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Clive M. Brasier - One of the best experts on this subject based on the ideXlab platform.
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Sequence of RNA-dependent RNA Polymerase Genes Provides Evidence for Three More Distinct Mitoviruses in Ophiostoma Novo-ulmi Isolate Ld
Virus Genes, 2006Co-Authors: Michelle Doherty, Robert H. A. Coutts, Clive M. Brasier, Kenneth W. BuckAbstract:Three of the twelve double-stranded (ds) RNAs, dsRNAs 1a, 1b and 3b, which are located in the mitochondria of a Diseased isolate, Ld, of the Dutch Elm Disease fungus, Ophiostoma novo-ulmi have been cDNA cloned and sequenced. Examination of the sequences of the RdRp genes predicted from the nucleotide sequences of the three dsRNAs suggest that they constitute the genome of three new mitoviruses.
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cloning and sequence analysis of the mat b mat 2 genes from the three Dutch Elm Disease pathogens ophiostoma ulmi o novo ulmi and o himal ulmi
Fungal Biology, 2005Co-Authors: Mathieu Paoletti, Kenneth W. Buck, Clive M. BrasierAbstract:There were two successive pandemics of Dutch Elm Disease (DED) in Europe, parts of Asia and North America in the last century, caused by two ascomycete fungal species, Ophiostoma ulmi and O. novo-ulmi. A third DED species, O. himal-ulmi was later discovered in the Himalayas. For each of these three species, we now report on the cloning and analysis of a 2.2 kb sequence containing the coding region and 5′ and 3′ flanking sequences of the mating type B (MAT-B) gene, which is involved in the control of sexual compatibility. The amino acid sequence of the single protein encoded by the gene for each species contained a conserved DNA-binding motif called the high mobility group (HMG) box which showed significant sequence similarity to corresponding sequences in many ascomycete MAT-2 genes. Phylogenetic trees constructed from the MAT-B (renamed MAT-2 ) nucleotide and derived amino acid sequences showed distinct clades corresponding to the three Ophiostoma species and a clear separation of the O. novo-ulmi clade into the two subspecies americana and novo-ulmi. The 3′ flanking regions have been shown to contain variable numbers of repeated oligonucleotide sequences, the number of which is species-specific and readily distinguished by a simple PCR assay.
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Rapid Evolution of Introduced Plant Pathogens via Interspecific Hybridization
BioScience, 2001Co-Authors: Clive M. BrasierAbstract:P lant Disease epidemics resulting from introduction of exotic fungal pathogens are a well-known phenom- enon. Limited resistance in the host and excessive aggres- siveness in the pathogen (reflecting their lack of prior co- evolution) can result in an explosive outbreak of Disease. Introduction events also present a window of evolutionary op- portunity for the pathogen. In its endemic location, a plant pathogen tends to be subject to routine selection constraints, favoring maintenance of a relatively stable, if fluctuating, population structure over time. When introduced into a new environment, it will often be subject to novel or episodic se- lection, reflecting sudden exposure to new biotic and abiotic influences, such as a new host population, new vectors, new competitors, or a different climate. These influences provide the potential for rapid evolution (Brasier 1995). Falling within the category of episodic selection is the sud- den contact that can occur between closely related but pre- viously geographically isolated pathogens as a result of in- troductions. Theoretically, this process presents an opportunity for rapid emergence of new or modified pathogens via interspecific gene flow (Brasier 1995). Until recently, this phenomenon has been little studied. Now Dutch Elm Disease, a major ecological accident of the 20th century (Heybroek 1993), is providing remarkable insights into rapid evolution of a plant pathogen outside its en- demic environment. This article describes the migratory events and unusual genetic events that have occurred in this fungus and other new examples of rapid pathogen evo- lution via interspecific gene flow, and discusses some of the wider environmental, evolutionary, and quarantine impli- cations. The Dutch Elm Disease pathogens Elm trees (Ulmus) are confined mainly to the temperate re- gions of the Northern Hemisphere. China and Japan have a total of about 25 Elm species, while Eurasia, North Amer- ica, and the Himalayas each have about five or six species. Dutch Elm Disease (so called because the early seminal re- search was in The Netherlands (Holmes and Heybroek 1990)) is the Elm's main enemy. It is a wilt Disease, caused by ascomycete fungi of the genus Ophiostoma, that spreads within the tree's vascular system. The pathogens are trans- mitted from Diseased to healthy Elms by Elm bark beetles of the genus Scolytus (Fransen 1935, Webber and Brasier 1984).
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evolutionary relationships of the Dutch Elm Disease fungus ophiostoma novo ulmi to other ophiostoma species investigated by restriction fragment length polymorphism analysis of the rdna region
Journal of Phytopathology, 2000Co-Authors: N D Pipe, Clive M. Brasier, Kenneth W. BuckAbstract:Restriction fragment length polymorphisms (RFLPs) in the ribosomal RNA gene (rDNA) region were used to assess relationships between the Dutch Elm Disease fungi Ophiostoma novo-ulmi and Ophiostoma ulmi, the recently described Himalayan Dutch Elm Disease pathogen, Ophiostoma himal-ulmi, the morphologically similar sapstain fungi, Ophiostoma piceae and Ophiostoma quercus, and several Ophiostoma species from hardwood trees, including Ophiostoma stenoceras and Ophiostoma proliferum. A distance matrix and cluster analysis indicated that the rDNA region of O. himal-ulmi is more closely related to those of O. novo-ulmi and O. ulmi than to those of O. piceae and O. quercus and is more distantly related to O. stenoceras and the other Ophiostoma species, which formed a separate clade. The rDNA region of O. quercus was found to be at least as closely related to that of O. novo-ulmi and O. ulmi as it is to that of O. piceae. The implications of these results for the evolution of the Dutch Elm Disease fungi are discussed.
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viruses as biological control agents of the Dutch Elm Disease fungus ophiostoma novo ulmi
2000Co-Authors: Clive M. BrasierAbstract:Dutch Elm Disease (DED) is not a three organism “Elm-fungus-bark beetle” system, as originally believed. The DED fungus, Ophiostoma novo-ulmi, also often carries with it its own natural enemy, a type of virus known as a “d-factor.” These viruses are probably specific to the fungus. DED is therefore really an “Elm-fungus-fungal virus-bark beetle” system. A virus can sometimes so severely debilitate the O. novo-ulmi fungus that it critically reduces its effectiveness as an Elm pathogen, preventing it from entering the sapstream of Elm trees via the feeding wounds of the Elm bark beetles. Indeed in some situations, the viruses may exert a strong natural biological control over the O. novo-ulmi population. Their properties are therefore being studied under field conditions and in the laboratory with a view to their possible release either as natural or genetically modified biological control agents. Washington DC, Oregon, and New Zealand appear particularly favorable target areas for experimental release of natural viruses.
Louis Bernier - One of the best experts on this subject based on the ideXlab platform.
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RNAseq Analysis Highlights Specific Transcriptome Signatures of Yeast and Mycelial Growth Phases in the Dutch Elm Disease Fungus Ophiostoma novo-ulmi
G3: Genes Genomes Genetics, 2015Co-Authors: Martha Nigg, Jérôme Laroche, Christian R. Landry, Louis BernierAbstract:Fungal dimorphism is a complex trait and our understanding of the ability of fungi to display different growth morphologies is limited to a small number of model species. Here we study a highly aggressive dimorphic fungus, the ascomycete Ophiostoma novo-ulmi, which is a model in plant pathology and the causal agent of Dutch Elm Disease. The two growth phases that this fungus displays, i.e., a yeast phase and mycelial phase, are thought to be involved in key steps of Disease development. We used RNAseq to investigate the genome-wide gene expression profiles that are associated with yeast and mycelial growth phases in vitro. Our results show a clear molecular distinction between yeast and mycelial phase gene expression profiles. Almost 12% of the gene content is differentially expressed between the two phases, which reveals specific functions related to each growth phase. We compared O. novo-ulmi transcriptome profiles with those of two model dimorphic fungi, Candida albicans and Histoplasma capsulatum. Few orthologs showed similar expression regulation between the two growth phases, which suggests that, globally, the genes associated with these two life forms are poorly conserved. This poor conservation underscores the importance of developing specific tools for emerging model species that are distantly related to the classical ones. Taken together, our results provide insights into transcriptome regulation and molecular specificity in O. novo-ulmi and offer a new perspective for understanding fungal dimorphism.
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Genomics of the Dutch Elm Disease pathosystem: are we there yet?
iForest - Biogeosciences and Forestry, 2015Co-Authors: Louis Bernier, Mirella Aoun, J Dufour, Guillaume F Bouvet, Martha Nigg, André M. Comeau, Erika Sayuri Naruzawa, Karine V PlourdeAbstract:Abstract: During the last decades, the development of ever more powerful genetic, molecular and omic approaches has provided plant pathologists with a wide array of experimental tools for elucidating the intricacies of plant-pathogen interactions and proposing new control strategies. In the case of the Dutch Elm Disease (DED) pathosystem, these tools have been applied for advancing knowledge of the host (Ulmus spp.) and the causal agents (Ophiostoma ulmi, O. novo-ulmi and O. himal-ulmi). Genetic and molecular analyses have led to the identification, cloning and characterization of a few genes that contribute to parasitic fitness in the pathogens. Quantitative PCR and high-throughput methods, such as expressed sequence tag analysis, have been used for measuring gene expression and identifying subsets of Elm genes that are differentially expressed in the presence of O. novo-ulmi. These analyses have also helped identify genes that were differentially expressed in DED fungi grown under defined experimental conditions. Until recently, however, functional analysis of the DED fungi was hampered by the lack of protocols for efficient gene knockout and by the unavailability of a full genome sequence. While the selective inactivation of Ophiostoma genes by insertional mutagenesis remains a challenge, an alternative approach based on RNA interference is now available for down-regulating the expression of targeted genes. In 2013, the genome sequences of O. ulmi and O. novo-ulmi were publicly released. The ongoing annotation of these genomes should spark a new wave of interest in the DED pathosystem, as it should lead to the formal identification of genes modulating parasitic fitness. A better understanding of DED, however, also requires that omic approaches are applied to the study of the other biotic components of this pathosystem.
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Functional Annotation of the Ophiostoma novo-ulmi Genome: Insights into the Phytopathogenicity of the Fungal Agent of Dutch Elm Disease
Genome Biology and Evolution, 2015Co-Authors: Anne Marie Comeau, Volker Jacobi, Guillaume F Bouvet, Martha Nigg, Jérôme Laroche, Josée Dufour, Roger C. Levesque, Bernard Henrissat, Louis BernierAbstract:The ascomycete fungus Ophiostoma novo-ulmi is responsible for the pandemic of Dutch Elm Disease that has been ravaging Europe and North America for 50 years. We proceeded to annotate the genome of the O. novo-ulmi strain H327 that was sequenced in 2012. The 31.784-Mb nuclear genome (50.1% GC) is organized into 8 chromosomes containing a total of 8,640 protein-coding genes that we validated with RNA sequencing analysis. Approximately 53% of these genes have their closest match to Grosmannia clavigera kw1407, followed by 36% in other close Sordariomycetes, 5% in other Pezizomycotina, and surprisingly few (5%) orphans. A relatively small portion (~3.4%) of the genome is occupied by repeat sequences; however, the mechanism of repeat-induced point mutation appears active in this genome. Approximately 76% of the proteins could be assigned functions using Gene Ontology analysis; we identified 311 carbohydrate-active enzymes, 48 cytochrome P450s, and 1,731 proteins potentially involved in pathogen– host interaction, along with 7 clusters of fungal secondary metabolites. Complementary mating-type locus sequencing, mating tests, and culturing in the presence of Elm terpenes were conducted. Our analysis identified a specific genetic arsenal impacting the sexual and vegetative growth, phytopathogenicity, and signaling/plant–defense–degradation relationship between O. novo-ulmi and its Elm host and insect vectors. Introduction During the last centuries, increased movements of people and goods across countries and continents have favored the emergence and global spread of plant pathogens, insect pests, and invasive weeds which have substantially altered the landscape of several parts of the world. One well-documented example is Dutch Elm Disease (DED), the most destructive Disease of Elms. It has been estimated that over 1 billion mature Elms were killed by two successive pandemics since the early 1900s (Paoletti et al. 2005). The first pandemic, which prompted initial investigations by Dutch scientists shortly after the First World War (Holmes and Heybroek 1990), was caused by the ascomycete fungus Ophiostoma ulmi (Buisman) Nannf. As it spread relentlessly over Western Europe and, a few decades
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identification of transcripts up regulated in asexual and sexual fruiting bodies of the Dutch Elm Disease pathogen ophiostoma novo ulmi
Canadian Journal of Microbiology, 2010Co-Authors: Volker Jacobi, Mirella Aoun, J Dufour, Guillaume F Bouvet, Louis BernierAbstract:Suppression subtractive hybridization cDNA libraries were prepared from asexual synnemata (S-lib) and sexual perithecia (P-lib) fruiting bodies of the Dutch Elm Disease pathogen Ophiostoma novo-ulmi subsp. novo-ulmi isolate H327 (mating-type MAT1-1) consisting of 630 and 401 cDNA clones, respectively. Both libraries were differentially screened in duplicate with forward and reverse subtracted probes. Up-regulated S-lib transcripts included those with homologies to phosphoenolpyruvate carboxykinase and aquaporin. Up-regulated P-lib transcripts included those with homologies to aspartyl proteinase, DNA lyase 2, and part of a mating-type (MAT) protein containing a DNA-binding domain of the high-mobility group (HMG) type. Phylogenetic analyses of HMG domains present within the putative O. novo-ulmi MAT protein and within MAT1-1-3 and MAT1-2-1 proteins of other ascomycete fungi identified the O. novo-ulmi protein as a homologue of the MAT1-1-3 protein, which represents part of the so far uncharacterized O. novo-ulmi MAT1-1 idiomorph. Reverse transcription - quantitative real-time PCR indicated up-regulation of the MAT1-1-3 homologue in O. novo-ulmi perithecia and synnemata. The present work identifies, for the first time, proteins involved in the formation of asexual and sexual fruiting bodies in O. novo-ulmi and should be of interest to researchers concerned with reproduction, mating type, and sexuality of filamentous ascomycete fungi.
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identification and monitoring of ulmus americana transcripts during in vitro interactions with the Dutch Elm Disease pathogen ophiostoma novo ulmi
Physiological and Molecular Plant Pathology, 2010Co-Authors: Mirella Aoun, Brian Boyle, Volker Jacobi, Louis BernierAbstract:Molecular mechanisms underlying the interaction leading to Dutch Elm Disease were studied in vitro using Ulmus americana L. callus culture inoculated with budding cells of the fungal pathogen Ophiostoma novo-ulmi (Brasier). An interaction cDNA library employing suppression subtractive hybridization was constructed from infected Elm callus tissue 72 h post-inoculation. Five hundred and thirty-five expressed sequence tags, mostly from the host, were grouped into 314 unisequences and distributed into functional categories. After differential screening, 53 U. americana unisequences were considered upregulated during the interaction. The expression profiles at six time points of a subset of 18 Elm transcripts were analyzed in more detail by quantitative reverse-transcriptase polymerase chain reaction. Upregulated sequences included transcripts with sequence similarity to genes coding for different classes of pathogenesis-related proteins and enzymes belonging to different branches of the phenylpropanoid pathway. The possible association with compartmentalization-related compounds and phytoalexin production is discussed. This study provides, for the first time, snapshots of molecular mechanisms involved in the compatible interaction between U. americana and O. novo-ulmi. The interaction library dataset also represents a valuable genomic resource for the highly appreciated urban tree U. americana.
Kenneth W. Buck - One of the best experts on this subject based on the ideXlab platform.
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Sequence of RNA-dependent RNA Polymerase Genes Provides Evidence for Three More Distinct Mitoviruses in Ophiostoma Novo-ulmi Isolate Ld
Virus Genes, 2006Co-Authors: Michelle Doherty, Robert H. A. Coutts, Clive M. Brasier, Kenneth W. BuckAbstract:Three of the twelve double-stranded (ds) RNAs, dsRNAs 1a, 1b and 3b, which are located in the mitochondria of a Diseased isolate, Ld, of the Dutch Elm Disease fungus, Ophiostoma novo-ulmi have been cDNA cloned and sequenced. Examination of the sequences of the RdRp genes predicted from the nucleotide sequences of the three dsRNAs suggest that they constitute the genome of three new mitoviruses.
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cloning and sequence analysis of the mat b mat 2 genes from the three Dutch Elm Disease pathogens ophiostoma ulmi o novo ulmi and o himal ulmi
Fungal Biology, 2005Co-Authors: Mathieu Paoletti, Kenneth W. Buck, Clive M. BrasierAbstract:There were two successive pandemics of Dutch Elm Disease (DED) in Europe, parts of Asia and North America in the last century, caused by two ascomycete fungal species, Ophiostoma ulmi and O. novo-ulmi. A third DED species, O. himal-ulmi was later discovered in the Himalayas. For each of these three species, we now report on the cloning and analysis of a 2.2 kb sequence containing the coding region and 5′ and 3′ flanking sequences of the mating type B (MAT-B) gene, which is involved in the control of sexual compatibility. The amino acid sequence of the single protein encoded by the gene for each species contained a conserved DNA-binding motif called the high mobility group (HMG) box which showed significant sequence similarity to corresponding sequences in many ascomycete MAT-2 genes. Phylogenetic trees constructed from the MAT-B (renamed MAT-2 ) nucleotide and derived amino acid sequences showed distinct clades corresponding to the three Ophiostoma species and a clear separation of the O. novo-ulmi clade into the two subspecies americana and novo-ulmi. The 3′ flanking regions have been shown to contain variable numbers of repeated oligonucleotide sequences, the number of which is species-specific and readily distinguished by a simple PCR assay.
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evolutionary relationships of the Dutch Elm Disease fungus ophiostoma novo ulmi to other ophiostoma species investigated by restriction fragment length polymorphism analysis of the rdna region
Journal of Phytopathology, 2000Co-Authors: N D Pipe, Clive M. Brasier, Kenneth W. BuckAbstract:Restriction fragment length polymorphisms (RFLPs) in the ribosomal RNA gene (rDNA) region were used to assess relationships between the Dutch Elm Disease fungi Ophiostoma novo-ulmi and Ophiostoma ulmi, the recently described Himalayan Dutch Elm Disease pathogen, Ophiostoma himal-ulmi, the morphologically similar sapstain fungi, Ophiostoma piceae and Ophiostoma quercus, and several Ophiostoma species from hardwood trees, including Ophiostoma stenoceras and Ophiostoma proliferum. A distance matrix and cluster analysis indicated that the rDNA region of O. himal-ulmi is more closely related to those of O. novo-ulmi and O. ulmi than to those of O. piceae and O. quercus and is more distantly related to O. stenoceras and the other Ophiostoma species, which formed a separate clade. The rDNA region of O. quercus was found to be at least as closely related to that of O. novo-ulmi and O. ulmi as it is to that of O. piceae. The implications of these results for the evolution of the Dutch Elm Disease fungi are discussed.
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MULTIPLE MITOCHONDRIAL VIRUSES IN AN ISOLATE OF THE Dutch Elm Disease FUNGUS OPHIOSTOMA NOVO-ULMI
Virology, 1999Co-Authors: Yiguo Hong, Sharon L Dover, Thomas E. Cole, Clive M. Brasier, Kenneth W. BuckAbstract:Abstract The nucleotide sequences of three mitochondrial virus double-stranded (ds) RNAs, RNA-4 (2599 nucleotides), RNA-5 (2474 nucleotides), and RNA-6 (2343 nucleotides), in a Diseased isolate Log1/3–8d 2 (Ld) of the Dutch Elm Disease fungus Ophiostoma novo-ulmi have been determined. All these RNAs are A-U-rich (71–73% A + U residues). Using the fungal mitochondrial genetic code in which UGA codes for tryptophan, the positive-strand of each of RNAs 4, 5, and 6 contains a single open reading frame (ORF) with the potential to encode a protein of 783, 729, and 695 amino acids, respectively, all of which contain conserved motifs characteristic of RNA-dependent RNA polymerases (RdRps). Sequence comparisons showed that these RNAs are related to each other and to a previously characterized RNA, RNA-3a, from the same O. novo-ulmi isolate, especially within the RdRp-like motifs. However, the overall RNA nucleotide and RdRp amino acid sequence identities were relatively low (43–55% and 20–32%, respectively). The 5′- and 3′-terminal sequences of these RNAs are different, but they can all be folded into potentially stable stem-loop structures. Those of RNA-4 and RNA-6 have inverted complementarity, potentially forming panhandle structures. Their molecular and biological properties indicate that RNAs 3a, 4, 5, and 6 are the genomes of four different viruses, which replicate independently in the same cell. These four viruses are also related to a mitochondrial RNA virus from another fungus, Cryphonectria parasitica , recently designated the type species of the Mitovirus genus of the Narnaviridae family, and to a virus from the fungus Rhizoctonia solani . It is proposed that the four O. novo-ulmi mitochondrial viruses are assigned to the Mitovirus genus and designated O. novo-ulmi mitovirus (OnuMV) 3a-Ld, 4-Ld, 5-Ld, and 6-Ld, respectively. Northern blot analysis indicated that O. novo-ulmi Ld nucleic acid extracts contain more single-stranded (ss, positive-stranded) RNA than dsRNA for all three newly described mitoviruses. O. novo-ulmi RNA-7, previously believed to be a satellite-like RNA, is shown to be a defective RNA, derived from OnuMV4-Ld RNA by multiple internal deletions. OnuMV4-Ld is therefore the helper virus for the replication of both RNA-7 and another defective RNA, RNA-10. Sequence comparisons indicate that RNA-10 could be derived from RNA-7, as previously suggested, or derived directly from RNA-4.
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complexity of virus like double stranded rn a elements in a Diseased isolate of the Dutch Elm Disease fungus ophiostoma novo ulmi
Journal of Phytopathology, 1998Co-Authors: Thomas E. Cole, Yiguo Hong, Clive M. Brasier, B M Mcller, Kenneth W. BuckAbstract:High resolution polyacrylamide gel electrophoresis has shown that a Diseased isolate of the Dutch Elm Disease fungus, Ophiostoma novo-ulmi, Logl/3–8d2 (Ld), contains 12 virus-like double-stranded (ds) RNA segmetits instead of the 10 segments previously reported. DsRNAs 1 and 3 were each separated into two segtnents, designated dsRNA-la, dsRNA-lb, dsRNA-3a and dsRNA-3b, respectively. The relative nnobilities of dsRNAs 3a and 3b were reversed when electrophoresed in 4 and 8% gels, indicating that structure as well as size cati contribute to electrophoretic mobility. Analysis of the dsRNA profiles of healthy isolate W2toll (the progenitor of Ld), and healthy single-conidial isolates derived from Ld, showed that dsRNAs la, lb, 3a and 3b were not the cause of the Ld Diseased phenotype. Two single conidial isolates were obtained which contained only dsRNA-6 which therefore replicates atitonomously. Overall the results indicated that the 12 Ld dsRNAs are comprised of several independent replicons. The single-stranded form of dsRNA-10, which potentially has a high level of base-pairing, was shown to fractionate with the dsRNA. Zusammenfassung Mit Hilfe der Hochauflosungspolyacrylamidgelelektrophorese konnte gezeigt werden, dasein erkranktes Isolat des Ulmensterbenerregers Ophiostoma novo-ulmi, Log1/3–8d2 (Ld) 12 statt 10 der vorherbeschriebenen virusahnlichen, doppelstrangigen (ds) RNA-Segmente enthielt. DsRNA 1 und 3 wurden in je zwei Segmente aufgeteilt, die als dsRNA-la, dsRNA-lb, dsRNA-3a bzw. dsRNA-3b gekennzeichnet wurden. Die relativen Mobilitaten von dsRNA-3a und -3b wurden nach einer Elektrophorese in 4%igem bzw. 8%igem Gel umgekehrt, ein Zeichen dafur das sowohl die Struktur als auch die Grose der elektrophoretiscben Mobilitat bestimmt warden kann. Eine Analyse der dsRNA-Profile des gesunden Isolates W2toll (der Vorfahre von Ld), sowie gesunden Einzelsporisolaten von Ld zeigten, das die dsRNA 1a, 1b, 3a und 3b nicht die Ursache des erkrankten Ld-Phenotyps waren. Zwei Einzelsporisolate wurden gewonnen, die nur dsRNA-6 enthielten, die dsRNA-6 mus sich also selbstandig vermehren. Im allgemeinen zeigten die Ergebnisse, das die 12 Kd dsRNA-Segmente aus mehreren unabhangigen Replikons bestehen. Es konnte gezeigt werden, das die einzelstrangige Form des dsRNA-10-Segments, welches das Potential fur einen hohen Grad von Basenpaarungen hat, mit den dsRNA-Segmenten fraktioniert.
N D Pipe - One of the best experts on this subject based on the ideXlab platform.
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evolutionary relationships of the Dutch Elm Disease fungus ophiostoma novo ulmi to other ophiostoma species investigated by restriction fragment length polymorphism analysis of the rdna region
Journal of Phytopathology, 2000Co-Authors: N D Pipe, Clive M. Brasier, Kenneth W. BuckAbstract:Restriction fragment length polymorphisms (RFLPs) in the ribosomal RNA gene (rDNA) region were used to assess relationships between the Dutch Elm Disease fungi Ophiostoma novo-ulmi and Ophiostoma ulmi, the recently described Himalayan Dutch Elm Disease pathogen, Ophiostoma himal-ulmi, the morphologically similar sapstain fungi, Ophiostoma piceae and Ophiostoma quercus, and several Ophiostoma species from hardwood trees, including Ophiostoma stenoceras and Ophiostoma proliferum. A distance matrix and cluster analysis indicated that the rDNA region of O. himal-ulmi is more closely related to those of O. novo-ulmi and O. ulmi than to those of O. piceae and O. quercus and is more distantly related to O. stenoceras and the other Ophiostoma species, which formed a separate clade. The rDNA region of O. quercus was found to be at least as closely related to that of O. novo-ulmi and O. ulmi as it is to that of O. piceae. The implications of these results for the evolution of the Dutch Elm Disease fungi are discussed.
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rare interspecific hybrids in natural populations of the Dutch Elm Disease pathogens ophiostoma ulmi and o novo ulmi
Fungal Biology, 1998Co-Authors: Clive M. Brasier, N D Pipe, Susan Kirk, K W BuckAbstract:Ophiostoma ulmi and O. novo-ulmi are partly reproductively isolated, morphologically, behaviourally and molecularly distinct species responsible for the first and current pandemics of Dutch Elm Disease, respectively. Among >11000 isolates sampled from Dutch Elm Disease sites across Eurasia and North America since 1973, nine could not be assigned to O. ulmi or O. novo-ulmi . Of these isolates one (P129) was from Poland and eight (d10, d11, e12, e27, e28, e37, f30 and g3) were from a single bark sample in Portugal. These nine isolates were termed ‘fast-waxy’ isolates because of their unusual cultural characteristics. The possibility that they were interspecific hybrids was investigated. When compared with O. ulmi and O. novo-ulmi for colony pattern, growth-rate, optimum temperature for growth, vascular wilt ability, Elm bark colonizing ability, cerato-ulmin toxin production, ability to fertilize (as ♂) O. novo-ulmi , and ability to be fertilized (as ♀) by O. ulmi , they exhibited a combination of O. ulmi -like, O. novo-ulmi -like, intermediate or novel characters (female sterility) consistent with their being hybrids. P129 and representative Portuguese isolates d10 and e27 each exhibited a different combination of characters, indicating each was a different hybrid genotype. When d10 and e27 were independently crossed to the same O. novo-ulmi isolate, differences in their F 1 progeny sets for growth-rate and pathogenicity distributions were consistent with their being different recombinant genotypes. A molecular analysis of P129, d10 and e27 using RAPDs of genomic DNA, rDNA RFLPs and cerato-ulmin gene sequences confirmed that each was a unique interspecific hybrid. The mechanism of origin of these hybrids and their evolutionary significance are discussed. Combined experimental and circumstantial evidence indicates that they are relatively unfit, rare and probably transient, and that they arise when O. novo-ulmi invades territory occupied by O. ulmi and replaces it. Nonetheless, the possibility that the hybrids act as a genetic bridge, facilitating transfer of novel vegetative compatibility loci and other loci form O. ulmi to O. novo-ulmi at recent epidemic fronts, requires investigation.
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comparison of the cerato ulmin cu gene sequences of the himalayan Dutch Elm Disease fungus ophiostoma himal ulmi with those of o ulmi and o novo ulmi suggests that the cu gene of o novo ulmi is unlikely to have been acquired recently from o himal ulmi
Fungal Biology, 1997Co-Authors: N D Pipe, Kenneth W. Buck, Clive M. BrasierAbstract:Cerato-ulmin (CU) is a low molecular weight hydrophobin protein secreted at high levels in vitro by the highly aggressive Dutch Elm Disease pathogen, O. novo-ulmi, but at much lower levels by the less aggressive O. ulmi. The recent discovery of an endemic Dutch Elm Disease fungus in the Himalayas, Ophiostoma himal-ulmi, which is a separate species from O. ulmi and O. novo-ulmi, yet like O. novo-ulmi produces high levels of CU in vitro, suggested that O. novo-ulmi may have acquired its cu gene from O. himal-ulmi. To investigate this possibility we have compared the nucleotide sequences of the cu gene isolates of O. himal-ulmi with those of O. ulmi and of the EAN and NAN races of O. novo-ulmi. Alignments of nucleotide sequences and their derived amino acid sequences are presented, allowing estimations of evolutionary relationships to be made. These comparisons indicate that the cu gene of O. himal-ulmi is less closely related to the cu gene of either O. ulmi or O. novo-ulmi than the cu gene of O. novo-ulmi is to that of O. ulmi; hence the cu gene of O. novo-ulmi is unlikely to have been acquired recently from O. himal-ulmi.
M D Mehrotra - One of the best experts on this subject based on the ideXlab platform.
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ophiostoma himal ulmi sp nov a new species of Dutch Elm Disease fungus endemic to the himalayas
Fungal Biology, 1995Co-Authors: Clive M. Brasier, M D MehrotraAbstract:In September–October 1993 a research survey was conducted in northern Himachal Pradesh, western Himalayas, as part of an investigation into the origins of Dutch Elm Disease. No Disease symptoms were observed in the area, but an apparently endemic Ophiostoma similar to the known Dutch Elm Disease pathogens Ophiostoma ulmi and O. novo-ulmi was isolated from around breeding galleries of scolytid beetles in the bark of Ulmus wallichiana . Over 200 isolations of the fungus were made. These were later resolved into a minimum of 20 different genotypes, which were used to further characterize the fungus. Like O. ulmi and O. novo-ulmi the Himalayan Ophiostoma is outcrossing and heterothallic, with two sexual compatibility types, A and B, occurring in a near 1:1 ratio in nature. In interfertility tests, strong pre- and post-zygotic reproductive isolation was revealed between the Himalayan Ophiostoma and sexually compatible isolates of O. ulmi or the EAN or NAN races of O. novo-ulmi . The Himalayan Ophiostoma also exhibits a unique combination of physiological and morphological characteristics including a distinctive colony type, ability to produce synnemata on malt extract agar, production of perithecia with long necks, a very high level of cerato-ulmin toxin production in liquid shake cultures, and moderate to strong vascular wilt pathogenicity on U. procera . Its reproductive isolation from O. ulmi and O. novo-ulmi and its other biological features demonstrate that it is a distinct sibling species from O. ulmi and O. novo-ulmi , and it is designated as a new species, Ophiostoma himal-ulmi sp. nov. The discovery of O. himal-ulmi should help resolve the problem of the origins of Dutch Elm Disease, while the occurrence of an apparently endemic Dutch Elm Disease system in the Himalayas may present new opportunities for the biological control of the Disease elsewhere. These possibilities are discussed.
