Fungus Diversity Notes

Characteristics of Fungi

  • Multicellular and eukaryotic.

  • Cell wall composed of chitin with supportive β-glucans and mannoproteins.

  • Asexual and sexual life cycles. Variable life cycle prominence among major groups.

  • Reproduction (both sexual and asexual) is by the release of vast numbers of haploid spores.

  • Most cells are haploid. Only the zygote (usually short-lived) is diploid.

  • Osmotrophic: Energy-rich molecules are absorbed directly from the environment or from a host.

  • Most structures are embedded in the substrate.

Plasmogamy

  • Plasmogamy and karyogamy are two important processes in the sexual life cycle of some fungi

  • Plasmogamy Definition: [Completed by student]

Karyogamy

  • Plasmogamy and karyogamy are two important processes in the sexual life cycle of some fungi

  • Karyogamy Definition: [Completed by student]

Fungus Life Cycle

  • Includes both asexual and sexual cycles.

  • Key Structures and Stages:

    • Mycelium (n): Mass of hyphae.

    • Spores (n): Reproductive units.

    • Zygote (2n): Only diploid stage, formed during sexual reproduction.

    • Spore-producing structures (n).

Origin of Fungi

  • Fungi likely originated in an aquatic environment with flagella.

  • Chytrids, the most primitive major fungi group, are primarily aquatic.

  • Colonization of land occurred over 500 million years ago, possibly as early as 635 million years ago.

  • Terrestrial fungal fossils become common around 400 million years ago.

  • Ascomycota and Basidiomycota diverged approximately 360 million years ago.

Nucleariid Protists

  • Definition or description of nucleariid unicellular protists: [Completed by student]

Relationship Between Fungi, Animals, and Protists

  • Summary of the relationship among fungi, animals, and protists, including insights into the evolution of multicellularity in fungi and animals: [Completed by student]

Eukaryotic Phylogeny

  • Opisthokonta:

    • Metazoa (Animals)

    • Choanoflagellates

    • Fungi

  • Ochrophyta

    • Bacillariophyceae (diatoms)

    • Phaeophyceae (brown algae)

  • Alveolata (incl. Dinoflagellates)

  • Rhizaria

    • Foraminiferida

    • Radiolaria

  • Archaeplastida

    • Viridiplantae (green algae and plants)

    • Rhodophyta (Red algae)

  • Eukaryota

Fungus Morphology

  • Fungi are composed of a network of long, thin, branching filaments called hyphae.

  • Hyphae can form dense masses known as mycelium, typically embedded within the substrate.

  • Some hyphae are organized into spore-producing fruiting bodies that emerge above the substrate.

Basic Fungus Organization and Composition

  • Hyphae: The basic structural units.

  • Mycelium: A mass of hyphae.

  • Reproductive structure: spore-producing structures.

  • Fruiting body

Basidiomycota "Fairy Ring"

  • Illustration of a Fairy Ring formed by Basidiomycota fungi.

Chitin

  • Definition or description of chitin: [Completed by student]

Basic Fungus Cell Wall Construction

  • Mannoproteins

  • β-glucans

  • Chitin

  • Membrane proteins

  • Cell membrane

Septate and Coenocytic Hyphae

  • Septate hyphae: Hyphae with cross-walls (septa) that divide the hyphae into distinct cells.

  • Coenocytic hyphae: Hyphae lacking septa, resulting in a continuous cytoplasmic mass with multiple nuclei.

Structure of a Septate Hypha

  • Key components:

    • Septum: Perforated cross-wall allowing passage of materials.

    • Hyphal wall: The outer layer of the hypha.

    • Plasma membrane: Encloses the cytoplasm.

    • Organelles: Nucleus, endoplasmic reticulum, ribosomes, Golgi apparatus, mitochondrion, vacuoles, and lipid bodies are all present.

Mycorrhiza (plural = Mycorrhizae)

  • Definition or description of mycorrhizae: [Completed by student]

Ectomycorrhizae

  • Forms a mantle (fungal sheath) around the root.

  • Hyphae form a Hartig net between cortical cells.

Arbuscular Mycorrhizae

  • Hyphae penetrate root cells, forming arbuscules.

  • Key structures:

    • Appressorium: Structure used for penetration.

    • Intracellular hyphae: Hyphae inside the root cells.

    • Arbuscules: Branched structures for nutrient exchange.

    • Vesicle: Storage structure.

    • Infection thread.

    • Fungal cell wall.

Sexual Reproduction Fungi (Basic Model)

  1. Hyphae of different mating types (+ and –) come into contact. Evidence suggests that mating types of the same species release pheromones that facilitate contact.

  2. Plasmogamy occurs, initiating the dikaryotic stage. The dikaryotic stage typically involves numerous mycelia (networks of hyphae). In the Basidiomycota, most of the mycelia are dikaryotic and the dikaryotic stage is long-lived.

  3. Eventually karyogamy occurs.

  4. Karyogamy produces a short-lived diploid zygote that undergoes meiosis to form haploid spores.

Conjugation in Zygomycota Fungi

  • Illustration of conjugation in Zygomycota fungi.

Life Cycle of Basidiomycota

  • Plasmogamy: + and - fuse, creating dikaryotic mycelium.

  • Dikaryotic Mycelium

  • Karyogamy: Produces a diploid zygote (2n).

  • Meiosis: Basidium with 4 nuclei (1n).

  • Basidiospores: Form and disperse.

  • Germination: Mycelia (1n) develop.

  • Mitosis: Basidiocarp (mushroom) forms.

Mechanism of Food Acquisition by Fungi

  • Fungi are osmotrophic; they absorb organic molecules from a substrate or organism on which they are living.

  • Fungal hyphae have a high surface area-to-volume ratio, enhancing the rate of absorption of organic molecules.

  • Many fungi absorb organic molecules from soil and decaying matter.

  • Some fungi release enzymes that break down dead or living biomass.

Five (5) Major Groups of Fungi

  • List of the five major groups of fungi: [Completed by student]