microbial pathogenesis and plant immunity
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Different shades of JAZ during plant growth and defense -

Different shades of JAZ during plant growth and defense - | microbial pathogenesis and plant immunity | Scoop.it
Ever since their discovery as key regulators of the jasmonate (JA) signaling pathway (Chini et al., 2007; Thines et al., 2007; Yan et al., 2007), repressor proteins of the JASMONATE ZIM-domain (JAZ) family have been rising stars in research on hormonal regulation of plant growth and defense. In plant cells, JAZ repressor proteins interact with an E3 ubiquitin ligase complex (SCFCOI1) that together function as a JA receptor. In resting cells, JAZs block the activity of transcriptional regulators of JA responses by physically binding to them. Upon perception of bioactive JAs, JAZ proteins are rapidly degraded via the ubiquitin/26S proteasome-dependent proteolytic pathway. This releases the JAZ-bound transcription factors, resulting in the activation of downstream JA responses (Fig. 1a). JAs play a dominant role in regulating defense responses against herbivorous insects and necrotrophic pathogens, and in adaptive responses to beneficial soilborne microbes (Wasternack & Hause, 2013; Pieterse et al., 2014). In addition, JAs have a signal function in a myriad other processes, including abiotic stress reactions and plant growth responses to environmental cues (Wasternack & Hause, 2013). The JA pathway functions in the context of a complex network of hormone-regulated signaling pathways that, depending on the environmental or developmental condition, can act antagonistically or synergistically on each other to finely balance resource allocation between growth and defense and minimize fitness tradeoffs (Pieterse et al., 2012; Vos et al., 2013). In the process of balancing plant growth and defense, gibberellins (GAs) have emerged as dominant antagonists of the JA signaling output (Hou et al., 2013). GAs regulate different aspects of plant growth via DELLA repressor proteins that block the activity of transcriptional regulators of GA responses by physically binding to them.
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Are microbiome studies ready for hypothesis-driven research?


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Nature Plants: Polymorphic residues in rice NLRs expand binding and response to effectors of the blast pathogen (2018)

Nature Plants: Polymorphic residues in rice NLRs expand binding and response to effectors of the blast pathogen (2018) | microbial pathogenesis and plant immunity | Scoop.it

Accelerated adaptive evolution is a hallmark of plant–pathogen interactions. Plant intracellular immune receptors (NLRs) often occur as allelic series with differential pathogen specificities. The determinants of this specificity remain largely unknown. Here, we unravelled the biophysical and structural basis of expanded specificity in the allelic rice NLR Pik, which responds to the effector AVR-Pik from the rice blast pathogen Magnaporthe oryzae. Rice plants expressing the Pikm allele resist infection by blast strains expressing any of three AVR-Pik effector variants, whereas those expressing Pikp only respond to one. Unlike Pikp, the integrated heavy metal-associated (HMA) domain of Pikm binds with high affinity to each of the three recognized effector variants, and variation at binding interfaces between effectors and Pikp-HMA or Pikm-HMA domains encodes specificity. By understanding how co-evolution has shaped the response profile of an allelic NLR, we highlight how natural selection drove the emergence of new receptor specificities. This work has implications for the engineering of NLRs with improved utility in agriculture.


Via The Sainsbury Lab
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Large-scale replicated field study of maize rhizosphere identifies heritable microbes


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Defining essential processes in plant pathogenesis with Pseudomonas syringae pv. tomato DC3000 disarmed polymutants and a subset of key type III effectors - Wei - 2018 - Molecular Plant Pathology -...

Defining essential processes in plant pathogenesis with Pseudomonas syringae pv. tomato DC3000 disarmed polymutants and a subset of key type III effectors - Wei - 2018 - Molecular Plant Pathology -... | microbial pathogenesis and plant immunity | Scoop.it
Pseudomonas syringae pv. tomato DC3000 and its derivatives cause disease in tomato, Arabidopsis and Nicotiana benthamiana. The primary virulence factors include a repertoire of 29 effector proteins injected into plant cells by the type III secretion system and the phytotoxin coronatine. The complete repertoire of effector genes and key coronatine biosynthesis genes have been progressively deleted and minimally reassembled to reconstitute basic pathogenic ability in N. benthamiana, and in Arabidopsis plants that have mutations in target genes that mimic effector actions. This approach and molecular studies of effector activities and plant immune system targets have highlighted a small subset of effectors that contribute to essential processes in pathogenesis. Most notably, HopM1 and AvrE1 redundantly promote an aqueous apoplastic environment, and AvrPtoB and AvrPto redundantly block early immune responses, two conditions that are sufficient for substantial bacterial growth in planta. In addition, disarmed DC3000 polymutants have been used to identify the individual effectors responsible for specific activities of the complete repertoire and to more effectively study effector domains, effector interplay and effector actions on host targets. Such work has revealed that AvrPtoB suppresses cell death elicitation in N. benthamiana that is triggered by another effector in the DC3000 repertoire, highlighting an important aspect of effector interplay in native repertoires. Disarmed DC3000 polymutants support the natural delivery of test effectors and infection readouts that more accurately reveal effector functions in key pathogenesis processes, and enable the identification of effectors with similar activities from a broad range of other pathogens that also defeat plants with cytoplasmic effectors.

Via Christophe Jacquet
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Rescooped by Jim Alfano from Plant-Microbe Interactions: Pathogenesis & Symbiosis
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Two chloroplast-localized proteins: AtNHR2A and AtNHR2B, contribute to callose deposition during nonhost disease resistance in Arabidopsis | Molecular Plant-Microbe Interactions

Plants are naturally resistant to most pathogens through a broad and durable defense response called nonhost disease resistance. Nonhost disease resistance is a complex process that includes preformed physical and chemical barriers and induced responses. In spite of its importance, many components of nonhost disease resistance remain to be identified and characterized. Using virus-induced gene silencing in Nicotiana benthamiana, we discovered a novel gene that we named NbNHR2 (N. benthamiana nonhost resistance 2). NbNHR2-silenced plants were susceptible to the non-adapted pathogen Pseudomonas syringae pv. tomato T1 that does not cause disease in wild-type or non-silenced N. benthamiana plants. We found two orthologous genes in Arabidopsis thaliana: AtNHR2A and AtNHR2B. Similar to the results obtained in N. benthamiana, Atnhr2a and Atnhr2b mutants were susceptible to the non-adapted bacterial pathogen of A. thaliana, P. syringae pv. tabaci. We further found that these mutants were also defective in callose deposition. AtNHR2A and AtNHR2B fluorescent protein fusions transiently expressed in N. benthamiana localized predominantly to chloroplasts and a few unidentified dynamic puncta. RFP-AtNHR2A and AtNHR2B-GFP displayed overlapping signals in chloroplasts indicating that the two proteins could interact; a notion supported by co-immunoprecipitation studies. We propose that AtNHR2A and AtNHR2B are new components of a chloroplast-signaling pathway that activates callose deposition to the cell wall in response to bacterial pathogens.

Via Philip Carella
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Rescooped by Jim Alfano from Host-Microbe Interactions. Plant Biology.
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The Defense Phytohormone Signaling Network Enables Rapid, High-amplitude Transcriptional Reprogramming During Effector-Triggered Immunity

The Defense Phytohormone Signaling Network Enables Rapid, High-amplitude Transcriptional Reprogramming During Effector-Triggered Immunity | microbial pathogenesis and plant immunity | Scoop.it
The phytohormone network consisting of jasmonate (JA), ethylene, PHYTOALEXIN-DEFICIENT 4 (PAD4) and salicylic acid (SA) signaling is required for the two modes of plant immunity, pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). A previous study showed that during PTI, the transcriptional responses of over five thousand genes qualitatively depend on complex interactions between the network components. However, the role of the network in transcriptional reprogramming during ETI and whether it differs between PTI and ETI remain elusive. Here, we generated time-series RNA-sequencing data of Arabidopsis thaliana wild-type and combinatorial mutant plants deficient in components of the network upon challenge with virulent or ETI-triggering avirulent strains of the foliar bacterial pathogen Pseudomonas syringae. Resistant plants such as the wild type achieved high-amplitude transcriptional reprogramming four hours after challenge with avirulent strains and sustained this transcriptome response. Strikingly, susceptible plants including the quadruple network mutant showed almost identical transcriptome responses to resistant plants but with several hours delay. Furthermore, gene co-expression network structure was highly conserved between the wild-type and quadruple mutant. Thus, in contrast to PTI, the phytohormone network is required only for achieving high-amplitude transcriptional reprogramming within the early time window of ETI against this bacterial pathogen.

Via Tatsuya Nobori
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Modular Study of the Type III Effector Repertoire in Pseudomonas syringae pv. tomato DC3000 Reveals a Matrix of Effector Interplay in Pathogenesis

Modular Study of the Type III Effector Repertoire in Pseudomonas syringae pv. tomato DC3000 Reveals a Matrix of Effector Interplay in Pathogenesis | microbial pathogenesis and plant immunity | Scoop.it
The bacterial pathogen Pseudomonas syringae pv. tomato DC3000 suppresses the two-tiered innate immune system of Nicotiana benthamiana and other plants by injecting a complex repertoire of type III secretion effector (T3E) proteins. Effectorless polymutant DC3000D36E was used with a modularized system for native delivery of the 29 DC3000 T3Es singly and in pairs. Assays of the performance of this T3E library in N. benthamiana leaves revealed a matrix of T3E interplay, with six T3Es eliciting death and eight others variously suppressing the death activity of the six. The T3E library was also interrogated for effects on DC3000D36E elicitation of a reactive oxygen species burst, for growth in planta, and for T3Es that reversed these effects. Pseudomonas fluorescens and Agrobacterium tumefaciens heterologous delivery systems yielded notably different sets of death-T3Es. The DC3000D36E T3E library system highlights the importance of 13 T3Es and their interplay in interactions with N. benthamiana.

Via Suayib Üstün
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Phyllosphere microbiology: at the interface between microbial individuals and the plant host - Remus‐Emsermann - 2018 - New Phytologist -

Phyllosphere microbiology: at the interface between microbial individuals and the plant host - Remus‐Emsermann - 2018 - New Phytologist - | microbial pathogenesis and plant immunity | Scoop.it
Leaf surfaces are home to diverse bacterial communities. Within these communities, every individual cell perceives its unique environment and responds accordingly. In this insight article, the perspective of the bacterial individual is assumed in an attempt to describe how the spatially heterogeneous leaf surface determines the fate of bacteria. To investigate behaviour at scales relevant to bacteria, single‐cell approaches are essential. Single‐cell studies provide important lessons about how current ‘omics’ approaches fail to give an accurate picture of the behaviour of bacterial populations in heterogeneous environments. Upcoming techniques will soon allow us to combine the power of single‐cell and omics approaches.

Via Christophe Jacquet
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The bacterial type III-secreted protein AvrRps4 is a bipartite effector

The bacterial type III-secreted protein AvrRps4 is a bipartite effector | microbial pathogenesis and plant immunity | Scoop.it
Author summary An important component of the plant immune system relies on the detection of pathogen-derived effectors by immune receptors called resistance proteins. Bacterial pathogens inject effectors into the host cell via a dedicated secretion system to suppress defenses and to manipulate the physiology of the host cell to the pathogen's advantage. Usually, a single resistance protein recognizes a single effector, but an increasing number of exceptions and elaborations on this one-to-one relationship are known. The plant Arabidopsis uses a pair of resistance proteins, RRS1 and RPS4, to detect the effector AvrRps4. After injection into the cell, AvrRps4 is cleaved into two protein parts, and it had been assumed that only the C-terminal part needs to be present to trigger RPS4/RRS1. We show here that both AvrRps4 parts are required for triggering resistance in Arabidopsis, and that the N-terminal part, which previously had been assumed to only function in effector secretion into the host cell, in fact on its own has some functions of an effector. This conclusion is supported by the observation that the N-terminal part of AvrRps4 is sufficient to trigger resistance in lettuce. The fusion of the two AvrRps4 parts may have arisen to counteract plant defenses.

Via Tatsuya Nobori
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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 | microbial pathogenesis and plant immunity | 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
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Disease-induced assemblage of a plant-beneficial bacterial consortium

Disease-induced assemblage of a plant-beneficial bacterial consortium | microbial pathogenesis and plant immunity | Scoop.it
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Via Tatsuya Nobori
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Bacteria exploit autophagy for proteasome degradation and enhanced virulence in plants

Bacteria exploit autophagy for proteasome degradation and enhanced virulence in plants | microbial pathogenesis and plant immunity | Scoop.it
Autophagy and the ubiquitin-proteasome system (UPS) are two major protein degradation pathways implicated in the response to microbial infections in eukaryotes. In animals, the contribution of autophagy and the UPS to anti-bacterial immunity is well documented and several bacteria have evolved measures to target and exploit these systems to the benefit of infection. In plants, the UPS has been established as a hub for immune responses and is targeted by bacteria to enhance virulence. However, the role of autophagy during plant-bacterial interactions is less understood. Here, we have identified both pro- and anti-bacterial functions of autophagy mechanisms upon infection of Arabidopsis with virulent Pseudomonas syringae pv. tomato DC3000 (Pst). We show that Pst activates autophagy in a type-III effector (T3E)-dependent manner, and stimulates the autophagic removal of proteasomes (proteaphagy) to support bacterial proliferation. We further identify the T3E Hrp outer protein M1 (HopM1) as a principle mediator of autophagy-inducing activities during infection. In contrast to the pro-bacterial effects of Pst-induced proteaphagy, NEIGHBOR OF BRCA1 (NBR1)-dependent selective autophagy counteracts disease progression and limits the formation of HopM1-mediated water-soaked lesions. Together, we demonstrate that distinct autophagy pathways contribute to host immunity and bacterial pathogenesis during Pst infection, and provide evidence for an intimate crosstalk between proteasome and autophagy in plant-bacterial interactions.

Via Suayib Üstün
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Compositional shifts in root-associated bacterial and archaeal microbiota track the plant life cycle in field-grown rice

Compositional shifts in root-associated bacterial and archaeal microbiota track the plant life cycle in field-grown rice | microbial pathogenesis and plant immunity | Scoop.it
Author summary Plant roots are colonized by complex communities of bacterial and archaeal microbiota from the soil, with the potential to affect plant nutrition and fitness. Although root-associated microbes are known to have the potential to be utilized to promote crop productivity, their exploitation has been hindered by a lack of understanding of the compositional dynamics of these communities. Here we investigate temporal changes in the root-associated bacterial and archaeal communities throughout the plant life cycle in field-grown rice over multiple seasons and locations. Our results indicate that root microbiota composition varies with both chronological age and the developmental stage of the plants. We find that a major compositional shift correlates with the transition to reproductive growth, suggestive of distinct root microbiota associations for the juvenile and adult plant phases. The results from this study highlight dynamic relationships between plant growth and associated microbiota that should be considered in strategies for the successful manipulation of microbial communities to enhance crop performance.

Via Tatsuya Nobori
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Defining microbiome function

Defining microbiome function | microbial pathogenesis and plant immunity | Scoop.it
This Perspective argues that microbiome research needs to consider the different philosophical definitions of function to avoid confusion in the field, and uses the hologenome concept as an example.

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Rescooped by Jim Alfano from Plant-Microbe Interactions: Pathogenesis & Symbiosis
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A Secreted ‘Candidatus Liberibacter asiaticus’ Peroxiredoxin Simultaneously Suppresses Both Localized and Systemic Innate Immune Responses in Planta | Molecular Plant-Microbe Interactions

The oxidative (H2O2) burst is a seminal feature of the basal plant defense response to attempted pathogen invasions. In ‘Candidatus Liberibacter asiaticus’ strain UF506, expression of the SC2 prophage-encoded secreted peroxidase (F489_gp15) likely increases bacterial fitness and delays symptom progression in citrus. Two chromosomal 1-Cys peroxiredoxins genes, CLIBASIA_RS00940 (Lasprx5) and CLIBASIA_RS00445 (Lasbcp), are conserved among all sequenced ‘Ca. Liberibacter asiaticus’ strains, including those lacking prophages. Both LasBCP and LasdPrx5 have only a single conserved peroxidatic Cys (CP/SH) and lack the resolving Cys (CR/SH). Lasprx5 appeared to be a housekeeping gene with similar moderate transcript abundance in both ‘Ca. Liberibacter asiaticus’-infected psyllids and citrus. By contrast, Lasbcp was expressed only in citrus, similar to the expression of the SC2 peroxidase. Since ‘Ca. Liberibacter asiaticus’ is uncultured, Lasbcp and Lasprx5 were functionally validated in a cultured surrogate species, L. crescens; and both genes significantly increased oxidative stress tolerance and cell viability in culture. LasBCP was nonclassically secreted and in L. crescens, conferred 214-fold more resistance to tert-butyl hydroperoxide (tBOOH) than wild type. Transient overexpression of Lasbcp in tobacco suppressed H2O2-mediated transcriptional activation of RbohB, the key gatekeeper of the systemic plant defense signaling cascade. Lasbcp expression did not interfere with the perception of ‘Ca. Liberibacter asiaticus’ flagellin (flg22Las) but interrupted the downstream activation of RbohB and stereotypical deposition of callose in tobacco. Critically, LasBCP also protected against tBOOH induced peroxidative degradation of lipid membranes in planta, preventing subsequent accumulation of antimicrobial oxylipins that can also trigger the localized hypersensitive cell death response.

Via Philip Carella
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eLife: Host autophagy machinery is diverted to the pathogen interface to mediate focal defense responses against the Irish potato famine pathogen (2018)

eLife: Host autophagy machinery is diverted to the pathogen interface to mediate focal defense responses against the Irish potato famine pathogen (2018) | microbial pathogenesis and plant immunity | Scoop.it

During plant cell invasion, the oomycete Phytophthora infestans remains enveloped by host-derived membranes whose functional properties are poorly understood. P. infestans secretes a myriad of effector proteins through these interfaces for plant colonization. Recently we showed that the effector protein PexRD54 reprograms host-selective autophagy by antagonising antimicrobial-autophagy receptor Joka2/NBR1 for ATG8CL binding (Dagdas, 2016). Here, we show that during infection, ATG8CL/Joka2 labelled defense-related autophagosomes are diverted toward the perimicrobial host membrane to restrict pathogen growth. PexRD54 also localizes to autophagosomes across the perimicrobial membrane, consistent with the view that the pathogen remodels host-microbe interface by co-opting the host autophagy machinery. Furthermore, we show that the host-pathogen interface is a hotspot for autophagosome biogenesis. Notably, overexpression of the early autophagosome biogenesis protein ATG9 enhances plant immunity. Our results implicate selective autophagy in polarized immune responses of plants and point to more complex functions for autophagy than the widely known degradative roles.


Via Kamoun Lab @ TSL, Rey Thomas
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Novel soil bacteria possess diverse genes for secondary metabolite biosynthesis

Novel soil bacteria possess diverse genes for secondary metabolite biosynthesis | microbial pathogenesis and plant immunity | Scoop.it
Metagenomic and soil microcosm analyses identify abundant biosynthetic gene clusters in genomes of microorganisms from a northern Californian grassland ecosystem that provide a potential source for the future development of bacterial natural products.

Via Tatsuya Nobori
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Best practices for analysing microbiomes

Best practices for analysing microbiomes | microbial pathogenesis and plant immunity | Scoop.it
Review Article

Via Tatsuya Nobori
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Organic Amendments, Beneficial Microbes, and Soil Microbiota: Toward a Unified Framework for Disease Suppression | Annual Review of Phytopathology

Organic Amendments, Beneficial Microbes, and Soil Microbiota: Toward a Unified Framework for Disease Suppression | Annual Review of Phytopathology | microbial pathogenesis and plant immunity | Scoop.it

Via Tatsuya Nobori
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Rescooped by Jim Alfano from Plants and Microbes
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Science: Plants send small RNAs in extracellular vesicles to fungal pathogen to silence virulence genes (2018)

Science: Plants send small RNAs in extracellular vesicles to fungal pathogen to silence virulence genes (2018) | microbial pathogenesis and plant immunity | Scoop.it

Some pathogens and pests deliver small RNAs (sRNAs) into host cells to suppress host immunity. Conversely, hosts also transfer sRNAs into pathogens and pests to inhibit their virulence. Although sRNA trafficking has been observed in a wide variety of interactions, how sRNAs are transferred, especially from hosts to pathogens/pests, is still unknown. Here we show that host Arabidopsis cells secrete exosome-like extracellular vesicles to deliver sRNAs into fungal pathogen Botrytis cinerea. These sRNA-containing vesicles accumulate at the infection sites and are taken up by the fungal cells. Transferred host sRNAs induce silencing of fungal genes critical for pathogenicity. Thus, Arabidopsis has adapted exosome-mediated cross-kingdom RNA interference as part of its immune responses during the evolutionary arms race with the pathogen.


Via Kamoun Lab @ TSL
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Rescooped by Jim Alfano from xiao lin
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Cladosporium fulvum Effectors: Weapons in the Arms Race with Tomato | Annual Review of Phytopathology

Cladosporium fulvum Effectors: Weapons in the Arms Race with Tomato | Annual Review of Phytopathology | microbial pathogenesis and plant immunity | Scoop.it

Via Xiao Lin
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Microbial interactions within the plant holobiont | Microbiome |

Microbial interactions within the plant holobiont | Microbiome | | microbial pathogenesis and plant immunity | 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, Giannis Stringlis
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Autophagy: The Master of Bulk and Selective Recycling | Annual Review of Plant Biology

Autophagy: The Master of Bulk and Selective Recycling | Annual Review of Plant Biology | microbial pathogenesis and plant immunity | Scoop.it
Plants have evolved sophisticated mechanisms to recycle intracellular constituents, which are essential for developmental and metabolic transitions; for efficient nutrient reuse; and for the proper disposal of proteins, protein complexes, and even entire organelles that become obsolete or dysfunctional. One major route is autophagy, which employs specialized vesicles to encapsulate and deliver cytoplasmic material to the vacuole for breakdown. In the past decade, the mechanics of autophagy and the scores of components involved in autophagic vesicle assembly have been documented. Now emerging is the importance of dedicated receptors that help recruit appropriate cargo, which in many cases exploit ubiquitylation as a signal. Although operating at a low constitutive level in all plant cells, autophagy is upregulated during senescence and various environmental challenges and is essential for proper nutrient allocation. Its importance to plant metabolism and energy balance in particular places autophagy at the nexus of robust crop performance, especially under suboptimal conditions.

Via Suayib Üstün
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The Xanthomonas effector XopL uncovers the role of microtubules in stromule extension and dynamics in Nicotiana benthamiana - Erickson - 2018 - The Plant Journal -

The Xanthomonas effector XopL uncovers the role of microtubules in stromule extension and dynamics in Nicotiana benthamiana - Erickson - 2018 - The Plant Journal - | microbial pathogenesis and plant immunity | Scoop.it
Xanthomonas campestris pv. vesicatoria type III-secreted effectors were screened for candidates influencing plant cell processes relevant to the formation and maintenance of stromules in Nicotiana benthamiana lower leaf epidermis. Transient expression of XopL, a unique type of E3 ubiquitin ligase, led to a nearly complete elimination of stromules and the relocation of plastids to the nucleus. Further characterization of XopL revealed that the E3 ligase activity is essential for the two plastid phenotypes. In contrast to the XopL wild type, a mutant XopL lacking E3 ligase activity specifically localized to microtubules. Interestingly, mutant XopL-labeled filaments frequently aligned with stromules, suggesting an important, yet unexplored, microtubule–stromule relationship. High time-resolution movies confirmed that microtubules provide a scaffold for stromule movement and contribute to stromule shape. Taken together, this study has defined two populations of stromules: microtubule-dependent stromules, which were found to move slower and persist longer, and microtubule-independent stromules, which move faster and are transient. Our results provide the basis for a new model of stromule dynamics including interactions with both actin and microtubules.
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Rescooped by Jim Alfano from Publications from The Sainsbury Laboratory
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Nature Plants: An apoplastic peptide activates salicylic acid signalling in maize (2018)

Nature Plants: An apoplastic peptide activates salicylic acid signalling in maize (2018) | microbial pathogenesis and plant immunity | Scoop.it
Localized control of cell death is crucial for the resistance of plants to pathogens. Papain-like cysteine proteases (PLCPs) regulate plant defence to drive cell death and protection against biotrophic pathogens. In maize (Zea mays), PLCPs are crucial in the orchestration of salicylic acid (SA)-dependent defence signalling. Despite this central role in immunity, it remains unknown how PLCPs are activated, and which downstream signals they induce to trigger plant immunity. Here, we discover an immune signalling peptide, Z. mays immune signalling peptide 1 (Zip1), which is produced after salicylic acid (SA) treatment. In vitro studies demonstrate that PLCPs are required to release bioactive Zip1 from its propeptide precursor. Conversely, Zip1 treatment strongly elicits SA accumulation in leaves. Moreover, transcriptome analyses revealed that Zip1 and SA induce highly overlapping transcriptional changes. Consequently, Zip1 promotes the infection of the necrotrophic fungus Botrytis cinerea, while it reduces virulence of the biotrophic fungus Ustilago maydis. Thus, Zip1 represents the previously missing signal that is released by PLCPs to activate SA defence signalling.

Via The Sainsbury Lab
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