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Title:   Author  item
                                            Baumgartner, Kendraitem
                                            Fujiyoshi, Phillip
  Submitted to: Fungal Genetics Conference
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 3/15/2011
                                    Publication  Date: 3/15/2011
                                    Citation: Baumgartner, K., Fujiyoshi, P.T. 2011. The role of somatic recombination in natural populations of the root pathogen Armillaria mellea. Fungal Genetics Conference/Asilomar. 58:217.Interpretive Summary: Fungi have evolved various mechanisms of shuffling genetic material, which can occur in the absence of fruiting and meiosis. In the homobasidiomycete Armillaria (causal agent of Armillaria root disease), the predominant vegetative stage is diploid. Diploid and haploid mycelia can fuse and undergo karyogamy to create a recombinant diploid mycelium, although the mechanism by which this occurs is not known. Nonetheless, evidence of somatic recombination in natural populations of Armillaria suggests that this process may be important in the pathogen’s ecology. Within the genus, A. mellea in particular has a very broad host range (500+ plant species) and among different hosts it exhibits different types of symbioses (pathogen, saprophyte, or mycorrhiza). Such characteristics require phenotypic plasticity. Somatic recombination in A. mellea may facilitate genetic adaptation, as the diploid genome is thought to be particularly resistant to mutation, genotypes are long-lived, fruiting is seasonal and the pathogen does not form asexual spores. Our goal is to evaluate the role of somatic recombination in adaptation of A. mellea. As a first step, we mated diploid and haploid mycelia, and are characterizing the stability of the synthesized mycelia. In matings between a wild-type diploid and transgenic, hygromycin-resistant haploids, we identified recombinant, hygromycin-resistant diploids, and additionally, hygromycin-resistant triploids. Genotype and uninucleate status of each recombinant diploid and hybrid triploid strain were found to be stable in serial transfers carried out over a 4-mo. period (to date), replicated with and without selection. Greater fitness of diploid and especially triploid strains, relative to haploid strains, suggests that ploidy influences fitness in A. mellea. On-going steps in the experiment are to determine the influence of environmental stress on fitness and stability of the synthesized mycelia, and to assess the fertility of the triploid strains.
                                Technical Abstract: Fungi have evolved various mechanisms of shuffling genetic material, which can occur in the absence of fruiting and meiosis. In the homobasidiomycete Armillaria (causal agent of Armillaria root disease), the predominant vegetative stage is diploid. Diploid and haploid mycelia can fuse and undergo karyogamy to create a recombinant diploid mycelium, although the mechanism by which this occurs is not known. Nonetheless, evidence of somatic recombination in natural populations of Armillaria suggests that this process may be important in the pathogen’s ecology. Within the genus, A. mellea in particular has a very broad host range (500+ plant species) and among different hosts it exhibits different types of symbioses (pathogen, saprophyte, or mycorrhiza). Such characteristics require phenotypic plasticity. Somatic recombination in A. mellea may facilitate genetic adaptation, as the diploid genome is thought to be particularly resistant to mutation, genotypes are long-lived, fruiting is seasonal and the pathogen does not form asexual spores. Our goal is to evaluate the role of somatic recombination in adaptation of A. mellea. As a first step, we mated diploid and haploid mycelia, and are characterizing the stability of the synthesized mycelia. In matings between a wild-type diploid and transgenic, hygromycin-resistant haploids, we identified recombinant, hygromycin-resistant diploids, and additionally, hygromycin-resistant triploids. Genotype and uninucleate status of each recombinant diploid and hybrid triploid strain were found to be stable in serial transfers carried out over a 4-mo. period (to date), replicated with and without selection. Greater fitness of diploid and especially triploid strains, relative to haploid strains, suggests that ploidy influences fitness in A. mellea. On-going steps in the experiment are to determine the influence of environmental stress on fitness and stability of the synthesized mycelia, and to assess the fertility of the triploid strains.


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