Fungi

Fungi habitat and function

Most fungi are found in soil and function as decomposers

Origin of Fungi

• Fungi and animals are related protists from the opisthokonts of the Amorphea cluster

  • ancestor of fungi was aquatic, unicellular, flagellated protist

• Fungi are closely related to unicellular nucleariids, which are non-flagellated, spherical or flat amoebae

Three Synapomorphies of Fungi

• absorptive nutrition

• hyphae and mycelium

• chitinous cell walls

Absorptive Nutrition

Fungi obtain nutrients by absorbing organic molecules from outside of their bodies

• fungi are absorptive chemoheterotrophic eukaryotes

• organic compounds used as sources of carbon and energy

• fungi can digest cellulose and lignin from plants, chitin and keratin from animal tissues

• achieved via external digestion: enzymes secreted by fungi break down large and complex organic molecules, simple organic molecules are absorbed by fungal bodies

Fungi Anatomy

• non-motile

• nutrients located and acquired by growing

• hyphae: cylindrical, branched and multicellular filaments that absorb nutrients

  • present in fruiting body

  • filament network called mycelium

Yeast

• unicellular

• liquid or moist environments

• evolved independently multiple times from a hypha-forming ancestor

• do not produce hyphae

• commonly found in ascomycetes and basidiomycetes

• some texan can flexibly shift between yeast and hyphen forms based on environmental conditions

Hyphae Morphology

• thin, tubular cells ranging from from 2 - 10 micrometers filled with cytoplasm and organelles

• mycelium’s filamentous structure increases surface-area-to-volume ratio

• chitin cell walls

Internal Arrangements of Hyphae

Coenocytic Structure

• form continuous compartment without division

• numerous nuclei

• present in earliest lineages called coenocytic fungi

Septa

• wall-like structures

• develop along with nuclear division

• cytoplasm divided into separate, uninuclear cells

• pores are present for cell-to-cell movements of molecules and small organelles

• present in most fungi

Fungi Reproduction

• create and disperse high quantity of spores that have chitin cell walls for rigidity and protections, which can be produced sexually or asexually

• processes for fungal spore production are mitosis and meiosis, plant spores are only produced via meiosis

Fungi Life Cycle

• life cycle resembles haploid-dominant eukaryotic organisms

• plasmogamy involves fusion of cytoplasm but not nuclei: dikaryotic

• karyogamy is fusion of nuclei

• zygote stage after karyogamy is transient and fungi lack a diploid multicellular stage

Phylogeny of Fungi

• Kingdom Fungi is a monophyletic group

• Around 100,000 species have been identified but 1.5 million species could exist

• Fungi likely formed mutualistic relationship with earliest land plants

• Classified into five diverse phyla

Five Phyla of Fungi

• Chytrids from phylum Chytridomyctoa

• Zygomycetes from phylum Zygomycota

• Glomeromycetes from phylum Glomeromycota

• Ascomycetes from phylum Ascomyctoa

• Basidiomycetes from phylum Basidiomycota

Chytrids

• most basal groups, paraphyletic, consists of about 1000 species in aquatic or moist environments

• motile, asexual zoospores

• can produce hyphae, but don’t have true mycelium

• Mostly unicellular, others have coenocytic bodies

• chitin in cell wall

• external digestion

• decomposers, parasites, or mutualists

Zygomycetes

• paraphyletic group, consisting os less than 1% of fungi; sepecies

• coenycotic hyphae

• zygosporangia

• parasites, commensal symbionts

Zygomycetes life cycle

• asexual sporgania produce haploid spores that are dispersed through air

• sexual reproductions occur through formation of zygosporangia, which forms after fusion of specialized hyphae

  • karyogamy occurs within zygosporangia

  • zygosporangia are resistant to harsh environments

Glomeromycetes

• small monphyletic group

• asexual reproduction by soil spores

• form of endomycorrhizae called arbuscular mycorrhizal associations with over 80% of extant plant species

• symbiotic relationship with plant roots: facilitate minerals and nutrient exchange for host plants

Dikarya

• Monophyletic group consisting of 98% of fungal species

• septate hyphae

• eukaryotic hyphae after plasmogamy

• edible mushroom

• yeasts for making bread, beer, and cheese

• pathogens

• Includes ascomycetes and basidiomycetes

Ascomycetes

• most diverse group

  • wide range of environments

  • range from unicellular heat to fungi with multicellular, complex structures

• sexual reproduction: brief dikaryotic stage, plasmogamy and karyogamy take place in quick succession

• Presence of sac-like sexual spores called asci contained in furring body called ascocarp

• asexual reproduction: vast quantities of spores called conidia inside of specialized hyphae called conidiophores

• decomposer, mutualists, pathogens

Basidiomycetes

• Include fungi known for production of sexual spores called basidiospore on specialized structures called basidia

• sexual reproduction is most common but asexual reproduction is also known

• elongated eukaryotic stage

• basidiocarp

• significant decomposer, known to breakdown lignin

Moulds

• fast-growing

• filamentous

• primarily reproduce asexually

• fuzzy growths of hype often formed on surface or organic materials

• mould taxa found in zygomycetes and ascomycetes

Mycorrhizae

• mutualistic symbiotic relationship between fungi and vascular plant roots

• ectomycorrhizae: fungus forms hyphal sheath surrounding roots

• endomycorrhizae: fungus penetrates the host plant cells to form arbuscules and vesicles

• multiple fungal groups can contribute to ectomycorrhiza but around 10% of vascular plants can form ectomycorrhizal associations

• arbuscular mycorrhizae are found in a monophyletic group of glomeromycetes, and about 85% vascular plants can form arbuscular mycorrhizal associations