Li, Dan (2003-05). A map kinase pathway essential for mating and contributing to asexual development in Neurospora Crassa. Doctoral Dissertation. Thesis uri icon

abstract

  • MAP kinases and transcription factors homologous to Saccharomyces cerevisiae Fus3p/Kss1p and Ste12p have been identified in several plant pathogenic fungi and found to be required for pathogenicity and sexual reproduction. A gene encoding the homolog of Fus3p/Kss1p in Neurospora crassa was isolated previously and named mak- 2 (mitogen activated kinase -2). This dissertation describes the isolation of the Ste12p homolog, pp-1 (protoperithecia-1) and the comparison of the phenotypes of the mak-2 and pp-1 mutants. The similar phenotypes of the mak-2 and pp-1 null mutants suggest that these proteins are part of the same MAP kinase signaling cascade in N. crassa. In addition to reduced growth rate, the phenotypes of the mutants demonstrate that this pathway is required for female fertility, contributes to aerial hyphal development and repression of conidiophore development. The mak-2 MAP kinase pathway also regulates several genes putatively involved in secondary metabolism during the mating process. Among these is a gene cluster that is likely to be involved in the production of a polyketide secondary metabolite. An orthologous gene cluster was also identified in M. grisea, and the structural and functional homology of these two related gene clusters was characterized. Microarray analysis was used to extend the analysis of gene expression in mak-2 and pp-1 mutants, and a number of downstream target genes of the MAP kinase pathway were identified and called mak-2 kinase-regulated genes (mkr). A model of this MAP kinase pathway in N. crassa was developed. Since N. crassa is a saprophytic fungus but closely related to several plant pathogens, this research may provide an important perspective on the evolution of a major regulatory pathway governing fungal pathogenesis.
  • MAP kinases and transcription factors homologous to Saccharomyces cerevisiae
    Fus3p/Kss1p and Ste12p have been identified in several plant pathogenic fungi and
    found to be required for pathogenicity and sexual reproduction. A gene encoding the
    homolog of Fus3p/Kss1p in Neurospora crassa was isolated previously and named mak-
    2 (mitogen activated kinase -2). This dissertation describes the isolation of the Ste12p
    homolog, pp-1 (protoperithecia-1) and the comparison of the phenotypes of the mak-2
    and pp-1 mutants. The similar phenotypes of the mak-2 and pp-1 null mutants suggest
    that these proteins are part of the same MAP kinase signaling cascade in N. crassa. In
    addition to reduced growth rate, the phenotypes of the mutants demonstrate that this
    pathway is required for female fertility, contributes to aerial hyphal development and
    repression of conidiophore development. The mak-2 MAP kinase pathway also regulates
    several genes putatively involved in secondary metabolism during the mating process.
    Among these is a gene cluster that is likely to be involved in the production of a
    polyketide secondary metabolite. An orthologous gene cluster was also identified in M.
    grisea, and the structural and functional homology of these two related gene clusters was
    characterized. Microarray analysis was used to extend the analysis of gene expression in
    mak-2 and pp-1 mutants, and a number of downstream target genes of the MAP kinase
    pathway were identified and called mak-2 kinase-regulated genes (mkr). A model of this
    MAP kinase pathway in N. crassa was developed. Since N. crassa is a saprophytic
    fungus but closely related to several plant pathogens, this research may provide an
    important perspective on the evolution of a major regulatory pathway governing fungal
    pathogenesis.

publication date

  • May 2003