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European Journal of Plant Pathology (2018): Small RNA molecules and their role in plant disease

European Journal of Plant Pathology (2018): Small RNA molecules and their role in plant disease | WU_Phyto-Publications | Scoop.it

All plant species are subject to disease. Plant diseases are caused by parasites, e.g. viruses, bacteria, oomycetes, parasitic plants, fungi, or nematodes. In all organisms, gene expression is tightly regulated and underpins essential functions and physiology. The coordination and regulation of both host and pathogen gene expression is essential for pathogens to infect and cause disease. One mode of gene regulation is RNA silencing. This biological process is widespread in the natural world, present in plants, animals and several pathogens. In RNA silencing, small (20–40 nucleotides) non-coding RNAs (small-RNAs, sRNAs) accumulate and regulate gene expression transcriptionally or post-transcriptionally in a sequence-specific manner. Regulation of sRNA molecules provides a fast mode to alter gene activity of multiple gene transcripts. RNA silencing is an ancient mechanism that protects the most sensitive part of an organism: its genetic code. sRNA molecules emerged as regulators of plant development, growth and plant immunity. sRNA based RNA silencing functions both within and between organisms. Here we present the described sRNAs from plants and pathogens and discuss how they regulate host immunity and pathogen virulence. We speculate on how sRNA molecules can be exploited to develop disease resistant plants. Finally, the activity of sRNA molecules can be prevented by proteins that suppress RNA silencing. This counter silencing response completes the dialog between plants and pathogens controlling plant disease or resistance outcome on the RNA (controlling gene expression) and protein level.

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Fungal Genetics & Biology (2018): The G-protein γ subunit of Phytophthora infestans is involved in sporangial development

Fungal Genetics & Biology (2018): The G-protein γ subunit of Phytophthora infestans is involved in sporangial development | WU_Phyto-Publications | Scoop.it
The oomycete Phytophthora infestans is a notorious plant pathogen with potato and tomato as its primary hosts. Previous research showed that the heterotrimeric G-protein subunits Gα and Gβ have a role in zoospore motility and virulence, and sporangial development, respectively. Here, we present analyses of the gene encoding a Gγ subunit in P. infestans, Pigpg1. The overall similarity of PiGPG1 with non-oomycete Gγ subunits is low, with only the most conserved amino acids maintained, but similarity with its homologs in other oomycetes is high. Pigpg1 is expressed in all life stages and shows a similar expression profile as the gene encoding the Gβ subunit, Pigpb1. To elucidate its function, transformants were generated in which Pigpg1 is silenced or overexpressed and their phenotypes were analyzed. Pigpg1-silenced lines produce less sporangia, which are malformed. Altogether, the results show that PiGPG1 is crucial for proper sporangia development and zoosporogenesis. PiGPG1 is a functional Gγ, and likely forms a dimer with PiGPB1 that mediates signaling.
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Studies in Mycology (2018): RXLR effector diversity in Phytophthora infestans isolates determines recognition by potato resistance proteins; the case study AVR1 and R1

Studies in Mycology (2018): RXLR effector diversity in Phytophthora infestans isolates determines recognition by potato resistance proteins; the case study AVR1 and R1 | WU_Phyto-Publications | Scoop.it
Late blight disease caused by the plant pathogenic oomycete pathogen Phytophthora infestans is one of the most limiting factors in potato production. P. infestans is able to overcome introgressed late blight resistance by adaptation of effector genes. AVR1 is an RXLR effector that triggers immune responses when recognized by the potato resistance protein R1. P. infestans isolates avirulent on R1 plants were found to have AVR1 variants that are recognized by R1. Virulent isolates though, lack AVR1 but do contain a close homologue of AVR1, named A-L, of which all variants escape recognition by R1. Co-expression of AVR1 and R1 in Nicotiana benthamiana results in a hypersensitive response (HR). In contrast, HR is not activated when A-L is co-expressed with R1. AVR1 and A-L are highly similar in structure. They share two W motifs and one Y motif in the C-terminal part but differ in the T-region, a 38 amino acid extension at the carboxyl-terminal tail of AVR1 lacking in A-L. To pinpoint what determines R1-mediated recognition of AVR1 we tested elicitor activity of AVR1 and A-L chimeric and deletion constructs by co-expression with R1. The T-region is important as it enables R1-mediated recognition of A-L, not only when fused to A-L but also via trans-complementation. Yet, AVR1 lacking the T-region is still active as an elicitor of HR, but this activity is lost when certain motifs are swapped with A-L. These data show that A-L circumvents R1 recognition not only because it lacks the T-region, but also because of differences in the conserved C-terminal effector motifs.
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MPMI (2018): The ELR-SOBIR1 complex functions as a two-component RLK to mount defense against Phytophthora infestans

MPMI (2018): The ELR-SOBIR1 complex functions as a two-component RLK to mount defense against Phytophthora infestans | WU_Phyto-Publications | Scoop.it
The ELICITIN RESPONSE (ELR) protein from Solanum microdontum can recognize INF1 elicitin of Phytophthora infestans and trigger defense responses. ELR is a receptor-like protein (RLP) that lacks a cytoplasmic signaling domain and is anticipated to require interaction with a signaling-competent receptor-like kinase (RLK). SUPPRESSOR OF BIR1-1 (SOBIR1) has been proposed as a general interactor for RLPs involved in immunity and as such, is a potential interactor for ELR. Here we investigate whether SOBIR1 is required for response to INF1 and resistance to P. infestans and whether it associates with ELR. Our results show that virus-induced gene silencing (VIGS) of SOBIR1 in Nicotiana benthamiana leads to loss of INF1-triggered cell death and increased susceptibility to P. infestans. Using genetic complementation, we found that the kinase activity of SOBIR1 is required for INF1-triggered cell death. Co-immunoprecipitation experiments showed that ELR constitutively associates with potato SOBIR1 in planta, forming a bi-partite receptor complex. Upon INF1 elicitation, this ELR-SOBIR1 complex recruits SOMATIC EMPBRYOGENESIS RECEPTOR KINASE 3 (SERK3) leading to downstream signaling activation. Overall, our study shows that SOBIR1 is required for basal resistance to P. infestans and for INF1-triggered cell death, and functions as an adaptor kinase for ELR.
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mBio (2018): Functional Analysis of Mating Type Genes and Transcriptome Analysis during Fruiting Body Development of Botrytis cinerea

mBio (2018): Functional Analysis of Mating Type Genes and Transcriptome Analysis during Fruiting Body Development of Botrytis cinerea | WU_Phyto-Publications | Scoop.it
Botrytis cinerea is a plant-pathogenic fungus producing apothecia as sexual fruiting bodies. To study the function of mating type (MAT) genes, single-gene deletion mutants were generated in both genes of the MAT1-1 locus and both genes of the MAT1-2 locus. Deletion mutants in two MAT genes were entirely sterile, while mutants in the other two MAT genes were able to develop stipes but never formed an apothecial disk. Little was known about the reprogramming of gene expression during apothecium development. We analyzed transcriptomes of sclerotia, three stages of apothecium development (primordia, stipes, and apothecial disks), and ascospores by RNA sequencing. Ten secondary metabolite gene clusters were upregulated at the onset of sexual development and downregulated in ascospores released from apothecia. Notably, more than 3,900 genes were differentially expressed in ascospores compared to mature apothecial disks. Among the genes that were upregulated in ascospores were numerous genes encoding virulence factors, which reveals that ascospores are transcriptionally primed for infection prior to their arrival on a host plant. Strikingly, the massive transcriptional changes at the initiation and completion of the sexual cycle often affected clusters of genes, rather than randomly dispersed genes. Thirty-five clusters of genes were jointly upregulated during the onset of sexual reproduction, while 99 clusters of genes (comprising >900 genes) were jointly downregulated in ascospores. These transcriptional changes coincided with changes in expression of genes encoding enzymes participating in chromatin organization, hinting at the occurrence of massive epigenetic regulation of gene expression during sexual reproduction.
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Journal of Experimental Botany (2018): Solanaceous exocyst subunits are involved in immunity to diverse plant pathogens

Journal of Experimental Botany (2018): Solanaceous exocyst subunits are involved in immunity to diverse plant pathogens | WU_Phyto-Publications | Scoop.it
The exocyst, a multiprotein complex consisting of eight subunits, plays an essential role in many biological processes by mediating secretion of post-Golgi-derived vesicles towards the plasma membrane. In recent years, roles for plant exocyst subunits in pathogen defence have been uncovered, largely based on studies in the model plant Arabidopsis. Only a few studies have been undertaken to assign the role of exocyst subunits in plant defence in other plants species, including crops. In this study, predicted protein sequences from exocyst subunits were retrieved by mining databases from the Solanaceous plants Nicotiana benthamiana, tomato, and potato. Subsequently, their evolutionary relationship with Arabidopsis exocyst subunits was analysed. Gene silencing in N. benthamiana showed that several exocyst subunits are required for proper plant defence against the (hemi-)biotrophic plant pathogens Phytophthora infestans and Pseudomonas syringae. In contrast, some exocyst subunits seem to act as susceptibility factors for the necrotrophic pathogen Botrytis cinerea. Furthermore, the majority of the exocyst subunits were found to be involved in callose deposition, suggesting that they play a role in basal plant defence. This study provides insight into the evolution of exocyst subunits in Solanaceous plants and is the first to show their role in immunity against multiple unrelated pathogens.
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Frontiers in Microbiology (2017): Current Insights into the Role of Rhizosphere Bacteria in Disease Suppressive Soils

Frontiers in Microbiology (2017): Current Insights into the Role of Rhizosphere Bacteria in Disease Suppressive Soils | WU_Phyto-Publications | Scoop.it
Disease suppressive soils offer effective protection to plants against infection by soil-borne pathogens, including fungi, oomycetes, bacteria and nematodes. The specific disease suppression that operates in these soils is, in most cases, microbial in origin. Therefore, suppressive soils are considered as a rich resource for the discovery of beneficial microorganisms with novel antimicrobial and other plant protective traits. To date, several microbial genera have been proposed as key players in disease suppressiveness of soils, but the complexity of the microbial interactions as well as the underlying mechanisms and microbial traits remain elusive for most disease suppressive soils. Recent developments in next generation sequencing and other ‘omics technologies have provided new insights into the microbial ecology of disease suppressive soils and the identification of microbial consortia and traits involved in disease suppressiveness. Here, we review the results of recent ‘omics-based studies on the microbial basis of disease suppressive soils, with specific emphasis on the role of rhizosphere bacteria in this intriguing microbiological phenomenon.
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Plant Methods (2017): Infection of a tomato cell culture by Phytophthora infestans ; a versatile tool to study Phytophthora -host interactions

Plant Methods (2017): Infection of a tomato cell culture by Phytophthora infestans ; a versatile tool to study Phytophthora -host interactions | WU_Phyto-Publications | Scoop.it

The oomycete Phytophthora infestans causes late blight on potato and tomato. Despite extensive research, the P. infestans-host interaction is still poorly understood. To find new ways to further unravel this interaction we established a new infection system using MsK8 tomato cells. These cells grow in suspension and can be maintained as a stable cell line that is representative for tomato.

MsK8 cells can host several Phytophthora species pathogenic on tomato. Species not pathogenic on tomato could not infect. Microscopy revealed that 16 h after inoculation up to 36% of the cells were infected. The majority were penetrated by a germ tube emerging from a cyst (i.e. primary infection) while other cells were already showing secondary infections including haustoria. In incompatible interactions, MsK8 cells showed defense responses, namely reactive oxygen species production and cell death leading to a halt in pathogen spread at the single cell level. In compatible interactions, several P. infestans genes, including RXLR effector genes, were expressed and in both, compatible and incompatible interactions tomato genes involved in defense were differentially expressed.

Our results show that P. infestans can prosper as a pathogen in MsK8 cells; it not only infects, but also makes haustoria and sporulates, and it receives signals that activate gene expression. Moreover, MsK8 cells have the ability to support pathogen growth but also to defend themselves against infection in a similar way as whole plants. An advantage of MsK8 cells compared to leaves is the more synchronized infection, as all cells have an equal chance of being infected. Moreover, analyses and sampling of infected tissue can be performed in a non-destructive manner from early time points of infection onwards and as such the MsK8 infection system offers a potential platform for large-scale omics studies and activity screenings of inhibitory compounds.

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Molecular and Cellular Proteomics (2017): Proteomic analysis of Phytophthora infestans reveals the importance of cell wall proteins in pathogenicity

Molecular and Cellular Proteomics (2017): Proteomic analysis of Phytophthora infestans reveals the importance of cell wall proteins in pathogenicity | WU_Phyto-Publications | Scoop.it
The oomycete Phytophthora infestans is the most harmful pathogen of potato. It causes the disease late blight, which generates increased yearly costs of up to one billion euro in the EU alone and is difficult to control. We have performed a large-scale quantitative proteomics study of six P. infestans life stages with the aim to identify proteins that change in abundance during development, with a focus on pre-infectious life stages. Over 10 000 peptides from 2061 proteins were analysed. We identified a number of abundance profiles of proteins that were up- or downregulated in different combinations of life stages. One of these profiles contained 59 proteins that were more abundant in germinated cysts and appressoria. A large majority of these proteins were not previously recognized as being appressorial proteins or involved in the infection process. Among those are proteins with putative roles in transport, amino acid metabolism, pathogenicity (including one RXLR effector) and cell wall structure modification. We analysed the expression of the genes encoding nine of these proteins using RT-qPCR and found an increase in transcript levels during disease progression, in agreement with the hypothesis that these proteins are important in early infection. Among the nine proteins was a group involved in cell wall structure modification and adhesion, including three closely related, uncharacterized proteins encoded by PITG_01131, PITG_01132, and PITG_16135, here denoted Piacwp1-3. Transient silencing of these genes resulted in reduced severity of infection, indicating that these proteins are important for pathogenicity. Our results contribute to further insight into P. infestans biology, and indicate processes that might be relevant for the pathogen while preparing for host cell penetration and during infection. The mass spectrometry data have been deposited to ProteomeXchange via the PRIDE partner repository with the dataset identifier PXD002446.
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PhD thesis Hanna Rovenich (2017): Evasion of chitin-triggered immunity by fungal plant pathogens

PhD thesis Hanna Rovenich (2017): Evasion of chitin-triggered immunity by fungal plant pathogens | WU_Phyto-Publications | Scoop.it
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PLoS Pathogens (2017): L-type lectin receptor kinases: New forces in plant immunity

PLoS Pathogens (2017): L-type lectin receptor kinases: New forces in plant immunity | WU_Phyto-Publications | Scoop.it
To halt pathogen invasion, plants—unlike animals—solely depend on an innate immune system. They possess an expanded arsenal of cell surface-localized pattern recognition receptors (PRRs) to perceive microbe- and damage-associated molecular patterns (M/DAMPs), here collectively termed invasions patterns [1]. Prominent examples are flagellin sensing 2 (FLS2) and elongation factor Tu (EF-Tu) receptor (EFR), 2 receptor-like kinases (RLKs) with leucine-rich repeat (LRR) ectodomains that initiate defense upon recognition of bacterial flagellin and EF-Tu, respectively [2]. Emerging key players in plant immunity are the lectin receptor kinases, RLKs that are subdivided in 3 distinct classes based on their extracellular lectin domains, i.e., G- (GNA-related or S-locus), C- (calcium-dependent), and L- (legume) type [3]. All 3 are omnipresent in plants but absent in animals, which deploy distinct C-type lectin receptors (CLRs) to initiate innate immunity [4]. Recent years have witnessed an accelerated interest in plant lectin receptors kinases. In this Pearl, we summarize our current knowledge on L-type lectin receptor kinases (LecRKs) in plant immunity.
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PhD thesis Viviane Cordovez da Cunha (2017): Volatile-mediated interactions in the rhizosphere

PhD thesis Viviane Cordovez da Cunha (2017): Volatile-mediated interactions in the rhizosphere | WU_Phyto-Publications | Scoop.it
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Evolutionary Applications (2017): Experimental evolution to increase the efficacy of the entomopathogenic fungus Beauveria bassiana against malaria mosquitoes: Effects on mycelial growth and virulence

Evolutionary Applications (2017): Experimental evolution to increase the efficacy of the entomopathogenic fungus Beauveria bassiana against malaria mosquitoes: Effects on mycelial growth and virulence | WU_Phyto-Publications | Scoop.it
Entomopathogenic fungi such as Beauveria bassiana are currently considered as a potential control agent for malaria mosquitoes. The success of such strategies depends among others on the efficacy of the fungus to kill its hosts. As B. bassiana can use various resources for growth and reproduction, increasing the dependency on mosquitoes as a nutritional source may be instrumental for reaching this goal. Passage of entomopathogenic fungi through an insect host has been shown to increase its virulence. We evaluated the virulence, fungal outgrowth, mycelial growth rate, and sporulation rate of two B. bassiana isolates (Bb1520 and Bb8028) that underwent 10 consecutive selection cycles through malaria mosquitoes (Anopheles coluzzii) using an experimental evolution approach. This cycling resulted in an altered capacity of evolved B. Bassiana lineages to grow on different substrates while maintaining the ability to kill insects. Notably, however, there were no significant changes in virulence or speed of outgrowth when comparing the evolved lineages against their unevolved ancestors. These results suggest that fungal growth and sporulation evolved through successive and exclusive use of an insect host as a nutritional resource. We discuss the results in light of biocontrol and provide suggestions to increase fungal virulence.
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PloS Pathogens (2018): GPCR-bigrams: Enigmatic signaling components in oomycetes

PloS Pathogens (2018): GPCR-bigrams: Enigmatic signaling components in oomycetes | WU_Phyto-Publications | Scoop.it
Oomycetes are diverse eukaryotic microorganisms, comprising important pathogens as well as free-living saprophytes [1]. Plant pathogenic oomycetes cause enormous yield losses in crop plants but also threaten natural vegetation. Phytophthora infestans, the causal agent of potato late blight, is without a doubt the most (in)famous. Other important plant pathogenic oomycetes include downy mildews and Albugo [2]. Animal pathogenic oomycetes (such as Saprolegnia, Aphanomyces, and Pythium) primarily affect marine organisms such as fish and crustaceans but can also cause harmful diseases in humans and cattle. Here, we outline unique features of oomycetes and their cellular signaling systems. We focus on one particularly interesting class of signaling components, the so-called GPCR-bigrams, in which a typical signaling domain is preceded by a G-protein coupled receptor (GPCR) domain and propose future directions to elucidate the function and activity of this exceptional group of signaling proteins.
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Frontiers in Microbiology (2018): Comparative Microbiome Analysis of a Fusarium Wilt Suppressive Soil and a Fusarium Wilt Conducive Soil From the Châteaurenard Region

Frontiers in Microbiology (2018): Comparative Microbiome Analysis of a Fusarium Wilt Suppressive Soil and a Fusarium Wilt Conducive Soil From the Châteaurenard Region | WU_Phyto-Publications | Scoop.it
Disease-suppressive soils are soils in which specific soil-borne plant pathogens cause only limited disease although the pathogen and susceptible host plants are both present. Suppressiveness is in most cases of microbial origin. We conducted a comparative metabarcoding analysis of the taxonomic diversity of fungal and bacterial communities from suppressive or non-suppressive (conducive) soils as regards Fusarium wilts sampled from the Châteaurenard region (France). Bioassays confirmed that disease incidence was significantly lower in the suppressive soil than in the conducive soil. Furthermore, we succeeded in partly transferring Fusarium wilt-suppressiveness to the conducive soil by mixing 10% (w/w) of the suppressive soil into the conducive soil. Fungal diversity differed significantly between the suppressive and conducive soils. Among dominant fungal operational taxonomic units (OTUs) affiliated to known genera, seventeen OTUs were detected exclusively in the suppressive soil. These OTUs were assigned to the Acremonium, Chaetomium, Cladosporium, Clonostachys, Fusarium, Ceratobasidium, Mortierella, Penicillium, Scytalidium, and Verticillium genera. Additionally, the relative abundance of specific members of the bacterial community was significantly higher in the suppressive and mixed soils than in the conducive soil. OTUs found more abundant in Fusarium wilt-suppressive soils were affiliated to the bacterial genera Adhaeribacter, Massilia, Microvirga, Rhizobium
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MPMI (2018): Gapless Genome Assembly of the Potato and Tomato Early Blight Pathogen Alternaria solani

The Alternaria genus consists of saprophytic fungi as well as plant pathogenic species that have significant economic impact. To date, the genomes of multiple Alternaria species have been sequenced. These studies have yielded valuable data for molecular studies on Alternaria fungi. However, most of the current Alternaria genome assemblies are highly fragmented, thereby hampering the identification of genes that are involved in causing disease. Here, we report a gapless genome assembly of A. solani, the causal agent of early blight in tomato and potato. The genome assembly is a significant step towards a better understanding of pathogenicity of A. solani.
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Nature Genetics (2018): Stress and sexual reproduction affect the dynamics of the wheat pathogen effector AvrStb6 and strobilurin resistance

Nature Genetics (2018): Stress and sexual reproduction affect the dynamics of the wheat pathogen effector AvrStb6 and strobilurin resistance | WU_Phyto-Publications | Scoop.it
Host resistance and fungicide treatments are cornerstones of plant-disease control. Here, we show that these treatments allow sex and modulate parenthood in the fungal wheat pathogen Zymoseptoria tritici. We demonstrate that the Z. tritici–wheat interaction complies with the gene-for-gene model by identifying the effector AvrStb6, which is recognized by the wheat resistance protein Stb6. Recognition triggers host resistance, thus implying removal of avirulent strains from pathogen populations. However, Z. tritici crosses on wheat show that sex occurs even with an avirulent parent, and avirulence alleles are thereby retained in subsequent populations. Crossing fungicide-sensitive and fungicide-resistant isolates under fungicide pressure results in a rapid increase in resistance-allele frequency. Isolates under selection always act as male donors, and thus disease control modulates parenthood. Modeling these observations for agricultural and natural environments reveals extended durability of host resistance and rapid emergence of fungicide resistance. Therefore, fungal sex has major implications for disease control.
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Molecular Plant Pathology (2018): Plant pathogen effector proteins as manipulators of host microbiomes?

To understand the mechanisms underlying disease development in plants, molecular plant pathology research has mostly focused on the characterization of direct interactions between plant pathogens and their hosts. Collectively, this research has demonstrated that plants sense microbial invaders using various types of receptors (recently coined as ‘invasion pattern receptors’, IPRs) that sense microbial invasion and activate defence responses upon recognition of various molecular patterns that betray microbial invasion (recently coined as ‘invasion patterns’, IPs) (Cook et al., 2015). While these IPRs comprise cell surface-localized as well as intracellular receptors, IPs comprise microbe-associated molecular patterns (MAMPs) and other microbially secreted components, as well as host-derived damage-associated molecular patterns (DAMPs) (Cook et al., 2015)...

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mBio (2018): The Ancient Link between G-Protein-Coupled Receptors and C-Terminal Phospholipid Kinase Domains

mBio (2018): The Ancient Link between G-Protein-Coupled Receptors and C-Terminal Phospholipid Kinase Domains | WU_Phyto-Publications | Scoop.it
Sensing external signals and transducing these into intracellular responses requires a molecular signaling system that is crucial for every living organism. Two important eukaryotic signal transduction pathways that are often interlinked are G-protein signaling and phospholipid signaling. Heterotrimeric G-protein subunits activated by G-protein-coupled receptors (GPCRs) are typical stimulators of phospholipid signaling enzymes such as phosphatidylinositol phosphate kinases (PIPKs) or phospholipase C (PLC). However, a direct connection between the two pathways likely exists in oomycetes and slime molds, as they possess a unique class of GPCRs that have a PIPK as an accessory domain. In principle, these so-called GPCR-PIPKs have the capacity of perceiving an external signal (via the GPCR domain) that, via PIPK, directly activates downstream phospholipid signaling. Here we reveal the sporadic occurrence of GPCR-PIPKs in all eukaryotic supergroups, except for plants. Notably, all species having GPCR-PIPKs are unicellular microorganisms that favor aquatic environments. Phylogenetic analysis revealed that GPCR-PIPKs are likely ancestral to eukaryotes and significantly expanded in the last common ancestor of oomycetes. In addition to GPCR-PIPKs, we identified five hitherto-unknown classes of GPCRs with accessory domains, four of which are universal players in signal transduction. Similarly to GPCR-PIPKs, this enables a direct coupling between extracellular sensing and downstream signaling. Overall, our findings point to an ancestral signaling system in eukaryotes where GPCR-mediated sensing is directly linked to downstream responses.
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BMC Plant Biology (2017): Silencing of DND1 in potato and tomato impedes conidial germination, attachment and hyphal growth of Botrytis cinerea

BMC Plant Biology (2017): Silencing of DND1 in potato and tomato impedes conidial germination, attachment and hyphal growth of Botrytis cinerea | WU_Phyto-Publications | Scoop.it

Botrytis cinerea, a necrotrophic pathogenic fungus, attacks many crops including potato and tomato. Major genes for complete resistance to B. cinerea are not known in plants, but a few quantitative trait loci have been described in tomato. Loss of function of particular susceptibility (S) genes appears to provide a new source of resistance to B. cinerea in Arabidopsis. In this study, orthologs of Arabidopsis S genes (DND1, DMR6, DMR1 and PMR4) were silenced by RNAi in potato and tomato (only for DND1). DND1 well-silenced potato and tomato plants showed significantly reduced diameters of B. cinerea lesions as compared to control plants, at all-time points analysed. Reduced lesion diameter was also observed on leaves of DMR6 silenced potato plants but only at 3 days post inoculation (dpi). The DMR1 and PMR4 silenced potato transformants were as susceptible as the control cv Desiree. Microscopic analysis was performed to observe B. cinerea infection progress in DND1 well-silenced potato and tomato leaves. A significantly lower number of B. cinerea conidia remained attached to the leaf surface of DND1 well-silenced potato and tomato plants and the hyphal growth of germlings was hampered. This is the first report of a cytological investigation of Botrytis development on DND1-silenced crop plants. Silencing of DND1 led to reduced susceptibility to Botrytis, which was associated with impediment of conidial germination and attachment as well as hyphal growth. Our results provide new insights regarding the use of S genes in resistance breeding.
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MPP (2017): Genome‐wide characterization of Phytophthora infestans metabolism: a systems biology approach

MPP (2017): Genome‐wide characterization of Phytophthora infestans metabolism: a systems biology approach | WU_Phyto-Publications | Scoop.it
Genome-scale metabolic models (GEMs) provide a functional view of the complex network of biochemical reactions in the living cell. Initially mainly applied to reconstruct the metabolism of model organisms, the availability of increasingly sophisticated reconstruction methods and more extensive biochemical databases now make it possible to reconstruct GEMs for less characterized organisms as well, and have the potential to unravel the metabolism in pathogen-host systems. Here we present a GEM for the oomycete plant pathogen Phytophthora infestans as a first step towards an integrative model with its host. We predict the biochemical reactions in different cellular compartments and investigate the gene-protein-reaction associations in this model to get an impression of the biochemical capabilities of P. infestans. Furthermore, we generate life stage-specific models to place the transcriptomic changes of genes encoding metabolic enzymes into a functional context. In sporangia and zoospores there is an overall downregulation, most strikingly reflected in the fatty acid biosynthesis pathway. To investigate the robustness of the GEM, we simulate gene deletions to predict which enzymes are essential for in vitro growth. This model is an essential first step towards an understanding of P. infestans and its interactions with plants as a system, which will help to formulate new hypotheses on infection mechanisms and disease prevention.
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 Molecular Plant-Microbe Interactions (2017): The bacterial effector AvrPto targets the regulatory co-receptor SOBIR1 and suppresses defence signalling mediated by the receptor-like protein Cf-4

 Molecular Plant-Microbe Interactions (2017): The bacterial effector AvrPto targets the regulatory co-receptor SOBIR1 and suppresses defence signalling mediated by the receptor-like protein Cf-4 | WU_Phyto-Publications | Scoop.it
Receptor-like proteins (RLPs) and receptor-like kinases (RLKs) are cell surface receptors that are essential for detecting invading pathogens and subsequent activation of plant defence responses. RLPs lack a cytoplasmic kinase domain to trigger downstream signalling leading to host resistance. The RLK SOBIR1 constitutively interacts with the tomato RLP Cf-4, thereby providing Cf-4 with a kinase domain. SOBIR1 is required for Cf-4-mediated resistance to strains of the fungal tomato pathogen Cladosporium fulvum that secrete the effector Avr4. Upon perception of this effector by the Cf-4/SOBIR1 complex, the central regulatory RLK SERK3a is recruited to the complex and defence signalling is triggered. SOBIR1 is also required for RLP-mediated resistance to bacterial, fungal and oomycete pathogens and we hypothesized that SOBIR1 is targeted by effectors of such pathogens to suppress host defence responses. In this study we show that Pseudomonas syringae pv. tomato DC3000 effector AvrPto interacts with Arabidopsis SOBIR1 and its orthologs of tomato and Nicotiana benthamiana, independent of SOBIR1 kinase activity. Interestingly, AvrPto suppresses Arabidopsis SOBIR1-induced cell death in N. benthamiana. Furthermore, AvrPto compromises Avr4-triggered cell death in Cf-4-transgenic N. benthamiana, without affecting Cf-4/SOBIR1/SERK3a complex formation. Our study shows that the RLP co-receptor SOBIR1 is targeted by a bacterial effector, which results in compromised defence responses.
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Environmental Microbiology (2017): Genome‐wide analysis of bacterial determinants of plant growth promotion and induced systemic resistance by Pseudomonas fluorescens

Environmental Microbiology (2017): Genome‐wide analysis of bacterial determinants of plant growth promotion and induced systemic resistance by Pseudomonas fluorescens | WU_Phyto-Publications | Scoop.it

Pseudomonas fluorescens strain SS101 (Pf.SS101) promotes growth of Arabidopsis thaliana, enhances greening and lateral root formation, and induces systemic resistance (ISR) against the bacterial pathogen Pseudomonas syringae pv. tomato (Pst). Here, targeted and untargeted approaches were adopted to identify bacterial determinants and underlying mechanisms involved in plant growth promotion and ISR by Pf.SS101. Based on targeted analyses, no evidence was found for volatiles, lipopeptides and siderophores in plant growth promotion by Pf.SS101. Untargeted, genome-wide analyses of 7,488 random transposon mutants of Pf.SS101 led to the identification of 21 mutants defective in both plant growth promotion and ISR. Many of these mutants, however, were auxotrophic and impaired in root colonization. Genetic analysis of three mutants followed by site-directed mutagenesis, genetic complementation and plant bioassays revealed the involvement of the phosphogluconate dehydratase gene edd, the response regulator gene colR and the adenylsulfate reductase gene cysH in both plant growth promotion and ISR. Subsequent comparative plant transcriptomics analyses strongly suggest that modulation of sulfur assimilation, auxin biosynthesis and transport, steroid biosynthesis and carbohydrate metabolism in Arabidopsis are key mechanisms linked to growth promotion and ISR by Pf.SS101

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Frontiers in Plant Science (2017): Plant Phenotypic and Transcriptional Changes Induced by Volatiles from the Fungal Root Pathogen Rhizoctonia solani

Frontiers in Plant Science (2017): Plant Phenotypic and Transcriptional Changes Induced by Volatiles from the Fungal Root Pathogen Rhizoctonia solani | WU_Phyto-Publications | Scoop.it
Beneficial soil microorganisms can affect plant growth and resistance by the production of volatile organic compounds (VOCs). Yet, little is known on how VOCs from soil-borne plant pathogens affect plant growth and resistance. Here we show that VOCs released from mycelium and sclerotia of the fungal root pathogen Rhizoctonia solani enhance growth and accelerate development of Arabidopsis thaliana. Seedlings briefly exposed to the fungal VOCs showed similar phenotypes, suggesting that enhanced biomass and accelerated development are primed already at early developmental stages. Fungal VOCs did not affect plant resistance to infection by the VOC-producing pathogen itself but reduced aboveground resistance to the herbivore Mamestra brassicae. Transcriptomics of A. thaliana revealed that genes involved in auxin signaling were up-regulated, whereas ethylene and jasmonic acid signaling pathways were down-regulated by fungal VOCs. Mutants disrupted in these pathways showed similar VOC-mediated growth responses as the wild-type A. thaliana, suggesting that other yet unknown pathways play a more prominent role. We postulate that R. solani uses VOCs to predispose plants for infection from a distance by altering root architecture and enhancing root biomass. Alternatively, plants may use enhanced root growth upon fungal VOC perception to sacrifice part of the root biomass and accelerate development and reproduction to survive infection.
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PhD thesis Ruth Gomez Exposito (2017): Microbiome dynamics of disease suppresive soils

PhD thesis Ruth Gomez Exposito (2017): Microbiome dynamics of disease suppresive soils | WU_Phyto-Publications | Scoop.it
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