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Rescooped by Yogesh Gupta from Plant pathogenic fungi
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Distinct domains of the AVRPM3A2/F2 avirulence protein from wheat powdery mildew are involved in immune receptor recognition and putative effector function - McNally - 2018 - New Phytologist -

Recognition of the AVRPM3A2/F2 avirulence protein from powdery mildew by the wheat PM3A/F immune receptor induces a hypersensitive response after co‐expression in Nicotiana benthamiana. The molecular determinants of this interaction and how they shape natural AvrPm3a2/f2 allelic diversity are unknown.
We sequenced the AvrPm3a2/f2 gene in a worldwide collection of 272 mildew isolates. Using the natural polymorphisms of AvrPm3a2/f2 as well as sequence information from related gene family members, we tested 85 single‐residue‐altered AVRPM3A2/F2 variants with PM3A, PM3F and PM3FL456P/Y458H (modified for improved signaling) in Nicotiana benthamiana for effects on recognition.
An intact AvrPm3a2/f2 gene was found in all analyzed isolates and the protein variant recognized by PM3A/F occurred globally at high frequencies. Single‐residue alterations in AVRPM3A2/F2 mostly disrupted, but occasionally enhanced, the recognition response by PM3A, PM3F and PM3FL456P/Y458H. Residues enhancing hypersensitive responses constituted a protein domain separate from both naturally occurring polymorphisms and positively selected residues of the gene family.
These results demonstrate the utility of using gene family sequence diversity to screen residues for their role in recognition. This approach identified a putative interaction surface in AVRPM3A2/F2 not polymorphic in natural alleles. We conclude that molecular mechanisms besides recognition drive AvrPm3a2/f2 diversification.

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Fungal G-protein-coupled receptors: mediators of pathogenesis and targets for disease control | Nature Microbiology

Fungal G-protein-coupled receptors: mediators of pathogenesis and targets for disease control | Nature Microbiology | Plant Pathogens | Scoop.it
G-protein signaling pathways are involved in sensing the environment, enabling fungi to coordinate cell function, metabolism and development with their surroundings, thereby promoting their survival, propagation, and virulence. G-protein-coupled receptors (GPCRs) are the largest class of cell surface receptors in fungi. Despite the apparent importance of GPCR signaling to fungal biology and virulence, relatively few GPCR–G-protein interactions, and even fewer receptor-binding ligands, have been identified. Approximately 40% of current pharmaceuticals target human GPCRs, due to their cell surface location and central role in cell signaling. Fungal GPCRs do not belong to any of the mammalian receptor classes, making them druggable targets for antifungal development. This Review Article evaluates developments in our understanding of fungal GPCR-mediated signaling while substantiating the rationale for considering these receptors as potential antifungal targets. The need for insights into the structure-function relationship of receptor-ligand interactions is highlighted, which could facilitate the development of receptor-interfering compounds that could be used in disease control.
 
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Exploring and exploiting the boundaries of host specificity using the cereal rust and mildew models - Dracatos - 2018 - New Phytologist - Wiley Online Library

Exploring and exploiting the boundaries of host specificity using the cereal rust and mildew models - Dracatos - 2018 - New Phytologist - Wiley Online Library | Plant Pathogens | Scoop.it
Individual plants encounter a vast number of microbes including bacteria, viruses, fungi, and oomycetes through their growth cycle, yet few of these pathogens are able to infect them.Plant species have diverged over millions of years, co-evolving with few specific pathogens.The host boundaries of most pathogen species can be clearly defined. In general, the greater the genetic divergence from the preferred host, the less likely that pathogen would be able to infect that plant species. Co-evolution and divergence also occur within pathogen species, leading to highly specialized subspecies with narrow host ranges. For example, cereal rust and mildew pathogens (Puccinia and Blumeria spp.) display high host specificity as a result of ongoing co-evolution with a narrow range of grass species. In rare cases, however, some plant species are in a transition from host to nonhost or are intermediate hosts (near nonhost). Barley was reported as a useful model for genetic and molecular studies of nonhost resistance due to rare susceptibility to numerous heterologous rust and mildew fungi. This review evaluates host specificity in numerous Puccinia/Blumeria–cereal pathosystems and discusses various approaches for transferring nonhost resistance (NHR) genes between crop species to reduce the impact of important diseases in food production
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Deciphering interfungal relationships in the 410-million-yr-old Rhynie chert: Glomoid spores under attack

Deciphering interfungal relationships in the 410-million-yr-old Rhynie chert: Glomoid spores under attack | Plant Pathogens | Scoop.it
Various types of other fungi colonize glomeromycotinan (Mucoromycota) spores in the Early Devonian Rhynie chert. However, relatively few of these associations have been described and evaluated in detail. One particular type of glomoid spore located in degrading land plant axes from the Rhynie chert provides evidence of (simultaneous) interaction with three different fungi. Massive callosities occur around the intrusion filaments of a chytrid-like parasite with epibiotic sporangia, while the hyphae of a delicate mycelial fungus extend into the spore lumen without triggering a recognizable host response. Several spores show large numbers of inwardly directed projections, which are regularly distributed and consist of a short hyphal branch encased in host wall material. The projections represent the penetration sites of a distinctive, mycelial fungus that forms a mantle-like hyphal sheath around the spores. This type of fungal interaction with glomeromycotinan spores has not previously been reported, and thus expands our knowledge of the numerous interfungal relationships that existed in early continental ecosystems.


Via Jean-Michel Ané
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Cryo-EM structure of the exocyst complex

Cryo-EM structure of the exocyst complex | Plant Pathogens | Scoop.it

The exocyst is an evolutionarily conserved octameric protein complex that mediates the tethering of post-Golgi secretory vesicles to the plasma membrane during exocytosis and is implicated in many cellular processes such as cell polarization, cytokinesis, ciliogenesis and tumor invasion. Using cryo-EM and chemical cross-linking MS (CXMS), we solved the structure of the Saccharomyces cerevisiae exocyst complex at an average resolution of 4.4 Å. Our model revealed the architecture of the exocyst and led to the identification of the helical bundles that mediate the assembly of the complex at its core. Sequence analysis suggests that these regions are evolutionarily conserved across eukaryotic systems. Additional cell biological data suggest a mechanism for exocyst assembly that leads to vesicle tethering at the plasma membrane.

 
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Sustaining global agriculture through rapid detection and deployment of genetic resistance to deadly crop diseases

Sustaining global agriculture through rapid detection and deployment of genetic resistance to deadly crop diseases | Plant Pathogens | Scoop.it

Genetically encoded resistance is a major component of crop disease management. Historically, gene loci conferring resistance to pathogens have been identified through classical genetic methods. In recent years, accelerated gene cloning strategies have become available through advances in sequencing, gene capture and strategies for reducing genome complexity. Here, I describe these approaches with key emphasis on the isolation of resistance genes to the cereal crop diseases that are an ongoing threat to global food security. Rapid gene isolation enables their efficient deployment through marker-assisted selection and transgenic technology. Together with innovations in genome editing and progress in pathogen virulence studies, this creates further opportunities to engineer long-lasting resistance. These approaches will speed progress towards a future of farming using fewer pesticides.

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Transcriptome based analyses of phosphite mediated suppression of rust pathogens, Puccinia emaculata and Phakopsora pachyrhizi, and functional characterization of selected fungal target genes

Transcriptome based analyses of phosphite mediated suppression of rust pathogens, Puccinia emaculata and Phakopsora pachyrhizi, and functional characterization of selected fungal target genes | Plant Pathogens | Scoop.it

Phosphite (Phi) is commercially used to manage diseases mainly caused by Oomycetes, primarily due to its low-cost compared to other fungicides, and persistent control of oomycetous pathogens. We explored the use of Phi in controlling fungal pathogens Puccinia emaculata and Phakopsora pachyrhizi the causal agents of the switchgrass rust and the Asian soybean rust, respectively. Phi primes host defenses and efficiently inhibits growth of P. emaculata, P. pachyrhizi, and several other fungal pathogens tested. To understand the Phi-mediated effects, a detailed molecular analysis was undertaken in both the host and the pathogen. Transcriptomic studies in switchgrass revealed that Phi activates plant defense signaling as early as 1 h after application, by increasing the expression of several cytoplasmic and membrane receptor like kinases and defense related genes within 24 h of application. Unlike Oomycetes, RNA sequencing (RNAseq) of P. emaculata and P. pachyrhizi did not exhibit Phi-mediated retardation of cell wall biosynthesis in these pathogens. The genes with reduced expression in either or both rust fungi belonged to functional categories such as ribosomal protein, actin, RNA-dependent RNA polymerase, and aldehyde dehydrogenase. A few P. emaculata genes that had reduced expression upon Phi treatment were further characterized. Application of double-stranded (ds) RNAs specific to P. emaculata genes encoding Glutamate N-acetyltransferase and Cystathionine gamma-synthase to switchgrass leaves resulted in reduced disease severity upon P. emaculata inoculation, suggesting their role in pathogen survival and/or pathogenesis.


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A role for small RNA in regulating innate immunity during plant growth

A role for small RNA in regulating innate immunity during plant growth | Plant Pathogens | Scoop.it
Author summary In plants, nucleotide-binding (NB) leucine-rich repeat (LRR) receptors (NLR) mediate pathogen-specific effector triggered immunity and are widely used in breeding to generate pathogen-resistant crops. However, dysregulation of NLR expression can inhibit plant growth and how NLR expression and function are regulated in different stages of plant growth is poorly understood. Using a high-throughput sequencing and bioinformatics approach, we found an overall increase in NLR expression, but expression of NLR-targeting sRNA during plant growth was decreased. We also used resistance to tobacco mosaic virus (TMV) mediated by the resistance gene N as a model system to study the biological significance of growth regulation of NLR by miRNAs. We found that N-mediated TMV immunity strengthened and N transcript levels increased during plant maturation. Using genetic analysis, we showed that up-regulation of N was due to transcriptional down-regulation of the N-targeting miR6019/6020 cluster during plant growth. We also showed that sRNA-mediated growth regulation of N expression and function was conserved between tobacco and tomato plants. This study therefore reveals a role for miRNAs in regulating innate immunity during plant growth.
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RNA-Seq differential expression analysis: An extended review and a software tool

RNA-Seq differential expression analysis: An extended review and a software tool | Plant Pathogens | Scoop.it
The correct identification of differentially expressed genes (DEGs) between specific conditions is a key in the understanding phenotypic variation. High-throughput transcriptome sequencing (RNA-Seq) has become the main option for these studies. Thus, the number of methods and softwares for differential expression analysis from RNA-Seq data also increased rapidly. However, there is no consensus about the most appropriate pipeline or protocol for identifying differentially expressed genes from RNA-Seq data. This work presents an extended review on the topic that includes the evaluation of six methods of mapping reads, including pseudo-alignment and quasi-mapping and nine methods of differential expression analysis from RNA-Seq data. The adopted methods were evaluated based on real RNA-Seq data, using qRT-PCR data as reference (gold-standard). As part of the results, we developed a software that performs all the analysis presented in this work, which is freely available at https://github.com/costasilvati/consexpression. The results indicated that mapping methods have minimal impact on the final DEGs analysis, considering that adopted data have an annotated reference genome. Regarding the adopted experimental model, the DEGs identification methods that have more consistent results were the limma+voom, NOIseq and DESeq2. Additionally, the consensus among five DEGs identification methods guarantees a list of DEGs with great accuracy, indicating that the combination of different methods can produce more suitable results. The consensus option is also included for use in the available software.
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A plant effector‐triggered immunity signaling sector is inhibited by pattern‐triggered immunity

A plant effector‐triggered immunity signaling sector is inhibited by pattern‐triggered immunity | Plant Pathogens | Scoop.it
Since signaling machineries for two modes of plant‐induced immunity, pattern‐triggered immunity (PTI) and effector‐triggered immunity (ETI), extensively overlap, PTI and ETI signaling likely interact. In an Arabidopsis quadruple mutant, in which four major sectors of the signaling network, jasmonate, ethylene, PAD4, and salicylate, are disabled, the hypersensitive response (HR) typical of ETI is abolished when the Pseudomonas syringae effector AvrRpt2 is bacterially delivered but is intact when AvrRpt2 is directly expressed in planta. These observations led us to discovery of a network‐buffered signaling mechanism that mediates HR signaling and is strongly inhibited by PTI signaling. We named this mechanism the ETI‐Mediating and PTI‐Inhibited Sector (EMPIS). The signaling kinetics of EMPIS explain apparently different plant genetic requirements for ETI triggered by different effectors without postulating different signaling machineries. The properties of EMPIS suggest that information about efficacy of the early immune response is fed back to the immune signaling network, modulating its activity and limiting the fitness cost of unnecessary immune responses.
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Bacterial endosymbionts influence host sexuality and reveal reproductive genes of early divergent fungi

Bacterial endosymbionts influence host sexuality and reveal reproductive genes of early divergent fungi | Plant Pathogens | Scoop.it
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Do fungi have an innate immune response? An NLR-based comparison to plant and animal immune systems

Do fungi have an innate immune response? An NLR-based comparison to plant and animal immune systems | Plant Pathogens | Scoop.it
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Prediction of protein–protein interactions between fungus ( Magnaporthe grisea ) and rice ( Oryza sativa L.) | Briefings in Bioinformatics | Oxford Academic

Prediction of protein–protein interactions between fungus ( Magnaporthe grisea ) and rice ( Oryza sativa  L.) | Briefings in Bioinformatics | Oxford Academic | Plant Pathogens | Scoop.it

Rice blast disease caused by the fungus Magnaporthe grisea (M. grisea) is one of the most serious diseases for the cultivated rice Oryza sativa (O. sativa). A key factor causing rice blast disease and defense might be protein–protein interactions (PPIs) between rice and fungus. In this research, we have developed a computational pipeline to predict PPIs between blast fungus and rice. After cross-prediction by interolog-based and domain-based method, we achieved 532 potential PPIs between 27 fungus proteins and 236 rice proteins. Accuracy of jackknife test, 10-fold cross-validation test and independent test for these PPIs were 90.43, 93.85 and 84.67%, respectively, by using support vector machine classification method. Meanwhile, the pathogenic genes of blast fungus were enriched in the predicted PPIs network when compared with 1000 random interaction networks. The rice regulatory network was downloaded and divided into 228 subnetworks with over six nodes, and the top seven subnetworks affected by blast fungus through PPIs were investigated. The results indicated that 34 upregulated and 12 downregulated master regulators in rice interacting with the fungus proteins in response to the infection of blast fungus. The common master regulators in rice in response to the infection of M. grisea, Xanthomonas oryzae pv.oryzae and rice stripe virus were analyzed. The ubiquitin proteasome pathway was the common pathway in rice regulated by these three pathogens, while apoptosis signaling pathway was induced by fungus and bacteria. In summary, the results in this article provide insight into the process of blast fungus infection.

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The transcription factor PstSTE12 is required for virulence of Puccinia striiformis f. sp. tritici - Zhu - 2018 - Molecular Plant Pathology -

The transcription factor PstSTE12 is required for virulence of Puccinia striiformis f. sp. tritici - Zhu - 2018 - Molecular Plant Pathology - | Plant Pathogens | Scoop.it
Puccinia striiformis f. sp. tritici (Pst) is an obligate biotrophic fungus that causes extensive damage in wheat. The pathogen is now known to be a heteroecious fungus with an intricate life cycle containing sexual and asexual stages. Orthologues of the STE12 transcription factor that regulate mating and filamentation in Saccharomyces cerevisiae, as well as virulence in other fungi, have been extensively described. Because reliable transformation and gene disruption methods are lacking for Pst, knowledge about the function of its STE12 orthologue is limited. In this study, we identified a putative orthologue of STE12 from Pst in haustoria‐enriched transcripts and designated it as PstSTE12. The gene encodes a protein of 879 amino acids containing three helices in the homeodomain, conserved phenylalanine and tryptophan sites, and two C2/H2‐Zn2+ finger domains. Real‐time reverse transcription‐polymerase chain reaction (RT‐PCR) analyses revealed that the expression of PstSTE12 was highly induced during the early infection stages and peaked during haustorium formation and the pycniospore stage in the aecial host barberry. Subcellular localization assays indicated that PstSTE12 is localized in the nucleus and functions as a transcriptional activator. Yeast one‐hybrid assays revealed that PstSTE12 exhibits transcriptional activity, and that its C‐terminus is necessary for the activation of transcription. PstSTE12 complemented the mating defect in an α ste12 mutant of S. cerevisiae. In addition, it partially complemented the defects of the Magnaporthe oryzae mst12 mutant in plant infection. Knocking down PstSTE12 via host‐induced gene silencing (HIGS) mediated by Barley stripe mosaic virus (BSMV) resulted in a substantial reduction in the growth and spread of hyphae in Pst and weakened the virulence of Pst on wheat. Our results suggest that PstSTE12 probably acts at an intersection participating in the invasion and mating processes of Pst, and provide new insights into the comprehension of the variation of virulence in cereal rust fungi.

Via Steve Marek
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Out of Water: The Origin and Early Diversification of Plant R-Genes

Out of Water: The Origin and Early Diversification of Plant R-Genes | Plant Pathogens | Scoop.it
During plant-pathogen interactions, plants use intracellular proteins with nucleotide-binding site and leucine-rich repeat (NBS-LRR) domains to detect pathogens. NBS-LRR proteins represent a major class of plant disease resistance genes (R-genes). Whereas R-genes have been well characterized in angiosperms, little is known about their origin and early diversification. Here we perform comprehensive evolutionary analyses of R-genes in plants and report the identification of R-genes in basal-branching streptophytes, including charophytes, liverworts, and mosses. Phylogenetic analyses suggest that plant R-genes originated in charophytes and R-proteins diversified into TIR-NBS-LRR proteins (TNLs) and non-TIR-NBS-LRR proteins (nTNLs) in charophytes. Moreover, we show that plant R-proteins evolved in a modular fashion through frequent gain or loss of protein domains. Most of the R-genes in basal-branching streptophytes underwent adaptive evolution, indicating an ancient involvement of R-genes in plant-pathogen interactions. Our findings provide novel insights into the origin and evolution of R-genes and the mechanisms underlying colonization of terrestrial environments by plants.
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Stromule extension along microtubules coordinated with actin-mediated anchoring guides perinuclear chloroplast movement during innate immunity

Stromule extension along microtubules coordinated with actin-mediated anchoring guides perinuclear chloroplast movement during innate immunity | Plant Pathogens | Scoop.it

Dynamic tubular extensions from chloroplasts called stromules have recently been shown to connect with nuclei and function during innate immunity. We demonstrate that stromules extend along microtubules (MTs) and MT organization directly affects stromule dynamics since stabilization of MTs chemically or genetically increases stromule numbers and length. Although actin filaments (AFs) are not required for stromule extension, they provide anchor points for stromules. Interestingly, there is a strong correlation between the direction of stromules from chloroplasts and the direction of chloroplast movement. Stromule-directed chloroplast movement was observed in steady-state conditions without immune induction, suggesting it is a general function of stromules in epidermal cells. Our results show that MTs and AFs may facilitate perinuclear clustering of chloroplasts during an innate immune response. We propose a model in which stromules extend along MTs and connect to AF anchor points surrounding nuclei, facilitating stromule-directed movement of chloroplasts to nuclei during innate immunity.

 
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Superresolution and pulse-chase imaging reveal the role of vesicle transport in polar growth of fungal cells

Superresolution and pulse-chase imaging reveal the role of vesicle transport in polar growth of fungal cells | Plant Pathogens | Scoop.it

Polarized growth of filamentous fungi requires continuous transport of biomolecules to the hyphal tip. To this end, construction materials are packaged in vesicles and transported by motor proteins along microtubules and actin filaments. We have studied these processes with quantitative superresolution localization microscopy of live Aspergillus nidulans cells expressing the photoconvertible protein mEosFP thermo fused to the chitin synthase ChsB. ChsB is mainly located at the Spitzenkörper near the hyphal tip and produces chitin, a key component of the cell wall. We have visualized the pulsatory dynamics of the Spitzenkörper, reflecting vesicle accumulation before exocytosis and their subsequent fusion with the apical plasma membrane. Furthermore, high-speed pulse-chase imaging after photoconversion of mEosFP thermo in a tightly focused spot revealed that ChsB is transported with two different speeds from the cell body to the hyphal tip and vice versa. Comparative analysis using motor protein deletion mutants allowed us to assign the fast movements (7 to 10 μm s−1) to transport of secretory vesicles by kinesin-1, and the slower ones (2 to 7 μm s−1) to transport by kinesin-3 on early endosomes. Our results show how motor proteins ensure the supply of vesicles to the hyphal tip, where temporally regulated exocytosis results in stepwise tip extension.

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Population genomic footprints of host adaptation, introgression and recombination in Coffee Leaf Rust

Population genomic footprints of host adaptation, introgression and recombination in Coffee Leaf Rust | Plant Pathogens | Scoop.it

Coffee Leaf Rust, caused by Hemileia vastatrix (Hv), represents the biggest threat to coffee production worldwide and ranks amongst the most serious fungal diseases in history. Despite a recent series of outbreaks and emergence of hyper-virulent strains, the population evolutionary history and potential of this pathogen remains poorly understood. To address this issue, we used RADseq to generate ∼19,000 SNPs across a worldwide collection of 37 Hv samples. Contrarily to the longstanding idea that Hv represents a genetically unstructured and cosmopolitan species, our results reveal the existence of a cryptic species complex with marked host tropism. Using phylogenetic and pathological data, we show that one of these lineages (C3) infects almost exclusively the most economically valuable coffee species (tetraploids that include Coffea arabica and inter-specific hybrids) while the other lineages (C1-C2) are severely maladapted to these hosts but successfully infect diploid coffee species. Population dynamic analyses suggest that the C3 group may be a recent “domesticated” lineage that emerged via host-shift from diploid coffee hosts. We also found evidence of recombination occurring within this group, which could explain the high pace of pathotype emergence despite the low genetic variation. Moreover, genomic footprints of introgression between the C3 and C2 groups were discovered and raise the possibility that virulence factors may be quickly exchanged between groups with different pathogenic abilities. This work advances our understanding on the evolutionary strategies used by plant pathogens in agro-ecosystems with direct and far-reaching implications for disease control.

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Pangenome analyses of the wheat pathogen Zymoseptoria tritici reveal the structural basis of a highly plastic eukaryotic genome

Pangenome analyses of the wheat pathogen Zymoseptoria tritici reveal the structural basis of a highly plastic eukaryotic genome | Plant Pathogens | Scoop.it
Structural variation contributes substantially to polymorphism within species. Chromosomal rearrangements that impact genes can lead to functional variation among individuals and influence the expression of phenotypic traits. Genomes of fungal pathogens show substantial chromosomal polymorphism that can drive virulence evolution on host plants. Assessing the adaptive significance of structural variation is challenging, because most studies rely on inferences based on a single reference genome sequence. We constructed and analyzed the pangenome of Zymoseptoria tritici, a major pathogen of wheat that evolved host specialization by chromosomal rearrangements and gene deletions. We used single-molecule real-time sequencing and high-density genetic maps to assemble multiple genomes. We annotated the gene space based on transcriptomics data that covered the infection life cycle of each strain. Based on a total of five telomere-to-telomere genomes, we constructed a pangenome for the species and identified a core set of 9149 genes. However, an additional 6600 genes were exclusive to a subset of the isolates. The substantial accessory genome encoded on average fewer expressed genes but a larger fraction of the candidate effector genes that may interact with the host during infection. We expanded our analyses of the pangenome to a worldwide collection of 123 isolates of the same species. We confirmed that accessory genes were indeed more likely to show deletion polymorphisms and loss-of-function mutations compared to core genes. The pangenome construction of a highly polymorphic eukaryotic pathogen showed that a single reference genome significantly underestimates the gene space of a species. The substantial accessory genome provides a cradle for adaptive evolution.
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How to make a tumour: cell type specific dissection of Ustilago maydis‐induced tumour development in maize leaves

How to make a tumour: cell type specific dissection of Ustilago maydis‐induced tumour development in maize leaves | Plant Pathogens | Scoop.it

The biotrophic fungus Ustilago maydis causes smut disease on maize (Zea mays), which is characterized by immense plant tumours. To establish disease and reprogram organ primordia to tumours, U. maydis deploys effector proteins in an organ-specific manner. However, the cellular contribution to leaf tumours remains unknown. 


We investigated leaf tumour formation at the tissue- and cell type-specific levels. Cytology and metabolite analysis were deployed to understand the cellular basis for tumourigenesis. Laser-capture microdissection was performed to gain a cell type-specific transcriptome of U. maydis during tumour formation. 


In vivo visualization of plant DNA synthesis identified bundle sheath cells as the origin of hyperplasic tumour cells, while mesophyll cells become hypertrophic tumour cells. Cell type-specific transcriptome profiling of U. maydis revealed tailored expression of fungal effector genes. Moreover, U. maydis See1 was identified as the first cell type-specific fungal effector, being required for induction of cell cycle reactivation in bundle sheath cells. 


Identification of distinct cellular mechanisms in two different leaf cell types and of See1 as an effector for induction of proliferation of bundle sheath cells are major steps in understanding U. maydis-induced tumour formation. Moreover, the cell type-specific U. maydis transcriptome data are a valuable resource to the scientific community.


Via Steve Marek, Francis Martin, Ronny Kellner
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Symbiotic root infections in Medicago truncatula require remorin-mediated receptor stabilization in membrane nanodomains

Symbiotic root infections in Medicago truncatula require remorin-mediated receptor stabilization in membrane nanodomains | Plant Pathogens | Scoop.it

Plant cell infection is tightly controlled by cell surface receptor-like kinases (RLKs) Alike other RLKs the Medicago truncatula entry receptor LYK3 laterally segregates into membrane nanodomains in a stimulus-dependent manner. Although nanodomain localization arises as a generic feature of plant membrane proteins, molecular mechanisms underlying such dynamic transitions and their functional relevance remained poorly understood. Here, we demonstrate that actin and the flotillin protein FLOT4 form the primary and indispensable core of a specific nanodomain. Infection-dependent induction of the remorin protein and secondary molecular scaffold SYMREM1 results in subsequent recruitment of ligand-activated LYK3 and its stabilization within these membrane subcompartments. Reciprocally, the majority of this LYK3 receptor pool is destabilized at the plasma membrane and undergoes rapid endocytosis in symrem1 mutants upon rhizobial inoculation resulting in premature abortion of host cell infections. These data reveal that receptor recruitment into nanodomains is indispensable for their function during host cell infection.

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bioRxiv: Extremely flexible infection programs in a fungal plant pathogen (2017)

bioRxiv: Extremely flexible infection programs in a fungal plant pathogen (2017) | Plant Pathogens | Scoop.it

Filamentous plant pathogens exhibit extraordinary levels of genomic variability that is proposed to facilitate rapid adaptation to changing host environments. However, the impact of genomic variation on phenotypic differentiation in pathogen populations is largely unknown. Here, we address the extent of variability in infection phenotypes of the hemibiotrophic wheat pathogen Zymoseptoria tritici by studying three field isolates collected in Denmark, Iran, and the Netherlands. These three isolates differ extensively in genome structure and gene content, but produce similar disease symptoms in the same susceptible wheat cultivar. Using advanced confocal microscopy, staining of reactive oxygen species, and comparative analyses of infection stage-specific RNA-seq data, we demonstrate considerable variation in the temporal and spatial course of infection of the three isolates. Based on microscopic observation, we determined four core infection stages: establishment, biotrophic growth, lifestyle transition, and necrotrophic growth and asexual reproduction. Comparative analyses of the fungal transcriptomes, sequenced for every infection stage, revealed that the gene expression profiles of the isolates differed significantly, and 20% of the genes are differentially expressed between the three isolates during infection. The genes exhibiting isolate-specific expression patterns are enriched in genes encoding effector candidates that are small, secreted, cysteine-rich proteins and putative virulence determinants. Moreover, the differentially expressed genes were located significantly closer to transposable elements, which are enriched for the heterochromatin-associated histone marks H3K9me3 and H3K27me3 on the accessory chromosomes. This observation indicates that transposable elements and epigenetic regulation contribute to the infection-associated transcriptional variation between the isolates. Our findings illustrate how high genetic diversity in a pathogen population can result in highly differentiated infection and expression phenotypes that can support rapid adaptation in changing environments. Furthermore, our study reveals an exceptionally high extent of plasticity in the infection program of an important wheat pathogen and shows a substantial redundancy in infection-related gene expression.


Via Kamoun Lab @ TSL
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Sequestration and activation of plant toxins protect the western corn rootworm from enemies at multiple trophic levels

Sequestration and activation of plant toxins protect the western corn rootworm from enemies at multiple trophic levels | Plant Pathogens | Scoop.it

Highly adapted herbivores can phenocopy two-component systems by stabilizing, sequestering and reactivating plant toxins. However, whether these traits protect herbivores against their enemies is poorly understood. We demonstrate that the western corn rootworm Diabrotica virgifera virgifera, the most damaging maize pest on the planet, specifically accumulates the root-derived benzoxazinoid glucosides HDMBOA-Glc and MBOA-Glc. MBOA-Glc is produced by D. virgifera through stabilization of the benzoxazinoid breakdown product MBOA by N-glycosylation. The larvae can hydrolyze HDMBOA-Glc, but not MBOA-Glc, to produce toxic MBOA upon predator attack. Accumulation of benzoxazinoids renders D. virgifera highly resistant to nematodes which inject and feed on entomopathogenic symbiotic bacteria. While HDMBOA-Glc and MBOA reduce the growth and infectivity of both the nematodes and the bacteria, MBOA-Glc repels infective juvenile nematodes. Our results illustrate how herbivores combine stabilized and reactivated plant toxins to defend themselves against a deadly symbiosis between the third and the fourth trophic level enemies.

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Effectors involved in fungal–fungal interaction lead to a rare phenomenon of hyperbiotrophy in the tritrophic system biocontrol agent–powdery mildew–plant

Effectors involved in fungal–fungal interaction lead to a rare phenomenon of hyperbiotrophy in the tritrophic system biocontrol agent–powdery mildew–plant | Plant Pathogens | Scoop.it

Tritrophic interactions involving a biocontrol agent, a pathogen and a plant have been analyzed predominantly from the perspective of the biocontrol agent. We have conducted the first comprehensive transcriptomic analysis of all three organisms in an effort to understand the elusive properties of Pseudozyma flocculosa in the context of its biocontrol activity against Blumeria graminis f.sp. hordei as it parasitizes Hordeum vulgare. After inoculation of P. flocculosa, the tripartite interaction was monitored over time and samples collected for scanning electron microscopy and RNA sequencing. Based on our observations, P. flocculosa indirectly parasitizes barley, albeit transiently, by diverting nutrients extracted by B. graminis from barley leaves through a process involving unique effectors. This brings novel evidence that such molecules can also influence fungal–fungal interactions. Their release is synchronized with a higher expression of powdery mildew haustorial effectors, a sharp decline in the photosynthetic machinery of barley and a developmental peak in P. flocculosa. The interaction culminates with a collapse of B. graminis haustoria, thereby stopping P. flocculosa growth, as barley plants show higher metabolic activity. To conclude, our study has uncovered a complex and intricate phenomenon, described here as hyperbiotrophy, only achievable through the conjugated action of the three protagonists.


Via Steve Marek
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New insights into plant–microbe interactions through advances in fungal genetics

New insights into plant–microbe interactions through advances in fungal genetics | Plant Pathogens | Scoop.it
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