Fungi

Front 1

In what ways do fungi grow?

Back 1

• multicellular mycelia e.g., mushrooms
• single-celled yeasts
• baker’s yeast, Saccharomyces cerevisiae
• Candida albicans (can be pathogenic in humans)

Front 2

Multicellular mycelium

Back 2

• composed of filaments known as hyphae
• Mushrooms consist of densely packed hyphae
• Hyphae
– long narrow tubular filaments optimizes surface area/volume ratio which enhances absorption
– hyphae may be broken into compartments by septa that contain gaps which enables movement of materials between compartments

Front 3

Extracellular digestion by saprophytic fungi

Back 3

Fungi secrete digestive enzymes outside of their hyphae:
=> breakdown cellulose, starch, lignin, proteins, & RNA into
=> smaller compounds e.g., sugars, amino acids, nucleic acids
=> able to diffuse across the cell membrane into the hyphae

Front 4

Lignin and cellulose degrading fungi play important role in global carbon cycle

Back 4

• Lignin degradation:
– hyphae excrete lignin peroxidase into extracellular environment
- breaks down dense lignin matrix around long strands of cellulose
• Cellulose digestion:
– Cellulases excreted into extracellular environment breakdown cellulose

Front 5

Concentration of fungal spores are at times comparable to pollen grains in air samples

Back 5

• Spores fall on food source
- germinate
- mycelium forms
- grows in direction of food
- when food source diminishes, spores are produced
• With adequate food sources mycelia can be large and long-lived

Front 6

Mycorrhizae

Back 6

common association between fungi & land plant roots
• fungi make nitrogen and phosphorous available to plants
• fungi receive sugars & other carbon sources from plant

Front 7

Ectomycorrhizal Fungi (EMF)

Back 7

Dense network of hyphae around roots
• Found in almost all tree species in temperate & boreal forests
• Basidiomycetes form this type of association
• Short growing season in temperate areas
- slow decomposition
- nitrogen remains tied up in dead tissues
• EMF releases peptidases that cleave peptide bonds of amino acids

Front 8

Arbuscular mycorrhizal Fungi
(AMF) = Endomycorrhizae

Back 8

• Grow in cells of root tissue
• Found in 80% of all plant species
• Commonly are Glomeromycetes fungi
• Supply plants with phosphorous
• Especially in grasslands & forest in warm & tropical habitats where the growing season is long and nitrogen is available

Front 9

Lichens

Back 9

• Results from the symbiotic association of a true fungus and either a cyanobacteria or a green alga
• Most fungi are ascomycetes & some are basidiomyctes
• Live in tundras and on bare rock => contribute to rock breakdown and soil formation
• Fungi provides protection to cyanobacteria or green algae
• Algae or cyanobacteria provide carbohydrate to fungus

Front 10

Parasitism

Back 10

• On Plants:
– Parasitic fungi killed billions American chestnut & American elm trees (Dutch elm disease)
– Corn smut fungal infection
– Ergot infection (Claviceps pupurea) in rye grains
• On Animals:
– Chytridiomycota species infect & kill frogs
– Cordyceps fungi infects the heads of certain caterpillars
• On Humans:
– Coccidiodomycosis (Valley Fever) causes fungal infection in humans living in the central valley of California

Front 11

Evolution of Fungi

Back 11

• Chytridiomycota and Zygomycetes
– branched off very close together in time and are the earliest known fungal groups
• Glomeromycetes
– form endomycorrhizae called arbuscular mycorrhizae
• Basidiomycota and Ascomycota
– represent later, more derived groups

Front 12

Chytridiomycota

Back 12

• Only fungi group that are aquatic
• infections in frogs
• motile cells
– gametes in sexual reproduction
– spores in asexual reproduction
• centrioles associated with nuclear membrane during cell division

Front 13

Zygomycota

Back 13

• Most live in soil
• zygote with tough outer coat
• Some have mutualistic arbuscular mycorrhizal relationships
• Some live on bread e.g., Rhizopus stolonifer
• Hyphae are haploid

Front 14

Zygomycota Reproduction

Back 14

• Two different mating types become yoked together
- haploid nuclei fuse
- diploid zygote is resistant to extreme conditions
- favorable conditions enable meiosis
- meiotic products produce haploid cells
- spores are released, germinate, and grow into new mycelia

Front 15

Glomerulomycetes

Back 15

– All form distinct types of endomycorrhizae called abruscular mycorrhizae
– Tips of hyphae push into plant root cells and branch into treelike structures called arbuscules

Front 16

Ascomycota (sac fungi)

Back 16

• Some are microscopic yeast (e.g., Candida albicans)
• Some have sac-like spore producing structures and multicellular mycelia
• Some have dikaryotic stage like Basidiomycota
– Similar reproductive cycle as Basidiomycota except that meiosis takes place in the ascus sac

Front 17

Basidiomycota

Back 17

• club-fungi, club-like spore forming structures
• mushrooms, bracket fungi, & puffballs are reproductive structures
• hyphae from different mating types fuse & mix
their cytoplasms
- cytoplasms of two cells mixed (cytoplasmic fusion)
- each cell produced after initial fusion contains a haploid nucleus from each plant and are called dikaryotic hyphae

Front 18

Basidiomycota

Back 18

dikaryotic hyphae grow into spore-producing bodies (mushrooms, brackets, or puffballs)
- basidia (specialized club-like cells) form on hyphae tips
- two nuclei fuse inside (nuclear fusion) basidia cells to form diploid nucleus
- meiosis
- haploid spore production expelled from end of basidium & dispersed by wind