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Plant J: The Magnaporthe oryzae effector AVR1-C039 is translocated into rice cells independently of a fungal-derived machinery (2012)

Plant J: The Magnaporthe oryzae effector AVR1-C039 is translocated into rice cells independently of a fungal-derived machinery  (2012) | Plant-Microbe Interaction | Scoop.it

Effector proteins are key elements in plant fungal interactions. The rice blast fungus Magnaporthe oryzae secretes numerous effectors suspected to be translocated inside plant cells. However, their cellular targets and the mechanisms of translocation are still unknown. Here, we have identified the open reading frame (ORF3) corresponding to the M. oryzae avirulence gene AVR1-C039 interacting with the rice resistance gene Pi-CO39 and encoding a small secreted protein without homologies to other proteins. We demonstrate that AVR1-C039 is specifically expressed and secreted at the plant fungal interface during the biotrophic phase of infection. Live cell imaging with M. oryzae transformants expressing a translational fusion between AVR1-C039 and the monomeric red fluorescent protein (mRFP), indicates that AVR1-C039 is translocated into the cytoplasm of infected rice cells. Transient expression of an AVR1-C039 isoform without signal peptide in rice protoplasts triggers a Pi-C039 specific HR suggesting that the recognition of AVR1-C039 by the Pi-C039 gene product occurs in the cytoplasm of rice cells. The native AVR1-C039 enters into the secretory pathway of rice protoplasts as demonstrated by the ER localization of AVR1-CO39:mRFP:HDEL translational fusions and is correctly processed as shown by Western blotting. However, this secreted AVR1-C039 isoform triggers Pi-CO39 specific HR and accumulates inside rice protoplasts as shown by western blotting and localisation of AVR1-C039:mRFP translational fusions. This indicates that AVR1-C039 is secreted by rice protoplasts and re-enters into the cytoplasm by unknown mechanisms suggesting that translocation of AVR1-C039 into rice cells occurs independently of fungal factors.


Via Nicolas Denancé, Kamoun Lab @ TSL
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The Arabidopsis Malectin-Like Leucine-Rich Repeat Receptor-Like Kinase IOS1 Associates with the Pattern Recognition Receptors FLS2 and EFR and Is Critical for Priming of Pattern-Triggered Immunity

The Arabidopsis Malectin-Like Leucine-Rich Repeat Receptor-Like Kinase IOS1 Associates with the Pattern Recognition Receptors FLS2 and EFR and Is Critical for Priming of Pattern-Triggered Immunity | Plant-Microbe Interaction | Scoop.it

Plasma membrane-localized pattern recognition receptors such as FLAGELLIN SENSING2 (FLS2) and EF-TU RECEPTOR (EFR) recognize microbe-associated molecular patterns (MAMPs) to activate the first layer of plant immunity termed pattern-triggered immunity (PTI). A reverse genetics approach with genes responsive to the priming agent β-aminobutyric acid (BABA) revealed IMPAIRED OOMYCETE SUSCEPTIBILITY1 (IOS1) as a critical PTI player. Arabidopsis thaliana ios1 mutants were hypersusceptible to Pseudomonas syringae bacteria. Accordingly, ios1 mutants demonstrated defective PTI responses, notably delayed upregulation of PTI marker genes, lower callose deposition, and mitogen-activated protein kinase activities upon bacterial infection or MAMP treatment. Moreover, Arabidopsis lines overexpressing IOS1 were more resistant to P. syringae and demonstrated a primed PTI response. In vitro pull-down, bimolecular fluorescence complementation, coimmunoprecipitation, and mass spectrometry analyses supported the existence of complexes between the membrane-localized IOS1 and FLS2 and EFR. IOS1 also associated with BRASSINOSTEROID INSENSITIVE1-ASSOCIATED KINASE1 (BAK1) in a ligand-independent manner and positively regulated FLS2/BAK1 complex formation upon MAMP treatment. Finally, ios1 mutants were defective in BABA-induced resistance and priming. This work reveals IOS1 as a regulatory protein of FLS2- and EFR-mediated signaling that primes PTI activation upon bacterial elicitation.


Via Suayib Üstün
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Rescooped by Guogen Yang from Plant-Microbe Symbioses
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Understanding the rhizosphere better ... Trends in Plant Science

Understanding the rhizosphere better ... Trends in Plant Science | Plant-Microbe Interaction | Scoop.it

Evidence is mounting for the importance of understanding the rhizosphere better in order to lay the foundation for the next green revolution. Root biology and how they interact with their environment may well be one of the fastest growing areas in plant science and in this focus issue we are following some of the latest trends, such as root architecture, root development, and plant–soil fungal interactions. On pages 419–425 Arthur Q. Villordon and colleagues propose that unraveling the role of root architecture in root and tuber crop productivity will improve global food security, especially in regions with marginal soil fertility and low-input agricultural systems. On pages 426–431 Zhaojun Ding and colleagues highlight how differential growth dynamics between primary and lateral roots appear to be crucial for plants to adapt to changing environmental conditions. Finally, on pages 432–438 Matthias C. Rillig and colleagues propose a new framework for studying the complexity of soil fungal communities


Via Francis Martin, Jean-Michel Ané
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Jean-Michel Ané's curator insight, July 23, 8:48 AM

Yeahhhh... a focus issue on the rhizosphere.!

Rescooped by Guogen Yang from Plant-Microbe Symbioses
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Untapped Plant Microbiome Could Help Feed Billions

Untapped Plant Microbiome Could Help Feed Billions | Plant-Microbe Interaction | Scoop.it
The Human Microbiome Project revealed tens of trillions of microbes residing in and on humans. Now scientists are taking a census of plant microbes—and not just the hundreds of billions found in soils. Distinct microbial communities live inside roots, on leaves and within flowers, and all in all have an estimated three to six orders of magnitude greater genetic diversity than their plant hosts. This second genome, much like the human microbiome, provides plants access to nutrients and helps to suppress disease. Scientists and farmers alike think it represents the next big thing in agriculture.

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

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

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


Via Kamoun Lab @ TSL
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Rescooped by Guogen Yang from Fungal|Oomycete Biology
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New Phytol: Reprogramming of plant cells by filamentous plant-colonizing microbes

New Phytol: Reprogramming of plant cells by filamentous plant-colonizing microbes | Plant-Microbe Interaction | Scoop.it

Although phylogenetically unrelated, filamentous oomycetes and fungi establish similar structures to colonize plants and they represent economically the most important microbial threat to crop production. In mutualistic interactions established by root-colonizing fungi, clear differences to pathogens can be seen, but there is mounting evidence that their infection strategies and molecular interactions have certain common features. To infect the host, fungi and oomycetes employ similar strategies to circumvent plant innate immunity. This process involves the suppression of basal defence responses which are triggered by the perception of conserved molecular patterns. To establish biotrophy, effector proteins are secreted from mutualistic and pathogenic microbes to the host tissue, where they play central roles in the modulation of host immunity and metabolic reprogramming of colonized host tissues. This review article discusses key effector mechanisms of filamentous pathogens and mutualists, how they modulate their host targets and the fundamental differences or parallels between these different interactions. The orchestration of effector actions during plant infection and the importance of their localization within host tissues are also discussed.


Via Stéphane Hacquard, Alejandro Rojas
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Rescooped by Guogen Yang from Plant Pathogenomics
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Genome Biology and Evolution: Gene loss rather than gene gain is associated with a host jump from monocots to dicots in the smut fungus Melanopsichium pennsylvanicum (2014)

Genome Biology and Evolution: Gene loss rather than gene gain is associated with a host jump from monocots to dicots in the smut fungus Melanopsichium pennsylvanicum (2014) | Plant-Microbe Interaction | Scoop.it

Smut fungi are well-suited to investigate the ecology and evolution of plant pathogens, as they are strictly biotrophic, yet cultivable on media. Here we report the genome sequence of Melanopsichium pennsylvanicum, closely related to Ustilago maydis and other Poaceae-infecting smuts, but parasitic to a dicot plant. To explore the evolutionary patterns resulting from host adaptation after this huge host jump, the genome of M. pennsylvanicum was sequenced and compared to the genomes of Ustilago maydis, Sporisorium reilianum, and Ustilago hordei. While all four genomes had a similar completeness in CEGMA analyses, gene absence was highest in M. pennsylvanicum, and most pronounced in putative secreted proteins, which are often considered as effector candidates. In contrast, the amount of private genes was similar among the species, highlighting that gene loss rather than gene gain is the hallmark of adaptation after the host jump to the dicot host. Our analyses revealed a trend of putative effectors to be next to another putative effector, but the majority of these are not in clusters and thus the focus on pathogenicity clusters might not be appropriate for all smut genomes. Positive selection studies revealed that M. pennsylvanicum has the highest number and proportion of genes under positive selection. In general, putative effectors showed a higher proportion of positively selected genes than non-effector candidates. The 248 putative secreted effectors found in all four smut genomes might constitute a core set needed for pathogenicity, while those 92 that are found in all grass-parasitic smuts, but have no ortholog in M. pennsylvanicum might constitute a set of effectors important for successful colonization of grass hosts.


Via Francis Martin, Kamoun Lab @ TSL
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Rescooped by Guogen Yang from MycorWeb Plant-Microbe Interactions
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Prevalence of transcription factors in ascomycete and basidiomycete fungi

Prevalence of transcription factors in ascomycete and basidiomycete fungi | Plant-Microbe Interaction | Scoop.it
Gene regulation underlies fungal physiology and therefore is a major factor in fungal biodiversity. Analysis of genome sequences has revealed a large number of putative transcription factors in most fungal genomes. The presence of fungal orthologs for individual regulators has been analysed and appears to be highly variable with some regulators widely conserved and others showing narrow distribution. Although genome-scale transcription factor surveys have been performed before, no global study into the prevalence of specific regulators across the fungal kingdom has been presented.

Via Francis Martin
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Rescooped by Guogen Yang from How microbes emerge
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Nature: The long-term maintenance of a resistance polymorphism through diffuse interactions (2014)

Nature: The long-term maintenance of a resistance polymorphism through diffuse interactions (2014) | Plant-Microbe Interaction | Scoop.it

Plant resistance (R) genes are a crucial component in plant defence against pathogens1. Although R genes often fail to provide durable resistance in an agricultural context, they frequently persist as long-lived balanced polymorphisms in nature2, 3, 4. Standard theory explains the maintenance of such polymorphisms through a balance of the costs and benefits of resistance and virulence in a tightly coevolving host–pathogen pair5, 6. However, many plant–pathogen interactions lack such specificity7. Whether, and how, balanced polymorphisms are maintained in diffusely interacting species8 is unknown. Here we identify a naturally interacting R gene and effector pair in Arabidopsis thaliana and its facultative plant pathogen, Pseudomonas syringae. The protein encoded by the R gene RPS5 recognizes an AvrPphB homologue (AvrPphB2) and exhibits a balanced polymorphism that has been maintained for over 2 million years (ref. 3). Consistent with the presence of an ancient balanced polymorphism, the R gene confers a benefit when plants are infected with P. syringae carrying avrPphB2 but also incurs a large cost in the absence of infection. RPS5alleles are maintained at intermediate frequencies in populations globally, suggesting ubiquitous selection for resistance. However, the presence of P. syringae carrying avrPphB is probably insufficient to explain the RPS5 polymorphism. First, avrPphB homologues occur at very low frequencies in P. syringae populations on A. thaliana. Second, AvrPphB only rarely confers a virulence benefit to P. syringae on A. thaliana. Instead, we find evidence that selection for RPS5 involves multiple non-homologous effectors and multiple pathogen species. These results and an associated model suggest that the R gene polymorphism in A. thaliana may not be maintained through a tightly coupled interaction involving a single coevolved R gene and effector pair. More likely, the stable polymorphism is maintained through complex and diffuse community-wide interactions.


Via Kamoun Lab @ TSL, Niklaus Grunwald
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Rescooped by Guogen Yang from MycorWeb Plant-Microbe Interactions
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Contrasting soil fungal community responses to experimental nitrogen addition using the large subunit rRNA taxonomic marker and cellobiohydrolase I functional marker

Human activities have resulted in increased nitrogen inputs into terrestrial ecosystems, but the impact of nitrogen on ecosystem function, such as nutrient cycling, will depend at least in part on the response of soil fungal communities. We examined the response of soil fungi to experimental nitrogen addition in a loblolly pine forest (North Carolina, USA) using a taxonomic marker (large subunit rDNA, LSU) and a functional marker involved in a critical step of cellulose degradation (cellobiohydrolase, cbhI) at five time points that spanned fourteen months. Sampling date had no impact on fungal community richness or composition for either gene. Based on the LSU, nitrogen addition led to increased fungal community richness, reduced relative abundance of fungi in the phylum Basidiomycota, and altered community composition; however, similar shifts were not observed with cbhI. Fungal community dissimilarity of the LSU and cbhI genes was significantly correlated in the ambient plots, but not in nitrogen-amended plots, suggesting either functional redundancy of fungi with the cbhI gene, or shifts in other functional groups in response to nitrogen addition. To determine if sequence similarity of cbhI could be predicted based on taxonomic relatedness of fungi, we conducted a phylogenetic analysis of publically-available cbhI sequences from known isolates, and found that for a subset of isolates, similar cbhI genes were found within distantly related fungal taxa. Together, these findings suggest that taxonomic shifts in the total fungal community do not necessarily result in changes in the functional diversity of fungi.


Via Francis Martin
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Rescooped by Guogen Yang from Plant-microbe interactions (on the plant's side)
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Arabidopsis LIP5, a Positive Regulator of Multivesicular Body Biogenesis, Is a Critical Target of Pathogen-Responsive MAPK Cascade in Plant Basal Defense

Arabidopsis LIP5, a Positive Regulator of Multivesicular Body Biogenesis, Is a Critical Target of Pathogen-Responsive MAPK Cascade in Plant Basal Defense | Plant-Microbe Interaction | Scoop.it

Multivesicular bodies (MVBs) play essential roles in many cellular processes. The MVB pathway requires reversible membrane association of the endosomal sorting complexes required for transports (ESCRTs) for sustained protein trafficking. Membrane dissociation of ESCRTs is catalyzed by the AAA ATPase SKD1, which is stimulated by LYST-INTERACTING PROTEIN 5 (LIP5). We report here that LIP5 is a target of pathogen-responsive mitogen-activated protein kinases (MPKs) and plays a critical role in plant basal resistance. Arabidopsis LIP5 interacts with MPK6 and MPK3 and is phosphorylated in vitro by activated MPK3 and MPK6 and in vivo upon expression of MPK3/6-activating NtMEK2DD and pathogen infection. Disruption of LIP5 has little effects on flg22-, salicylic acid-induced defense responses but compromises basal resistance to Pseudomonas syringae. The critical role of LIP5 in plant basal resistance is dependent on its ability to interact with SKD1. Mutation of MPK phosphorylation sites in LIP5 does not affect interaction with SKD1 but reduces the stability and compromises the ability to complement the lip5 mutant phenotypes. Using the membrane-selective FM1–43 dye and transmission electron microscopy, we demonstrated that pathogen infection increases formation of both intracellular MVBs and exosome-like paramural vesicles situated between the plasma membrane and the cell wall in a largely LIP5-dependent manner. These results indicate that the MVB pathway is positively regulated by pathogen-responsive MPK3/6 through LIP5 phosphorylation and plays a critical role in plant immune system likely through relocalization of defense-related molecules.

 

 


Via Christophe Jacquet
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Annual Review of Phytopathology: Susceptibility Genes 101: How to Be a Good Host (2014)

Annual Review of Phytopathology: Susceptibility Genes 101: How to Be a Good Host (2014) | Plant-Microbe Interaction | Scoop.it

To confer resistance against pathogens and pests in plants, typically dominant resistance genes are deployed. However, because resistance is based on recognition of a single pathogen-derived molecular pattern these narrowspectrum genes are usually readily overcome. Disease arises from a compatible interaction between plant and pathogen. Hence, altering a plant gene that critically facilitates compatibility could provide a more broad-spectrum and durable type of resistance. Here, such susceptibility (S) genes are reviewed with a focus on the mechanisms underlying loss of compatibility. We distinguish three groups of S genes acting during different stages of infection: early pathogen establishment, modulation of host defenses, and pathogen sustenance. The many examples reviewed here show that S genes have the potential to be used in resistance breeding. However, because S genes have a function other than being a compatibility factor for the pathogen, the side effects caused by their mutation demands a one-by-one assessment of their usefulness for application.


Via Kamoun Lab @ TSL
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Agrobacterium tumefaciens Deploys a Superfamily of Type VI Secretion DNase Effectors as Weapons for Interbacterial Competition In Planta: Cell Host & Microbe

Agrobacterium tumefaciens Deploys a Superfamily of Type VI Secretion DNase Effectors as Weapons for Interbacterial Competition In Planta: Cell Host & Microbe | Plant-Microbe Interaction | Scoop.it

The type VI secretion system (T6SS) is a widespread molecular weapon deployed by many Proteobacteria to target effectors/toxins into both eukaryotic and prokaryotic cells. We report that Agrobacterium tumefaciens, a soil bacterium that triggers tumorigenesis in plants, produces a family of type VI DNase effectors (Tde) that are distinct from previously known polymorphic toxins and nucleases. Tde exhibits an antibacterial DNase activity that relies on a conserved HxxD motif and can be counteracted by a cognate immunity protein, Tdi. In vitro, A. tumefaciens T6SS could kill Escherichia coli but triggered a lethal counterattack by Pseudomonas aeruginosa upon injection of the Tde toxins. However, in an in planta coinfection assay, A. tumefaciens used Tde effectors to attack both siblings cells and P. aeruginosa to ultimately gain a competitive advantage. Such acquired T6SS-dependent fitness in vivo and conservation of Tde-Tdi couples in bacteria highlights a widespread antibacterial weapon beneficial for niche colonization


Via Suayib Üstün
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Rescooped by Guogen Yang from Plant-microbe interactions (on the plant's side)
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Kelps feature systemic defense responses: insights into the evolution of innate immunity in multicellular eukaryotes -

Kelps feature systemic defense responses: insights into the evolution of innate immunity in multicellular eukaryotes - | Plant-Microbe Interaction | Scoop.it

Brown algae are one of the few eukaryotic lineages that have evolved complex multicellularity, together with Opisthokonts (animals, fungi) and Plantae (land plants, green and red algae). In these three lineages, biotic stresses induce similar local defense reactions. Animals and land plants also feature a systemic immune response, protecting the whole organism after an attack on one of its parts. However, the occurrence of systemic defenses has never been investigated in brown algae.We elicited selected parts of the kelp Laminaria digitata and monitored distant, nonchallenged areas of the same individual for subsequent defense reactions.A systemic reaction was detected following elicitation on a distant area, including an oxidative response, an increase in haloperoxidase activities and a stronger resistance against herbivory. Based on experiments with pharmacological inhibitors, the liberation of free fatty acids is proposed to play a key role in systemic signaling, reminiscent of what is known in land plants.This study is the first report, outside the phyla of Opisthokonts and Plantae, of an intraorganism communication leading to defense reactions. These findings indicate that systemic immunity emerged independently at least three times, as a consequence of convergent evolution in multicellular eukaryotic lineages.


Via Christophe Jacquet
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Rescooped by Guogen Yang from Plant-Microbe Symbioses
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Shaping a root system: regulating lateral versus primary root growth: Trends in Plant Science

Shaping a root system: regulating lateral versus primary root growth: Trends in Plant Science | Plant-Microbe Interaction | Scoop.it

Primary and lateral roots comprise root systems, which are vital to the growth and survival of plants. Several molecular mechanisms associated with primary and lateral root growth have been described, including some common regulatory factors for their initiation and development. However, in this opinion article, we discuss the distinct growth behavior of lateral roots in response to environmental cues, such as salinity, gravity, and nutrient availability, which are mediated via specific regulators. We propose that differential growth dynamics between primary and lateral roots are crucial for plants to adapt to the ever-changing environmental conditions.


Via Francis Martin, Jean-Michel Ané
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Frontiers | Killing two birds with one stone: trans-kingdom suppression of PAMP/MAMP-induced immunity by T3E from enteropathogenic bacteria | Plant-Microbe Interaction

Frontiers | Killing two birds with one stone: trans-kingdom suppression of PAMP/MAMP-induced immunity by T3E from enteropathogenic bacteria | Plant-Microbe Interaction | Plant-Microbe Interaction | Scoop.it

Within the past decade, remarkable similarities between the molecular organization of animal and plant systems for non-self discrimination were revealed. Obvious parallels exist between the molecular structures of the receptors mediating the recognition of pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs) with plant pattern recognition receptors strikingly resembling mammalian Toll-like receptors. Mitogen-activated protein kinase cascades, leading to the transcriptional activation of immunity-associated genes, illustrate the conservation of whole molecular building blocks of PAMP/MAMP-induced signaling. Enteropathogenic Salmonella and Escherichia coli use a type three secretion system (T3SS) to inject effector proteins into the mammalian host cell to subvert defense mechanisms and promote gut infection. Lately, disease occurrence was increasingly associated with bacteria-contaminated fruits and vegetables and common themes have emerged with regard to whether and how effectors target innate immune responses in a trans-kingdom manner. We propose that numerous Salmonella or E. coli effectors may be active in planta and tend to target central components (hubs) of immune signaling pathways.


Via Jim Alfano, Suayib Üstün
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Evidence for biological denitrification inhibition (BDI) by plant secondary metabolites

Evidence for biological denitrification inhibition (BDI) by plant secondary metabolites | Plant-Microbe Interaction | Scoop.it
Previous studies on the effect of secondary metabolites on the functioning of rhizosphere microbial communities have often focused on aspects of the nitrogen (N) cycle but have overlooked biological denitrification inhibition (BDI), which can affect plant N-nutrition. Here, we investigated the BDI by the compounds of Fallopia spp., an invasive weed shown to be associated with a low potential denitrification of the soil.Fallopia spp. extracts were characterized by chromatographic analysis and were used to test the BDI effects on the metabolic and respiratory activities of denitrifying bacteria, under aerobic and anaerobic (denitrification) conditions. The BDI of Fallopia spp. extracts was tested on a complex soil community by measuring denitrification enzyme activity (DEA), substrate induced respiration (SIR), as well as abundances of denitrifiers and total bacteria.In 15 strains of denitrifying bacteria, extracts led to a greater BDI (92%) than respiration inhibition (50%). Anaerobic metabolic activity reduction was correlated with catechin concentrations and the BDI was dose dependent. In soil, extracts reduced the DEA/SIR ratio without affecting the denitrifiers: total bacteria ratio.We show that secondary metabolite(s) from Fallopia spp. inhibit denitrification. This provides new insight into plant–soil interactions and improves our understanding of a plant's ability to shape microbial soil functioning.
Via Jean-Michel Ané
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Plant Cell: Interaction of the Arabidopsis GTPase RabA4c with Its Effector PMR4 Results in Complete Penetration Resistance to Powdery Mildew (2014)

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

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


Via Kamoun Lab @ TSL
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Rescooped by Guogen Yang from Fungal|Oomycete Biology
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New Phytologist: Hitchhiker's guide to multi-dimensional plant pathology (2014)

New Phytologist: Hitchhiker's guide to multi-dimensional plant pathology (2014) | Plant-Microbe Interaction | Scoop.it

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


Via Kamoun Lab @ TSL, Alejandro Rojas
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Marie Zen Attitude's curator insight, July 26, 5:21 AM

Un petit lien spécial pour Emeric ;)

 

Rescooped by Guogen Yang from Plant Immunity And Microbial Effectors
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Elicitin-like proteins Oli-D1 and Oli-D2 from Pythium oligandrum trigger hypersensitive response in Nicotiana benthamiana and induce resistance against Botrytis cinerea in tomato

Elicitin-like proteins Oli-D1 and Oli-D2 from Pythium oligandrum trigger hypersensitive response in Nicotiana benthamiana and induce resistance against Botrytis cinerea in tomato | Plant-Microbe Interaction | Scoop.it
Summary
The biocontrol agent Pythium oligandrum and its elicitin-like proteins oligandrins have been shown to induce disease resistance in a range of plants.

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

Mashable: Chinese Researchers Create Disease-Resistant Wheat by Deleting Genes (2014) | Plant-Microbe Interaction | Scoop.it

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

 

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

 

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

 

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

 

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


Via Kamoun Lab @ TSL
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Interaction of the Arabidopsis GTPase RabA4c with Its Effector PMR4 Results in Complete Penetration Resistance to Powdery Mildew

Interaction of the Arabidopsis GTPase RabA4c with Its Effector PMR4 Results in Complete Penetration Resistance to Powdery Mildew | Plant-Microbe Interaction | Scoop.it

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


Via Suayib Üstün
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Rescooped by Guogen Yang from Plant Immunity And Microbial Effectors
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Simultaneous editing of three homoeoalleles in hexaploid bread wheat confers heritable resistance to powdery mildew : Nature Biotechnology : Nature Publishing Group

Simultaneous editing of three homoeoalleles in hexaploid bread wheat confers heritable resistance to powdery mildew : Nature Biotechnology : Nature Publishing Group | Plant-Microbe Interaction | Scoop.it

Sequence-specific nucleases have been applied to engineer targeted modifications in polyploid genomes1, but simultaneous modification of multiple homoeoalleles has not been reported. Here we use transcription activator–like effector nuclease (TALEN)2, 3 and clustered, regularly interspaced, short palindromic repeats (CRISPR)-Cas9 (refs. 4,5) technologies in hexaploid bread wheat to introduce targeted mutations in the three homoeoalleles that encode MILDEW-RESISTANCE LOCUS (MLO) proteins6. Genetic redundancy has prevented evaluation of whether mutation of all three MLO alleles in bread wheat might confer resistance to powdery mildew, a trait not found in natural populations7. We show that TALEN-induced mutation of all three TaMLO homoeologs in the same plant confers heritable broad-spectrum resistance to powdery mildew. We further use CRISPR-Cas9 technology to generate transgenic wheat plants that carry mutations in the TaMLO-A1 allele. We also demonstrate the feasibility of engineering targeted DNA insertion in bread wheat through nonhomologous end joining of the double-strand breaks caused by TALENs. Our findings provide a methodological framework to improve polyploid crops.


Via IPM Lab
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Rescooped by Guogen Yang from MycorWeb Plant-Microbe Interactions
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New Phytol.: Gate control: guard cell regulation by microbial stress

New Phytol.: Gate control: guard cell regulation by microbial stress | Plant-Microbe Interaction | Scoop.it

Terrestrial plants rely on stomata, small pores in the leaf surface, for photosynthetic gas exchange and transpiration of water. The stomata, formed by a pair of guard cells, dynamically increase and decrease their volume to control the pore size in response to environmental cues. Stresses can trigger similar or opposing movements: for example, drought induces closure of stomata, whereas many pathogens exploit stomata and cause them to open to facilitate entry into plant tissues. The latter is an active process as stomatal closure is part of the plant's immune response. Stomatal research has contributed much to clarify the signalling pathways of abiotic stress, but guard cell signalling in response to microbes is a relatively new area of research. In this article, we discuss present knowledge of stomatal regulation in response to microbes and highlight common points of convergence, and differences, compared to stomatal regulation by abiotic stresses. We also expand on the mechanisms by which pathogens manipulate these processes to promote disease, for example by delivering effectors to inhibit closure or trigger opening of stomata. The study of pathogen effectors in stomatal manipulation will aid our understanding of guard cell signalling.

 

Deirdre H. McLachlan, Michaela Kopischke and Silke Robatzek

 


Via Nicolas Denancé, Jim Alfano, Francis Martin
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Rescooped by Guogen Yang from Plants and Microbes
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EMBO J: The NB-LRR proteins RGA4 and RGA5 interact functionally and physically to confer disease resistance (2014)

EMBO J: The NB-LRR proteins RGA4 and RGA5 interact functionally and physically to confer disease resistance (2014) | Plant-Microbe Interaction | Scoop.it

Plant resistance proteins of the class of nucleotide-binding and leucine-rich repeat domain proteins (NB-LRRs) are immune sensors which recognize pathogen-derived molecules termed avirulence (AVR) proteins. We show that RGA4 and RGA5, two NB-LRRs from rice, interact functionally and physically to mediate resistance to the fungal pathogen Magnaporthe oryzae and accomplish different functions in AVR recognition. RGA4 triggers an AVR-independent cell death that is repressed in the presence of RGA5 in both rice protoplasts and Nicotiana benthamiana. Upon recognition of the pathogen effector AVR-Pia by direct binding to RGA5, repression is relieved and cell death occurs. RGA4 and RGA5 form homo- and hetero-complexes and interact through their coiled-coil domains. Localization studies in rice protoplast suggest that RGA4 and RGA5 localize to the cytosol. Upon recognition of AVR-Pia, neither RGA4 nor RGA5 is re-localized to the nucleus. These results establish a model for the interaction of hetero-pairs of NB-LRRs in plants: RGA4 mediates cell death activation, while RGA5 acts as a repressor of RGA4 and as an AVR receptor.


Via Kamoun Lab @ TSL
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Rescooped by Guogen Yang from Plant-microbe interactions (on the plant's side)
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The interplay between central metabolism and innate immune responses -

A growing body of recent studies bring into light an important cross-talk between immune response and metabolism not only at the level of the organism as a whole, but also at the level of the individual cells. Cellular bioenergetics functions not only as a power plant to fuel up the cells, but the intermediate metabolites are shown to play an important role to modulate cellular responses. It is especially the pathways through which a cell metabolizes glucose that have been recently shown to influence both innate and adaptive immune responses, with oxidative phosphorylation used by resting or tolerant cells, while aerobic glycolysis (also termed ‘Warburg effect’) fueling activated cells. In this review we will address how the center metabolism shifts upon activation in the innate immune cells and how the intermediate metabolites modulate the function of immune cells.


Via Christophe Jacquet
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