In addition, XB25 associates with XA21 in planta. Down-regulation of Xb25 results in reduced levels of XA21 and compromised XA21-mediated disease resistance at the adult stage. Moreover, accumulation of XB25 is induced by Xoo infection. Taken together, these results indicate that XB25 is required for maintaining XA21-mediated disease resistance.

Yingnan Jiang, Xiuhua Chen, Xiaodong Ding, Yongsheng Wang, Qiang Chen, Wen-Yuan Song
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Current Biology: Mycorrhizal Symbiosis: Ancient Signalling Mechanisms Co-opted (2012)

Current Biology: Mycorrhizal Symbiosis: Ancient Signalling Mechanisms Co-opted (2012) | Effectors and Plant Immunity | Scoop.it

Mycorrhizal root endosymbiosis is an ancient property of land plants. Two parallel studies now provide novel insight into the mechanism driving this interaction and how it is used by other filamentous microbes like pathogenic oomycetes.

 

René Geurts and Vivianne G.A.A. Vleeshouwers


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Frontiers in Plant Science: A gene for plant protection: expression of a bean polygalacturonase inhibitor in tobacco confers a strong resistance against Rhizoctonia solani and two oomycetes (2012)

Frontiers in Plant Science: A gene for plant protection: expression of a bean polygalacturonase inhibitor in tobacco confers a strong resistance against Rhizoctonia solani and two oomycetes (2012) | Effectors and Plant Immunity | Scoop.it

We have tested whether a gene encoding a polygalacturonase-inhibiting protein (PGIP) protects tobacco against a fungal pathogen (Rhizoctonia solani) and two oomycetes (Phytophthora parasitica var. nicotianae and Peronospora hyoscyami f. sp. tabacina). The trials were performed in greenhouse conditions for R. solani and P. parasitica and in the field for P. hyoscyami. Our results show that expression of PGIP is a powerful way of engineering a broad-spectrum disease resistance.

 

Orlando Borras-Hidalgo, Claudio Caprari, Ingrid Hernandez-Estevez, Giulia De Lorenzo and Felice Cervone

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Emerald ash borer found in Massachusetts (USA)

Emerald ash borer found in Massachusetts (USA) | Effectors and Plant Immunity | Scoop.it

The presence of the Emerald ash borer (Agrilus planipennis) has recently been confirmed in Massachusetts (USA).


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Science: Copy Number Variation of Multiple Genes at Rhg1 Mediates Nematode Resistance in Soybean (2012)

Science: Copy Number Variation of Multiple Genes at Rhg1 Mediates Nematode Resistance in Soybean (2012) | Effectors and Plant Immunity | Scoop.it

The rhg1-b allele of soybean is widely used for resistance against soybean cyst nematode (SCN), the most economically damaging pathogen of soybeans in the United States. Gene silencing showed that genes in a 31-kilobase segment at rhg1-b, encoding an amino acid transporter, an α-SNAP protein, and a WI12 (wound-inducible domain) protein, each contribute to resistance. There is one copy of the 31-kilobase segment per haploid genome in susceptible varieties, but 10 tandem copies are present in an rhg1-b haplotype. Overexpression of the individual genes in roots was ineffective, but overexpression of the genes together conferred enhanced SCN resistance. Hence, SCN resistance mediated by the soybean quantitative trait locus Rhg1 is conferred by copy number variation that increases the expression of a set of dissimilar genes in a repeated multigene segment.

 

David E. Cook, Tong Geon Lee, Xiaoli Guo, Sara Melito, Kai Wang, Adam M. Bayless, Jianping Wang, Teresa J. Hughes, David K. Willis, Thomas E. Clemente, Brian W. Diers, Jiming Jiang, Matthew E. Hudson, Andrew F. Bent

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Cold Spring Harbor Symposium on Quantitative Biology: Effector Biology of Plant-Associated Organisms: Concepts and Perspectives (2012)

Cold Spring Harbor Symposium on Quantitative Biology: Effector Biology of Plant-Associated Organisms: Concepts and Perspectives (2012) | Effectors and Plant Immunity | Scoop.it

Every plant is closely associated with a variety of living organisms. Therefore, deciphering howplants interact with mutualistic and parasitic organisms is essential for a comprehensive understanding of the biology of plants. The field of plant–biotic interactions has recently coalesced around an integrated model. Major classes of molecular players both from plants and their associated organisms have been revealed. These include cell surface and intracellular immune receptors of plants, as well as apoplastic and host-cell translocated (cytoplasmic) effectors of the invading organism. This article focuses on effectors, molecules secreted by plant-associated organisms that alter plant processes. Effectors have emerged as a central class of molecules in our integrated view of plant–microbe interactions. Their study has significantly contributed to advancing our knowledge of plant hormones, plant development, plant receptors, and epigenetics. Many pathogen effectors are extraordinary examples of biological innovation; they include some of themost remarkable proteins knownto function inside plant cells. Here, we review some of the key concepts that have emerged from the study of the effectors of plant-associated organisms. In particular, we focus on how effectors function in plant tissues and discuss future perspectives in the field of effector biology.

 

http://kamounlab.dreamhosters.com/pdfs/CSHSQB_2012.pdf


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New Phytol.: Emerging role for RNA-based regulation in plant immunity (2012)

New Phytol.: Emerging role for RNA-based regulation in plant immunity (2012) | Effectors and Plant Immunity | Scoop.it

Infection by phytopathogenic bacteria triggers massive changes in plant gene expression, which are thought to be mostly a result of transcriptional reprogramming. However, evidence is accumulating that plants additionally use post-transcriptional regulation of immune-responsive mRNAsas a strategic weapon to shape the defense-related transcriptome. Cellular RNA-binding
proteins regulate RNA stability, splicing or mRNA export of immune-response transcripts. In particular, mutants defective in alternative splicing of resistance genes exhibit compromised
disease resistance. Furthermore, detection of bacterial pathogens induces the differential
expression of small non-coding RNAs including microRNAs that impact the host defense transcriptome. Phytopathogenic bacteria in turn have evolved effector proteins to inhibit
biogenesis and/or activity of cellular microRNAs. WhereasRNAsilencing has longbeenknownas
an antiviral defense response, recent findings also reveal a major role of this process in
antibacterial defense. Here we review the function of RNA-binding proteins and small RNAdirected post-transcriptional regulation in antibacterial defense.We mainly focus on studies that used the model system Arabidopsis thaliana and also discuss selected examples from other plants.

 

Dorothee Staiger, Christin Korneli, Martina Lummer and Lionel Navarro

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Curr. Op. Plant Biol.: Symbiosis and the social network of higher plants (2012)

Curr. Op. Plant Biol.: Symbiosis and the social network of higher plants (2012) | Effectors and Plant Immunity | Scoop.it
In the Internet era, communicating with friends and colleagues via social networks constitutes a significant proportion of our daily activities. Similarly animals and plants also interact with many organisms, some of which are pathogens and do no good for the plant, while others are beneficial symbionts. Almost all plants indulge in developing social networks with microbes, in particular with arbuscular mycorrhizal fungi, and emerging evidence indicates that most employ an ancient and widespread central ‘social media’ pathway made of signaling molecules within what is called the SYM pathway. Some plants, like legumes, are particularly active recruiters of friends, as they have established very sophisticated and beneficial interactions with nitrogen-fixing bacteria, also via the SYM pathway. Interestingly, many members of the Brassicaceae, including the model plant Arabidopsis thaliana, seem to have removed themselves from this ancestral social network and lost the ability to engage in mutually favorable interactions with arbuscular mycorrhizal fungi. Despite these generalizations, recent studies exploring the root microbiota of A. thaliana have found that in natural conditions, A. thaliana roots are colonized by many different bacterial species and therefore may be using different and probably more recent ‘social media’ for these interactions. In general, recent advances in the understanding of such molecular machinery required for plant–symbiont associations are being obtained using high throughput genomic profiling strategies including transcriptomics, proteomics and metabolomics. The crucial mechanistic understanding that such data reveal may provide the infrastructure for future efforts to genetically manipulate crop social networks for our own food and fiber needs.

Muthusubramanian Venkateshwaran, Jeremy D Volkening, Michael R Sussman, Jean-Michel Ané
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Plant Methods: CalloseMeasurer: a novel software solution to measure callose deposition and recognise spreading callose patterns (2012)

Plant Methods: CalloseMeasurer: a novel software solution to measure callose deposition and recognise spreading callose patterns (2012) | Effectors and Plant Immunity | Scoop.it
Quantification of callose deposits is a useful measure for the activities of plant immunity and pathogen growth by fluorescence imaging. For robust scoring of differences, this normally requires many technical and biological replicates and manual or automated quantification of the callose deposits. However, previously available software tools for quantifying callose deposits from bioimages were limited, making batch processing of callose image data problematic. In particular, it is challenging to perform large-scale analysis on images with high background noise and fused callose deposition signals.
We developed CalloseMeasurer, an easy-to-use application that quantifies callose deposition, a plant immune response triggered by potentially pathogenic microbes. Additionally, by tracking identified callose deposits between multiple images, the software can recognise patterns of how a given filamentous pathogen grows in plant leaves. The software has been evaluated with typical noisy experimental images and can be automatically executed without the need for user intervention. The automated analysis is achieved by using standard image analysis functions such as image enhancement, adaptive thresholding, and object segmentation, supplemented by several novel methods which filter background noise, split fused signals, perform edge-based detection, and construct networks and skeletons for extracting pathogen growth patterns. To efficiently batch process callose images, we implemented the algorithm in C/C++ within the AcapellaTM framework. Using the tool we can robustly score significant differences between different plant genotypes when activating the immune response. We also provide examples for measuring the in planta hyphal growth of filamentous pathogens.
CalloseMeasurer is a new software solution for batch-processing large image data sets to quantify callose deposition in plants. We demonstrate its high accuracy and usefulness for two applications: 1) the quantification of callose deposition in different genotypes as a measure for the activity of plant immunity; and 2) the quantification and detection of spreading networks of callose deposition triggered by filamentous pathogens as a measure for growing pathogen hyphae. The software is an easy-to-use protocol which is executed within the Acapella software system without requiring any additional libraries. The source code of the software is freely available at https://sourceforge.net/projects/bioimage/files/Callose.

Ji Zhou, Thomas Spallek, Christine Faulkner and Silke Robatzek
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New Phytol.: Comparative genomic and transcriptomic analyses reveal the hemibiotrophic stage shift of Colletotrichum fungi (2012)

New Phytol.: Comparative genomic and transcriptomic analyses reveal the hemibiotrophic stage shift of Colletotrichum fungi (2012) | Effectors and Plant Immunity | Scoop.it
Hemibiotrophic fungal plant pathogens represent a group of agronomically significant disease-causing agents that grow first on living tissue and then cause host death in later, necrotrophic growth. Among these, Colletotrichum spp. are devastating pathogens of many crops. Identifying expanded classes of genes in the genomes of phytopathogenic Colletotrichum, especially those associated with specific stages of hemibiotrophy, can provide insights on how these pathogens infect a large number of hosts.
The genomes of Colletotrichum orbiculare, which infects cucurbits and Nicotiana benthamiana, and C. gloeosporioides, which infects a wide range of crops, were sequenced and analyzed, focusing on features with potential roles in pathogenicity. Regulation of C. orbiculare gene expression was investigated during infection of N. benthamiana using a custom microarray.
Genes expanded in both genomes compared to other fungi included sequences encoding small, secreted proteins (SSPs), secondary metabolite synthesis genes, proteases and carbohydrate-degrading enzymes. Many SSP and secondary metabolite synthesis genes were upregulated during initial stages of host colonization, whereas the necrotrophic stage of growth is characterized by upregulation of sequences encoding degradative enzymes.
Hemibiotrophy in C. orbiculare is characterized by distinct stage-specific gene expression profiles of expanded classes of potential pathogenicity genes.

Pamela Gan, Kyoko Ikeda, Hiroki Irieda, Mari Narusaka, Richard J. O'Connell, Yoshihiro Narusaka, Yoshitaka Takano, Yasuyuki Kubo, Ken Shirasu
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OpenAshDieBack: A hub for crowdsourcing information and genomic resources for Ash Dieback

OpenAshDieBack: A hub for crowdsourcing information and genomic resources for Ash Dieback | Effectors and Plant Immunity | Scoop.it
Welcome to Open Access Data and Crowdsourced analyses!

On this website you'll be able to get data to do your own analyses on ash and ash dieback. You can see the results of other peoples work as soon as it is available and share your own discoveries in the same way.

You will always get full credit for your work and in doing so contribute to a real community effort.

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Science: Beyond TALENs (2012)

Science: Beyond TALENs (2012) | Effectors and Plant Immunity | Scoop.it
Zinc finger nucleases and TALENS are not the only up-and-coming genome engineering tools. There are meganucleases that are DNA-cutting enzymes encoded by certain mobile elements, nucleases that might do the job solo, and a potential bacterial defense system.

Elizabeth Pennisi

See also (by Emmanuelle Charpentier et al.):
http://www.sciencemag.org.gate1.inist.fr/content/337/6096/816.full
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Nature: A soybean cyst nematode resistance gene points to a new mechanism of plant resistance to pathogens (2012)

Nature: A soybean cyst nematode resistance gene points to a new mechanism of plant resistance to pathogens (2012) | Effectors and Plant Immunity | Scoop.it
Soybean (Glycine max (L.) Merr.) is an important crop that provides a sustainable source of protein and oil worldwide. Soybean cyst nematode (Heterodera glycines Ichinohe) is a microscopic roundworm that feeds on the roots of soybean and is a major constraint to soybean production. This nematode causes more than US$1 billion in yield losses annually in the United States alone1, making it the most economically important pathogen on soybean. Although planting of resistant cultivars forms the core management strategy for this pathogen, nothing is known about the nature of resistance. Moreover, the increase in virulent populations of this parasite on most known resistance sources necessitates the development of novel approaches for control. Here we report the map-based cloning of a gene at the Rhg4 (for resistance to Heterodera glycines 4) locus, a major quantitative trait locus contributing to resistance to this pathogen. Mutation analysis, gene silencing and transgenic complementation confirm that the gene confers resistance. The gene encodes a serine hydroxymethyltransferase, an enzyme that is ubiquitous in nature and structurally conserved across kingdoms. The enzyme is responsible for interconversion of serine and glycine and is essential for cellular one-carbon metabolism. Alleles of Rhg4 conferring resistance or susceptibility differ by two genetic polymorphisms that alter a key regulatory property of the enzyme. Our discovery reveals an unprecedented plant resistance mechanism against a pathogen. The mechanistic knowledge of the resistance gene can be readily exploited to improve nematode resistance of soybean, an increasingly important global crop.

Shiming Liu, Pramod K. Kandoth, Samantha D. Warren, Greg Yeckel, Robert Heinz, John Alden, Chunling Yang, Aziz Jamai, Tarik El-Mellouki, Parijat S. Juvale, John Hill, Thomas J. Baum, Silvia Cianzio, Steven A. Whitham, Dmitry Korkin, Melissa G. Mitchum & Khalid Meksem
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Cold Spring Harb Symp Quant Biol: Mechanisms of Nuclear Suppression of Host Immunity by Effectors from the Arabidopsis Downy Mildew Pathogen H. arabidopsidis (2012)

Filamentous phytopathogens form sophisticated intracellular feeding structures called haustoria in plant cells. Pathogen effectors are likely to play a role in the establishment and maintenance of haustoria additional to their more characterized role of suppressing plant defense. Recent studies suggest that effectors may manipulate host transcription or other nuclear regulatory components for the benefit of pathogen development. However, the specific mechanisms by which these effectors promote susceptibility remain unclear. Of two recent screenings, we identified 15 nuclear-localized Hpa effectors (HaRxLs) that interact directly or indirectly with host nuclear components. When stably expressed in planta, nuclear HaRxLs cause diverse developmental phenotypes highlighting that nuclear effectors might interfere with fundamental plant regulatory mechanisms. Here, we report recent advances in understanding how a pathogen can manipulate nuclear processes in order to cause disease


M.-C. Caillaud, L. Wirthmueller, G. Fabro, S.J.M. Piquerez, S. Asai, N. Ishaque and J.D.G. Jones

 

 

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PLOS Pathogens: Intramolecular Interaction Influences Binding of the Flax L5 and L6 Resistance Proteins to their AvrL567 Ligands (2012)

PLOS Pathogens: Intramolecular Interaction Influences Binding of the Flax L5 and L6 Resistance Proteins to their AvrL567 Ligands (2012) | Effectors and Plant Immunity | Scoop.it

L locus resistance (R) proteins are nucleotide binding (NB-ARC) leucine-rich repeat (LRR) proteins from flax (Linum usitatissimum) that provide race-specific resistance to the causal agent of flax rust disease, Melampsora lini. L5 and L6 are two alleles of the L locus that directly recognize variants of the fungal effector AvrL567. In this study, we have investigated the molecular details of this recognition by site-directed mutagenesis of AvrL567 and construction of chimeric L proteins. Single, double and triple mutations of polymorphic residues in a variety of AvrL567 variants showed additive effects on recognition strength, suggesting that multiple contact points are involved in recognition. Domain-swap experiments between L5 and L6 show that specificity differences are determined by their corresponding LRR regions. Most positively selected amino acid sites occur in the N- and C-terminal LRR units, and polymorphisms in the first seven and last four LRR units contribute to recognition specificity of L5 and L6 respectively. This further confirms that multiple, additive contact points occur between AvrL567 variants and either L5 or L6. However, we also observed that recognition of AvrL567 is affected by co-operative polymorphisms between both adjacent and distant domains of the R protein, including the TIR, ARC and LRR domains, implying that these residues are involved in intramolecular interactions to optimize detection of the pathogen and defense signal activation. We suggest a model where Avr ligand interaction directly competes with intramolecular interactions to cause activation of the R protein.

 

Michael Ravensdale, Maud Bernoux, Thomas Ve, Bostjan Kobe, Peter H. Thrall, Jeffrey G. Ellis, Peter N. Dodds

 

 

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Plant Cell: The Coronatine Toxin of Pseudomonas syringae Is a Multifunctional Suppressor of Arabidopsis Defense (2012)

Plant Cell: The Coronatine Toxin of Pseudomonas syringae Is a Multifunctional Suppressor of Arabidopsis Defense (2012) | Effectors and Plant Immunity | Scoop.it

The phytotoxin coronatine (COR) promotes various aspects of Pseudomonas syringae virulence, including invasion through stomata, growth in the apoplast, and induction of disease symptoms. COR is a structural mimic of active jasmonic acid (JA) conjugates. Known activities of COR are mediated through its binding to the F-box–containing JA coreceptor CORONATINE INSENSITIVE1. By analyzing the interaction of P. syringae mutants with Arabidopsis thaliana mutants, we demonstrate that, in the apoplastic space of Arabidopsis, COR is a multifunctional defense suppressor. COR and the critical P. syringae type III effector HopM1 target distinct signaling steps to suppress callose deposition. In addition to its well-documented ability to suppress salicylic acid (SA) signaling, COR suppresses an SA-independent pathway contributing to callose deposition by reducing accumulation of an indole glucosinolate upstream of the activity of the PEN2 myrosinase. COR also suppresses callose deposition and promotes bacterial growth in coi1 mutant plants, indicating that COR may have multiple targets inside plant cells.

 

Xueqing Geng, Jiye Cheng, Anju Gangadharan and David Mackey


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The history of gene discovery in banana

The history of gene discovery in banana | Effectors and Plant Immunity | Scoop.it

Attentive readers may well remember a Nibble from a couple of months back announcing the “Discovery of genes for resistance to black Sigatoka in bananas”. Rodomiro Ortiz writes on Host plant resistance genes for black Sigatoka in banana and plantain: two decades of research on the genetics and inheritance of host plant resistance to black Sigatoka in Musa. Black Sigatoka (or black leaf streak) is a major global constraint for growing one of our favorite fruits: banana and plantain (Musa spp.). The disease develops faster where humidity and rainfall are high. Yield loss to black Sigatoka ranges from 33 to 50% because this leaf spot disease affects negatively both fruit number and weight. (Picture shows red thrip damage not Sigatoka - but a dead leaf with no fruit does not suggest banana! PHH)

 

Luigi Garino


Via Annals of Botany: Plant Science Research
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PLOS Genetics: The Genomes of the Fungal Plant Pathogens Cladosporium fulvum and Dothistroma septosporum Reveal Adaptation to Different Hosts and Lifestyles But Also Signatures of Common Ancestry (...

PLOS Genetics: The Genomes of the Fungal Plant Pathogens Cladosporium fulvum and Dothistroma septosporum Reveal Adaptation to Different Hosts and Lifestyles But Also Signatures of Common Ancestry (... | Effectors and Plant Immunity | Scoop.it

We sequenced and compared the genomes of the Dothideomycete fungal plant pathogens Cladosporium fulvum (Cfu) (syn. Passalora fulva) and Dothistroma septosporum (Dse) that are closely related phylogenetically, but have different lifestyles and hosts. Although both fungi grow extracellularly in close contact with host mesophyll cells, Cfu is a biotroph infecting tomato, while Dse is a hemibiotroph infecting pine. The genomes of these fungi have a similar set of genes (70% of gene content in both genomes are homologs), but differ significantly in size (Cfu >61.1-Mb; Dse 31.2-Mb), which is mainly due to the difference in repeat content (47.2% in Cfu versus 3.2% in Dse). Recent adaptation to different lifestyles and hosts is suggested by diverged sets of genes. Cfu contains an α-tomatinase gene that we predict might be required for detoxification of tomatine, while this gene is absent in Dse. Many genes encoding secreted proteins are unique to each species and the repeat-rich areas in Cfu are enriched for these species-specific genes. In contrast, conserved genes suggest common host ancestry. Homologs of Cfu effector genes, including Ecp2 and Avr4, are present in Dse and induce a Cf-Ecp2- and Cf-4-mediated hypersensitive response, respectively. Strikingly, genes involved in production of the toxin dothistromin, a likely virulence factor for Dse, are conserved in Cfu, but their expression differs markedly with essentially no expression by Cfu in planta. Likewise, Cfu has a carbohydrate-degrading enzyme catalog that is more similar to that of necrotrophs or hemibiotrophs and a larger pectinolytic gene arsenal than Dse, but many of these genes are not expressed in planta or are pseudogenized. Overall, comparison of their genomes suggests that these closely related plant pathogens had a common ancestral host but since adapted to different hosts and lifestyles by a combination of differentiated gene content, pseudogenization, and gene regulation.

 

Pierre J. G. M. de Wit, Ate van der Burgt, Bilal Ökmen, Ioannis Stergiopoulos, Kamel A. Abd-Elsalam, Andrea L. Aerts, Ali H. Bahkali, Henriek G. Beenen, Pranav Chettri, Murray P. Cox, Erwin Datema, Ronald P. de Vries, Braham Dhillon, Austen R. Ganley, Scott A. Griffiths, Yanan Guo, Richard C. Hamelin, Bernard Henrissat, M. Shahjahan Kabir, Mansoor Karimi Jashni, Gert Kema, Sylvia Klaubauf, Alla Lapidus, Anthony Levasseur, Erika Lindquist, Rahim Mehrabi, Robin A. Ohm, Timothy J. Owen, Asaf Salamov, Arne Schwelm, Elio Schijlen, Hui Sun, Harrold A. van den Burg, Roeland C. H. J. van Ham, Shuguang Zhang, Stephen B. Goodwin, Igor V. Grigoriev, Jérôme Collemare, Rosie E. Bradshaw

 

 

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New Phytol.: One world, many pathogens! (2012)

Forest insect and pathogen species are expanding their geographical ranges through international trade at a rate that most pest specialists and ecologists find alarming. While many invaders are relatively innocuous, several species have damaging impacts on agricultural and natural resources. Furthermore, some of these non-native pests have had catastrophic impacts on ecosystem functions when they invade native communities in which they have no prior evolutionary history. Examples include the demise of chestnut trees in North America, major losses of elms in Europe and North America, Jarrah dieback in Australia, and the devastating effects of pine wood nematode in Asia. Predicting which insects or pathogens will become most problematic and devising mitigation measures to reduce the risk of their arrival and establishment has become the ‘holy grail’ for many entomologists and plant pathologists worldwide. Analysis of historical data is an essential tool for identifying important invasion pathways and weak links in the chain of biosecurity measures that must be strengthened to protect local economies and ecosystem stability. In this issue of New Phytologist, Santini et al. (pp. 238–250), provide a comprehensive and insightful analysis of historical forest pathogen establishment and spread records from Europe. A product of a collaborative (20 nations) European Union-funded project, the paper identifies dominant plant pathogen invasion pathways and key factors predicting pathogen species invasiveness, as well as habitat characteristics that render certain regions more vulnerable to pathogen invasion. All of these associations have implications for preventing future invasions.

 

Kerry O. Britton, Andrew M. Liebhold

 

See also the article by Santini et al. (previously scooped here):

http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2012.04364.x/abstract

 

 

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