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Barry J Saville - One of the best experts on this subject based on the ideXlab platform.

  • fungal pathogen emergence investigations with an ustilago maydis sporisorium reilianum hybrid
    Journal of Fungi, 2021
    Co-Authors: Emilee R M Storfie, Barry J Saville
    Abstract:

    The emergence of new fungal pathogens threatens sustainable crop production worldwide. One mechanism by which new pathogens may arise is hybridization. To investigate hybridization, the related smut fungi, Ustilago maydis and Sporisorium reilianum, were selected because they both infect Zea mays, can hybridize, and tools are available for their analysis. The hybrid Dikaryons of these fungi grew as filaments on plates but their colonization and virulence in Z. mays were reduced compared to the parental Dikaryons. The anthocyanin induction caused by the hybrid Dikaryon infections was distinct, suggesting its interaction with the host was different from that of the parental Dikaryons. Selected virulence genes previously characterized in U. maydis and their predicted S. reilianum orthologs had altered transcript levels during hybrid infection of Z. mays. The downregulated U. maydis effectors, tin2, pit2, and cce1, and transcription factors, rbf1, hdp2, and nlt1, were constitutively expressed in the hybrid. Little impact was observed with increased effector expression; however, increased expression of rbf1 and hdp2, which regulate early pathogenic development by U. maydis, increased the hybrid’s capacity to induce symptoms including the rare induction of small leaf tumors. These results establish a base for investigating molecular aspects of smut fungal hybrid pathogen emergence.

  • Fungal Pathogen Emergence: Investigations with an Ustilago maydis × Sporisorium reilianum Hybrid
    'MDPI AG', 2021
    Co-Authors: Emilee R M Storfie, Barry J Saville
    Abstract:

    The emergence of new fungal pathogens threatens sustainable crop production worldwide. One mechanism by which new pathogens may arise is hybridization. To investigate hybridization, the related smut fungi, Ustilago maydis and Sporisorium reilianum, were selected because they both infect Zea mays, can hybridize, and tools are available for their analysis. The hybrid Dikaryons of these fungi grew as filaments on plates but their colonization and virulence in Z. mays were reduced compared to the parental Dikaryons. The anthocyanin induction caused by the hybrid Dikaryon infections was distinct, suggesting its interaction with the host was different from that of the parental Dikaryons. Selected virulence genes previously characterized in U. maydis and their predicted S. reilianum orthologs had altered transcript levels during hybrid infection of Z. mays. The downregulated U. maydis effectors, tin2, pit2, and cce1, and transcription factors, rbf1, hdp2, and nlt1, were constitutively expressed in the hybrid. Little impact was observed with increased effector expression; however, increased expression of rbf1 and hdp2, which regulate early pathogenic development by U. maydis, increased the hybrid’s capacity to induce symptoms including the rare induction of small leaf tumors. These results establish a base for investigating molecular aspects of smut fungal hybrid pathogen emergence

  • phytohormone involvement in the ustilago maydis zea mays pathosystem relationships between abscisic acid and cytokinin levels and strain virulence in infected cob tissue
    PLOS ONE, 2015
    Co-Authors: Erin N. Morrison, R. Neil J. Emery, Barry J Saville
    Abstract:

    Ustilago maydis is the causative agent of common smut of corn. Early studies noted its ability to synthesize phytohormones and, more recently these growth promoting substances were confirmed as cytokinins (CKs). Cytokinins comprise a group of phytohormones commonly associated with actively dividing tissues. Lab analyses identified variation in virulence between U. maydis Dikaryon and solopathogen infections of corn cob tissue. Samples from infected cob tissue were taken at sequential time points post infection and biochemical profiling was performed using high performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI MS/MS). This hormone profiling revealed that there were altered levels of ABA and major CKs, with a marked reduction in CK glucosides, increases in methylthiol CKs and a particularly dramatic increase in cisZ CK forms, in U. maydis infected tissue. These changes were more pronounced in the more virulent Dikaryon relative to the solopathogenic strain suggesting a role for cytokinins in moderating virulence during biotrophic infection. These findings highlight the fact that U. maydis does not simply mimic a fertilized seed but instead reprograms the host tissue. Results underscore the suitability of the Ustilago maydis– Zea mays model as a basis for investigating the control of phytohormone dynamics during biotrophic infection of plants.

  • Representative time course of disease progression for Zea mays- U. maydis cob assay.
    2015
    Co-Authors: Erin N. Morrison, R. Neil J. Emery, Barry J Saville
    Abstract:

    (a) Mock-infected controls (b) Dikaryon (FB1 x FB2) infected (c) Solopathogen (SG200) infected. Days post infection (dpi) appear in the top right-hand corners of individual photographs.

  • Cytokinin concentrations (pmol g -1 FW) in U. maydis Dikaryon infected Z. mays cob tissue, during the U. maydis- Z. mays infection time course.
    2015
    Co-Authors: Erin N. Morrison, R. Neil J. Emery, Barry J Saville
    Abstract:

    Values are means ± standard error (SE) (n = 2–15) at specific days post infection (dpi). Empty cells indicate values of zero for those analytes. In cases where an analyte was detected in only one sample the presented mean concentration is equivalent to the SE.Cytokinin concentrations (pmol g -1 FW) in U. maydis Dikaryon infected Z. mays cob tissue, during the U. maydis- Z. mays infection time course.

Regine Kahmann - One of the best experts on this subject based on the ideXlab platform.

  • Identification of a motor protein required for filamentous growth in Ustilago maydis
    The EMBO journal, 1997
    Co-Authors: Christiane Lehmler, Regine Kahmann, Gero Steinberg, Karen M. Snetselaar, Manfred Schliwa, Michael Bölker
    Abstract:

    The phytopathogenic fungus Ustilago maydis exists in two stages, the yeast-like haploid form and the filamentous Dikaryon. Both pathogenicity and dimorphism are genetically controlled by two mating-type loci, with only the filamentous stage being pathogenic on corn. We have identified two genes (kin1 and kin2) encoding motor proteins of the kinesin family. Kin1 is most similar to the human CENP-E gene product, while Kin2 is most closely related to the conventional kinesin Nkin of Neurospora crassa. Deletion mutants of kin1 had no discernible phenotype; delta kin2 mutants, however, were severely affected in hyphal extension and pathogenicity. The wild-type Dikaryon showed rapid tip growth, with all the cytoplasm being moved to the tip compartment. Left behind are septate cell wall tubes devoid of cytoplasm. In delta kin2 mutants, dikaryotic cells were formed after cell fusion, but these hyphal structures remained short and filled with cytoplasm. A functional green fluorescent protein (GFP)-Kin2 fusion was generated and used to determine the localization of the motor protein by fluorescence microscopy. Inspection of the hyphal tips by electron microscopy revealed a characteristic accumulation of darkly stained vesicles which was absent in mutant cells. We suggest that the motor protein Kin2 is involved in organizing this specialized growth zone at the hyphal tip, probably by affecting the vectorial transport of vesicles.

  • green fluorescent protein gfp as a new vital marker in the phytopathogenic fungus ustilago maydis
    Molecular Genetics and Genomics, 1996
    Co-Authors: Tilman Spellig, Arnaud Bottin, Regine Kahmann
    Abstract:

    Pathogenic development ofUstilago maydis, the causative agent of corn smut disease, is a multistep process. Compatible yeast-like cells fuse and this generates the infectious Dikaryon which grows filamentously. Having entered the plant the Dikaryon induces tumors in its host in which massive proliferation of fungal material, karyogamy and spore formation occur. In order to follow fungal development from the initial steps to the final stage we have expressed the green fluorescent protein (GFP) fromAequorea victoria as a vital marker inU. maydis and demonstrate that GFP-tagged strains can be used to study host-pathogen interactions in vivo.

  • Filament-specific expression of a cellulase gene in the dimorphic fungus Ustilago maydis.
    Biological chemistry Hoppe-Seyler, 1995
    Co-Authors: Florian Schauwecker, Gerhard Wanner, Regine Kahmann
    Abstract:

    The phytopathogenic fungus Ustilago maydis exists in a yeast-like haploid form and as a filamentous Dikaryon. Only the Dikaryon can infect corn plants. We have isolated a gene, egl1, that is not expressed in haploid cells but strongly induced in the filament. Molecular and biochemical analyses revealed that egl1 encodes a cellulase. By immunogold labelling, secreted protein could be detected at the hyphal tip. Mutants deleted for egl1 are viable and are affected neither in filament formation nor in pathogenic development under the conditions tested.

Jeanclaude Debaud - One of the best experts on this subject based on the ideXlab platform.

  • auxin overproducer mutants of hebeloma cylindrosporum romagnesi have increased mycorrhizal activity
    New Phytologist, 1994
    Co-Authors: L Normand, Roland Marmeisse, B Sotta, Jeanclaude Debaud
    Abstract:

    summary The ectomycorrhizal activity (expressed as the number of mycorrhizas per plant) of indole-3-acetic acid (IAA) overproducer mutants of Hebeloma cylindruspurum Rumagnesi and of their mono- and dikaryotic progenies has been studied in an attempt to clarify the role of fungal IAA in the establishment of ectomycorrhizal symbiosis, The original mutants obtained from the hi monokaryon produced a higher number of mycorrhizas than did the wild type. The study of the mycorrhizal activity of synthesized Dikaryons heterozygous for the FIR (fluoroindoleresistant) mutations, which are responsible for IAA overproduction, showed that these mutations are recessive. The vitro fruiting of a Dikaryon heterozygous for a FIR mutation allowed the isolation of IAA-overproducing sib-monokaryons. Their average mycorrhizal activity was higher than that of non-overproducers. indicating that, although the mycorrhizal activity of sib-monokaryons is under polygenic control, high IAA production gives an advantage in mycorrhiza formation. This was confirmed by the higher number of mycorrhizas formed by synthesized Dikaryons homozygous for a FIR mutation than by wild type mycelia. The mycorrhizas formed by the mono- or dikaryotic wild types were characterized by a uniseriate Hartig net, whereas it was pluriseriate in the case of mycorrhizas formed by IAA overproducer mutants. The mutants stimulated the growth of the host plants to the same extent as did the wild types, indicating that growth stimulation is not a direct consequence of fungal auxin production. The usefulness of these mutants as a model to study the role of fungal IAA in mycorrhiza formation is discussed.

  • isolation and preliminary characterization of 5 fluoroindole resistant and iaa overproducer mutants of the ectomycorrhizal fungus hebeloma cylindrosporum romagnesi
    New Phytologist, 1992
    Co-Authors: N Durand, Jeanclaude Debaud, L A Casselton
    Abstract:

    summary IAA-overproducer mutants of the ectomycorrhizal basidiomycete Hebeloma cylindrosporum Romagnesi were isolated in an attempt to clarify the role of fungal IAA in ectomycorrhiza formation. By contrast to the wild type, mutants are able to metabolize endogenous Trp to IAA. They were isolated using a two-step method. One hundred and forty-four mutants with altered regulation of the Trp branch of the shikimate pathway were isolated from two compatible monokaryons by selecting for resistance to the indole analogue, 5-fluoroindole. These mutants are Trp-overproducers and most of them accumulate free Trp. Seventeen mutants able to synthesize IAA in the absence of exogenous precursor (tryptophan or intermediates of the tryptophan biosynthetic pathway) were identified by screening for the ability to metabolize endogenous Trp into IAA. By studying the activity of key enzymes of the Trp biosynthetic pathway (i.e. anthranilate synthase and Trp synthase), it was evident that different mechanisms led to IAA-overproduction. A correlation was detected between the level of intracellular Trp accumulation and the ability of the mutants to metabolize endogenous Trp to IAA. This indicates that, irrespective of the mutation, intracellular Trp accumulation is a prerequisite for IAA overproduction. A positive correlation was also detected between, on the one hand, resistance to fluoroindole and, on the other hand, intracellular Trp accumulation and, subsequently, IAA-overproduction. Thus, resistance to high fluoroindole concentrations appeared to provide a method for the direct selection of IAA-overproducer mutants. In order to be able to compare these mutants with the wild parental Dikaryon and to perform genetic analyses, the mutants were fused with a compatible wild monokaryon. The resulting Dikaryons were able to form mycorrhizas with the normal host plant, Pinus pinaster, and to fruit under controlled culture conditions, thus allowing stabilization and purification of the mutations. IAA-overproducer monokaryons were detected within the progeny of all the mutants. They are now being used to study the role of fungal IAA in ectomycorrhizas.

Nicolas Corradi - One of the best experts on this subject based on the ideXlab platform.

  • homo and Dikaryons of the arbuscular mycorrhizal fungus rhizophagus irregularis differ in life history strategy
    Frontiers in Plant Science, 2021
    Co-Authors: Edward Umberto Serghi, Vasilis Kokkoris, Calvin Cornell, Jeremy Dettman, Franck Stefani, Nicolas Corradi
    Abstract:

    Arbuscular mycorrhizal fungi (AMF) are obligate plant symbionts that have the potential to improve crop yield. These multinucleate organisms are either homokaryotic (AMF homokaryons) or heterokaryotic (AMF Dikaryons). In AMF Dikaryons thousands of nuclei originating from two parental strains co-exist in the cytoplasm. In other fungi, homokaryotic and dikaryotic strains show distinct life history traits (LHT) such as variation in growth speed and fitness, but how such traits compare between AMF Dikaryons and homokaryotic relatives is unknown. To address this, we measured 20 life history traits across three root organ cultures (Carrot, Chicory, Nicotiana) for 10 phylogenetically distinct strains (four Dikaryons, six homokaryons) of the model species R. irregularis. Our analyses show that AMF Dikaryons have clearly distinct life history strategies (LHS) compared to AMF homokaryons. In particular, while AMF homokaryons have significantly higher germination ability and germinate faster, AMF Dikaryons grow significantly faster and create a more complex hyphal network post-germination across hosts. These findings link nuclear organization with the emergence of key ecological and evolutionary traits in a widespread group of multinucleate plant symbionts.

Frédéric G. Masclaux - One of the best experts on this subject based on the ideXlab platform.

  • generation of unequal nuclear genotype proportions in rhizophagus irregularis progeny causes allelic imbalance in gene transcription
    New Phytologist, 2021
    Co-Authors: Chanz Robbins, Consolée Aletti, Ivan D Mateus, Joaquim Cruz Corella, Rejane Seiler, Soonjae Lee, Frédéric G. Masclaux
    Abstract:

    Arbuscular mycorrhizal fungi (AMF) form mutualisms with most plant species. The model AMF Rhizophagus irregularis is common in many ecosystems and naturally forms homokaryons and Dikaryons. Quantitative variation in allele frequencies in clonally Dikaryon offspring suggests they disproportionately inherit two distinct nuclear genotypes from their parent. This is interesting, because such progeny strongly and differentially affect plant growth. Neither the frequency and magnitude of this occurrence nor its effect on gene transcription are known. Using reduced representation genome sequencing, transcriptomics, and quantitative analysis tools, we show that progeny of homokaryons and Dikaryons are qualitatively genetically identical to the parent. However, Dikaryon progeny differ quantitatively due to unequal inheritance of nuclear genotypes. Allele frequencies of actively transcribed biallelic genes resembled the frequencies of the two nuclear genotypes. More biallelic genes showed transcription of both alleles than monoallelic transcription, but biallelic transcription was less likely with greater allelic divergence. Monoallelic transcription levels of biallelic genes were reduced compared with biallelic gene transcription, a finding consistent with genomic conflict. Given that genetic variation in R. irregularis is associated with plant growth, our results establish quantitative genetic variation as a future consideration when selecting AMF lines to improve plant production.

  • Investigating unexplained genetic variation and its expression in the arbuscular mycorrhizal fungus Rhizophagus irregularis
    2019
    Co-Authors: Frédéric G. Masclaux, Tania Wyss, Marco Pagni, Pawel Rosikiewicz
    Abstract:

    Arbuscular mycorrhizal fungi (AMF) are important symbionts of plants. Recently, studies of the AMF Rhizophagus irregularis recorded within-isolate genetic variation that does not match the proposed monokaryon or Dikaryon state. We re-analysed published data showing that bi-allelic sites (and their frequencies), detected in monosporic R. irregularis isolates, were similar across independent studies using different techniques. This indicated that observed within-fungus genetic variation was not an artefact of sequencing and that such within- fungus genetic variation exists. Bi-allelic transcripts from three R. irregularis isolates matched those observed in the genome. In putative monokaryon isolates, very few bi-allelic transcripts could be found in the genome. In a putative Dikaryon, a large number of bi-allelic transcripts matched those in the genome. Bi-allelic transcripts also occurred in the same frequency in the putative Dikaryon as predicted from allele frequency in the genome. Our results indicate that while within-fungus genome variation in putative monokaryon and Dikaryon AMF was highly similar in 2 independent studies, there was little support that this variation is transcribed in monokaryons. In contrast, within-fungus variation thought to be segregated among nuclei in a Dikaryon isolate is indeed transcribed in a way that is proportional to that seen in the genome.