Biology subjects

Seidl, M.

Publications and source records attributed to Seidl, M..

At least 19 recordsLinked to original sources

bioRxiv2024

Exploiting Pseudomonas syringae Type 3 secretion to study effector contribution to disease in spinach

Intensive spinach cultivation creates favourable conditions for the emergence and rapid evolution of pathogens, leading to substantial economic losses. Research on host-pathogen interactions in leafy greens would benefit from advanced biotechnological tools, however absence of such tools in spinach hampers our understanding of spinach immunity. Here, we explored the potential of Type III Secretion System (T3SS)-mediated effector delivery to study pathogen effector activity in spinach. We identified the Pseudomonas syringae pv. tomato DC3000 (DC3000) polymutant D36E, which lacks 36 known T3SS effectors (T3Es), as a promising T3SS-dependent effector delivery system for spinach. Unlike DC3000, which causes necrotic symptoms on spinach and reaches high bacterial titres, D36E did not proliferate and caused no visible symptoms. Using D36E, we screened 28 DC3000 T3Es in spinach, assessing symptom development, bacterial proliferation, and reactive oxygen species (ROS) bursts as a proxy for early immune responses. AvrE1 and HopM1 emerged as key determinants of DC3000-like infection, inducing water-soaked lesions, while HopAD1 strongly suppressed ROS production. Our findings establish the D36E-based effector delivery system as a powerful tool for high-throughput effector studies in spinach. It bridges the gap between genomics-based effector predictions and experimental validation, paving the way for knowledge-driven resistance breeding in non-model crops like spinach.

plant biology↗

bioRxiv2023

Segmental Duplications Drive the Evolution of Accessory Regions in a Major Crop Pathogen

O_LIMany pathogens evolved compartmentalized genomes with conserved core and variable accessory regions which carry effector genes mediating virulence. The fungal plant pathogen Fusarium oxysporum has such accessory regions often spanning entire chromosomes. The presence of specific accessory regions influences the host range, and horizontal transfer of some accessory regions can modify the pathogenicity of the receiving strain. However, understanding how these accessory regions evolve in strains that infect the same host remains limited. C_LIO_LIHere, we define the pan-genome of 69 diverse Fusarium strains that cause Fusarium wilt of banana, a significant constraint to global banana production. In this diverse panel of Fusarium strains infecting banana, we analyzed the diversity and evolution of the accessory regions. C_LIO_LIAccessory regions in Fusarium strains infecting the same banana cultivar are highly diverse, and we could not identify any shared genomic regions and in planta induced effectors. We demonstrate that segmental duplications drive the evolution of accessory regions. Furthermore, we show that recent segmental duplications and aneuploidy occur specifically in accessory chromosomes and cause the expansion of accessory regions in F. oxysporum. C_LIO_LITaken together we conclude that extensive recent duplications drive the evolution of accessory regions in Fusarium, which contribute to the evolution of virulence. C_LI

genomics↗

bioRxiv2021

An ancient antimicrobial protein co-opted by a fungal plant pathogen for in planta mycobiome manipulation

Microbes typically secrete a plethora of molecules to promote niche colonization. Soil-dwelling microbes are well-known producers of antimicrobials that are exploited to outcompete microbial co-inhabitants. Also plant pathogenic microbes secrete a diversity of molecules into their environment for niche establishment. Upon plant colonization, microbial pathogens secrete so-called effector proteins that promote disease development. While such effectors are typically considered to exclusively act through direct host manipulation, we recently reported that the soil-borne fungal xylem-colonizing vascular wilt pathogen Verticillium dahliae exploits effector proteins with antibacterial properties to promote host colonization through the manipulation of beneficial host microbiota. Since fungal evolution preceded land plant evolution, we now speculate that a subset of the pathogen effectors involved in host microbiota manipulation evolved from ancient antimicrobial proteins of terrestrial fungal ancestors that served in microbial competition prior to the evolution of plant pathogenicity. Here, we show that V. dahliae has co-opted an ancient antimicrobial protein as effector, named VdAMP3, for mycobiome manipulation in planta. We show that VdAMP3 is specifically expressed to ward off fungal niche competitors during resting structure formation in senescing mesophyll tissues. Our findings indicate that effector-mediated microbiome manipulation by plant pathogenic microbes extends beyond bacteria and also concerns eukaryotic members of the plant microbiome. Finally, we demonstrate that fungal pathogens can exploit plant microbiome-manipulating effectors in a life-stage specific manner, and that a subset of these effectors has evolved from ancient antimicrobial proteins of fungal ancestors that likely originally functioned in manipulation of terrestrial biota. SIGNIFICANCE STATEMENTMicrobes secrete a diversity of molecules into their environment to mediate niche colonization. During host ingress, plant pathogenic microbes secrete effector proteins that facilitate disease development, many of which deregulate host immune responses. We recently demonstrated that plant pathogens additionally exploit effectors with antibacterial activities to manipulate beneficial plant microbiota to promote host colonization. Here, we show that the fungal pathogen Verticillium dahliae has co-opted an ancient antimicrobial protein, that likely served in microbial competition in terrestrial environments before land plants existed, as effector for the manipulation of fungal competitors during host colonization. Thus, we demonstrate that pathogen effector repertoires comprise antifungal proteins, and speculate such effectors could be exploited for the development of novel antimycotics.

microbiology↗

bioRxiv2021

Local rather than global H3K27me3 dynamics associates with differential gene expression in Verticillium dahliae

Differential growth conditions typically trigger global transcriptional responses in filamentous fungi. Such fungal responses to environmental cues involve epigenetic regulation, including chemical histone modifications. It has been proposed that conditionally expressed genes, such as those that encode secondary metabolites but also effectors in pathogenic species, are often associated with a specific histone modification, lysine27 methylation of H3 (H3K27me3). However, thus far no analyses on the global H3K27me3 profiles have been reported under differential growth conditions in order to assess if H3K27me3 dynamics governs differential transcriptional. Using ChIP- and RNA-sequencing data from the plant pathogenic fungus Verticillium dahliae grown in three in vitro cultivation media, we now show that a substantial number of the identified H3K27me3 domains globally display stable profiles among these growth conditions. However, we do observe local quantitative differences in H3K27me3 ChIP-seq signal that associate with a subset of differentially transcribed genes between media. Comparing the in vitro results to expression during plant infection suggests that in planta-induced genes may require chromatin remodelling to achieve expression. Overall, our results demonstrate that some loci display H3K27me3 dynamics associated with concomitant transcriptional variation, but many differentially expressed genes are associated with stable H3K27me3 domains. Thus, we conclude that while H3K27me3 is required for transcriptional repression, it does not appear that transcriptional activation requires global erasure of H3K27me3. We propose that the H3K27me3 domains that do not undergo dynamic methylation may contribute to transcription through other mechanisms or may serve additional genomic regulatory functions.

microbiology↗

bioRxiv2020

DNA methylation in Verticillium dahliae requires only one of three putative DNA methyltransferases, yet is dispensable for growth, development and virulence

DNA methylation is an important epigenetic control mechanism that in many fungi is restricted to genomic regions containing transposons. Two DNA methyltransferases, Dim2 and Dnmt5, are known to perform methylation at cytosines in fungi. While most ascomycete fungi encode both Dim2 and Dnmt5, only few functional studies have been performed in species containing both. In this study, we report functional analysis of both Dim2 and Dnmt5 in the plant pathogenic fungus Verticillium dahliae. Our results show that Dim2, but not Dnmt5 or the putative sexual-cycle related DNA methyltransferase Rid, is responsible for nearly all DNA methylation. Single or double DNA methyltransferase mutants did not show altered development, virulence, or transcription of genes or transposons. In contrast, Hp1 and Dim5 mutants that are impacted in chromatin-associated processes upstream of DNA methylation are severely affected in development and virulence and display extensive transcriptional reprogramming in specific hypervariable genomic regions (so-called lineage-specific (LS) regions) that contain genes associated with host colonization. As these LS regions are largely devoid of DNA methylation and of Hp1- and Dim5-associated heterochromatin, the differential transcription is likely caused by pleiotropic effects rather than by differential DNA methylation. Overall, our study suggests that Dim2 is the main DNA methyltransferase in V. dahliae and, in conjunction with work on other fungi, is likely the main active DNMT in ascomycetes, irrespective of Dnmt5 presence. We speculate that Dnmt5 acts under specific, presently enigmatic, conditions or, alternatively, acts in DNA-associated processes other than DNA methylation.

microbiology↗

bioRxiv2020

Centromere evolution in the fungal genus Verticillium

ABSTRACTCentromeres are chromosomal regions that are crucial for chromosome segregation during mitosis and meiosis, and failed centromere formation can contribute to chromosomal anomalies. Despite this conserved function, centromeres differ significantly between and even within species. Thus far, systematic studies into the organization and evolution of fungal centromeres remain scarce. In this study, we identified the centromeres in each of the ten species of the fungal genus Verticillium and characterized their organization and evolution. Chromatin immunoprecipitation of the centromere-specific histone CenH3 (ChIP-seq) and chromatin conformation capture (Hi-C) followed by high-throughput sequencing identified eight conserved, large (∼150 kb), AT-, and repeat-rich regional centromeres that are embedded in heterochromatin in the plant pathogen V. dahliae. Using Hi-C, we similarly identified repeat-rich centromeres in the other Verticillium species. Strikingly, a single repetitive element is strongly associated with centromeric regions in some but not all Verticillium species. Extensive chromosomal rearrangements occurred during Verticillium evolution, yet only a minority could be linked to centromeres, suggesting that centromeres played a minor role in chromosomal evolution. Nevertheless, the size and organization of centromeres differ considerably between species, and centromere size was found to correlate with the genome-wide repeat content. Overall, our study highlights the contribution of repetitive elements to the diversity and rapid evolution of centromeres within the fungal genus Verticillium.IMPORTANCE The genus Verticillium contains ten species of plant-associated fungi, some of which are notorious pathogens. Verticillium species evolved by frequent chromosomal rearrangements that contribute to genome plasticity. Centromeres are instrumental for separation of chromosomes during mitosis and meiosis, and failed centromere functionality can lead to chromosomal anomalies. Here, we used a combination of experimental techniques to identify and characterize centromeres in each of the Verticillium species. Intriguingly, we could strongly associate a single repetitive element to the centromeres of some of the Verticillium species. The presence of this element in the centromeres coincides with increased centromere sizes and genome-wide repeat expansions. Collectively, our findings signify a role of repetitive elements in the function, organization and rapid evolution of centromeres in a set of closely related fungal species.View Full Text

genetics↗

bioRxiv2020

ADA2 is a lysosomal DNase regulating the type-I interferon response

Deficiency of adenosine deaminase 2 (DADA2) is a severe, congenital syndrome, which manifests with hematologic, immunologic and inflammatory pathologies. DADA2 is caused by biallelic mutations in ADA2, but the function of ADA2, and the mechanistic link between ADA2 deficiency and the severe inflammatory phenotype remains unclear. Here, we show that monocyte-derived proteomes from DADA2 patients are highly enriched in interferon response proteins. Using immunohistochemistry and detailed glycan analysis we demonstrate that ADA2 is post-translationally modified for sorting to the lysosomes. At acidic, lysosomal pH, ADA2 acts as a novel DNase that degrades cGAS/Sting-activating ligands. Furthermore, we define a clear structure-function relationship for this acidic DNase activity. Deletion of ADA2 increased the production of cGAMP and type I interferons upon exposure to dsDNA, which was reverted by ADA2 overexpression or deletion of STING. Our results identify a new level of control in the nucleic acid sensing machinery and provide a mechanistic explanation for the pathophysiology of autoinflammation in DADA2. One Sentence SummaryADA2 is a lysosomal nuclease controlling nucleic acid sensing and type I interferon production.

immunology↗

bioRxiv2020

Comparative genomics of Verticillium dahliae isolates reveals the in planta-secreted effector protein recognized in V2 tomato plants

Plant pathogens secrete effector molecules during host invasion to promote host colonization. However, some of these effectors become recognized by host receptors, encoded by resistance genes, to mount defense response and establish immunity. Recently, a novel resistance was identified in tomato, mediated by the single dominant V2 locus, to control strains of the soil-borne vascular wilt fungus Verticillium dahliae that belong to race 2. We performed comparative genomics between race 2 strains and resistance-breaking race 3 strains to identify the avirulence effector that activates V2 resistance, termed Av2. We identified 277 kb of race 2-specific sequence comprising only two genes that encode predicted secreted proteins, both of which are expressed by V. dahliae during tomato colonization. Subsequent functional analysis based on genetic complementation into race 3 isolates confirmed that one of the two candidates encodes the avirulence effector Av2 that is recognized in V2 tomato plants. The identification of Av2 will not only be helpful to select tomato cultivars that are resistant to race 2 strains of V. dahliae, as the corresponding V2 resistance gene has not yet been mapped, but also to monitor adaptations in the V. dahliae population to deployment of V2-containing tomato cultivars in agriculture.

plant biology↗

bioRxiv2019

The genome of Peronospora belbahrii reveals high heterozygosity, a low number of canonical effectors and CT-rich promoters

Along with Plasmopara destructor, Peronosopora belbahrii has arguably been the economically most important newly emerging downy mildew pathogen of the past two decades. Originating from Africa, it has started devastating basil production throughout the world, most likely due to the distribution of infested seed material. Here we present the genome of this pathogen and results from comparisons of its genomic features to other oomycetes. The assembly of the nuclear genome was ca. 35.4 Mbp in length, with an N50 scaffold length of ca. 248 kbp and an L50 scaffold count of 46. The circular mitochondrial genome consisted of ca. 40.1 kbp. From the repeat-masked genome 9049 protein-coding genes were predicted, out of which 335 were predicted to have extracellular functions, representing the smallest secretome so far found in peronosporalean oomycetes. About 16 % of the genome consists of repetitive sequences, and based on simple sequence repeat regions, we provide a set of microsatellites that could be used for population genetic studies of Pe. belbahrii. Peronospora belbahrii has undergone a high degree of convergent evolution, reflecting its obligate biotrophic lifestyle. Features of its secretome, signalling networks, and promoters are presented, and some patterns are hypothesised to reflect the high degree of host specificity in Peronospora species. In addition, we suggest the presence of additional virulence factors apart from classical effector classes that are promising candidates for future functional studies.

genomics↗

bioRxiv2019

Verticillium dahliae strains that infect the same host plant display highly divergent effector catalogs

Originality and significance statementDuring host colonization, plant pathogens secrete molecules that enable host colonization, also known as effector proteins. Here, we show that strains of the fungal plant pathogen Verticillium dahliae that are able to infect the same host plant harbour highly divergent LS effector repertoires. Our study outlines the variability within LS effector gene repertoires of V. dahliae strains, which may allow the various strains to be competitive in the co-evolution with their hosts. SummaryEffectors are proteins secreted by pathogens to support colonization of host plants, often by deregulating host immunity. Effector genes are often localized within dynamic lineage-specific (LS) genomic regions, allowing rapid evolution of effector catalogues. Such localization permits pathogens to be competitive in the co-evolutionary arms races with their hosts. For a broad host-range pathogen such as Verticillium dahliae it is unclear to what extent single members of their total effector repertoires contribute to disease development on multiple hosts. Here, we determined the core and LS effector repertoires of a collection of V. dahliae strains, as well as the ability of these strains to infect a range of plant species comprising tomato, cotton, Nicotiana benthamiana, Arabidopsis, and sunflower to assess whether the presence of particular LS effectors correlates with the ability to infect particular plant species. Surprisingly, we found that V. dahliae strains that are able to infect the same host plant harbor highly divergent LS effector repertoires. Furthermore, we observed differential V. dahliae core effector gene expression between host plants. Our data suggest that different V. dahliae lineages utilise divergent effector catalogs to colonize the same host plant, suggesting considerable redundancy among the activities of effector catalogs between lineages.

plant biology↗

bioRxiv2018

The genome of the fungal pathogen Verticillium dahliae reveals extensive bacterial to fungal gene transfer

Horizontal gene transfer (HGT) involves the transmission of genetic material between distinct evolutionary lineages and can be an important source of biological innovation. Reports of inter-kingdom HGT to eukaryotic microbial pathogens have accumulated over recent years. Verticillium dahliae is a notorious plant pathogen that causes vascular wilt disease on hundreds of plant species, resulting in high economic losses every year. Previously, the effector gene Ave1 and a glucosyltransferase-encoding gene were identified as virulence factor-encoding genes that were proposed to be horizontally acquired from a plant and a bacterial donor, respectively. However, to what extent HGT contributed to the overall genome composition of V. dahliae remained elusive. Here, we systematically searched for evidence of inter-kingdom HGT events in the genome of V. dahliae and provide evidence for extensive horizontal gene acquisition from bacterial origin.

microbiology↗

bioRxiv2018

In silico prediction and characterisation of secondary metabolite clusters in the plant pathogenic fungus Verticillium dahliae

Fungi are renowned producers of natural compounds, also known as secondary metabolites (SMs) that display a wide array of biological activities. Typically, the genes that are involved in the biosynthesis of SMs are located in close proximity to each other in so-called secondary metabolite clusters (SMCs). Many plant-pathogenic fungi secrete SMs during infection in order to promote disease establishment, for instance as cytocoxic compounds. Verticillium dahliae is a notorious plant pathogen that can infect over 200 host plants worldwide. However, the SM repertoire of this vascular pathogen remains mostly uncharted. To unravel the SM potential of V. dahliae, we performed in silico predictions and in-depth analyses of its SM clusters (SMC). We identified 25 potential SMCs in the V. dahliae genome, including loci that can be implicated in DHN-melanin, ferricrocin, triacetyl fusarinine and fujikurin production.

microbiology↗

bioRxiv2018

Homogenization of sub-genome secretome gene expression patterns in the allodiploid fungus Verticillium longisporum

Hybridization is an important evolutionary mechanism that can enable organisms to adapt to environmental challenges. It has previously been shown that the fungal allodiploid species Verticillium longisporum, causal agent of Verticillium stem striping in rape seed, has originated from at least three independent hybridization events between two haploid Verticillium species. To reveal the impact of genome duplication as a consequence of the hybridization, we studied the genome and transcriptome dynamics upon two independent V. longisporum hybridization events, represented by the hybrid lineages "A1/D1" and "A1/D3". We show that the V. longisporum genomes are characterized by extensive chromosomal rearrangements, including between parental chromosomal sets. V. longisporum hybrids display signs of evolutionary dynamics that are typically associated with the aftermath of allodiploidization, such as haploidization and a more relaxed gene evolution. Expression patterns of the two sub-genomes within the two hybrid lineages are more similar than those of the shared A1 parent between the two lineages, showing that expression patterns of the parental genomes homogenized within a lineage. However, as genes that display differential parental expression in planta do not typically display the same pattern in vitro, we conclude that sub-genome-specific responses occur in both lineages. Overall, our study uncovers the genomic and transcriptomic plasticity during evolution of the filamentous fungal hybrid V. longisporum and illustrate its adaptive potential. ImportanceVerticillium is a genus of plant-associated fungi that include a handful of plant pathogens that collectively affect a wide range of hosts. On several occasions, haploid Verticillium species hybridized into the stable allodiploid species Verticillium longisporum, which is, in contrast to haploid Verticillium species, a Brassicaceae specialist. Here, we studied the evolutionary genome and transcriptome dynamics of V. longisporum and the impact of the hybridization. V. longisporum genomes display a mosaic structure due do genomic rearrangements between the parental chromosome sets. Similar to other allopolyploid hybrids, V. longisporum displays an ongoing loss of heterozygosity and a more relaxed gene evolution. Also, differential parental gene expression is observed, with an enrichment for genes that encode secreted proteins. Intriguingly, the majority of these genes displays sub-genome-specific responses under differential growth conditions. In conclusion, hybridization has incited the genomic and transcriptomic plasticity that enables adaptation to environmental changes in a parental allele-specific fashion.

microbiology↗

bioRxiv2018

Dynamic virulence-related regions of the fungal plant pathogen Verticillium dahliae display remarkably enhanced sequence conservation

Selection pressure impacts genomes unevenly, as different genes adapt with differential speed to establish an organisms optimal fitness. Plant pathogens co-evolve with their hosts, which implies continuously adaption to evade host immunity. Effectors are secreted proteins that mediate immunity evasion, but may also typically become recognized by host immune receptors. To facilitate effector repertoire alterations, in many pathogens, effector genes reside in dynamic genomic regions that are thought to display accelerated evolution, a phenomenon that is captured by the two-speed genome hypothesis. The genome of the vascular wilt pathogen Verticillium dahliae has been proposed to obey to a similar two-speed regime with dynamic, lineage-specific regions that are characterized by genomic rearrangements, increased transposable element activity and enrichment in in planta-induced effector genes. However, little is known of the origin of, and sequence diversification within, these lineage-specific regions. Based on comparative genomics among Verticillium spp. we now show differential sequence divergence between core and lineage-specific genomic regions of V. dahliae. Surprisingly, we observed that lineage-specific regions display markedly increased sequence conservation. Since single nucleotide diversity is reduced in these regions, host adaptation seems to be merely achieved through presence/absence polymorphisms. Increased sequence conservation of genomic regions important for pathogenicity is an unprecedented finding for filamentous plant pathogens and signifies the diversity of genomic dynamics in host-pathogen co-evolution.

microbiology↗

bioRxiv2018

Nuclear and mitochondrial genomes of the hybrid fungal plant pathogen Verticillium longisporum display a mosaic structure

Allopolyploidization, genome duplication through interspecific hybridization, is an important evolutionary mechanism that can enable organisms to adapt to environmental changes or stresses. This increased adaptive potential of allopolyploids can be particularly relevant for plant pathogens in their quest for host immune response evasion. Allodiploidization likely caused the shift in host range of the fungal pathogen plant Verticillium longisporum, as V. longisporum mainly infects Brassicaceae plants in contrast to haploid Verticillium spp. In this study, we investigated the allodiploid genome structure of V. longisporum and its evolution in the hybridization aftermath. The nuclear genome of V. longisporum displays a mosaic structure, as numerous contigs consists of sections of both parental origins. V. longisporum encountered extensive genome rearrangements, whereas the contribution of gene conversion is negligible. Thus, the mosaic genome structure mainly resulted from genomic rearrangements between parental chromosome sets. Furthermore, a mosaic structure was also found in the mitochondrial genome, demonstrating its bi-parental inheritance. In conclusion, the nuclear and mitochondrial genomes of V. longisporum parents interacted dynamically in the hybridization aftermath. Conceivably, novel combinations of DNA sequence of different parental origin facilitated genome stability after hybridization and consecutive niche adaptation of V. longisporum.

genomics↗

bioRxiv2017

Evolution within the fungal genus Verticillium is characterized by chromosomal rearrangement and gene loss

The fungal genus Verticillium contains ten species, some of which are notorious plant pathogens causing vascular wilt diseases in host plants, while others are known as saprophytes and opportunistic plant pathogens. Whereas the genome of V. dahliae, the most notorious plan pathogen of the genus, has been well characterized, evolution and speciation of other members of the genus received little attention thus far. Here, we sequenced the genomes of the nine haploid Verticillium spp. to study evolutionary trajectories of their divergence from a last common ancestor. Frequent occurrence of chromosomal rearrangement and gene family loss was identified. In addition to ~11,000 core genes that are shared among all species, only 200-600 species-specific genes occur. Intriguingly, these species-specific genes show different features than core genes.

microbiology↗

bioRxiv2017

Tomato immune receptor Ve1 recognizes surface-exposed co-localized N- and C-termini of Verticillium dahliae effector Ave1

Effectors are secreted by plant pathogens to facilitate infection, often through deregulation of host immune responses. During host colonization, race 1 strains of the soil-borne vascular wilt fungus Verticillium dahliae secrete the effector protein Ave1 that triggers immunity in tomato genotypes that encode the Ve1 immune receptor. Homologs of V. dahliae Ave1 (VdAve1) are found in plants and in few plant pathogenic microbes, and are differentially recognized by Ve1. However, how VdAve1 is recognized by Ve1 remained unknown. Interestingly, C-terminally affinity-tagged versions of VdAve1 failed to activate Ve1-mediated immunity, suggesting that exposure of the C-terminus of VdAve1 is required for Ve1-mediated recognition. This was confirmed by subsequent analysis of C-terminal deletion mutants, and by domain swap experiments. Although required, only the C-terminus of VdAve1 is not sufficient to activate Ve1-mediated immunity. Intriguingly, a three-dimensional structural model of VdAve1 revealed that the N- and C-termini co-localize on a surface-exposed patch of the VdAve1 protein. Indeed, subsequent analyses of N-terminal deletion mutants confirmed that also the N-terminus of VdAve1 is required to activate Ve1-mediated immunity. Thus, we conclude that a surface-exposed patch of the VdAve1 protein that is composed by co-localized N- and C-termini is recognized by the tomato immune receptor Ve1.

plant biology↗

bioRxiv2017

A previously established divergent lineage of the hybrid fungal pathogen Verticillium longisporum emerges as stem striping pathogen in British oilseed rape

Population genetic structures illustrate evolutionary trajectories of organisms adapting to differential environmental conditions. Pathogen populations are typically shaped by co-evolution with their hosts through genetic co-structuring. Verticillium stem striping was mainly observed in continental Europe, but has recently emerged in other countries including the United Kingdom. The disease is caused by the hybrid fungal species Verticilliumlongisporum that originates from at least three separate hybridization events, yet strains from the hybridization event between Verticillium progenitor species A1 and D1 are mainly responsible for Verticillium stem striping. By using multi-locus genotype analysis, we reveal a hitherto un-described dichotomy within V. longisporum lineage A1/D1 that correlates with the geographic distribution of the isolates with an \"A1/D1 West\" and an \"A1/D1 East\" cluster according to their relative location in Europe. Genome comparison between representatives of the A1/D1 West and East clusters confirmed mutual common origin, excluding distinctiveness through separate hybridization events. The A1/D1 West population is responsible for the sudden emergence of Verticillium stem striping in the UK. Remarkably, this emergence is caused by a British V. longisporum population that is genetically more diverse than the entire A1/D1 East cluster. Conceivably, V. longisporum has previously established in the UK, but remained latent or undiagnosed as an oilseed rape pathogen until recently. This finding illustrates that a recent introduction is not a prerequisite for a pathogen to emerge, as environmental factors and cultural practices can also play a pivotal role in outbreaks of novel diseases.

microbiology↗