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Rescooped by Bo Yang from Plant-Microbe Interactions: Pathogenesis & Symbiosis
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IJMS | Free Full-Text | Signals of Systemic Immunity in Plants: Progress and Open Questions

IJMS | Free Full-Text | Signals of Systemic Immunity in Plants: Progress and Open Questions | plant and microbes interaction | Scoop.it
Systemic acquired resistance (SAR) is a defence mechanism that induces protection against a wide range of pathogens in distant, pathogen-free parts of plants after a primary inoculation. Multiple mobile compounds were identified as putative SAR signals or important factors for influencing movement of SAR signalling elements in Arabidopsis and tobacco. These include compounds with very different chemical structures like lipid transfer protein DIR1 (DEFECTIVE IN INDUCED RESISTANCE1), methyl salicylate (MeSA), dehydroabietinal (DA), azelaic acid (AzA), glycerol-3-phosphate dependent factor (G3P) and the lysine catabolite pipecolic acid (Pip). Genetic studies with different SAR-deficient mutants and silenced lines support the idea that some of these compounds (MeSA, DIR1 and G3P) are activated only when SAR is induced in darkness. In addition, although AzA doubled in phloem exudate of tobacco mosaic virus (TMV) infected tobacco leaves, external AzA treatment could not induce resistance neither to viral nor bacterial pathogens, independent of light conditions. Besides light intensity and timing of light exposition after primary inoculation, spectral distribution of light could also influence the SAR induction capacity. Recent data indicated that TMV and CMV (cucumber mosaic virus) infection in tobacco, like bacteria in Arabidopsis, caused massive accumulation of Pip. Treatment of tobacco leaves with Pip in the light, caused a drastic and significant local and systemic decrease in lesion size of TMV infection. Moreover, two very recent papers, added in proof, demonstrated the role of FMO1 (FLAVIN-DEPENDENT-MONOOXYGENASE1) in conversion of Pip to N-hydroxypipecolic acid (NHP). NHP systemically accumulates after microbial attack and acts as a potent inducer of plant immunity to bacterial and oomycete pathogens in Arabidopsis. These results argue for the pivotal role of Pip and NHP as an important signal compound of SAR response in different plants against different pathogens.

Via Philip Carella
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Subtilisin‐like proteases in plant defence: the past, the present and beyond - Figueiredo - 2018 - Molecular Plant Pathology -

Subtilisin‐like proteases in plant defence: the past, the present and beyond - Figueiredo - 2018 - Molecular Plant Pathology - | plant and microbes interaction | Scoop.it
Subtilisin‐like proteases (or subtilases) are a very diverse family of serine peptidases present in many organisms, but mostly in plants. With a broad spectrum of biological functions, ranging from protein turnover and plant development to interactions with the environment, subtilases have been gaining increasing attention with regard to their involvement in plant defence responses against the most diverse pathogens. Over the last 5 years, the number of published studies associating plant subtilases with pathogen resistance and plant immunity has increased tremendously. In addition, the observation of subtilases and serine protease inhibitors secreted by pathogens has also gained prominence. In this review, we focus on the active participation of subtilases in the interactions established by plants with the environment, highlighting their role in plant–pathogen communication.
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Microbial interactions within the plant holobiont 

Microbial interactions within the plant holobiont  | plant and microbes interaction | Scoop.it
Since the colonization of land by ancestral plant lineages 450 million years ago, plants and their associated microbes have been interacting with each other, forming an assemblage of species that is often referred to as a “holobiont.” Selective pressure acting on holobiont components has likely shaped plant-associated microbial communities and selected for host-adapted microorganisms that impact plant fitness. However, the high microbial densities detected on plant tissues, together with the fast generation time of microbes and their more ancient origin compared to their host, suggest that microbe-microbe interactions are also important selective forces sculpting complex microbial assemblages in the phyllosphere, rhizosphere, and plant endosphere compartments. Reductionist approaches conducted under laboratory conditions have been critical to decipher the strategies used by specific microbes to cooperate and compete within or outside plant tissues. Nonetheless, our understanding of these microbial interactions in shaping more complex plant-associated microbial communities, along with their relevance for host health in a more natural context, remains sparse. Using examples obtained from reductionist and community-level approaches, we discuss the fundamental role of microbe-microbe interactions (prokaryotes and micro-eukaryotes) for microbial community structure and plant health. We provide a conceptual framework illustrating that interactions among microbiota members are critical for the establishment and the maintenance of host-microbial homeostasis.

Via Stéphane Hacquard, Jean-Michel Ané
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Bacterial and plant natriuretic peptides improve plant defence responses against pathogens - Ficarra - 2018 - Molecular Plant Pathology -

Bacterial and plant natriuretic peptides improve plant defence responses against pathogens - Ficarra - 2018 - Molecular Plant Pathology - | plant and microbes interaction | Scoop.it
Plant natriuretic peptides (PNPs) have been implicated in the regulation of ions and water homeostasis, and their participation in the plant immune response has also been proposed. Xanthomonas citri ssp. citri contains a gene encoding a PNP‐like protein (XacPNP) which has no homologues in other bacteria. XacPNP mimics its Arabidopsis thaliana homologue AtPNP‐A by modifying host responses to create favourable conditions for pathogen survival. However, the ability of XacPNP to induce plant defence responses has not been investigated. In order to study further the role of XacPNP in vivo, A. thaliana lines over‐expressing XacPNP, lines over‐expressing AtPNP‐A and AtPNP‐A‐deficient plants were generated. Plants over‐expressing XacPNP or AtPNP‐A showed larger stomatal aperture and were more resistant to saline or oxidative stress than were PNP‐deficient lines. In order to study further the role of PNP in biotic stress responses, A. thaliana leaves were infiltrated with pure recombinant XacPNP, and showed enhanced expression of genes related to the defence response and a higher resistance to pathogen infections. Moreover, AtPNP‐A expression increased in A. thaliana on Pseudomonas syringae pv. tomato (Pst) infection. This evidence led us to analyse the responses of the transgenic plants to pathogens. Plants over‐expressing XacPNP or AtPNP‐A were more resistant to Pst infection than control plants, whereas PNP‐deficient plants were more susceptible and showed a stronger hypersensitive response when challenged with non‐host bacteria. Therefore, XacPNP, acquired by horizontal gene transfer, is able to mimic PNP functions, even with an increase in plant defence responses
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Rescooped by Bo Yang from Plant-Microbe Interactions: Pathogenesis & Symbiosis
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N-hydroxy-pipecolic acid is a mobile signal that induces systemic disease resistance in Arabidopsis

Systemic acquired resistance (SAR) is a global response in plants induced at the site of infection that leads to long-lasting and broad-spectrum disease resistance at distal, uninfected tissues. Despite the importance of this priming mechanism, the identity of the mobile defense signal that moves systemically throughout plants to initiate SAR has remained elusive. In this paper, we describe a new metabolite, N-hydroxy-pipecolic acid (N-OH-Pip), and provide evidence that this molecule is a mobile signal that plays a central role in initiating SAR signal transduction in Arabidopsis thaliana. We demonstrate that FLAVIN-DEPENDENT MONOOXYGENASE 1 (FMO1), a key regulator of SAR-associated defense priming, can synthesize N-OH-Pip from pipecolic acid in planta, and exogenously applied N-OH-PIP moves systemically in Arabidopsis and can rescue the SAR-deficiency of fmo1 mutants. We also demonstrate that N-OH-Pip treatment causes systemic changes in the expression of pathogenesis-related genes and metabolic pathways throughout the plant, and enhances resistance to a bacterial pathogen. This work provides new insight into the chemical nature of a mobile signal for SAR and also suggests that the N-OH-Pip pathway is a promising target for metabolic engineering to enhance disease resistance.

Via Philip Carella
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Rescooped by Bo Yang from Plant hormones and signaling peptides
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Frontiers | Ethylene and 1-Aminocyclopropane-1-carboxylate (ACC) in Plant–Bacterial Interactions | Plant Science

Frontiers | Ethylene and 1-Aminocyclopropane-1-carboxylate (ACC) in Plant–Bacterial Interactions | Plant Science | plant and microbes interaction | Scoop.it
Ethylene and its precursor 1-aminocyclopropane-1-carboxylate (ACC) actively participate in plant developmental, defense and symbiotic programs. In this sense, ethylene and ACC play a central role in the regulation of bacterial colonization (rhizospheric, endophytic, and phyllospheric) by the modulation of plant immune responses and symbiotic programs, as well as by modulating several developmental processes, such as root elongation. Plant-associated bacterial communities impact plant growth and development, both negatively (pathogens) and positively (plant-growth promoting and symbiotic bacteria). Some members of the plant-associated bacterial community possess the ability to modulate plant ACC and ethylene levels and, subsequently, modify plant defense responses, symbiotic programs and overall plant development. In this work, we review and discuss the role of ethylene and ACC in several aspects of plant-bacterial interactions. Understanding the impact of ethylene and ACC in both the plant host and its associated bacterial community is key to the development of new strategies aimed at increased plant growth and protection.

Via Christophe Jacquet
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Rescooped by Bo Yang from MycorWeb Plant-Microbe Interactions
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Why did filamentous plant pathogens evolve the potential to secrete hundreds of effectors to enable disease? 

During the past decade, many genomes have been sequenced from fungal and oomycete pathogens that interact biotrophically with plants, i.e. they thrive at least initially on living plant tissue. This has revealed genomes that often encode hundreds of proteins predicted to be secreted on the basis of N-terminal signal peptides. Most of these proteins are unique or found only within restricted phylogenetic clades (Franceschetti et al., 2017). They are predicted to be ‘effectors’, i.e. proteins which, in some way, contribute to the virulence of the pathogen (see below). The fact that these filamentous microbes have hundreds of candidate effector genes is in stark contrast with bacterial pathogens, which typically have an order of magnitude fewer effector candidate genes. Although most of these hundreds of effectors currently lack evidence for significant roles in virulence, it is still striking that many of them appear to contribute measurably to virulence and that several of them seem to physically interact with numerous host proteins. In this Opinion Piece, we discuss these observations and attempt to address the apparent need for hundreds of effector candidate genes in these species. We suggest that this requirement reflects, in part, the need for effectors to target defence-unrelated susceptibility components. Many of these, in turn, may be monitored (‘guarded’) by resistance-triggering immune sensors. Potentially, pathogen success depends on additional sets of effectors dedicated to suppress this kind of surveillance.

Via Francis Martin
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Symbiosis genes for immunity and vice versa

Symbiosis genes for immunity and vice versa | plant and microbes interaction | Scoop.it

Highlights

• Several LysM receptor proteins have a dual function in symbiosis and immunity.
• Symbiotic transcription factors can also control pathogen infection.
• Genes of hormonal pathways regulate both pathogen and symbiont colonisation.
• Crosstalk between symbiosis and immunity also occurs within the flavonoid pathway.

Basic molecular knowledge on plant–pathogen interactions has largely been gained from reverse and forward genetics in Arabidopsis thaliana. However, as this model plant is unable to establish endosymbiosis with mycorrhizal fungi or rhizobia, plant responses to mutualistic symbionts have been studied in parallel in other plant species, mainly legumes. The resulting analyses led to the identification of gene networks involved in various functions, from microbe recognition to signalling and plant responses, thereafter assigned to either mutualistic symbiosis or immunity, according to the nature of the initially inoculated microbe. The increasing development of new pathosystems and genetic resources in model legumes and the implementation of reverse genetics in plants such as rice and tomato that interact with both mycorrhizal fungi and pathogens, have highlighted the dual role of plant genes previously thought to be specific to mutualistic or pathogenic interactions. The next challenges will be to determine whether such genes have similar functions in both types of interaction and if not, whether the perception of microbial compounds or the involvement of specific plant signalling components is responsible for the appropriate plant responses to the encountered microorganisms.

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The Soil-Borne Legacy - Cell

The Soil-Borne Legacy - Cell | plant and microbes interaction | Scoop.it
Plants greatly rely on their root microbiome for uptake of nutrients and protection against stresses. Recent studies have uncovered the involvement of plant stress responses in the assembly of plant-beneficial microbiomes. To facilitate durable crop production, deciphering the driving forces that shape the microbiome is crucial.

Via Ronny Kellner, Stéphane Hacquard
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Frontiers | Genetic and Molecular Mechanisms Underlying Symbiotic Specificity in Legume-Rhizobium Interactions | Plant Science

Frontiers | Genetic and Molecular Mechanisms Underlying Symbiotic Specificity in Legume-Rhizobium Interactions | Plant Science | plant and microbes interaction | Scoop.it
Legumes are able to form a symbiotic relationship with nitrogen-fixing soil bacteria called rhizobia. The result of this symbiosis is to form nodules on the plant root, within which the bacteria can convert atmospheric nitrogen into ammonia that can be used by the plant. Establishment of a successful symbiosis requires the two symbiotic partners to be compatible with each other throughout the process of symbiotic development. However, incompatibility frequently occurs, such that a bacterial strain is unable to nodulate a particular host plant or forms nodules that are incapable of fixing nitrogen. Genetic and molecular mechanisms that regulate symbiotic specificity are diverse, involving a wide range of host and bacterial genes/signals with various modes of action. In this review, we will provide an update on our current knowledge of how the recognition specificity has evolved in the context of symbiosis signaling and plant immunity.

Via Philip Carella
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The Biotrophic Development of Ustilago maydis Studied by RNA-Seq Analysis

The Biotrophic Development of Ustilago maydis Studied by RNA-Seq Analysis | plant and microbes interaction | Scoop.it
The maize smut fungus Ustilago maydis is a model organism for elucidating host colonization strategies of biotrophic fungi. Here, we performed an in depth transcriptional profiling of the entire plant-associated development of U. maydis wild-type strains. In our analysis, we focused on fungal metabolism, nutritional strategies, secreted effectors, and regulatory networks. Secreted proteins were enriched in three distinct expression modules corresponding to stages on the plant surface, establishment of biotrophy, and induction of tumors. These modules are likely the key determinants for U. maydis virulence. With respect to nutrient utilization, we observed that expression of several nutrient transporters was tied to these virulence modules rather than being controlled by nutrient availability. We show that oligopeptide transporters likely involved in nitrogen assimilation are important virulence factors. By measuring the intramodular connectivity of transcription factors, we identified the potential drivers for the virulence modules. While known components of the b-mating type cascade emerged as inducers for the plant surface and biotrophy module, we identified a set of yet uncharacterized transcription factors as likely responsible for expression of the tumor module. We demonstrate a crucial role for leaf tumor formation and effector gene expression for one of these transcription factors.
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Role of the Nod Factor Hydrolase MtNFH1 in Regulating Nod Factor Levels during Rhizobial Infection and in Mature Nodules of Medicago truncatula

Role of the Nod Factor Hydrolase MtNFH1 in Regulating Nod Factor Levels during Rhizobial Infection and in Mature Nodules of Medicago truncatula | plant and microbes interaction | Scoop.it
Establishment of symbiosis between legumes and nitrogen-fixing rhizobia depends on bacterial Nod factors (NFs) that trigger symbiosis-related NF signaling in host plants. NFs are modified oligosaccharides of chitin with a fatty acid moiety. NFs can be cleaved and inactivated by host enzymes, such as MtNFH1 (MEDICAGO TRUNCATULA NOD FACTOR HYDROLASE1). In contrast to related chitinases, MtNFH1 hydrolyzes neither chitin nor chitin fragments, indicating a high cleavage preference for NFs. Here, we provide evidence for a role of MtNFH1 in the symbiosis with Sinorhizobium meliloti. Upon rhizobial inoculation, MtNFH1 accumulated at the curled tip of root hairs, in the so-called infection chamber. Mutant analysis revealed that lack of MtNFH1 delayed rhizobial root hair infection, suggesting that excess amounts of NFs negatively affect the initiation of infection threads. MtNFH1 deficiency resulted in nodule hypertrophy and abnormal nodule branching of young nodules. Nodule branching was also stimulated in plants expressing MtNFH1 driven by a tandem CaMV 35S promoter and plants inoculated by a NF-overproducing S. meliloti strain. We suggest that fine-tuning of NF levels by MtNFH1 is necessary for optimal root hair infection as well as for NF-regulated growth of mature nodules.
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Pattern recognition receptors and signaling in plant–microbe interactions - Saijo - 2018 - The Plant Journal -

Pattern recognition receptors and signaling in plant–microbe interactions - Saijo - 2018 - The Plant Journal - | plant and microbes interaction | Scoop.it
Plants solely rely on innate immunity of each individual cell to deal with a diversity of microbes in the environment. Extracellular recognition of microbe- and host damage-associated molecular patterns leads to the first layer of inducible defenses, termed pattern-triggered immunity (PTI). In plants, pattern recognition receptors (PRRs) described to date are all membrane-associated receptor-like kinases or receptor-like proteins, reflecting the prevalence of apoplastic colonization of plant-infecting microbes. An increasing inventory of elicitor-active patterns and PRRs indicates that a large number of them are limited to a certain range of plant groups/species, pointing to dynamic and convergent evolution of pattern recognition specificities. In addition to common molecular principles of PRR signaling, recent studies have revealed substantial diversification between PRRs in their functions and regulatory mechanisms. This serves to confer robustness and plasticity to the whole PTI system in natural infections, wherein different PRRs are simultaneously engaged and faced with microbial assaults. We review the functional significance and molecular basis of PRR-mediated pathogen recognition and disease resistance, and also an emerging role for PRRs in homeostatic association with beneficial or commensal microbes.
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Arabidopsis thaliana SOBER1 (SUPPRESSOR OF AVRBST‐ELICITED RESISTANCE 1) suppresses plant immunity triggered by multiple bacterial acetyltransferase effectors - Choi - - New Phytologist - Wiley Onl...

Arabidopsis thaliana SOBER1 (SUPPRESSOR OF AVRBST‐ELICITED RESISTANCE 1) suppresses plant immunity triggered by multiple bacterial acetyltransferase effectors - Choi - - New Phytologist - Wiley Onl... | plant and microbes interaction | Scoop.it
Plants evolved disease resistance (R) proteins that recognize corresponding pathogen effectors and activate effector‐triggered immunity (ETI). However, it is largely unknown why, in some cases, a suppressor of ETI exists in plants.
Arabidopsis SOBER1 (Suppressor of AvrBsT‐elicited Resistance 1) was identified previously as a suppressor of Xanthomonas acetyltransferase effector AvrBsT‐triggered immunity. Nevertheless, the extent to which SOBER1 suppresses ETI is unclear.
Here, we identified SOBER1 as a suppressor of Pseudomonas acetyltransferase effector HopZ5‐triggered immunity in Arabidopsis using recombinant inbred lines. Further analysis showed that SOBER1 suppresses immunity triggered by multiple bacterial acetyltransferases.
Interestingly, SOBER1 interferes with the immunity signalling activated by some but not all tested acetyltransferase effectors, indicating that SOBER1 might target components that are shared between several ETI pathways.

Via Suayib Üstün
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Microbial effectors and the role of water and sugar in the infection battle ground

Microbial effectors and the role of water and sugar in the infection battle ground | plant and microbes interaction | Scoop.it
Phytopathogenic microbes multiply in the apoplast — a plant's intercellular spaces — of infected plants, and hence their success relies on the conditions in this habitat. Despite being extracellular parasites, most microbes translocate effectors into host cells that promote disease by acting inside cells. Initial studies suggested that effectors act predominantly as suppressors of plant immunity. These pioneering studies were trend-setting, causing a strong bias in the functional investigation of effectors. Yet, recent studies on bacterial model pathogens have identified effectors that promote disease by causing either increased sugar or water levels in the apoplast. These studies are likely to initiate a new era of effector research that will clarify the disease-promoting rather than defense-suppressing function of effectors, a molecular rather than genetic distinction.

Via Philip Carella
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Sniffing bacterial volatile compounds for healthier plants

Sniffing bacterial volatile compounds for healthier plants | plant and microbes interaction | Scoop.it
Bacterial volatile compounds (BVCs) are not waste or by-products of primary metabolism but rather have critical roles in the biology and ecological competence of bacteria. BVCs are exploited as a source of nutrients and information in plant–bacteria interactions. They target key points in plant physiology, activating downstream metabolic pathways by a domino effect. BVCs are an ancient signal and are involved in plant–bacteria communication, which was shaped during evolutionary history and established before the development of higher plants. This type of communication is not exclusive to mutualistic interactions, because pathogens also use volatiles to alter plant physiology. Here, fragmented information is drawn together to provide a clearer view of how BVCs affect such interactions.

Via Philip Carella
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Current Opinion Plant Biology: Extracellular vesicles as key mediators of plant–microbe interactions (2018)

Current Opinion Plant Biology: Extracellular vesicles as key mediators of plant–microbe interactions (2018) | plant and microbes interaction | Scoop.it
• Plants produce extracellular vesicles (EVs) in response to infection.• Recent advances in EV purification are now revealing the contents of plant EVs.• Plant EVs are enriched in stress-response proteins and signaling lipids.• EVs contain transporters for antimicrobial compounds such as glucosinolates.• Indirect evidence suggests that EVs may mediate inter-kingdom RNA interference.

Extracellular vesicles (EVs) are lipid compartments capable of trafficking proteins, lipids, RNA and metabolites between cells. Plant cells have been shown to secrete EVs during immune responses, but virtually nothing is known about their formation, contents or ultimate function. Recently developed methods for isolating plant EVs have revealed that these EVs are enriched in stress response proteins and signaling lipids, and appear to display antifungal activity. Comparison to work on animal EVs, and the observation that host-derived small interfering RNAs and microRNAs can silence fungal genes, suggests that plant EVs may also mediate trans-kingdom RNA interference. Many fundamental questions remain, however, regarding how plant EVs are produced, how they move, and if and how they are taken up by target cells.


Via Kamoun Lab @ TSL, Francis Martin
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Rescooped by Bo Yang from microbial pathogenesis and plant immunity
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Defense Priming: An Adaptive Part of Induced Resistance | Annual Review of Plant Biology

Defense Priming: An Adaptive Part of Induced Resistance | Annual Review of Plant Biology | plant and microbes interaction | Scoop.it
Priming is an adaptive strategy that improves the defensive capacity of plants. This phenomenon is marked by an enhanced activation of induced defense mechanisms. Stimuli from pathogens, beneficial microbes, or arthropods, as well as chemicals and abiotic cues, can trigger the establishment of priming by acting as warning signals. Upon stimulus perception, changes may occur in the plant at the physiological, transcriptional, metabolic, and epigenetic levels. This phase is called the priming phase. Upon subsequent challenge, the plant effectively mounts a faster and/or stronger defense response that defines the postchallenge primed state and results in increased resistance and/or stress tolerance. Priming can be durable and maintained throughout the plant's life cycle and can even be transmitted to subsequent generations, therefore representing a type of plant immunological memory.

Via Tatsuya Nobori, Jim Alfano
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Frontiers | The apoplastic secretome of Trichoderma virens during interaction with maize roots shows an inhibition of plant defence and scavenging oxidative stress secreted proteins. | Plant Science

In Nature, almost every plant is colonised by fungi. Trichoderma virens is a biocontrol fungus which has the capacity to behave as an opportunistic plant endophyte. Even though many plants are colonised by this symbiont, the exact mechanisms by which Trichoderma masks its entrance into its plant host remain unknown, but likely involve the secretion of different families of proteins into the apoplast that may play crucial roles in the suppression of plant immune responses. In this study, we studied T. virens colonization of maize roots under hydroponic conditions, evidencing inter and intracellular colonization by the fungus and modifications in root morphology and colouration. Moreover, we show that upon host penetration, T. virens secretes into the apoplast an arsenal of proteins to facilitate inter- and intracellular colonisation of maize root tissues. Using a gel-free shotgun proteomics approach, 95 and 43 secretory proteins were identified from maize and T. virens, respectively. A reduction in the maize secretome (46%) was induced by T. virens, including two major groups, glycosyl hydrolases and peroxidases. Furthermore, T. virens secreted proteins were mainly involved in cell wall hydrolysis, scavenging of reactive oxygen species and secondary metabolism, as well as putative effector-like proteins. Levels of peroxidase activity were reduced in the inoculated roots, suggesting a strategy used by T. virens to manipulate host immune responses. The results provide an insight into the crosstalk in the apoplast which is essential to maintain the T. virens-plant interaction.

Via Philip Carella
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Rescooped by Bo Yang from Plant Immunity And Microbial Effectors
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A multi-layered mechanistic modelling approach to understand how effector genes extend beyond phytoplasma to modulate plant hosts, insect vectors and the environment

Highlights



Phytoplasma effectors modulate plant host and insect vector processes.


Effector SAP11 destabilizes plant TCPs inducing witch's broom and suppressing JA.


Effector SAP54 degrades MADS-box transcription factors altering flower development.


Both effectors promote insect vector colonization of plants.


A multi-layered approach enables us to model the long reach of these effector genes.

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Pentapeptide Protection of Botrytis-Infected Tomato by Phytosulfokine

Pentapeptide Protection of Botrytis-Infected Tomato by Phytosulfokine | plant and microbes interaction | Scoop.it
Published March 2018. DOI: https://doi.org/10.1105/tpc.18.00215 This is a PDF-only article. The first page of the PDF of this article appears below. Previous Share Jump to section In this issue The Plant Cell Vol.

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Disease-induced assemblage of a plant-beneficial bacterial consortium

Disease-induced assemblage of a plant-beneficial bacterial consortium | plant and microbes interaction | Scoop.it
Disease suppressive soils typically develop after a disease outbreak due to the subsequent assembly of protective microbiota in the rhizosphere. The role of the plant immune system in the assemblage of a protective rhizosphere microbiome is largely unknown. In this study, we demonstrate that Arabidopsis thaliana specifically promotes three bacterial species in the rhizosphere upon foliar defense activation by the downy mildew pathogen Hyaloperonospora arabidopsidis. The promoted bacteria were isolated and found to interact synergistically in biofilm formation in vitro. Although separately these bacteria did not affect the plant significantly, together they induced systemic resistance against downy mildew and promoted growth of the plant. Moreover, we show that the soil-mediated legacy of a primary population of downy mildew infected plants confers enhanced protection against this pathogen in a second population of plants growing in the same soil. Together our results indicate that plants can adjust their root microbiome upon pathogen infection and specifically recruit a group of disease resistance-inducing and growth-promoting beneficial microbes, therewith potentially maximizing the chance of survival of their offspring that will grow in the same soil.


Via Jean-Michel Ané
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Ethylene Represses Gene Transcription via Histone Deacetylases

Ethylene Represses Gene Transcription via Histone Deacetylases | plant and microbes interaction | Scoop.it

Approximately half of all ethylene-responsive genes are downregulated in the presence in ethylene, but this repression has received relatively little attention compared with the ethylene-mediated activation of expression. The known positive regulators of ethylene signaling include ETHYLENE INSENSITIVE2 (EIN2) and the transcription factor EIN3. Intriguingly, EIN3 binds to promoters of both ethylene-activated and -repressed genes. EIN2, by contrast, affects gene expression via its C terminus, which is cleaved in the presence of ethylene and translocated to the nucleus, where it was recently shown to alter HISTONE3 acetylation levels in a process that involves EIN2 NUCLEAR ASSOCIATED PROTEIN1 (ENAP1; 2017). Now, Zhang et al. (2018) report that two histone deacetylases function with ENAP1 to repress gene expression in the presence of ethylene.


Via Christophe Jacquet
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Transcriptome landscape of a bacterial pathogen under plant immunity

Transcriptome landscape of a bacterial pathogen under plant immunity | plant and microbes interaction | Scoop.it
Plants have evolved a powerful innate immune system to defend against microbial pathogens. Despite extensive studies, how plant immunity ultimately inhibits bacterial pathogen growth is largely unknown, due to difficulties in profiling bacterial responses in planta . In this study, we established two methods for in planta bacterial transcriptome analysis using RNA sequencing. By analyzing 27 combinations of plant immunity mutants and Pseudomonas syringae strains, we succeeded in the identification of specific bacterial transcriptomic signatures that are influenced by plant immune activation. In addition, we found that overexpression of an immune-responsive P. syringae sigma factor gene involved in iron regulation could partially counter bacterial growth restriction during plant immunity. This study illuminates the enigmatic mechanisms of bacterial growth inhibition by plant immunity.

Plant pathogens can cause serious diseases that impact global agriculture. The plant innate immunity, when fully activated, can halt pathogen growth in plants. Despite extensive studies into the molecular and genetic bases of plant immunity against pathogens, the influence of plant immunity in global pathogen metabolism to restrict pathogen growth is poorly understood. Here, we developed RNA sequencing pipelines for analyzing bacterial transcriptomes in planta and determined high-resolution transcriptome patterns of the foliar bacterial pathogen Pseudomonas syringae in Arabidopsis thaliana with a total of 27 combinations of plant immunity mutants and bacterial strains. Bacterial transcriptomes were analyzed at 6 h post infection to capture early effects of plant immunity on bacterial processes and to avoid secondary effects caused by different bacterial population densities in planta . We identified specific “immune-responsive” bacterial genes and processes, including those that are activated in susceptible plants and suppressed by plant immune activation. Expression patterns of immune-responsive bacterial genes at the early time point were tightly linked to later bacterial growth levels in different host genotypes. Moreover, we found that a bacterial iron acquisition pathway is commonly suppressed by multiple plant immune-signaling pathways. Overexpression of a P. syringae sigma factor gene involved in iron regulation and other processes partially countered bacterial growth restriction during the plant immune response triggered by AvrRpt2. Collectively, this study defines the effects of plant immunity on the transcriptome of a bacterial pathogen and sheds light on the enigmatic mechanisms of bacterial growth inhibition during the plant immune response.

Via Giannis Stringlis, Steve Marek, Stéphane Hacquard
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Rescooped by Bo Yang from Phytophthora biology
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Phytophthora methylomes modulated by expanded 6mA methyltransferases are associated with adaptive genome regions - bioRxiv

Phytophthora methylomes modulated by expanded 6mA methyltransferases are associated with adaptive genome regions - bioRxiv | plant and microbes interaction | Scoop.it

Filamentous plant pathogen genomes often display a bipartite architecture with gene sparse, repeat-rich compartments serving as a cradle for adaptive evolution. However, the extent to which this "two-speed" genome architecture is associated with genome-wide epigenetic modifications is unknown. Here, we show that the oomycete plant pathogens Phytophthora infestans and Phytophthora sojae possess functional adenine N6-methylation (6mA) methyltransferases that modulate patterns of 6mA marks across the genome. In contrast, 5-methylcytosine (5mC) could not be detected in the two Phytophthora species. Methylated DNA IP Sequencing (MeDIP-seq) of each species revealed that 6mA is depleted around the transcriptional starting sites (TSS) and is associated with low expressed genes, particularly transposable elements. Remarkably, genes occupying the gene-sparse regions have higher levels of 6mA compared to the remainder of both genomes, possibly implicating the methylome in adaptive evolution of Phytophthora. Among three putative adenine methyltransferases, DAMT1 and DAMT3 displayed robust enzymatic activities. Surprisingly, single knockouts of each of the 6mA methyltransferases in P. sojae significantly reduced in vivo 6mA levels, indicating that the three enzymes are not fully redundant. MeDIP-seq of the damt3 mutant revealed uneven patterns of 6mA methylation across genes, suggesting that PsDAMT3 may have a preference for gene body methylation after the TSS. Our findings provide evidence that 6mA modification is an epigenetic mark of Phytophthora genomes and that complex patterns of 6mA methylation by the expanded 6mA methyltransferases may be associated with adaptive evolution in these important plant pathogens.


Via Kamoun Lab @ TSL, Francis Martin, Ronny Kellner, Niklaus Grunwald
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