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Rescooped by Kubilay Kurtulus BASTAS from Assoc. Prof. Dr.
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The Arabidopsis Metacaspase9 Degradome

The Arabidopsis Metacaspase9 Degradome | Assoc. Prof. Dr. | Scoop.it

Scooped from: The Plant Cell (2013)

Authors: Liana Tsiatsiani, Evy Timmerman, Pieter-Jan De Bock, Dominique Vercammen, Simon Stael, Brigitte van de Cotte, An Staes, Marc Goethal, Tine Beunens, Petra Van Damm, Kris Gevaert, and Frank Van Breusegem

 

Summary:

Metacaspases are distant relatives of the metazoan caspases, found in plants, fungi, and protists. However, in contrast with caspases, information about the physiological substrates of metacaspases is still scarce. By means of N-terminal combined fractional diagonal chromatography, the physiological substrates of metacaspase9 (MC9; AT5G04200) were identified in young seedlings of Arabidopsis thaliana on the proteome-wide level, providing additional insight into MC9 cleavage specificity and revealing a previously unknown preference for acidic residues at the substrate prime site position P1′. The functionalities of the identified MC9 substrates hinted at metacaspase functions other than those related to cell death. These results allowed us to resolve the substrate specificity of MC9 in more detail and indicated that the activity of phosphoenolpyruvate carboxykinase 1 (AT4G37870), a key enzyme in gluconeogenesis, is enhanced upon MC9-dependent proteolysis.

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Xanthomonas perforans Colonization Influences Salmonella enterica in the Tomato Phyllosphere

Xanthomonas perforans Colonization Influences Salmonella enterica in the Tomato Phyllosphere | Assoc. Prof. Dr. | Scoop.it

Scooped from: Applied Environmental Microbiology, 2014.

Authors: Neha Potnis, José Pablo Soto-Arias, Kimberly N. Cowles, Ariena H. C. van Bruggen, Jeffrey B. Jones and Jeri D. Barak

 

Summary:

Salmonella enterica rarely grows on healthy, undamaged plants, but its persistence is influenced by bacterial plant pathogens. The interactions betweenS. enterica, Xanthomonas perforans (a tomato bacterial spot pathogen), and tomato were characterized. We observed that virulent X. perforans, which establishes disease by suppressing pathogen-associated molecular pattern (PAMP)-triggered immunity that leads to effector-triggered susceptibility, created a conducive environment for persistence of S. enterica in the tomato phyllosphere, while activation of effector-triggered immunity by avirulent X. perforans resulted in a dramatic reduction in S. enterica populations. S. entericapopulations persisted at ∼10 times higher levels in leaves coinoculated with virulent X. perforans than in those where S. enterica was applied alone. In contrast, S. enterica populations were ∼5 times smaller in leaves coinoculated with avirulent X. perforans than in leaves inoculated with S. enterica alone. Coinoculation with virulent X. perforans increased S. enterica aggregate formation; however, S. enterica was not found in mixed aggregates with X. perforans. Increased aggregate formation by S. enterica may serve as the mechanism of persistence on leaves cocolonized by virulent X. perforans. S. enterica association with stomata was altered by X. perforans; however, it did not result in appreciable populations of S. enterica in the apoplast even in the presence of large virulent X. perforans populations. Gene-for-gene resistance against X. perforans successively restricted S. enterica populations. Given the effect of this interaction, breeding for disease-resistant cultivars may be an effective strategy to limit both plant disease and S. enterica populations and, consequently, human illness.

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The Arabidopsis Metacaspase9 Degradome

The Arabidopsis Metacaspase9 Degradome | Assoc. Prof. Dr. | Scoop.it

Scooped from: The Plant Cell (2013)

Authors: Liana Tsiatsiani, Evy Timmerman, Pieter-Jan De Bock, Dominique Vercammen, Simon Stael, Brigitte van de Cotte, An Staes, Marc Goethal, Tine Beunens, Petra Van Damm, Kris Gevaert, and Frank Van Breusegem

 

Summary:

Metacaspases are distant relatives of the metazoan caspases, found in plants, fungi, and protists. However, in contrast with caspases, information about the physiological substrates of metacaspases is still scarce. By means of N-terminal combined fractional diagonal chromatography, the physiological substrates of metacaspase9 (MC9; AT5G04200) were identified in young seedlings of Arabidopsis thaliana on the proteome-wide level, providing additional insight into MC9 cleavage specificity and revealing a previously unknown preference for acidic residues at the substrate prime site position P1′. The functionalities of the identified MC9 substrates hinted at metacaspase functions other than those related to cell death. These results allowed us to resolve the substrate specificity of MC9 in more detail and indicated that the activity of phosphoenolpyruvate carboxykinase 1 (AT4G37870), a key enzyme in gluconeogenesis, is enhanced upon MC9-dependent proteolysis.

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Plant lectin-like antibacterial proteins from phytopathogens Pseudomonas syringae and Xanthomonas citri

Plant lectin-like antibacterial proteins from phytopathogens Pseudomonas syringae and Xanthomonas citri | Assoc. Prof. Dr. | Scoop.it

Scooped from: Environmental Microbiology Reports, 2012

Authors: Maarten G. K. Ghequire, Wen Li, Paul Proost, Remy Loris and René De Mot

 

Summary:

The genomes of Pseudomonas syringae pv. syringae 642 and Xanthomonas citri pv. malvacearum LMG 761 each carry a putative homologue of the plant lectin-like bacteriocin (llpA) genes previously identified in the rhizosphere isolate Pseudomonas putida BW11M1 and the biocontrol strain Pseudomonas fluorescens Pf-5. The respective purified recombinant proteins, LlpAPss642 and LlpAXcm761, display genus-specific antibacterial activity across species boundaries. The inhibitory spectrum of the P. syringae bacteriocin overlaps partially with those of the P. putida and P. fluorescens LlpAs. Notably, Xanthomonas axonopodis pv. citri str. 306 secretes a protein identical to LlpAXcm761. The functional characterization of LlpA proteins from two different phytopathogenic γ-proteobacterial species expands the lectin-like bacteriocin family beyond the Pseudomonas genus and suggests its involvement in competition among closely related plant-associated bacteria with different lifestyles.

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Pseudomonas syringae pv. tomato DC3000: A Model Pathogen for Probing Disease Susceptibility and Hormone Signaling in Plants

Pseudomonas syringae pv. tomato DC3000: A Model Pathogen for Probing Disease Susceptibility and Hormone Signaling in Plants | Assoc. Prof. Dr. | Scoop.it

Scooped from: Annual Review of Phytopathology, 2013
Authors: Xiu-Fang Xin and Sheng Yang He

Summary: Since the early 1980s, various strains of the gram-negative bacterial pathogen Pseudomonas syringae have been used as models for understanding plant-bacterial interactions. In 1991, a P. syringae pathovar tomato (Pst) strain, DC3000, was reported to infect not only its natural host tomato but also Arabidopsis in the laboratory, a finding that spurred intensive efforts in the subsequent two decades to characterize the molecular mechanisms by which this strain causes disease in plants. Genomic analysis shows that Pst DC3000 carries a large repertoire of potential virulence factors, including proteinaceous effectors that are secreted through the type III secretion system and a polyketide phytotoxin called coronatine, which structurally mimics the plant hormone jasmonate ( JA). Study of Pst DC3000 pathogenesis has not only provided several conceptual advances in understanding how a bacterial pathogen employs type III effectors to suppress plant immune responses and promote disease susceptibility but has also facilitated the discovery of the immune function of stomata and key components of JA signaling in plants. The concepts derived from the study of Pst DC3000 pathogenesis may prove useful in understanding pathogenesis mechanisms of other plant pathogens.

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Damien Meyer's curator insight, June 19, 2013 3:25 PM

remarkable review

Rescooped by Kubilay Kurtulus BASTAS from Microbes, plant immunity, and crop science
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PLOS Pathogens: The Xanthomonas campestris Type III Effector XopJ Targets the Host Cell Proteasome to Suppress Salicylic-Acid Mediated Plant Defence

PLOS Pathogens: The Xanthomonas campestris Type III Effector XopJ Targets the Host Cell Proteasome to Suppress Salicylic-Acid Mediated Plant Defence | Assoc. Prof. Dr. | Scoop.it

(via @SuayibUestuen, thanks!)

 

The phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) requires type III effector proteins (T3Es) for virulence. After translocation into the host cell, T3Es are thought to interact with components of host immunity to suppress defence responses. XopJ is a T3E protein from Xcv that interferes with plant immune responses; however, its host cellular target is unknown. Here we show that XopJ interacts with the proteasomal subunit RPT6 in yeast andin planta to inhibit proteasome activity. A C235A mutation within the catalytic triad of XopJ as well as a G2A exchange within the N-terminal myristoylation motif abolishes the ability of XopJ to inhibit the proteasome. Xcv ΔxopJ mutants are impaired in growth and display accelerated symptom development including tissue necrosis on susceptible pepper leaves. Application of the proteasome inhibitor MG132 restored the ability of the Xcv ΔxopJ to attenuate the development of leaf necrosis. The XopJ dependent delay of tissue degeneration correlates with reduced levels of salicylic acid (SA) and changes in defence- and senescence-associated gene expression. Necrosis upon infection with Xcv ΔxopJ was greatly reduced in pepper plants with reduced expression of NPR1, a central regulator of SA responses, demonstrating the involvement of SA-signalling in the development of XopJ dependent phenotypes. Our results suggest that XopJ-mediated inhibition of the proteasome interferes with SA-dependent defence response to attenuate onset of necrosis and to alter host transcription. A central role of the proteasome in plant defence is discussed.


Via Nicolas Denancé
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A novel effector secretion mechanism based on proton-motive force-dependent type III secretion apparatus rotation

A novel effector secretion mechanism based on proton-motive force-dependent type III secretion apparatus rotation | Assoc. Prof. Dr. | Scoop.it

Scooped from: The Journal of the Federation of American Societies for Experimental Biology, 2013

Authors: Takashi Ohgita, Naoki Hayashi, Susumu Hama, Hiroyuki Tsuchiya, Naomasa Gotoh and Kentaro Kogure

 

Summary:

The type III secretion apparatus (T3SA) participates in the secretion of bacterial proteins called effectors, although the detailed mechanism of effector secretion remains unclear. T3SA and flagellum were shown to branch from a common ancestor and also show structural similarity. In addition, both T3SA-dependent effector secretion and flagellar rotation were reported to require proton-motive force (PMF) for activity. From these reports, we hypothesized that T3SA, like the flagellum, would rotate via PMF and that this rotation is responsible for effector secretion. To observe T3SA rotation, we constructed a novel observation system by modifying the tip of T3SA on bacterial cell membranes with an observation probe, which allowed documentation of T3SA rotation for the first time. T3SA rotation was stopped by the addition of a protonophore that decreases PMF. Moreover, increased viscosity of the observation medium inhibited both rotation of T3SA associated with beads and effector secretion. These results suggested that effector secretion would follow the PMF-dependent rotation of T3SA and could be inhibited by preventing T3SA rotation. Moreover, the motion-track analysis of bead rotation suggested that the T3SA needle might be flexible. Consequently, we propose a “rotational secretion model” as a novel effector secretion mechanism of T3SA.

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Plant lectin-like antibacterial proteins from phytopathogens Pseudomonas syringae and Xanthomonas citri

Plant lectin-like antibacterial proteins from phytopathogens Pseudomonas syringae and Xanthomonas citri | Assoc. Prof. Dr. | Scoop.it

Scooped from: Environmental Microbiology Reports, 2012

Authors: Maarten G. K. Ghequire, Wen Li, Paul Proost, Remy Loris and René De Mot

 

Summary:

The genomes of Pseudomonas syringae pv. syringae 642 and Xanthomonas citri pv. malvacearum LMG 761 each carry a putative homologue of the plant lectin-like bacteriocin (llpA) genes previously identified in the rhizosphere isolate Pseudomonas putida BW11M1 and the biocontrol strain Pseudomonas fluorescens Pf-5. The respective purified recombinant proteins, LlpAPss642 and LlpAXcm761, display genus-specific antibacterial activity across species boundaries. The inhibitory spectrum of the P. syringae bacteriocin overlaps partially with those of the P. putida and P. fluorescens LlpAs. Notably, Xanthomonas axonopodis pv. citri str. 306 secretes a protein identical to LlpAXcm761. The functional characterization of LlpA proteins from two different phytopathogenic γ-proteobacterial species expands the lectin-like bacteriocin family beyond the Pseudomonas genus and suggests its involvement in competition among closely related plant-associated bacteria with different lifestyles.

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Rescooped by Kubilay Kurtulus BASTAS from Plant Biology Teaching Resources (Higher Education)
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The Conversation Explainer: What is epigenetics?

The word epigenetics means things imposed “on top of genetics”. But what sort of things?Imagine a white mouse breeds with a black mouse – say you get three white babies and three black babies.

 

This is an interesting overview of what is and isn't epigenetics, and why epigenetics is only part of any story.


Via Mary Williams
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Mary Williams's curator insight, May 30, 2013 3:09 AM

Be sure to check out the cited article by Mark Ptashne too.

http://www.pnas.org/content/early/2013/04/11/1305399110

Rescooped by Kubilay Kurtulus BASTAS from Rice Blast
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Plant–pathogen interactions: disease resistance in modern agriculture

Plant–pathogen interactions: disease resistance in modern agriculture | Assoc. Prof. Dr. | Scoop.it

Here, we review these recent advances and progress towards the ultimate goal of developing disease-resistant crops


Via Elsa Ballini
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FlgM as a Secretion Moiety for the Development of an Inducible Type III Secretion System

FlgM as a Secretion Moiety for the Development of an Inducible Type III Secretion System | Assoc. Prof. Dr. | Scoop.it

Regulation and assembly of the flagellar type III secretion system is one of the most investigated and best understood regulational cascades in molecular biology. Depending on the host organism, flagellar morphogenesis requires the interplay of more than 50 genes. Direct secretion of heterologous proteins to the supernatant is appealing due to protection against cellular proteases and simplified downstream processing. As Escherichia coli currently remains the predominant host organism used for recombinant prokaryotic protein expression, the generation of a strain that exhibits inducible flagellar secretion would be highly desirable for biotechnological applications.

Here, we report the first engineered Escherichia coli mutant strain featuring flagellar morphogenesis upon addition of an external inducer. Using FlgM as a sensor for direct secretion in combination with this novel strain may represent a potent tool for significant improvements in future engineering of an inducible type III secretion for heterologous proteins

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Recognition of bacterial plant pathogens: local, systemic and transgenerational immunity

Recognition of bacterial plant pathogens: local, systemic and transgenerational immunity | Assoc. Prof. Dr. | Scoop.it

Summary:

Bacterial pathogens can cause multiple plant diseases and plants rely on their innate immune system to recognize and actively respond to these microbes. The plant innate immune system comprises extracellular pattern recognition receptors that recognize conserved microbial patterns and intracellular nucleotide binding leucine-rich repeat (NLR) proteins that recognize specific bacterial effectors delivered into host cells. Plants lack the adaptive immune branch present in animals, but still afford flexibility to pathogen attack through systemic and transgenerational resistance. Here, we focus on current research in plant immune responses against bacterial pathogens. Recent studies shed light onto the activation and inactivation of pattern recognition receptors and systemic acquired resistance. New research has also uncovered additional layers of complexity surrounding NLR immune receptor activation, cooperation and sub-cellular localizations. Taken together, these recent advances bring us closer to understanding the web of molecular interactions responsible for coordinating defense responses and ultimately resistance.

 

by:     Elizabeth Henry, Koste A. Yadeta, Gitta Coaker

 

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Pathogenicity and infection strategies of the fire blight pathogen Erwinia amylovora in Rosaceae: State of the Art

Summary: Plants are host to a large amount of pathogenic bacteria, of which fire blight, caused by the bacterium Erwinia amylovora, is an important disease in Rosaceae. Pathogenicity of E. amylovora is greatly influenced by the production of exopolysaccharides such as amylovoran and the use of the type III secretion system, which enables bacteria to penetrate their host tissue and cause disease. When infection takes place, plants have to rely on the ability of each cell to recognize the pathogen and the signals emanating from the infection site in order to generate several defense mechanisms. These mechanisms consist of physical barriers and the production of antimicrobial components, both in a preformed and an inducible manner. Inducible defense responses are activated upon the recognition by plant cell receptors of elicitor molecules, either derived from invading microorganisms or from pathogen-induced degradation of plant tissue. This recognition event triggers a signal transduction cascade, leading to a range of defense responses (reactive oxygen species (ROS), plant hormones, secondary metabolites, ...) and redeployment of cellular energy in a fast, efficient and multiresponse manner, which prevents further pathogen ingress. This review highlights the research that has been performed during the last years regarding this specific plant-pathogen interaction between Erwinia amylovora and Rosaceae, with a special emphasis on the pathogenicity and the infection strategy of E. amylovora and the possible defense mechanisms of the plant against this disease.

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PNAS: The syntaxin SYP132 contributes to plant resistance against bacteria and secretion of pathogenesis-related protein 1 (2007)

PNAS: The syntaxin SYP132 contributes to plant resistance against bacteria and secretion of pathogenesis-related protein 1 (2007) | Assoc. Prof. Dr. | Scoop.it

In contrast to many mammalian pathogens, potential bacterial pathogens of plants remain outside the host cell. The plant must, therefore, promote an active resistance mechanism to combat the extracellular infection. How this resistance against bacteria is manifested and whether similar processes mediate basal, gene-for-gene, and salicylate-associated defense, however, are poorly understood. Here, we identify a specific plasma membrane syntaxin, NbSYP132, as a component contributing to gene-for-gene resistance in Nicotiana benthamiana. Silencing NbSYP132 but not NbSYP121, the apparent orthologue of a syntaxin required for resistance to powdery mildew fungus, compromised AvrPto-Pto resistance. Because syntaxins may play a role in secretion of proteins to the extracellular space, we performed a limited proteomic analysis of the apoplastic fluid. We found that NbSYP132-silenced plants were impaired in the accumulation of at least a subset of pathogenesis-related (PR) proteins in the cell wall. These results were confirmed by both immunoblot analysis and imunolocalization of a PR protein, PR1a. These results implicate NbSYP132 as the cognate target soluble N-ethylmaleimide-sensitive factor attachment protein receptor for exocytosis of vesicles containing antimicrobial PR proteins. NbSYP132 also contributes to basal and salicylate-associated defense, indicating that SYP132-dependent secretion is a component of multiple forms of defense against bacterial pathogens in plants.


Via Kamoun Lab @ TSL, Kubilay Kurtulus BASTAS
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PNAS: The syntaxin SYP132 contributes to plant resistance against bacteria and secretion of pathogenesis-related protein 1 (2007)

PNAS: The syntaxin SYP132 contributes to plant resistance against bacteria and secretion of pathogenesis-related protein 1 (2007) | Assoc. Prof. Dr. | Scoop.it

In contrast to many mammalian pathogens, potential bacterial pathogens of plants remain outside the host cell. The plant must, therefore, promote an active resistance mechanism to combat the extracellular infection. How this resistance against bacteria is manifested and whether similar processes mediate basal, gene-for-gene, and salicylate-associated defense, however, are poorly understood. Here, we identify a specific plasma membrane syntaxin, NbSYP132, as a component contributing to gene-for-gene resistance in Nicotiana benthamiana. Silencing NbSYP132 but not NbSYP121, the apparent orthologue of a syntaxin required for resistance to powdery mildew fungus, compromised AvrPto-Pto resistance. Because syntaxins may play a role in secretion of proteins to the extracellular space, we performed a limited proteomic analysis of the apoplastic fluid. We found that NbSYP132-silenced plants were impaired in the accumulation of at least a subset of pathogenesis-related (PR) proteins in the cell wall. These results were confirmed by both immunoblot analysis and imunolocalization of a PR protein, PR1a. These results implicate NbSYP132 as the cognate target soluble N-ethylmaleimide-sensitive factor attachment protein receptor for exocytosis of vesicles containing antimicrobial PR proteins. NbSYP132 also contributes to basal and salicylate-associated defense, indicating that SYP132-dependent secretion is a component of multiple forms of defense against bacterial pathogens in plants.


Via Kamoun Lab @ TSL
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Recognition of bacterial plant pathogens: local, systemic and transgenerational immunity

Recognition of bacterial plant pathogens: local, systemic and transgenerational immunity | Assoc. Prof. Dr. | Scoop.it

Summary:

Bacterial pathogens can cause multiple plant diseases and plants rely on their innate immune system to recognize and actively respond to these microbes. The plant innate immune system comprises extracellular pattern recognition receptors that recognize conserved microbial patterns and intracellular nucleotide binding leucine-rich repeat (NLR) proteins that recognize specific bacterial effectors delivered into host cells. Plants lack the adaptive immune branch present in animals, but still afford flexibility to pathogen attack through systemic and transgenerational resistance. Here, we focus on current research in plant immune responses against bacterial pathogens. Recent studies shed light onto the activation and inactivation of pattern recognition receptors and systemic acquired resistance. New research has also uncovered additional layers of complexity surrounding NLR immune receptor activation, cooperation and sub-cellular localizations. Taken together, these recent advances bring us closer to understanding the web of molecular interactions responsible for coordinating defense responses and ultimately resistance.

 

by:     Elizabeth Henry, Koste A. Yadeta, Gitta Coaker

 

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Structure and Biophysics of Type III Secretion in Bacteria

Structure and Biophysics of Type III Secretion in Bacteria | Assoc. Prof. Dr. | Scoop.it

Scooped from: Biochemistry, 2013

Authors: Srirupa Chatterjee, Sukanya Chaudhury, Andrew C. McShan, Kawaljit Kaur and Roberto N. De Guzman

 

Summary:

Many plant and animal bacterial pathogens assemble a needle-like nanomachine, the type III secretion system (T3SS), to inject virulence proteins directly into eukaryotic cells to initiate infection. The ability of bacteria to inject effectors into host cells is essential for infection, survival, and pathogenesis for many Gram-negative bacteria, including Salmonella, Escherichia, Shigella, Yersinia, Pseudomonas, and Chlamydia spp. These pathogens are responsible for a wide variety of diseases, such as typhoid fever, large-scale food-borne illnesses, dysentery, bubonic plague, secondary hospital infections, and sexually transmitted diseases. The T3SS consists of structural and nonstructural proteins. The structural proteins assemble the needle apparatus, which consists of a membrane-embedded basal structure, an external needle that protrudes from the bacterial surface, and a tip complex that caps the needle. Upon host cell contact, a translocon is assembled between the needle tip complex and the host cell, serving as a gateway for translocation of effector proteins by creating a pore in the host cell membrane. Following delivery into the host cytoplasm, effectors initiate and maintain infection by manipulating host cell biology, such as cell signaling, secretory trafficking, cytoskeletal dynamics, and the inflammatory response. Finally, chaperones serve as regulators of secretion by sequestering effectors and some structural proteins within the bacterial cytoplasm. This review will focus on the latest developments and future challenges concerning the structure and biophysics of the needle apparatus.

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PLOS Pathogens: The Xanthomonas campestris Type III Effector XopJ Targets the Host Cell Proteasome to Suppress Salicylic-Acid Mediated Plant Defence

PLOS Pathogens: The Xanthomonas campestris Type III Effector XopJ Targets the Host Cell Proteasome to Suppress Salicylic-Acid Mediated Plant Defence | Assoc. Prof. Dr. | Scoop.it

(via @SuayibUestuen, thanks!)

 

The phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) requires type III effector proteins (T3Es) for virulence. After translocation into the host cell, T3Es are thought to interact with components of host immunity to suppress defence responses. XopJ is a T3E protein from Xcv that interferes with plant immune responses; however, its host cellular target is unknown. Here we show that XopJ interacts with the proteasomal subunit RPT6 in yeast andin planta to inhibit proteasome activity. A C235A mutation within the catalytic triad of XopJ as well as a G2A exchange within the N-terminal myristoylation motif abolishes the ability of XopJ to inhibit the proteasome. Xcv ΔxopJ mutants are impaired in growth and display accelerated symptom development including tissue necrosis on susceptible pepper leaves. Application of the proteasome inhibitor MG132 restored the ability of the Xcv ΔxopJ to attenuate the development of leaf necrosis. The XopJ dependent delay of tissue degeneration correlates with reduced levels of salicylic acid (SA) and changes in defence- and senescence-associated gene expression. Necrosis upon infection with Xcv ΔxopJ was greatly reduced in pepper plants with reduced expression of NPR1, a central regulator of SA responses, demonstrating the involvement of SA-signalling in the development of XopJ dependent phenotypes. Our results suggest that XopJ-mediated inhibition of the proteasome interferes with SA-dependent defence response to attenuate onset of necrosis and to alter host transcription. A central role of the proteasome in plant defence is discussed.


Via Nicolas Denancé, Kubilay Kurtulus BASTAS
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Pseudomonas syringae pv. tomato DC3000: A Model Pathogen for Probing Disease Susceptibility and Hormone Signaling in Plants

Pseudomonas syringae pv. tomato DC3000: A Model Pathogen for Probing Disease Susceptibility and Hormone Signaling in Plants | Assoc. Prof. Dr. | Scoop.it

Scooped from: Annual Review of Phytopathology, 2013
Authors: Xiu-Fang Xin and Sheng Yang He

Summary: Since the early 1980s, various strains of the gram-negative bacterial pathogen Pseudomonas syringae have been used as models for understanding plant-bacterial interactions. In 1991, a P. syringae pathovar tomato (Pst) strain, DC3000, was reported to infect not only its natural host tomato but also Arabidopsis in the laboratory, a finding that spurred intensive efforts in the subsequent two decades to characterize the molecular mechanisms by which this strain causes disease in plants. Genomic analysis shows that Pst DC3000 carries a large repertoire of potential virulence factors, including proteinaceous effectors that are secreted through the type III secretion system and a polyketide phytotoxin called coronatine, which structurally mimics the plant hormone jasmonate ( JA). Study of Pst DC3000 pathogenesis has not only provided several conceptual advances in understanding how a bacterial pathogen employs type III effectors to suppress plant immune responses and promote disease susceptibility but has also facilitated the discovery of the immune function of stomata and key components of JA signaling in plants. The concepts derived from the study of Pst DC3000 pathogenesis may prove useful in understanding pathogenesis mechanisms of other plant pathogens.

more...
Damien Meyer's curator insight, June 19, 2013 3:25 PM

remarkable review

Scooped by Kubilay Kurtulus BASTAS
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Structure and Biophysics of Type III Secretion in Bacteria

Structure and Biophysics of Type III Secretion in Bacteria | Assoc. Prof. Dr. | Scoop.it

Scooped from: Biochemistry, 2013

Authors: Srirupa Chatterjee, Sukanya Chaudhury, Andrew C. McShan, Kawaljit Kaur and Roberto N. De Guzman

 

Summary:

Many plant and animal bacterial pathogens assemble a needle-like nanomachine, the type III secretion system (T3SS), to inject virulence proteins directly into eukaryotic cells to initiate infection. The ability of bacteria to inject effectors into host cells is essential for infection, survival, and pathogenesis for many Gram-negative bacteria, including Salmonella, Escherichia, Shigella, Yersinia, Pseudomonas, and Chlamydia spp. These pathogens are responsible for a wide variety of diseases, such as typhoid fever, large-scale food-borne illnesses, dysentery, bubonic plague, secondary hospital infections, and sexually transmitted diseases. The T3SS consists of structural and nonstructural proteins. The structural proteins assemble the needle apparatus, which consists of a membrane-embedded basal structure, an external needle that protrudes from the bacterial surface, and a tip complex that caps the needle. Upon host cell contact, a translocon is assembled between the needle tip complex and the host cell, serving as a gateway for translocation of effector proteins by creating a pore in the host cell membrane. Following delivery into the host cytoplasm, effectors initiate and maintain infection by manipulating host cell biology, such as cell signaling, secretory trafficking, cytoskeletal dynamics, and the inflammatory response. Finally, chaperones serve as regulators of secretion by sequestering effectors and some structural proteins within the bacterial cytoplasm. This review will focus on the latest developments and future challenges concerning the structure and biophysics of the needle apparatus.

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The form of nitrogen nutrition affects resistance against Pseudomonas syringae pv. phaseolicola in tobacco

The form of nitrogen nutrition affects resistance against Pseudomonas syringae pv. phaseolicola in tobacco | Assoc. Prof. Dr. | Scoop.it

Scooped from: Journal of Experimental Botany, 2013

Authors: Kapuganti J. Gupta, Yariv Brotman, Shruthi Segu, Tatiana Zeier, Jürgen Zeier, Stefan T. Persijn, Simona M. Cristescu, Frans J. M. Harren, Hermann Bauwe, Alisdair R. Fernie, Werner M. Kaiser and Luis A. J. Mur

 

Summary:

Different forms of nitrogen (N) fertilizer affect disease development; however, this study investigated the effects of N forms on the hypersensitivity response (HR)-a pathogen-elicited cell death linked to resistance. HR-eliciting Pseudomonas syringae pv. phaseolicola was infiltrated into leaves of tobacco fed with either NO₃⁻ or NH₄⁺. The speed of cell death was faster in NO₃⁻-fed compared with NH₄⁺-fed plants, which correlated, respectively, with increased and decreased resistance. Nitric oxide (NO) can be generated by nitrate reductase (NR) to influence the formation of the HR. NO generation was reduced in NH₄⁺-fed plants where N assimilation bypassed the NR step. This was similar to that elicited by the disease-forming P. syringae pv. tabaci strain, further suggesting that resistance was compromised with NH₄⁺ feeding. PR1a is a biomarker for the defence signal salicylic acid (SA), and expression was reduced in NH₄⁺-fed compared with NO₃⁻ fed plants at 24h after inoculation. This pattern correlated with actual SA measurements. Conversely, total amino acid, cytosolic and apoplastic glucose/fructose and sucrose were elevated in - treated plants. Gas chromatography/mass spectroscopy was used to characterize metabolic events following different N treatments. Following NO₃⁻ nutrition, polyamine biosynthesis was predominant, whilst after NH₄⁺ nutrition, flux appeared to be shifted towards the production of 4-aminobutyric acid. The mechanisms whereby feeding enhances SA, NO, and polyamine-mediated HR-linked defence whilst these are compromised with NH₄⁺, which also increases the availability of nutrients to pathogens, are discussed.


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Plant Cell: Plant Immune Responses Against Viruses: How Does a Virus Cause Disease?

Plant Cell: Plant Immune Responses Against Viruses: How Does a Virus Cause Disease? | Assoc. Prof. Dr. | Scoop.it

New review article in Plant Cell.

"Recently, significant progress has been made in understanding RNA silencing and how viruses counter this apparently ubiquitous antiviral defense. In addition, plants also induce hypersensitive and systemic acquired resistance responses, which together limit the virus to infected cells and impart resistance to the noninfected tissues."


Via Mary Williams
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Andres Zurita's curator insight, May 29, 2013 8:28 AM

Open Access pdf

María Serrano's curator insight, June 24, 2014 12:30 PM
Respuesta inmune de las plantas frente a los virus.
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Methods - Virus-induced gene silencing in plants

Methods - Virus-induced gene silencing in plants | Assoc. Prof. Dr. | Scoop.it

Virus-induced gene silencing (VIGS) is a technology that exploits an RNA-mediated antiviral defense mechanism. In plants infected with unmodified viruses the mechanism is specifically targeted against the viral genome. However, with virus vectors carrying inserts derived from host genes the process can be additionally targeted against the corresponding mRNAs. VIGS has been used widely in plants for analysis of gene function and has been adapted for high-throughput functional genomics. Until now most applications of VIGS have been in Nicotiana benthamiana. However, new vector systems and methods are being developed that could be used in other plants, including Arabidopsis. Here we discuss practical and theoretical issues that are specific to VIGS rather than other gene "knock down" or "knockout" approaches to gene function. We also describe currently used protocols that have allowed us to apply VIGS to the identification of genes required for disease resistance in plants. These methods and the underlying general principles also apply when VIGS is used in the analysis of other aspects of plant biology.

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Secretome analysis of the rice bacterium Xanthomonas oryzae (Xoo) using in vitro and in planta systems

Secretome analysis of the rice bacterium Xanthomonas oryzae (Xoo) using in vitro and in planta systems | Assoc. Prof. Dr. | Scoop.it

Summary:

Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight disease in rice, and that severely affects yield loss (upto 50%) of total rice production. Here, we report a proteomics investigation of Xoo (compatible race K3)-secreted proteins, isolated from its in vitro culture and in planta infected rice leaves. Two-dimensional gel electrophoresis (2-DE) coupled with MALDI-TOF-MS and/or nLC-ESI-MS/MS approach identified 139 protein spots (out of 153 differential spots), encoding 109 unique proteins. Identified proteins belonged to multiple biological and molecular functions. Metabolic and nutrient uptake proteins were common up to both in vitro and in planta secretomes. However, pathogenicity, protease/peptidase, and host defense-related proteins were highly- or specifically-expressed during in planta infection. A good correlation was observed between protein and transcript abundances for nine proteins-secreted in planta as per semi-quantitative RT-PCR analysis. Transgenic rice leaf sheath (carrying PBZ1 promoter::GFP cell death reporter), when used to express a few of the identified secretory proteins, showed a direct activation of cell death signaling, suggesting their involvement in pathogenicity-related with secretion effectors. This work furthers our understanding of rice bacterial blight disease, and serves as a resource for possible translation in generating disease resistant rice plants for improved seed yield.

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Recognition of bacterial plant pathogens: local, systemic and transgenerational immunity

Recognition of bacterial plant pathogens: local, systemic and transgenerational immunity | Assoc. Prof. Dr. | Scoop.it

Summary:

Bacterial pathogens can cause multiple plant diseases and plants rely on their innate immune system to recognize and actively respond to these microbes. The plant innate immune system comprises extracellular pattern recognition receptors that recognize conserved microbial patterns and intracellular nucleotide binding leucine-rich repeat (NLR) proteins that recognize specific bacterial effectors delivered into host cells. Plants lack the adaptive immune branch present in animals, but still afford flexibility to pathogen attack through systemic and transgenerational resistance. Here, we focus on current research in plant immune responses against bacterial pathogens. Recent studies shed light onto the activation and inactivation of pattern recognition receptors and systemic acquired resistance. New research has also uncovered additional layers of complexity surrounding NLR immune receptor activation, cooperation and sub-cellular localizations. Taken together, these recent advances bring us closer to understanding the web of molecular interactions responsible for coordinating defense responses and ultimately resistance.

 

by:     Elizabeth Henry, Koste A. Yadeta, Gitta Coaker

 

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