lecture 3

• Fungi


  • Can be unicellular or multicellular
  • Have chitin-rich cell walls
  • Store carbon as glycogen, like animals, not starch
  • Heterotrophs that engage in absorptive nutrition by secreting enzymes to digest food externally
  • Multicellular fungi are non-motile and filamentous
• Hypha


  A single filament
• Mycelium


  A network of hyphae
• Spore


  Single cells capable of growing into an adult organism
• Products of fungi


  • Antibiotics
  • Biosynthetic factories
  • Other potent toxins and chemicals
  • Industrial production
• Fungal life cycle


  1. Spore formation (sporogenesis)

  2. Gamete formation (gametogenesis)

  3. Meiosis

  4. Fertilization
• Fungi vs. animals and plants


  Fungi have a haploid multicellular phase that predominates, unlike animals which have a diploid multicellular phase, and unlike plants which have both haploid and diploid multicellular phases
• Mycorrhizal fungi


  • Arbuscular mycorrhizal fungi penetrate root cells and create structures called arbuscules
  • Ectomycorrhizal fungi form nets around the whole root and cell surfaces within root but do not enter cells
• Applications of mycelial networks


  • Mycofabrication
  • Mycoremediation
• Fungi diverged from a common ancestor with animals around 1 billion years ago
• Major fungal groups


  • Cryptomycetes
  • Microsporidians
  • Chytrids
  • Zoopagomycetes
  • Mucoromycetes
  • Ascomycetes
  • Basidiomycetes
• Basidiomycetes (Club Fungi)


  • Best decomposers of wood
  • Named for the club-like cell, the basidium, in which the zygote forms prior to meiosis
  • Basidia line the gills of the fruiting body (the basidiocarp, i.e., the mushroom)
  • A single mushroom can produce a billion spores

  
• Ancestral protist groups


  • Cryptomycetes
  • Microsporidians
  • Chytrids
  • Zoopagomycetes
  • Mucoromycetes
  • Ascomycetes
  • Basidiomycetes
• Fungal diversity


  • Multiple separate origins of multicellularity distinct from that in animals or plants
  • With move fully onto land, the remaining groups lost flagellated spores as they shift from water- to wind-based spore dispersal
  • Need a new spore dispersal solution: the fruiting body

  
• Basidiomycetes


  Also called Club Fungi, best decomposers of wood, named for the club like cell, the basidium, in which the zygote forms prior to meiosis, basidia line the gills of the fruiting body (the basidiocarp, i.e., the mushroom), a single mushroom can produce a billion spores

  
• Fungal life cycle


  1. Mitosis

  2. Meiosis

  3. Fertilization

  4. Plasmogamy (fusion of cytoplasm)

  5. Karyogamy (fusion of nuclei)

  6. Asexual reproduction

  7. Sexual reproduction
• Complexity of fungal life cycles


  • Asexual reproduction can make spores without going through a diploid zygote in many species
  • No distinct binary "gametes" like egg and sperm cells, instead there are hyphal tips that look the same but express different mating types, number of mating types often >2, and defined by protein pheromone signals
  • Fertilization is a two-step process: Plasmogamy (fusion of cytoplasm) and Karyogamy (fusion of nuclei)
• Mitosis can happen anytime from spore germination to plasmogamy, and can also happen while the mycelium is heterokaryotic post-plasmogamy, including forming the mushroom fruiting body (basidiocarp)

  
• No mitosis happens between zygote formation, karyogamy of nuclei within the basidia and conversion of that zygote into spores by meiosis
• Mycosis


  A fungal infection
• Many fungi are plant pathogens, many are pathogens of amphibians and insects, human fungal infections are rarely lethal except in immunocompromised individuals, though difficult to treat
• Coccidioides immitis


  A lethal exception of a human fungal infection (Valley Fever)
• Ophiocordyceps


  A genus of ascomycetes that is often known as "zombie fungi", the behavior induced is very specific - ant crawls to optimal dispersal height over foraging routes before death grip, at time of death grip, fungus takes up 40% body but not in brain, is in the jaw muscles
• Evidence of Ophiocordyceps death grips can be seen in fossil leaves ~48 million years old
• Key terms


  • mycorrhizal fungi (arbuscular and ecto-)
  • spores
  • meiosis/fertilization
  • sporogenesis / gametogenesis
  • sporophyte / gametophyte
  • fruiting body
  • basidium / basidiocarp
  • plasmogamy
  • heterokaryon
  • karyogamy
  • mycosis