Fungi Notes

Fungi

  • Fungi are more closely related to animals than plants.
  • Mycology is the study of fungi.

Opisthokonta

  • Includes fungi, choanoflagellates, and animals.

Earliest Fungus

  • Last common ancestor with animals at least 1.2 billion years ago.
  • Potential specimens as old as 2.4 billion years.
  • Fossil fungus from 715 MYA.
  • Florescent dye binds to chitin.

Major Fungi Groups

  • Seven major groups:
    • Blastocladiomycota
    • Zygomycota
    • Neocallimastigomycota
    • Chytridiomycota
    • Glomeromycota
    • Basidiomycota
    • Ascomycota
Blastocladiomycota
  • Only fungi with a haplodiplontic lifecycle.
Neocallimastigomycota
  • Group of fungi found within the digestive tract of animals to break down cellulose.
Chytridiomycota
  • Many pathogenic species, targeting both plants and animals.
Glomeromycota
  • Plant symbionts. Require plant hosts to survive.
Basidiomycota
  • Mushrooms! Most familiar fungal group.
Ascomycota
  • Yeasts, molds, and morels are members of this group.

General Characteristics of Fungi

  • Four shared characteristics:
    1. Presence of hyphae
    2. Cell walls made of chitin
    3. Multinucleated cells
    4. Closed mitosis
    5. Heterotroph decomposers
Hyphae
  • Filaments, strings of cells.
  • Underground, and often has continuous cytoplasm among all cells.
  • Septa with pores separates individual cells.
  • Able to rapidly share nutrients throughout an individual → Leads to rapid growth
Mycelium
  • Mass of connected hyphae.
  • Capable of growing into different materials and leads to digestion of adjacent organic material.
  • Produces above-ground reproductive structures in some groups (Mushrooms!).
Cell Walls
  • Cell walls made of chitin à Same protein made by animals.
  • Plant and protist cell wall protein à Cellulose
Multinucleated Cells
  • A single cell can have two or more nuclei:
    • Monokaryotic = One nucleus
    • Dikaryotic = Two nuclei, usually two haploid nuclei
  • Dikaryotic cell differs from diploid cell because haploid nuclei are separate and both undergo transcription.
Dikaryotic Cells
  • Two types of dikaryotic cells:
    • Heterokaryotic = Two nuclei from genetically distinct individuals
    • Homokaryotic = Two nuclei from genetically similar individuals
Closed Mitosis
  • Linked nature of cells à Cell is not relevant unit of reproduction
  • Nuclear envelope does not break down à spindle apparatus forms within
Reproduction
  • Can undergo asexual and sexual reproduction.
  • Sexual reproduction:
    • Two haploid hyphae fuse à Forms heterokaryotic stage, which forms spores.
Spores
  • Can form from either sexual or asexual reproduction, typically forms from an above-ground structure.
  • Spores are spread via wind and germinate to form new mycelium.
Heterotroph Decomposers
  • Does not undergo photosynthesis, and absorbs nutrients directly from the environment.
  • External digestion à Hyphae secrete digestive enzymes into surrounding environment and absorb broken down organic material.

Wood Decomposers

  • Fungi are the only major organism capable of breaking down lignin à Major organic molecule within plant cell walls that forms wood.
  • Also efficient at breaking down cellulose in plant cell walls.

Fungi Bioremediation

  • Fungi are capable of breaking down nearly every organic molecule, so are an important tool in bioremediation!

Fungi Ecology

  • Principle decomposer in the biosphere. Three major roles:
    1. Breakdown organic material
      • Breaks down all types of organic material. Even insoluble material such as cellulose and lignin.
    2. Return substances to circulate in ecosystem
      • Especially important for carbon, nitrogen, phosphorous
    3. Ecological interactions à Symbiotic relationships
      • Many types of interactions, including beneficial and costly interactions
Commensalism and Mutualism
  • Recall commensalism and mutualism
Endophytes
  • Live within plants, produce toxins to prevent herbivory
Lichens
  • Symbiosis between fungi and photosynthetic organism
Mycorrhizae
  • Fungal association with plant roots
Animal Mutualism
  • Live within animals to help breakdown plant material

Endophytes

  • Live within plants, produce toxins to prevent herbivory

Lichens

  • Symbiosis between fungi and photosynthetic organism à Typically green algae or cyanobacteria. Provides nutrients to fungus.
  • Fungus protects photosynthetic organism from desiccation à Capable of living in extreme environments

Mycorrhizae

  • Fungal association with plant roots that functions as an extensive root system. Two types:
    1. Arbuscular mycorrhizae à Fungus penetrates outer cell wall of plant
    2. Ectomycorrhizae à Surrounds roots, but does not penetrate cell walls

Animal Mutualism

  • Live within animals to help breakdown plant material
    • Ruminant mammals à Capable of breaking down cellulose
    • Termites à Capable of breaking down lignin

Pathogenic and Parasitic Fungi

  • Fungus gains resources from host, may cause disease
Zombie-ants
  • Cordyceps fungus from The Last of Us based on a real fungus!
Fusarium Wilt
  • Gros Michel banana major cultivar from the 18th century until the 1950s. The entire crop died due to Fusarium wilt à Fungal infection!
  • Cavendish banana was created to replace the Gros Michel because of its immunity to Fusarium wilt

New Mutations Threaten Cavendish Banana

  • All Cavendish bananas are genetically identical because they reproduce via vegetative reproduction rather than sexual reproduction.
  • Increasingly susceptible to Fusarium wilt due to lack of genetic variation. No variable immune response!
Chytridiomycosis
  • Deadly fungal disease affecting amphibian populations worldwide.
  • Grows within the skin, and affects the ability of amphibians to breathe, thermoregulate, and osmoregulate à Leads to 100% death rate in many amphibian species
  • Global decline in amphibian populations linked to the chytrid fungus
  • Initially spread through the wildlife trade in the 1980s. Nearly 30% of amphibians may have already gone extinct!