L1

• Fungi

  • phylogenetic tree: are eukaryotes, closely related to animals, not plants
  • decomposes and symbionts (heterotrophs)
  • mutualistic symbiosis
  • 110000 species of fungi have been describe and named
  • 6 million species of fungi may be formed
• Fungi importance

  • fungal mutualisms (for plants)
  • animals participate in fungal mutualisms
  • nutrient cycling
• Fungal mutualisms in plants

  • obtain nutrients
  • protect plants from herbivores
• Animals in fungal mutualisms

  • guts
  • garden
• fungi importance for humans

  • disease
  • essential for crop growth (parasitism, mutualism)
  • important in crop spoilage
  • food source, antibiotics
  • bread, beer, cheese, soy sauce, wine, chocolate
  • industrial enzymes
• Fungi more related to Animals than land plants

  • fungal infections in humans are more difficult to treat than bacterial infections
  • there are key traits linking animals and fungi
• fungal infections in humans

  • drugs that disrupt fungal physiology are likely to damage humans
  • share how they're built (common)
• key traits linking animals to fungi

  • DNA sequence data
  • both animals and fungi synthesize chitin
  • flagella in chytrid spores and gametes are similar to animal flagella
  • animals and fungi store glucose as the polysaccharide glycogen
• Phylogeny of the fungi

  • single-celled, parasitic eukaryotes (microsporidians) are fungi
  • Chytrids and zygomycetes are poorly resolved
  • Glomeromycota, Basidiomycetes, and Ascomycetes is monophyletic
  • Basidiomycota and Ascomycota form a monophyletic group
  • sister group to fungi compromises animals and choanoflagellates
• Microsporidians are fungi (single-celled)

  • not a distantly related sister group to fungi
  • hypothesis: fungicides can cure microsporidian infections in bee colonies, silkworm colonies and AIDS patients
• Fungicides are substances that can kill fungi or slow their growth
• Chytrids and zygomycetes are poorly resolved

  • polytomy on phylogenetic tree
  • swimming gametes and zygosporangium evolved more than once
  • or both were present in a common ancestor but lost in certain lineages
• Glomeromycota is monophyletic

  • adaptations that allow these species to live with plant roots as mycorrhizae evolved once
• Basidiomycetes are monophyletic

  • Basidiomycota, or club fungi
  • evolved once
• Ascomycetes are monophyletic

  • ascomycota or sac fungi
  • ascus evolved once
• Basidiomycota and Ascomycota form a monophyletic group

  • both septate hyphae and large fruiting stuctures
  • growth evolved once
• Sister group to fungi comprises animals plus choanoflagellates

  • hypothesis: earliest fungi were aquatic, and the switch to terrestrial life occurred early in evolution of fungi
• Fungi growth forms (some species adopt both)

  1. single-celled forms -- yeasts
  2. multicellular, filamentous forms-- mycelia (singular: mycelium)
• Mycelia are made of branching networks of very thin hyphae:

  • fungi have the highest surface-area-to-volume ratio of all multicellular organisms
  • nutrient absorption is extremely efficient
• Prone to drying out:

  • most abundant in moist environments
  • reproductive spores are resistant to drying out
  • spores can endure dry periods and then germinate
• Multicellular Fungi have unusual bodies

  1. The nature of the fungal mycelium (dynamic)
  2. Reproductive structures
  3. nature of Hyphae (septa)
  4. Coenocytic fungi
• All mycelia are dynamic

  • constantly grow in the direction of food sources and die back in areas where food in running out
  • body shape of a fungus changes continuously
• reproductive structures of multicellular fungi

  • mycelia are an adaptation that supports external digestion and the absorption lifestyle of fungi
  • fungi produce dense, freshly reproductive structures
  • many species do not reproduce sexually
• Hyphae are the long, narrow filaments of mycelium
• septa are cross-walls
• coenocytic means fungi lacking septa
• Coenocytic fungi

  • many nuclei scattered throughout the mycelium
  • nutrients can move rapidly through septa pores or through coenocytic fungal from uptake to growth areas
• Septa in multicellular fungi

  • pores allow materials to flow between compartments
• Fungal asexual reproduction

  1. mycelium, haploid (n) has black nuclei (mycelia)
  2. mitosis occurs: creates spore-producing structure (n)
  3. dispersed by wind, mitosis: spores (n) produced
  4. spores placed back to mycellium
• Fungal sexual reproduction

  1. mycelium, haploid (n) has black nuclei
  2. Plasmogamy: two different nuclei fuse (n + n)
  3. karyogamy: fully fuses them together (2n)
  4. meiosis: creates spore-producing structure (n)
  5. mitosis: spores dispersed by wind (n) recombination
  6. mitosis of spores: go back to mycelium (n)
• Plasmogamy is the fusion of cytoplasm from different individuals
• heterokaryotic mycelium (n+n) two different nuclei
• Key stages of the chytrid life cycle:

  1. haploid adults form gametangia (mitosis produces male and female swimming gametes
  2. gametes fuse to form a diploid zygote
  3. the zygote grows into a diploid sporophyte
  4. haploid spores, which disperse by swimming, are produced by meiosis inside the sporophytes sporangium
• motile fungal cells: sexually produced gametes and sexually produced spores of chytrids have flagella
• Zygomycetes

  • Sexual reproduction starts when hyphae from different mating types fuse
  • Plasmogamy forms a spore-forming zygosporangium that develops tough, resistant coat
  • inside the zygosporangium, nuclei from the mating partners fuse -- karyogamy occurs
  • mycelia can also reproduce asexually by making sporangia, which produce haploid spores by mitosis: spores are dispersed by wind
• Zygosporangia

  • distinctive spore-producing structures of zygomycetes
  • formed from fusion of cells from joined together haploid hyphae from two individuals
• Basidiomycetes

  • mushrooms are sexual reproductive structures produced by basidiomycetes
  • all basidiomycete reproductive structures originate from dikaryotic hyphae of mated individuals
• reproduction structures in basidiomycete

  • basidia form at the ends of dikaryotic hyphae
  • karyogamy occurs with the basidia
• Basidia

  • basidiomycetes/club fungi form basidia, specialized club-like cells at the ends of hyphae
  • each basidium produces four spores
• Ascomycetes

  • hyphae or specialized structures from different mating types fuse: forms a heterokaryotic cell with many nuclei
  • short dikaryotic hypha with cells containing two nuclei emerges: grows into reproductive structure with asci at tips
  • after karyogamy, meiosis and one round of mitosis result in production of eight haploid spores
  • when the ascus matures, the spores inside are forcibly ejected