The Experts below are selected from a list of 666 Experts worldwide ranked by ideXlab platform

Louis Bernier - One of the best experts on this subject based on the ideXlab platform.

  • Hybridization and introgression drive genome evolution of Dutch elm disease pathogens
    Nature Ecology & Evolution, 2020
    Co-Authors: Pauline Hessenauer, Louis Bernier, Richard C Hamelin, Anna Fijarczyk, Hélène Martin, Julien Prunier, Guillaume Charron, Jérôme Chapuis, Philippe Tanguay, Christian R. Landry
    Abstract:

    Hybridization and the resulting introgression can drive the success of invasive species via the rapid acquisition of adaptive traits. The Dutch elm disease pandemics in the past 100 years were caused by three fungal lineages with permeable reproductive barriers: Ophiostoma ulmi , Ophiostoma Novo-Ulmi subspecies Novo-Ulmi and Ophiostoma Novo-Ulmi subspecies americana . Using whole-genome sequences and growth phenotyping of a worldwide collection of isolates, we show that introgression has been the main driver of genomic diversity and that it impacted fitness-related traits. Introgressions contain genes involved in host–pathogen interactions and reproduction. Introgressed isolates have enhanced growth rate at high temperature and produce different necrosis sizes on an in vivo model for pathogenicity. In addition, lineages diverge in many pathogenicity-associated genes and exhibit differential mycelial growth in the presence of a proxy of a host defence compound, implying an important role of host trees in the molecular and functional differentiation of these pathogens. Genome analysis of fungi responsible for Dutch elm disease shows that introgression has contributed to genomic diversity and has impacted fitness-related traits in these pathogens.

  • From yeast to hypha: defining transcriptomic signatures of the morphological switch in the dimorphic fungal pathogen Ophiostoma Novo-Ulmi.
    BMC Genomics, 2016
    Co-Authors: Martha Nigg, Louis Bernier
    Abstract:

    Yeast-to-hypha transition is a major morphological change in fungi. Molecular regulators and pathways that are involved in this process have been extensively studied in model species, including Saccharomyces cerevisiae. The Mitogen-Actived Protein Kinase (MAPK) cascade, for example, is known to be involved in the yeast-to-pseudohypha switch. Yet the conservation of mechanisms regulating such morphological changes in non-model fungi is still poorly understood. Here, we investigate cell remodeling and transcriptomic modifications that occur during this morphological switch in the highly aggressive ascomycete fungus Ophiostoma Novo-Ulmi, the causal agent of Dutch elm disease. Using a combination of light microscopy, scanning electron microscopy and flow cytometry, we demonstrate that the morphological switch occurs in less than 27 h, with phenotypic cell modifications being detected within the first 4 h. Using RNAseq, we found that over 22% of the genome of O. Novo-Ulmi is differentially expressed during the transition. By performing clustering analyses of time series gene expression data, we identified several sets of genes that are differentially expressed according to distinct and representative temporal profiles. Further, we found that several genes that are homologous to S. cerevisiae MAPK genes are regulated during the yeast-to-hypha transition in O. Novo-Ulmi and mostly over-expressed, suggesting convergence in gene expression regulation. Our results are the first report of a time-course experiment monitoring the morphological transition in a non-model Sordariomycota species and reveal many genes of interest for further functional investigations of fungal dimorphism.

  • Genome-wide analysis of parasitic fitness traits in a non-model tree pathogen
    Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2016
    Co-Authors: Louis Bernier
    Abstract:

    AbstractThe ascomycete fungus Ophiostoma Novo-Ulmi is the highly aggressive pathogen responsible for the current, highly destructive, pandemic of Dutch elm disease (DED). In spite of its economic and ecological impact, O. Novo-Ulmi is not considered a model species, even though this fungus is easily grown in the laboratory and amenable to standard genetic and molecular investigations. The nuclear genomes of O. Novo-Ulmi and related species O. ulmi were recently sequenced and annotated, thus providing new opportunities for deciphering the complex basis of parasitic fitness in these pathogens. Comparative in silico analyses with genomes from other, well-characterized fungal and bacterial genomes have confirmed that the DED pathogens possess several hundred orthologues of genes encoding putative pathogenicity factors. Physiological, molecular, genomic and transcriptomic approaches are currently being used for studying yeast-mycelium dimorphism, a trait that the DED fungi share with several other pathogens of...

  • Diversity in yeast-mycelium dimorphism response of the Dutch elm disease pathogens: the inoculum size effect
    Canadian Journal of Microbiology, 2016
    Co-Authors: Marie-Ève Wedge, Martha Nigg, Erika Sayuri Naruzawa, Louis Bernier
    Abstract:

    Dutch elm disease (DED) is caused by the dimorphic fungi Ophiostoma ulmi, Ophiostoma Novo-Ulmi, and Ophiostoma himal-ulmi. A cell population density-dependent phenomenon related to quorum sensing was previously shown to affect the reversible transition from yeast-like to mycelial growth in liquid shake cultures of O. Novo-Ulmi NRRL 6404. Since the response to external stimuli often varies among DED fungal strains, we evaluated the effect of inoculum size on 8 strains of the 3 species of DED agents by determining the proportion of yeast and mycelium produced at different spore inoculum concentrations in defined liquid shake medium. The results show that not all DED fungi strains respond similarly to inoculum size effect, since variations were observed among strains. It is thus possible that the different strains belonging to phylogenetically close species use different signalling molecules or molecular signalling pathways to regulate their growth mode via quorum-sensing mechanisms.

  • 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, 2015
    Co-Authors: Martha Nigg, Jérôme Laroche, Christian R. Landry, Louis Bernier
    Abstract:

    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.

Alejandro Solla - One of the best experts on this subject based on the ideXlab platform.

  • Genetic variation and heritability estimates of Ulmus minor and Ulmus pumila hybrids for budburst, growth and tolerance to Ophiostoma Novo-Ulmi
    Iforest - Biogeosciences and Forestry, 2015
    Co-Authors: Alejandro Solla, J. C. López-almansa, Juan A Martin
    Abstract:

    Abstract: Seedlings obtained by crossing Ulmus minor and U. minor × U. pumila clones were assessed for flowering, bark beetle damage, vegetative budburst, height growth and resistance to Ophiostoma Novo-Ulmi. Ramets and open pollinated seedlings obtained from the parent trees were assessed for the same traits. Most progenies had similar traits to their parents, but some presented heterosis in annual growth or resistance to O. Novo-Ulmi. Leaf wilting was significantly lower in progenies with U. minor × U. pumila rather than U. minor as female parent (21.5 and 30.6%, respectively; P

  • genetic variation and heritability estimates of ulmus minor and ulmus pumila hybrids for budburst growth and tolerance to Ophiostoma novo ulmi
    Iforest - Biogeosciences and Forestry, 2014
    Co-Authors: Alejandro Solla, J C Lopezalmansa, J. A. Martin
    Abstract:

    Abstract: Seedlings obtained by crossing Ulmus minor and U. minor × U. pumila clones were assessed for flowering, bark beetle damage, vegetative budburst, height growth and resistance to Ophiostoma Novo-Ulmi. Ramets and open pollinated seedlings obtained from the parent trees were assessed for the same traits. Most progenies had similar traits to their parents, but some presented heterosis in annual growth or resistance to O. Novo-Ulmi. Leaf wilting was significantly lower in progenies with U. minor × U. pumila rather than U. minor as female parent (21.5 and 30.6%, respectively; P<0.05). Resistance to O. Novo-Ulmi increased significantly as a function of increased amounts of U. pumila germplasm from the female parent, suggesting that resistance to Dutch elm disease is primarily transmitted from the mother. Budburst occurred earlier in seedlings with low rather than high growth rates (P=0.0007) and percentage of wilting was negatively related to early budburst (P<0.0001). Other phenotypic relations included percentage of flowering trees and annual height growth (rp=0.44; P=0.0042), percentage of flowering trees and vegetative budburst (rp=-0.53; P=0.0004) and percentage of beetle-affected trees and annual height growth (rp=0.60; P<0.0001). Heritability estimates obtained from the regression and variance components methods ranged from 0.06 ± 0.04 to 0.64 ± 0.18, 0.10 ± 0.05 to 0.69 ± 0.17, and 0.13 ± 0.32 to 0.71 ± 0.22 for budburst, growth and tolerance to O. Novo-Ulmi, respectively. Broad- and narrow-sense heritability values were higher when estimated 60 days post inoculation (dpi) than 15, 30 or 120 dpi. Heritability estimates and genetic gains reported indicate a high degree of additive genetic control and show the effectiveness of selection for Dutch elm disease resistance and rapid tree growth.

  • evaluating methyl jasmonate for induction of resistance to fusarium oxysporum f circinatum and Ophiostoma novo ulmi
    Forest Systems, 2012
    Co-Authors: Maria Vivas, Juan A Martin, Alejandro Solla
    Abstract:

    Damping off is probably the most common disease affecting seedlings in forest nurseries. In south-western Europe, the pitch canker and the Dutch elm disease cause relevant economic looses in forests, mostly in adult trees. The ability of the chemical plant elicitor methyl jasmonate (MeJA) to induce resistance in Pinus pinaster against Fusarium oxysporum and F. circinatum, and in Ulmus minor against Ophiostoma Novo-Ulmi was examined. In a first experiment, an aqueous solution of MeJA 5 mM was applied to P. pinaster seeds by immersion or spray, and different concentrations of MeJA (0, 0.1, 0.5, 1, 5 and 10 mM) were tested in seedlings before inoculations with F. oxysporum (105 and 107 spores mL–1). In a second experiment, 6-months-old P. pinaster seedlings were sprayed with 0 and 25 mM of MeJA, and later challenged with mycelium of F. circinatum. Finally, 4-year-old U. minor trees were sprayed with 0, 50 and 100 mM of MeJA and subsequently inoculated with O. Novo-Ulmi (106 spores mL–1). MeJA did not protect P. pinaster seeds and seedlings against F. oxysporum, probably because plants were too young for the physiological mechanisms responsible for resistance to be induced. Based on the morphological changes observed in the treated 6-months-old P. pinaster seedlings (reduction of growth and increased resin duct density), there is evidence that MeJA could have activated the mechanisms of resistance. However, 25 mM MeJA did not reduce plant mortality, probably because the spread of the virulent F. circinatum strain within the tree tissues was faster than the formation of effective defense responses. Based on the lack of phenological changes observed in the treated elms, there is no evidence that MeJA would cause induction of resistance. These results suggest that the use of MeJA to prevent F. oxysporum and F. circinatum in P. pinaster seedlings in nurseries and O. Novo-Ulmi in U. minor trees should be discarded.

  • bordered pit and ray morphology involvement in elm resistance to Ophiostoma novo ulmi
    Canadian Journal of Forest Research, 2009
    Co-Authors: Juan A Martin, Paloma De Palaciosp De Palacios, Alejandro Solla, Luis García Esteban
    Abstract:

    The main objective of this study was to identify differential anatomical features between Ulmus pumila L. and Ulmus minor Mill. clones resistant to Dutch elm disease and U. minor clones susceptible to Dutch elm disease, with a focus on the intervascular pits and medullary rays. Resistant elms showed lower mean values than susceptible elms for pit membrane diameter, pit aperture area, pit membrane abundance per vessel-wall area, ray width, and ray tangential area. A principal component analysis of the parameters measured revealed slight differentiation between species but clearly grouped U. minor clones according to their susceptibility group. In comparison with susceptible elms, the pit structure observed in resistant elms may limit passive fungal spread within the sapflow, lower the probability of fungal cells passively reaching pit membranes, and reduce the vulnerability of the xylem to cavitation. Similarly, the ray structure observed in the resistant elms is likely to reduce the amount of easily acces...

  • Detection of differential changes in lignin composition of elm xylem tissues inoculated with Ophiostoma novo‐ulmi using Fourier transform‐infrared spectroscopy
    Forest Pathology, 2007
    Co-Authors: Juan A Martin, Alejandro Solla, Stephen Woodward
    Abstract:

    Summary Differences in elm susceptibility against Ophiostoma Novo-Ulmi have been related with differences in timing and degree of the tree defence responses. In this study, we used Fourier transform-infrared spectroscopy, coupled with chemometric methods, to detect progressive changes in the metabolic profile of Ulmus minor and U. minor × U. pumila xylem tissues after inoculation with O. Novo-Ulmi. Differences between control and inoculated trees were detected at 30 and 60 days post-inoculation (dpi) in U. minor, and at 15, 30 and 60 dpi in U. minor × U. pumila. These differences were related with increased levels of lignin in the xylem tissues, suggesting an earlier defence response to the infection in the hybrids.

Juan A Martin - One of the best experts on this subject based on the ideXlab platform.

  • Functional traits of three Ulmus minor fungal endophytes and their role in host resistance to Ophiostoma Novo-Ulmi
    bioRxiv, 2020
    Co-Authors: Clara Martínez-arias, Juan Sobrino-plata, Sara Ormeño-moncalvillo, Jesús Rodríguez-calcerrada, Juan A Martin
    Abstract:

    Certain fungal endophytes are known to improve plant resistance to biotic stresses in forest trees. In this study, three stem fungal endophytes belonging to classes Cystobasidiomycetes, Eurotiomycetes and Dothideomycetes were selected among 210 isolates for their potential as enhancers of Ulmus minor resistance to Ophiostoma Novo-Ulmi. We evaluated phenotypic traits of these endophytes that could be beneficial for O. Novo-Ulmi inhibition in the host plant. Under in vitro conditions, the Dothideomycetous isolate YCB36 strongly inhibited O. Novo-Ulmi growth, released antipathogen VOCs, chitinases and siderophores, and overlapped with the pathogen in nutrient utilization patterns. These functional traits could explain the 40% reduction in leaf wilting due to O. Novo-Ulmi in elm trees pre-inoculated with this endophyte. Ulmus minor trees responded to endophyte inoculation with increased stomatal conductance and higher amounts of flavonoids and total phenolic compounds in xylem tissues, suggesting induction of defence metabolism.

  • Growth resilience and oxidative burst control as tolerance factors to Ophiostoma Novo-Ulmi in Ulmus minor.
    Tree Physiology, 2019
    Co-Authors: Juan A Martin, Juan Sobrino-plata, Begoña Coira, David Medel, Carmen Collada
    Abstract:

    : The Dutch elm disease (DED) pathogens, Ophiostoma ulmi (Buisman) Nannf. and the more aggressive Ophiostoma Novo-Ulmi Brasier, have decimated European elm populations in the last 100 years. Today, the number of tolerant elm varieties available on the market is limited, partly due to the long breeding cycles and expensive facilities they require. Developing a low-cost technique to allow early screening of elm tolerance based on simple morphological and/or biochemical traits would considerably boost elm breeding and research. Within this general aim, we developed an in vitro plant culture system to (i) characterize stress responses to O. Novo-Ulmi-root inoculation in two Ulmus minor Mill. clones of contrasting susceptibility level to DED (termed 'tolerant' and 'susceptible') and (ii) compare the upward dispersal rate of the pathogen in the two clones. Constitutive xylem anatomy was similar in both clones, indicating that differences in plant responses to the pathogen are not attributable to anatomical factors (e.g., conduit size). Susceptible plantlets suffered a significant delay in apical growth and a decrease in chlorophyll content at 21 days post-inoculation (dpi). The rate of pathogen dispersal from roots to aerial tissues was similar in both clones. However, the tolerant clone showed a marked increase in lipid peroxidation at 1 dpi, while the susceptible clone showed enhanced values of lipid peroxidation during most of the experimental period (1-21 dpi). Despite wide stem colonization by the pathogen, the tolerant clone effectively regulated the oxidative stress levels and showed remarkable resilience to inoculation. These results extend current knowledge on elm defense mechanisms, and the proposed in vitro plant culture system emerges as a promising early screening method for tolerance to improve elm breeding.

  • gene expression trade offs between defence and growth in english elm induced by Ophiostoma novo ulmi
    Plant Cell and Environment, 2018
    Co-Authors: Pedro Perdiguero, Juan A Martin, Juan Sobrinoplata, Martin Venturas, Carmen Collada
    Abstract:

    Wilt diseases caused by vascular pathogens include some of the most damaging stresses affecting trees. Dutch elm disease (DED), caused by the fungus Ophiostoma Novo-Ulmi, destroyed most of North American and European elm populations in the 20th century. The highly susceptible English elm, also known as Atinian clone, suffered the highest mortality rates during the last pandemic event, probably due to its lack of genetic diversity. To study the DED pathosystem, we inoculated English elm ramets with O. Novo-Ulmi and evaluated xylem anatomy, molecular response and disease symptoms. The high DED susceptibility of the clone was linked to xylem structure. The transcript levels changed significantly for 1,696 genes during O. Novo-Ulmi invasion. Genes covering different steps of the plant immune system were identified, many of which showed homology with Arabidopsis thaliana genes involved in systemic acquired resistance (SAR). Induction of several pathogenesis-related (PR) proteins and repression of fasciclin-like arabinogalactan proteins (FLAs) and other cell wall biosynthesis pathways evidence unbalanced costs between growth and defence mechanisms far from the inoculation point. This study sheds light on elm molecular defence mechanisms against DED.

  • Nutritional niche overlap potentiates the use of endophytes in biocontrol of a tree disease
    BioControl, 2015
    Co-Authors: Kathrin Blumenstein, Juan A Martin, Benedicte R. Albrectsen, Malin Hultberg, Thomas N. Sieber, Marjo Helander, Johanna Witzell
    Abstract:

    Asymptomatic endophytic fungi are often regarded as potent biocontrol agents in plants, but the competitive interactions between endophytes and other microbes within the same host plant are poorly understood. We tested a hypothesis that as compared to asymptomatic endophytes, an aggressive pathogen inhabiting the same host is able to utilize carbon substrates more efficiently. Using phenotype microarray, we determined the carbon utilization profiles of the highly virulent Dutch elm disease (DED) pathogen Ophiostoma novo - ulmi , and four asymptomatic elm ( Ulmus spp.) endophyte isolates that were selected based on their differential association to the DED-susceptibility pattern of the host elms. The competitive interactions between isolates were evaluated using a niche overlap index. In contrast to our hypothesis, the studied endophytes exhibited extensive niche overlap with the pathogen, suggesting that some endophyte strains might protect elms against DED-pathogen through competition for substrates and provide new tools for biocontrol of DED.

  • Genetic variation and heritability estimates of Ulmus minor and Ulmus pumila hybrids for budburst, growth and tolerance to Ophiostoma Novo-Ulmi
    Iforest - Biogeosciences and Forestry, 2015
    Co-Authors: Alejandro Solla, J. C. López-almansa, Juan A Martin
    Abstract:

    Abstract: Seedlings obtained by crossing Ulmus minor and U. minor × U. pumila clones were assessed for flowering, bark beetle damage, vegetative budburst, height growth and resistance to Ophiostoma Novo-Ulmi. Ramets and open pollinated seedlings obtained from the parent trees were assessed for the same traits. Most progenies had similar traits to their parents, but some presented heterosis in annual growth or resistance to O. Novo-Ulmi. Leaf wilting was significantly lower in progenies with U. minor × U. pumila rather than U. minor as female parent (21.5 and 30.6%, respectively; P

Clive M. Brasier - One of the best experts on this subject based on the ideXlab platform.

  • Viruses as Biological Control Agents of the Dutch Elm Disease Fungus Ophiostoma Novo-Ulmi
    The Elms, 2020
    Co-Authors: Clive M. Brasier
    Abstract:

    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.

  • Sequence of RNA-dependent RNA Polymerase Genes Provides Evidence for Three More Distinct Mitoviruses in Ophiostoma Novo-Ulmi Isolate Ld
    Virus Genes, 2006
    Co-Authors: Michelle Doherty, Robert H. A. Coutts, Clive M. Brasier, Kenneth W. Buck
    Abstract:

    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.

  • Selective acquisition of novel mating type and vegetative incompatibility genes via interspecies gene transfer in the globally invading eukaryote Ophiostoma Novo-Ulmi.
    Molecular Ecology, 2005
    Co-Authors: Mathieu Paoletti, Kenneth W. Buck, Clive M. Brasier
    Abstract:

    : The Dutch elm disease fungus Ophiostoma Novo-Ulmi, which has destroyed billions of elm trees worldwide, originally invaded Europe as a series of clonal populations with a single mating type (MAT-2) and a single vegetative incompatibility (vic) type. The populations then rapidly became diverse with the appearance of the MAT-1 type and many vegetative incompatibility types. Here, we have investigated the mechanism using isolates from sites in Portugal at which the rapid evolution of O. Novo-Ulmi populations from clonality to heterogeneity was well established. We show by genetic mapping of vic and MAT loci with AFLP markers and by sequence analysis of MAT loci that this diversification was due to selective acquisition by O. Novo-Ulmi of the MAT-1 and vic loci from another species, Ophiostoma ulmi. A global survey showed that interspecies transfer of the MAT-1 locus occurred on many occasions as O. Novo-Ulmi spread across the world. We discuss the possibility that fixation of the MAT-1 and vic loci occurred in response to spread of deleterious viruses in the originally clonal populations. The process demonstrates the potential of interspecies gene transfer for facilitating rapid adaptation of invasive organisms to a new environment.

  • Análisis molecular de los cambios evolutivos en poblaciones de Ophiostoma Novo-Ulmi
    Forest Systems, 2004
    Co-Authors: Clive M. Brasier, Kenneth W. Buck, Susan Kirk, Mathieu Paoletti, L. J. Crawford
    Abstract:

    La expansion de Ophiostoma Novo-Ulmi en Europa, Norteamerica y Asia central provoco la actual pandemia de grafiosis, altamente destructiva, y reemplazo a O. ulmi, responsable de la primera pandemia de grafiosis a principios del siglo XX. Este proceso ha provocado una serie de destacables desarrollos evolutivos y adaptativos. Los estudios realizados en la decada de 1980 en poblaciones de O. Novo-Ulmi, especialmente en Espana y Portugal, mostraron lo siguiente: 1) que inicialmente O. Novo-Ulmi se expandio a traves de Europa como una serie de clones geneticos; 2) que virus deletereos de RNA se trsmitieron dentro de los clones de O. Novo-Ulmi; 3) que hibridos naturales entre las subespecies americana y Novo-Ulmi de O. Novo-Ulmi aparecieron en muchas zonas de Europa; 4) que en toda Europa esta surgiendo un gran numero de hibridos naturales entre las subespecies americana y Novo-Ulmi de O. Novo-Ulmi. Los factores conducentes a estos cambios han sido examinados mediante analisis molecular. Los resultados son: 1) que el rapido paso desde una situacion de clonalidad a otra con gran variabilidad genetica supuso la aparicion de formas «utiles» para el apareamiento, formas con compatibilidad vegetativa, y otros genes de O. Novo-Ulmi por transferencia lateral (o interespecifica) a partir de O. ulmi; mientras que se descarto la presencia de genes «inutiles» de O. ulmi; 2) que los virus ARN presentes en las poblaciones de O. Novo-Ulmi se originaron probablemente a partir de O. ulmi; y 3) que en los lugares donde O. Novo-Ulmi subsp. americana y subsp. Novo-Ulmi coexisten, los hibridos naturales se generan libremente; en algunas areas la mayor parte de los O. Novo-Ulmi aislados son en realidad complejos hibridos subsp. americana x subsp. Novo-Ulmi. Estas caracteristicas son unicas, y tiene considerable implicaciones para la historia invasora, la exitosa dispersion y el futuro comportamiento de O. Novo-Ulmi.

  • Survival of clones of NAN Ophiostoma Novo-Ulmi around its probable centre of appearance in North America
    Fungal Biology, 2000
    Co-Authors: Clive M. Brasier, Susan Kirk
    Abstract:

    275 isolates of Ophiostoma Novo-Ulmi , sampled across the southern Great Lakes region of North America from Wisconsin to Ohio in 1996, were analysed for vegetative compatibility (vc) types. Over 60% of the sample was a clonal vc component, comprising only two vc types (the AMSG and EUSG); the remainder of the sample was highly heterogeneous for vc types. Vc diversity was highest in Indiana and Michigan; close to where NAN O. Novo-Ulmi probably first appeared in North America. Each vc clone exhibited a uniform RAPD haplotype and a lower frequency of the A compared with the B mating type. This is consistent with the clones being mainly asexually spread, but with a potential for inbreeding, an unusual feature in a ’genetic clone’. The heterogeneous component, however, exhibited diverse RAPD haplotypes and a near 1:1 ratio of A:B mating types, indicating that the mainly novel vc types of this component arise via sexual recombination. In Europe, dominant vc clones have been quickly replaced by novel vc types. In the Great Lakes region, however, vc clones appear to have survived for over 50 years despite a high potential for emergence of new vc types via sexual recombination. No differences were found between the clonal and heterogeneous components with regard to growth rate and pathogenicity, two important fitness parameters. Two other factors, a low level of selection imposed by deleterious d-factor viruses and a density dependent effect associated with vegetative incompatibility, may have favoured prolonged survival of the clones in North America.

William E. Hintz - One of the best experts on this subject based on the ideXlab platform.

  • Two novel mitoviruses from a Canadian isolate of the Dutch elm pathogen Ophiostoma Novo-Ulmi (93–1224)
    Virology Journal, 2013
    Co-Authors: William E. Hintz, Joyce S Carneiro, Irina Kassatenko, Aniko Varga, Delano James
    Abstract:

    Background Ophiostoma Novo-Ulmi is the causative agent of Dutch elm disease (DED). It is an ascomycetous filamentous fungus that ranks as the third most devastating fungal pathogen in Canada. The disease front has spread eastward and westward from the epicentre in Ontario and Quebec and is threatening elm populations across the country. Numerous mitigation strategies have been tried to eradicate this pathogen, but success has thus far been limited. An alternative approach might utilize double-stranded RNA (dsRNA) mycoviruses which have been reported to induce hypovirulence in other fungi. Methods Using a modified single primer amplification technique (SPAT) in combination with chromosomal walking, we have determined the genome sequence of two RdRp encoding dsRNA viruses from an O. Novo-Ulmi isolate (93–1224) collected from the disease front in Winnipeg. Results We propose that these viruses, which we have named OnuMV1c and OnuMV7 based on sequence similarity to other Ophiostoma mitoviruses, are two new members of the genus Mitovirus in the family Narnaviridae. Conclusions The discovery of such dsRNA elements raises the potential for engineering these viruses to include other genetic elements, such as anti-sense or interfering RNAs, to create novel and highly specific biological controls. Naïve fungal hosts could be infected with both the engineered molecule and a helper mitovirus encoding an RdRp which would provide replication capacity for both molecules.

  • two novel mitoviruses from a canadian isolate of the dutch elm pathogen Ophiostoma novo ulmi 93 1224
    Virology Journal, 2013
    Co-Authors: William E. Hintz, Joyce S Carneiro, Irina Kassatenko, Aniko Varga, Delano James
    Abstract:

    Background Ophiostoma Novo-Ulmi is the causative agent of Dutch elm disease (DED). It is an ascomycetous filamentous fungus that ranks as the third most devastating fungal pathogen in Canada. The disease front has spread eastward and westward from the epicentre in Ontario and Quebec and is threatening elm populations across the country. Numerous mitigation strategies have been tried to eradicate this pathogen, but success has thus far been limited. An alternative approach might utilize double-stranded RNA (dsRNA) mycoviruses which have been reported to induce hypovirulence in other fungi.

  • Two novel mitoviruses from a Canadian isolate of the Dutch elm pathogen Ophiostoma Novo-Ulmi (93–1224)
    Virology Journal, 2013
    Co-Authors: William E. Hintz, Joyce S Carneiro, Irina Kassatenko, Aniko Varga, Delano James
    Abstract:

    Background Ophiostoma Novo-Ulmi is the causative agent of Dutch elm disease (DED). It is an ascomycetous filamentous fungus that ranks as the third most devastating fungal pathogen in Canada. The disease front has spread eastward and westward from the epicentre in Ontario and Quebec and is threatening elm populations across the country. Numerous mitigation strategies have been tried to eradicate this pathogen, but success has thus far been limited. An alternative approach might utilize double-stranded RNA (dsRNA) mycoviruses which have been reported to induce hypovirulence in other fungi.

  • Regulated gene silencing in the fungal pathogen Ophiostoma Novo-Ulmi
    Physiological and Molecular Plant Pathology, 2013
    Co-Authors: Joyce S Carneiro, Paul Y. De La Bastide, William E. Hintz
    Abstract:

    Abstract Ophiostoma Novo-Ulmi is the third most devastating fungal pathogen in Canada, affecting native Ulmus spp. Control efforts are pursuing a gene regulation approach, using RNAi cassettes driven by constitutive heterologous promoters to evaluate virulence-related genes. A homologous carbon-catabolite regulated promoter (alcA) was developed for a cassette that regulates endopolygalacturonase (EPG) expression. Using the YFP reporter to assess promoter functionality, expression was repressed under glucose, released with its depletion and not repressed under glycerol. The EPG-alcA-RNAi cassette was similarly inactive under glucose, but highly expressed following glucose depletion, reducing EPG expression by 80–100%. Transfer to glucose medium restored native EPG expression as RNAi was down-regulated. This demonstration of RNAi regulation by carbon source offers a promising tool to evaluate gene functionality.

  • functional categorization of unique expressed sequence tags obtained from the yeast like growth phase of the elm pathogen Ophiostoma novo ulmi
    BMC Genomics, 2011
    Co-Authors: William E. Hintz, Volker Jacobi, Paul Y. De La Bastide, Michael Pinchback, Steven Burgess, Richard C Hamelin, Colette Breuil, Louis Bernier
    Abstract:

    The highly aggressive pathogenic fungus Ophiostoma Novo-Ulmi continues to be a serious threat to the American elm (Ulmus americana) in North America. Extensive studies have been conducted in North America to understand the mechanisms of virulence of this introduced pathogen and its evolving population structure, with a view to identifying potential strategies for the control of Dutch elm disease. As part of a larger study to examine the genomes of economically important Ophiostoma spp. and the genetic basis of virulence, we have constructed an expressed sequence tag (EST) library using total RNA extracted from the yeast-like growth phase of O. Novo-Ulmi (isolate H327). A total of 4,386 readable EST sequences were annotated by determining their closest matches to known or theoretical sequences in public databases by BLASTX analysis. Searches matched 2,093 sequences to entries found in Genbank, including 1,761 matches with known proteins and 332 matches with unknown (hypothetical/predicted) proteins. Known proteins included a collection of 880 unique transcripts which were categorized to obtain a functional profile of the transcriptome and to evaluate physiological function. These assignments yielded 20 primary functional categories (FunCat), the largest including Metabolism (FunCat 01, 20.28% of total), Sub-cellular localization (70, 10.23%), Protein synthesis (12, 10.14%), Transcription (11, 8.27%), Biogenesis of cellular components (42, 8.15%), Cellular transport, facilitation and routes (20, 6.08%), Classification unresolved (98, 5.80%), Cell rescue, defence and virulence (32, 5.31%) and the unclassified category, or known sequences of unknown metabolic function (99, 7.5%). A list of specific transcripts of interest was compiled to initiate an evaluation of their impact upon strain virulence in subsequent studies. This is the first large-scale study of the O. Novo-Ulmi transcriptome. The expression profile obtained from the yeast-like growth phase of this species will facilitate a multigenic approach to gene expression studies to assess their role in the determination of pathogenicity for this species. The identification and evaluation of gene targets in such studies will be a prerequisite to the development of biological control strategies for this pathogen.