Plant Immunity And Microbial Effectors
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Transcriptional responses towards diffusible signals from symbiotic microbes reveal MtNFP- and MtDMI3-dependent reprogramming of host gene expression by AM fungal LCOs

The formation of root nodules and arbuscular mycorrhizal (AM) roots is controled by a common signaling pathway including the calcium-calmodulin dependent kinase DMI3.
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Plant Immunity And Microbial Effectors
Dedicated to the research done on the molecular dialogue between plants and pathogens (but also to any interesting report)
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The biocontrol agent Pseudomonas chlororaphis PA23 primes Brassica napus defenses through distinct gene networks

The biological control agent Pseudomonas chlororaphis PA23 is capable of protecting Brassica napus (canola) from the necrotrophic fungus Sclerotinia sclerotiorum via direct antagonism. While we have elucidated bacterial genes and gene products responsible biocontrol, little is known about how the host plant responds to bacterial priming on the leaf surface, including global changes in gene activity in the presence and absence of S. sclerotiorum. Application of PA23 to the aerial surfaces of canola plants reduced the number of S. sclerotiorum lesion-forming petals by 91.1%. RNA sequencing of the host pathogen interface showed that pretreatment with PA23 reduced the number of genes upregulated in response to S. sclerotiorum by 16-fold. By itself, PA23 activated unique defense networks indicative of defense priming. Genes encoding MAMP-triggered immunity receptors detecting flagellin and peptidoglycan were downregulated in PA23 only-treated plants, consistent with post-stimulus desensitization. Downstream, we observed reactive oxygen species (ROS) production involving low levels of H2O2 and overexpression of genes associated with glycerol-3-phosphate (G3P)-mediated systemic acquired resistance (SAR). Leaf chloroplasts exhibited increased thylakoid membrane structures and chlorophyll content, while lipid metabolic processes were upregulated. In addition to directly antagonizing S. sclerotiorum, PA23 primes the plant defense response through induction of unique local and systemic defense networks. This study provides novel insight into the effects of biocontrol agents applied to the plant phyllosphere. Understanding these interactions will aid in the development of biocontrol systems as an alternative to chemical pesticides for protection of important crop systems.
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Lipid transfer from plants to arbuscular mycorrhiza fungi

Lipid transfer from plants to arbuscular mycorrhiza fungi | Plant Immunity And Microbial Effectors | Scoop.it
bioRxiv - the preprint server for biology, operated by Cold Spring Harbor Laboratory, a research and educational institution
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The effector AvrRxo1 phosphorylates NAD in planta

The effector AvrRxo1 phosphorylates NAD in planta | Plant Immunity And Microbial Effectors | Scoop.it
Author summary Infectious bacteria have many strategies to weaken the defenses of their hosts. One common strategy is to inject proteins called effectors into the host cells. Many effectors inactivate proteins that transmit defense signals, disabling the alarm systems that alert the plant to defend against the pathogen. In this paper, we show that pathogens can also target very important small molecules in eukaryotes. We found that the plant pathogen effector AvrRxo1 adds a modification to NAD, a molecule required for hundreds of respiratory and signaling reactions, when expressed inside yeast or plant cells. This modification produces an unusual molecule, 3’-NADP, that is not able to be used efficiently by the cell. This finding demonstrates a new way that effectors can target essential central metabolites to manipulate the host.
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Nonhost resistance: Reactive oxygen species (ROS) signal causes DNA damage prior to the induction of PR genes and disease resistance in pea tissue

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A first insight into the involvement of phytohormones pathways in coffee resistance and susceptibility to Colletotrichum kahawae

A first insight into the involvement of phytohormones pathways in coffee resistance and susceptibility to Colletotrichum kahawae | Plant Immunity And Microbial Effectors | Scoop.it
Understanding the molecular mechanisms underlying coffee-pathogen interactions are of key importance to aid disease resistance breeding efforts. In this work the expression of genes involved in salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) pathways were studied in hypocotyls of two coffee varieties challenged with the hemibiotrophic fungus Colletotrichum kahawae, the causal agent of Coffee Berry Disease. Based on a cytological analysis, key time-points of the infection process were selected and qPCR was used to evaluate the expression of phytohormones biosynthesis, reception and responsive-related genes. The resistance to C. kahawae was characterized by restricted fungal growth associated with early accumulation of phenolic compounds in the cell walls and cytoplasmic contents, and deployment of hypersensitive reaction. Similar responses were detected in the susceptible variety, but in a significantly lower percentage of infection sites and with no apparent effect on disease development. Gene expression analysis suggests a more relevant involvement of JA and ET phytohormones than SA in this pathosystem. An earlier and stronger activation of the JA pathway observed in the resistant variety, when compared with the susceptible one, seems to be responsible for the successful activation of defense responses and inhibition of fungal growth. For the ET pathway, the down or non-regulation of ET receptors in the resistant variety, together with a moderate expression of the responsive-related gene ERF1, indicates that this phytohormone may be related with other functions besides the resistance response. However, in the susceptible variety, the stronger activation of ERF1 gene at the beginning of the necrotrophic phase, suggests the involvement of ET in tissue senescence. As far as we know, this is the first attempt to unveil the role of phytohormones in coffee-C. kahawae interactions, thus contributing to deepen our understanding on the complex mechanisms of plant signaling and defense.
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Targeting pathogen sterols: Defence and counterdefence?

Targeting pathogen sterols: Defence and counterdefence? | Plant Immunity And Microbial Effectors | Scoop.it
Targeting pathogen sterols: Defence and counterdefence? https://t.co/kg0l6tHP1L
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The RxLR Motif of the Host Targeting Effector AVR3a of Phytophthora infestans Is Cleaved Before Secretion

When plant-pathogenic oomycetes infect their hosts, they employ a large arsenal of effector proteins to establish a successful infection. Some effector proteins are secreted and are destined to be translocated and function inside host cells. The largest group of translocated proteins from oomycetes are the RxLR effectors, defined by their conserved N-terminal Arg-Xaa-Leu-Arg (RxLR) motif. However, the precise role of this motif in the host cell translocation process is unclear. Here detailed biochemical studies of the RxLR effector AVR3a from the potato pathogen Phytophthora infestans are presented. Mass spectrometric analysis revealed that the RxLR sequence of native AVR3a is cleaved off prior to secretion by the pathogen and the N-terminus of the mature effector was found likely to be acetylated. High-resolution NMR structure analysis of AVR3a indicates that the RxLR motif is well accessible to potential processing enzymes. Processing and modification of AVR3a is to some extent similar to events occurring with the export element (PEXEL) found in malaria effector proteins from Plasmodium falciparum. These findings imply a role for the RxLR motif in the secretion of AVR3a by the pathogen, rather than a direct role in the host cell entry process itself.
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Frontiers | Transgenerational Defense Priming for Crop Protection against Plant Pathogens: A Hypothesis | Plant Science

Throughout evolution, plants have developed diverse mechanisms of defense that “prime” their innate immune system for more robust and active induction of defense responses against different types of stress. Nowadays there are numerous reports concerning the molecular bases of priming, as well as the generational priming mechanisms. Information concerning transgenerational priming, however, remains deficient. Some reports have indicated, nonetheless, that the priming status of a plant can be inherited to its offspring. Here, we show that the priming agent β-aminobutyric acid induced resistance to Pseudomonas syringae pv. phaseolicola infection in the common bean (Phaseolus vulgaris L.) We have analyzed the transgenerational patterns of gene expression of the PvPR1 gene (Phaseolus vulgaris PR1), a highly responsive gene to priming, and show that a transgenerational priming response against pathogen attack can last for at least two generations. We hypothesize that a defense-resistant phenotype and easily identifiable, generational and transgenerational, “primed patterns” of gene expression are excellent indicators of the priming response in crop plants. Furthermore, we propose here that modern plant breeding methods and crop improvement efforts must include the use of elicitors to prime induced resistance in the field and, above all, to select for induced heritable states in progeny that is primed for defense.
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Ancient Nubians Made Antibiotic Beer

Ancient Nubians Made Antibiotic Beer | Plant Immunity And Microbial Effectors | Scoop.it
Chemical analysis of the bones of ancient Sudanese Nubians who lived nearly 2000 years ago shows they were ingesting the antibiotic tetracycline on a regular basis, likely from a special brew of beer. The find is the strongest yet that antibiotics were previously discovered by humans before Alexander Fleming discovered penicillin in 1928. “I’m going to ask…
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The fog of war: How network buffering protects plants’ defense secrets from pathogens

The fog of war: How network buffering protects plants’ defense secrets from pathogens | Plant Immunity And Microbial Effectors | Scoop.it
New #Perspective from @BrettTylerOSU on Hillmer et al's research into the #Arabidopsis immune signaling network https://t.co/of1o9Xkdms https://t.co/tCTNWzCiTb
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The Botrytis cinerea elicitor protein BcIEB1 interacts with the tobacco PR5‐family protein osmotin and protects the fungus against its antifungal activity

The broad‐range phytopathogenic fungus Botrytis cinerea secretes hundreds of proteins during infection of its plant hosts. One of these proteins, BcIEB1, is abundantly secreted and is able to elici
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Frontiers | Key Components of Different Plant Defense Pathways Are Dispensable for Powdery Mildew Resistance of the Arabidopsis mlo2 mlo6 mlo12 Triple Mutant | Plant Science

Loss of function mutations of particular plant MILDEW RESISTANCE LOCUS O (MLO) proteins confer durable and broad-spectrum penetration resistance against powdery mildew fungi. Here, we combined genetic, transcriptomic and metabolomic analyses to explore the defense mechanisms in the fully resistant Arabidopsis thaliana mlo2 mlo6 mlo12 triple mutant. We found that this genotype unexpectedly overcomes the requirement for indolic antimicrobials and defense-related secretion, which are critical for incomplete resistance conferred by mlo2 single mutants. Comparative microarray-based transcriptome analysis of mlo2 mlo6 mlo12 mutants and wild type plants upon Golovinomyces orontii inoculation revealed an increased and accelerated accumulation of many defense-related transcripts. Despite the biotrophic nature of the interaction, this included the non-canonical activation of a jasmonic acid/ethylene-dependent transcriptional program. In contrast to a non-adapted powdery mildew pathogen, the adapted powdery mildew fungus is able to defeat the accumulation of defense-relevant indolic metabolites in an MLO protein-dependent manner. We suggest that a broad and fast activation of immune responses in mlo2 mlo6 mlo12 plants can compensate for the lack of single or few defense pathways. In addition, our results point to a role of Arabidopsis MLO2, MLO6 and MLO12 in enabling defense suppression during invasion by adapted powdery mildew fungi.
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Systemic Induction of the Defensin and Phytoalexin Pisatin Pathways in Pea (Pisum sativum) against Aphanomyces euteiches by Acetylated and Nonacetylated Oligogalacturonides

Oligogalacturonides (OGs) are known for their powerful ability to stimulate the plant immune system but little is known about their mode of action in pea (Pisum sativum). In the present study, we investigated the elicitor activity of two fractions of OGs, with polymerization degrees (DPs) of 2–25, in pea against Aphanomyces euteiches. One fraction was nonacetylated (OGs − Ac) whereas the second one was 30% acetylated (OGs + Ac). OGs were applied by injecting the upper two rachises of the plants at three- and/or four-weeks-old. Five-week-old roots were inoculated with 105 zoospores of A. euteiches. The root infection level was determined at 7, 10 and 14 days after inoculation using the quantitative real-time polymerase chain reaction (qPCR). Results showed significant root infection reductions namely 58, 45 and 48% in the plants treated with 80 µg OGs + Ac and 59, 56 and 65% with 200 µg of OGs − Ac. Gene expression results showed the upregulation of genes involved in the antifungal defensins, lignans and the phytoalexin pisatin pathways and a priming effect in the basal defense, SA and ROS gene markers as a response to OGs. The reduction of the efficient dose in OGs + Ac is suggesting that acetylation is necessary for some specific responses. Our work provides the first evidence for the potential of OGs in the defense induction in pea against Aphanomyces root rot.
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Biological control of tomato gray mold caused by Botrytis cinerea by using Streptomyces spp.

Streptomyces is a genus known for its ability to protect plants against many pathogens and various strains of this bacteria have been used as biological control agents. In this study, the efficacy of
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The Arabidopsis leucine-rich repeat receptor kinase MIK2/LRR-KISS connects cell wall integrity sensing, root growth and response to abiotic and biotic stresses

The Arabidopsis leucine-rich repeat receptor kinase MIK2/LRR-KISS connects cell wall integrity sensing, root growth and response to abiotic and biotic stresses | Plant Immunity And Microbial Effectors | Scoop.it
Author summary Plants are constantly exposed to external stresses of biotic and abiotic nature, as well as internal stresses, resulting from growth and mechanical tension. Feedback information about the integrity of the cell wall can enable the plant to perceive such stresses, and respond adequately. Plants are known to perceive signals from their environment through receptor kinases at the plant cell surface. Here, we reveal that the Arabidopsis thaliana receptor kinase MIK2 regulates responses to cell wall perturbation. Moreover, we find that MIK2 controls root growth angle, modulates cell wall structure in the root tip, contributes to salt stress tolerance, and is required for resistance against a root-infecting pathogen. Our data suggest that MIK2 is involved in sensing cell wall perturbations in plants, whereby it allows the plant to cope with a diverse range of environmental stresses. These data provide an important step forward in our understanding of the mechanisms plants deploy to sense internal and external danger.
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Frontiers | Genome-Wide Association Studies In Plant Pathosystems: Toward an Ecological Genomics Approach | Plant Science

The emergence and re-emergence of plant pathogenic microorganisms are processes that imply perturbations in both host and pathogen ecological niches. Global change is largely assumed to drive the emergence of new etiological agents by altering the equilibrium of the ecological habitats which in turn places hosts more in contact with pathogen reservoirs. In this context, the number of epidemics is expected to increase dramatically in the next coming decades both in wild and crop plants. Under these considerations, the identification of the genetic variants underlying natural variation of resistance is a pre-requisite to estimate the adaptive potential of wild plant populations and to develop new breeding resistant cultivars. On the other hand, the prediction of pathogen’s genetic determinants underlying disease emergence can help to identify plant resistance alleles. In the genomic era, whole genome sequencing combined with the development of statistical methods led to the emergence of Genome Wide Association (GWA) mapping, a powerful tool for detecting genomic regions associated with natural variation of disease resistance in both wild and cultivated plants. However, GWA mapping has been less employed for the detection of genetic variants associated with pathogenicity in microbes. Here, we reviewed GWA studies performed either in plants or in pathogenic microorganisms (bacteria, fungi and oomycetes). In addition, we highlighted the benefits and caveats of the emerging joint GWA mapping approach that allows for the simultaneous identification of genes interacting between genomes of both partners. Finally, based on co-evolutionary processes in wild populations, we highlighted a phenotyping-free joint GWA mapping approach as a promising tool for describing the molecular landscape underlying plant - microbe interactions.
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CRISPR–Cas9 strategy for activation of silent Streptomyces biosynthetic gene clusters

From BioPortfolio: Here we report an efficient CRISPR–Cas9 knock-in strategy to activate silent biosynthetic gene clusters (BGCs) in streptomycetes. We applied thi
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Water users urged to take precautions to limit an outbreak of Crayfish Plague on River Suir downstream of Clonmel to Carrick-on-Suir | Press releases | About us

Water users urged to take precautions to limit an outbreak of Crayfish Plague on River Suir downstream of Clonmel to Carrick-on-Suir | Press releases | About us | Plant Immunity And Microbial Effectors | Scoop.it
Water users urged to take precautions to limit outbreak of crayfish plague on R. Suir https://t.co/XZXydhgHX6
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Tomato root microbiota and Phytophthora parasitica -associated disease

Interactions between pathogenic oomycetes and microbiota residing on the surface of the host plant root are unknown, despite being critical to inoculum constitution. The nature of these interactions was explored for the polyphagous and telluric species Phytophthora parasitica. Composition of the rhizospheric microbiota of Solanum lycopersicum was characterized using deep re-sequencing of 16S rRNA gene to analyze tomato roots either free of or partly covered with P. parasitica biofilm. Colonization of the host root surface by the oomycete was associated with a shift in microbial community involving a Bacteroidetes/Proteobacteria transition and Flavobacteriaceae as the most abundant family. Identification of members of the P. parasitica-associated microbiota interfering with biology and oomycete infection was carried out by screening for bacteria able to (i) grow on a P. parasitica extract-based medium (ii), exhibit in vitro probiotic or antibiotic activity towards the oomycete (iii), have an impact on the oomycete infection cycle in a tripartite interaction S. lycopersicum-P. parasitica-bacteria. One Pseudomonas phylotype was found to exacerbate disease symptoms in tomato plants. The lack of significant gene expression response of P. parasitica effectors to Pseudomonas suggested that the increase in plant susceptibility was not associated with an increase in virulence. Our results reveal that Pseudomonas spp. establishes commensal interactions with the oomycete. Bacteria preferentially colonize the surface of the biofilm rather than the roots, so that they can infect plant cells without any apparent infection of P. parasitica. The presence of the pathogenic oomycete P. parasitica in the tomato rhizosphere leads to a shift in the rhizospheric microbiota composition. It contributes to the habitat extension of Pseudomonas species mediated through a physical association between the oomycete and the bacteria.
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Communication in the Phytobiome

The phytobiome is composed of plants, their environment, and diverse interacting microscopic and macroscopic organisms, which together influence plant health and productivity. These organisms form complex networks that are established and regulated through nutrient cycling, competition, antagonism, and chemical communication mediated by a diverse array of signaling molecules. Integration of knowledge of signaling mechanisms with that of phytobiome members and their networks will lead to a new understanding of the fate and significance of these signals at the ecosystem level. Such an understanding could lead to new biological, chemical, and breeding strategies to improve crop health and productivity.

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How filamentous plant pathogen effectors are translocated to host cells

Publication date: August 2017
Source:Current Opinion in Plant Biology, Volume 38
Author(s): Libera Lo Presti, Regine Kahmann
The interaction of microbes with “signature” plants is largely governed by secreted effector proteins, which serve to dampen plant defense responses and modulate host cell processes. Secreted effectors can function either in the apoplast or within plant cell compartments. How oomycetes and fungi translocate their effectors to plant cells is still poorly understood and controversial. While most oomycete effectors share a common ‘signature’ that was proposed to mediate their uptake via endocytosis, fungal effectors display no conserved motifs at the primary amino acid sequence level. Here we summarize current knowledge in the field of oomycete and fungal effector uptake and highlight emerging themes that may unite rather than set apart these unrelated filamentous pathogens.
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Biocontrôle : Micropep intègre le TWB

Biocontrôle : Micropep intègre le TWB | Plant Immunity And Microbial Effectors | Scoop.it
TweetPin It Voir aussi: Biocontrôle : M2i toujours décidé à lever des fonds Biocontrôle : M2i reporte son projet d’introduction en Bourse Antofénol valorise les déchets viticoles en produits de biocontrôle SAS Pivert se lance sur le marché du biocontrôle … Continuer la lecture →
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