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Allelic barley MLA immune receptors recognize sequence-unrelated avirulence effectors of the powdery mildew pathogen

National Academy of Sciences
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Here is  a SEMINAL paper on powdery mildew AVR proteins: well worth digesting in its entirety
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Unconventional protein secretion in plants: a critical assessment

Unconventional protein secretion in plants: a critical assessment | Plant and their microbe symbionts | Scoop.it
Unconventional protein secretion (UPS) is a collective term for mechanisms by which cytosolic proteins that lack a signal peptide (“leaderless secretory proteins” (LSPs)) can gain access to the cell e
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PLOS Pathogens: Escaping Host Immunity: New Tricks for Plant Pathogens (2016)

PLOS Pathogens: Escaping Host Immunity: New Tricks for Plant Pathogens (2016) | Plant and their microbe symbionts | Scoop.it

Fungal and oomycete plant pathogens cause destructive diseases in crops and pose real economic and food security threats [1]. These filamentous, eukaryotic organisms can also upset natural ecosystems when they spread invasively [2]. The capability of plant immune systems to detect and respond to pathogen effector proteins is a major determinant of disease susceptibility. Plant pathogen effector proteins that trigger host immunity are often encoded by conditionally detrimental genes that are under strong and contrasting selective pressures [3,4]. Pathogen effectors evolved to play a positive role in virulence by enabling growth and reproduction on host plants [5,6]. Nonetheless, effectors can meet their match with host immune receptors that recognize their presence, a result that ends badly for the pathogen. Such immunity-triggering proteins are known as avirulence (Avr) effectors, encoded by Avrgenes.


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Using decoys to expand the recognition specificity of a plant disease resistance protein

Using decoys to expand the recognition specificity of a plant disease resistance protein | Plant and their microbe symbionts | Scoop.it

Science Vol 351, Issue 6274 12 February 2016

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Cool decoys...

 

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BMC Genomics

BMC Genomics | Plant and their microbe symbionts | Scoop.it
BMC Genomics is an open access journal publishing original peer-reviewed research articles in all aspects of genome-scale analysis, functional genomics, and proteomics. BMC Genomics is part of the BMC series which publishes subject-specific journals focused on the needs of individual research communities across all areas of biology and medicine. We offer an efficient, fair and friendly peer review service, and are committed to publishing all sound science, provided that there is some advance in knowledge presented by the work. BMC series - open, inclusive and trusted.
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Copy number variation: another mechanism in the armory of pathogenic fungi to evolve resistance to things we throw at them

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Beyond Bar and Line Graphs: Time for a New Data Presentation Paradigm

Beyond Bar and Line Graphs: Time for a New Data Presentation Paradigm | Plant and their microbe symbionts | Scoop.it
A systematic review of research articles reveals widespread poor practice in the presentation of continuous data. The authors recommend training for investigators and supply templates for easy use.
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A must read paper, for anyone handling quantitative data

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1-s2.0-S1360138514003136-main.pdf?_tid=74bc12aa-9bdb-11e4-8de0-00000aacb362&acdnat=1421232938_3ae976cc4b3a1577adf25c7c4972cdd8

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Plants and microbes: common languages? Does anyone remember Esperanto?

 

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Frontiers: A novel conserved mechanism for plant NLR protein pairs: the ‘integrated decoy’ hypothesis (2014)

Frontiers: A novel conserved mechanism for plant NLR protein pairs: the ‘integrated decoy’ hypothesis (2014) | Plant and their microbe symbionts | Scoop.it

Plant immunity is often triggered by the specific recognition of pathogen effectors by intracellular nucleotide-binding, leucine-rich repeat (NLR) receptors. Plant NLRs contain an N-terminal signaling domain that is mostly represented by either a Toll-interleukin1 receptor (TIR) domain or a coiled coil (CC) domain. In many cases, single NLR proteins are sufficient for both effector recognition and signaling activation. However, many paired NLRs have now been identified where both proteins are required to confer resistance to pathogens. Recent detailed studies on the Arabidopsis thaliana TIR-NLR pair RRS1 and RPS4 and on the rice CC-NLR pair RGA4 and RGA5 have revealed for the first time how such protein pairs function together. In both cases, the paired partners interact physically to form a hetero-complex receptor in which each partner plays distinct roles in effector recognition or signaling activation, highlighting a conserved mode of action of NLR pairs across both monocotyledonous and dicotyledonous plants. We also discuss a new ‘integrated decoy’ effector recognition model to describe these receptor complexes that may be common to many other plant NLR pairs.


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Elsa Ballini's curator insight, October 29, 2014 4:21 AM

In Rice/Magnaporthe an example is RGA4-RGA5

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Frontiers: The past, present and future of breeding rust resistant wheat (2014)

Frontiers: The past, present and future of breeding rust resistant wheat (2014) | Plant and their microbe symbionts | Scoop.it

Two classes of genes are used for breeding rust resistant wheat. The first class, called R (for resistance) genes, are pathogen race-specific in their action, effective at all plant growth stages and probably mostly encode immune receptors of the nucleotide binding leucine rich repeat (NB-LRR) class. The second class called Adult Plant Resistance genes (APR) because resistance is usually functional only in adult plants, and, in contrast to most R genes, the levels of resistance conferred by single APR genes are only partial and allow considerable disease development. Some but not all APR genes provide resistance to all isolates of a rust pathogen species and a subclass of these provides resistance to several fungal pathogen species. Initial indications are that APR genes encode a more heterogeneous range of proteins than R proteins. Two APR genes, Lr34 and Yr36, have been cloned from wheat and their products are an ABC transporter and a protein kinase, respectively. Lr34 and Sr2 have provided long lasting and widely used (durable) partial resistance and are mainly used in conjunction with other R and APR genes to obtain adequate rust resistance. We caution that some APR genes indeed include race-specific, weak R genes which may be of the NB-LRR class. A research priority to better inform rust resistance breeding is to characterize further APR genes in wheat and to understand how they function and how they interact when multiple APR and R genes are stacked in a single genotype by conventional and GM breeding. An important message is do not be complacent about the general durability of all APR genes.


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The effective papilla hypothesis - Hückelhoven - 2014 - New Phytologist - Wiley Online Library

The effective papilla hypothesis - Hückelhoven - 2014 - New Phytologist - Wiley Online Library | Plant and their microbe symbionts | Scoop.it
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Brilliant commentary on the Papilla-Paper (see below)

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Frontiers | The role of effectors in nonhost resistance to filamentous plant pathogens | Plant-Microbe Interaction

In nature, most plants are resistant to a wide range of phytopathogens. However, mechanisms contributing to this so-called nonhost resistance (NHR) are poorly understood. Besides constitutive defen...
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Scientific Reports: Secret lifestyles of Neurospora crassa: can it be a plant pathogen? (2014)

Scientific Reports: Secret lifestyles of Neurospora crassa: can it be a plant pathogen? (2014) | Plant and their microbe symbionts | Scoop.it

Neurospora crassa has a long history as an excellent model for genetic, cellular, and biochemical research. Although this fungus is known as a saprotroph, it normally appears on burned vegetations or trees after forest fires. However, due to a lack of experimental evidence, the nature of its association with living plants remains enigmatic. Here we report that Scots pine (Pinus sylvestris) is a host plant for N. crassa. The endophytic lifestyle of N. crassa was found in its interaction with Scots pine. Moreover, the fungus can switch to a pathogenic state when its balanced interaction with the host is disrupted. Our data reveal previously unknown lifestyles of N. crassa, which are likely controlled by both environmental and host factors. Switching among the endophytic, pathogenic, and saprotrophic lifestyles confers upon fungi phenotypic plasticity in adapting to changing environments and drives the evolution of fungi and associated plants.


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Transposons passively and actively contribute to evolution of the two-speed genome of a fungal pathogen

An international, peer-reviewed genome sciences journal featuring outstanding original research that offers novel insights into the biology of all organisms
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Yet another case of transposons playing useful roles in (plant) pathogen evolution
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Current Biology: Pathogen Tactics to Manipulate Plant Cell Death (2016)

Current Biology: Pathogen Tactics to Manipulate Plant Cell Death (2016) | Plant and their microbe symbionts | Scoop.it

Programmed cell death (PCD) is a conserved process among eukaryotes that serves a multitude of functional roles during an organism’s natural life cycle. PCD involves the tightly regulated process of cell death cued by specific spatiotemporal stimuli, which confer survival benefits. In eukaryotes, PCD is an essential process involved in senescence, aging, embryo development, cell differentiation, and immunity. In animal systems, morphologically distinct forms of PCD have been described (Figure 1) [1, 2]. Type I, or apoptotic cell death, is the best understood form of PCD and is defined by cell shrinkage, nuclear condensation and fragmentation, and eventual disintegration of the cell into apoptotic bodies that are digested by phagocytes. Type II cell death is an autophagic process that is induced during nutrient deprivation and chronic stress. Autophagic cell death is characterized by the rupture of the lysosome and subsequent release of toxic chemicals that degrade the cell contents. Unlike type I and type II, type III PCD is distinguished by the swelling of organelles and subsequent rupture of the plasma membrane. A programmed necrosis or necroptosis was initially believed to be an uncontrolled process of necrosis, but has been recently reclassified as type III form of cell death. Finally, pyroptosis is another recently categorized form of cell death that is mediated by caspase-1 activity. Morphologically, pyroptotic cells share characteristics of both apoptosis and necrosis [1]. Noteworthy, necroptosis and pyroptosis are pro-inflammatory forms of PCD activated by microbial infections and diverse environmental stimuli.

 

In plants, PCD is less rigorously classified (Figure 1). One difficulty in distinguishing the forms of PCD in plants and animals comes as a result of the different cellular morphology in plant cells — most notably the presence of the cell wall and chloroplasts. Unlike the plasma membrane, the degradation of the cell wall is not a universal feature of PCD in plants. Additionally, the formation of apoptotic bodies is not observed in plant cells, as there are no circulating phagocytes to engulf them [3]. Instead, plant cells committed to PCD release autolytic compounds stored in the vacuole that degrade cell contents. In these cases, the cell wall may develop perforations for the absorption and recycling of cellular components by neighboring cells. Although not as well characterized as the mitochondria, the chloroplasts have been shown to induce light-dependent PCD through singlet oxygen species (1O2) that may function in parallel to mitochondrial-mediated PCD at an early step in initiating the rupture of the vacuole [3].

 

A specialized form of plant cell death called hypersensitive response (HR) is initiated as a defense response to pathogen infection. HR shares morphological features and molecular mechanisms reminiscent of both pyroptosis and necroptosis [4]. Moreover, HR is unique in that it induces a signaling cascade to propagate immunity in neighboring cells as well as priming distal tissues for potential pathogen challenge, a phenomenon known as systemic acquired resistance [5]. Here we will briefly describe diverse plant disease resistance pathways, early molecular events during pathogen perception, and downstream signaling components. We will thoroughly discuss how pathogens have evolved strategies to circumvent and/or suppress diverse immune responses, in particular plant cell death. While many of these mechanisms involve indirect disabling of upstream immune responses to avoid cell death, direct manipulation of PCD regulators by pathogen effectors has not been extensively explored in the literature, and will be the focal point of this article.


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Rakesh Yashroy's curator insight, July 27, 10:06 PM
Good description of APOPTOSIS in animal and plant cells. Gram negative pathogens like Salmonella use their outer membrane vesicles to signal hijacking and apoptosis in defense macrophages in animal body @ http://s3.amazonaws.com/academia.edu.documents/33932139/1211.pdf?AWSAccessKeyId=AKIAJ56TQJRTWSMTNPEA&Expires=1469674971&Signature=0HXlHa3eNfInsWTE0YqGOgD6HTA%3D&response-content-disposition=inline%3B%20filename%3DYashRoy_R_C_2007_Mechanism_of_infection.pdf
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Annu Rev Phytopathology: Plant Pathogen Effectors: Cellular Probes Interfering with Plant Defenses in Spatial and Temporal Manners (2016)

Annu Rev Phytopathology: Plant Pathogen Effectors: Cellular Probes Interfering with Plant Defenses in Spatial and Temporal Manners (2016) | Plant and their microbe symbionts | Scoop.it

Plants possess large arsenals of immune receptors capable of recognizing all pathogen classes. To cause disease, pathogenic organisms must be able to overcome physical barriers, suppress or evade immune perception, and derive nutrients from host tissues. Consequently, to facilitate some of these processes, pathogens secrete effector proteins that promote colonization. This review covers recent advances in the field of effector biology, focusing on conserved cellular processes targeted by effectors from diverse pathogens. The ability of effectors to facilitate pathogen entry into the host interior, suppress plant immune perception, and alter host physiology for pathogen benefit is discussed. Pathogens also deploy effectors in a spatial and temporal manner, depending on infection stage. Recent advances have also enhanced our understanding of effectors acting in specific plant organs and tissues. Effectors are excellent cellular probes that facilitate insight into biological processes as well as key points of vulnerability in plant immune signaling networks.


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bioRxiv: Tomato I2 immune receptor can be engineered to confer partial resistance to the oomycete Phytophthora infestans in addition to the fungus Fusarium oxysporum (2015)

bioRxiv: Tomato I2 immune receptor can be engineered to confer partial resistance to the oomycete Phytophthora infestans in addition to the fungus Fusarium oxysporum (2015) | Plant and their microbe symbionts | Scoop.it

Plants and animals rely on immune receptors, known as nucleotide-binding domain and leucine-rich repeat containing proteins (NB-LRR or NLR), to defend against invading pathogens and activate immune responses. How NLR receptors respond to pathogens is inadequately understood. We previously reported single-residue mutations that expand the response of the potato immune receptor R3a to AVR3aEM, a stealthy effector from the late blight oomycete pathogen Phytophthora infestans. I2, another NLR that mediates resistance to the wilt causing fungus Fusarium oxysporum f. sp. lycopersici, is the tomato ortholog of R3a. We transferred previously identified R3a mutations to I2 to assess the degree to which the resulting I2 mutants have an altered response. We discovered that wild-type I2 protein responds weakly to AVR3a. One mutant in the N-terminal coiled-coil domain, I2I141N, appeared sensitized and displayed markedly increased response to AVR3a. Remarkably, I2I141N conferred partial resistance to P. infestans. Further, I2I141N has an expanded response spectrum to F. oxysporum f. sp. lycopersici effectors compared to the wild-type I2 protein. Our results suggest that synthetic immune receptors can be engineered to confer resistance to phylogenetically divergent pathogens and indicate that knowledge gathered for one NLR could be exploited to improve NLRs from other plant species.


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New Phytologist: Host–microbe and microbe–microbe interactions in the evolution of obligate plant parasitism

New Phytologist: Host–microbe and microbe–microbe interactions in the evolution of obligate plant parasitism | Plant and their microbe symbionts | Scoop.it

Research on obligate biotrophic plant parasites, which reproduce only on living hosts, has revealed a broad diversity of filamentous microbes that have independently acquired complex morphological structures, such as haustoria. Genome studies have also demonstrated a concerted loss of genes for metabolism and lytic enzymes, and gain of diversity of genes coding for effectors involved in host defense suppression. So far, these traits converge in all known obligate biotrophic parasites, but unexpected genome plasticity remains. This plasticity is manifested as transposable element (TE)-driven increases in genome size, observed to be associated with the diversification of virulence genes under selection pressure. Genome expansion could result from the governing of the pathogen response to ecological selection pressures, such as host or nutrient availability, or to microbial interactions, such as competition, hyperparasitism and beneficial cooperations. Expansion is balanced by alternating sexual and asexual cycles, as well as selfing and outcrossing, which operate to control transposon activity in populations. In turn, the prevalence of these balancing mechanisms seems to be correlated with external biotic factors, suggesting a complex, interconnected evolutionary network in host–pathogen–microbe interactions. Therefore, the next phase of obligate biotrophic pathogen research will need to uncover how this network, including multitrophic interactions, shapes the evolution and diversity of pathogens.


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Plantago powdery mildews: diverse coinfections are more successful

 http://rdcu.be/bWYM

 

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Frontiers: A novel conserved mechanism for plant NLR protein pairs: the ‘integrated decoy’ hypothesis (2014)

Frontiers: A novel conserved mechanism for plant NLR protein pairs: the ‘integrated decoy’ hypothesis (2014) | Plant and their microbe symbionts | Scoop.it

Plant immunity is often triggered by the specific recognition of pathogen effectors by intracellular nucleotide-binding, leucine-rich repeat (NLR) receptors. Plant NLRs contain an N-terminal signaling domain that is mostly represented by either a Toll-interleukin1 receptor (TIR) domain or a coiled coil (CC) domain. In many cases, single NLR proteins are sufficient for both effector recognition and signaling activation. However, many paired NLRs have now been identified where both proteins are required to confer resistance to pathogens. Recent detailed studies on the Arabidopsis thaliana TIR-NLR pair RRS1 and RPS4 and on the rice CC-NLR pair RGA4 and RGA5 have revealed for the first time how such protein pairs function together. In both cases, the paired partners interact physically to form a hetero-complex receptor in which each partner plays distinct roles in effector recognition or signaling activation, highlighting a conserved mode of action of NLR pairs across both monocotyledonous and dicotyledonous plants. We also discuss a new ‘integrated decoy’ effector recognition model to describe these receptor complexes that may be common to many other plant NLR pairs.


Via Kamoun Lab @ TSL
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Elsa Ballini's curator insight, October 29, 2014 4:21 AM

In Rice/Magnaporthe an example is RGA4-RGA5

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1471-2164-15-891.pdf

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Another instance on transposons as genomic symbionts rather than parasites

 

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Differential accumulation of callose, arabinoxylan and cellulose in nonpenetrated versus penetrated papillae on leaves of barley infected with Blumeria graminis f. sp. hordei - Chowdhury - 2014 - N...

Differential accumulation of callose, arabinoxylan and cellulose in nonpenetrated versus penetrated papillae on leaves of barley infected with Blumeria graminis f. sp. hordei - Chowdhury - 2014 - N... | Plant and their microbe symbionts | Scoop.it
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Are papillae the key to cell penetration?

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Storify: #NPW10 Origin and evolution of plants and their interactions with fungi. 9–10 September 2014


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