Download I. Mycology: Mushrooms, molds, and yeasts. General Characteristics

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FUNGI
•  Key points:
•  Heterotrophs that obtain nutrition by
absorption.
•  Shared common ancestor of animal-like
protists with Animalia.
•  Vital symbionts of plants.
•  Classification based on reproductive
modes.
I. Mycology: Mushrooms, molds, and
yeasts. General Characteristics
Fruiting
body
•  Eukaryotes.
•  Predominant stage
haploid.
•  Both multicellular
(hyphae made up of
filaments) and
unicellular (yeasts).
•  Not photosynthetic, all
heterotrophic by
absorption.
Mycelium
Hyphae made up of filaments are organized into
mushroom body (mycelium and fruiting body)
• 
m
0
by
a
40
Share common ancestor with
animals and some Protists (to
the exclusion of other Protista
and Plants).
Ancient, fossils associated with
earliest land plants, ca. 400mya.
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ya
I. Mycology: Mushrooms, molds, and
yeasts. Evolutionary History
–  Molecular data suggests the
split between the lineage
leading to fungi and the lineage
leading to animals occurred ca.
1 bya.
• 
Have diversified into five main
lineages
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Five lineages of Fungi
(Chytrids paraphyletic)
I. Mycology: Mushrooms, molds, and
yeasts. The Absorptive Mode of Nutrition
•  Enzymes decompose organic materials.
•  Saprobes decompose and absorb nutrients from
non-living organic matter.
•  Parasitic fungi absorb nutrients from cells of living
hosts, some are pathogenic.
•  Mutualistic fungi also absorb from host organism,
but reciprocate with beneficial functions, e.g. uptake
of nutrients, minerals.
–  Most plants depend on mutualist relationship with fungi.
II. Structure: The mycelium
•  Vegetative (nonreproductive) body.
•  Basic units are hyphae
–  Filaments of cells with a wall
of chitin.
–  Septate cells (most
common)
–  Aseptate & coenocytic cells
•  Hyphae form interwoven mat
called the mycelium
Mycelium
–  10 cm3 of soil can contain 1
km of hyphae.
•  Haustoria are specialized
hyphae of parasitic fungi that
penetrate plant cells.
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II. 
Structure: Reproductive
body
•  Varies with taxonomic
group
•  All reproduce by
haploid spores in
specialized structures
peculiar to each group.
•  Evolution of fungi
toward larger, more
specialized sporebearing structures.
Zygomycete
Basidiomycete
Ascomycete
II. Structure:
Other Life Styles
•  Molds: Rapidly growing
asexual stage.
–  May develop sexual
stage as fruiting body
distinctive of one of 5
phyla.
–  Some without known
sexual stage, called
imperfect fungi or
deuteromycetes.
–  Important molds, e.g.
Penicillium (penicillin,
cheese)
II. Structure:
Other Life Styles
•  Yeasts: Unicellular fungi in
liquids or moisture including
sap and animal tissue.
–  Asexual cell division, or
budding; but some sexual
ascomycetes and
basidiomycetes are yeasts.
–  Saccharomyces: baker’s
yeast, brewer’s yeast; active
metabolically, release CO2
causes dough to rise, also
ferments sugars to alcohol.
–  Candida: pathogenic yeast
(vaginal, oral).
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Mutualistic Symbioses
II. Structure:
Other Life Styles
•  Mycorrhizae: “fungus roots”
–  Important mutualism.
–  Increases surface area for absorption and exchange of
nutrients.
–  Important in global Phosphorus cycle.
–  Over 95% of plants have mycorrhizae.
–  Ectomycorrhizae: Hyphal sheath covers root and hartig
net surrounds individual plant root cells.
•  Species of Zygomycetes, Ascomycetes, Basidiomycetes.
–  Arbuscular mycorrhizae: Hyphae enter plant cells via
invagination of plant cell membrane (do not enter
protoplast--the interior of the cell).
•  Only and all species of Glomeromycota.
Mutualistic Symbioses
II. Structure:
Other Life Styles
• 
Endophytes live within plant
tissues.
–  Provide fungi with protection,
nutrients, water.
–  May receive from fungi
chemical protection from
insects, protists, bacteria, other
fungi.
–  May receive ability to tolerate
stressful environmental
conditions.
–  Found in every plant studied to
date (do not know role of all).
–  Primarily Ascomyceta.
–  Taxol, effective anti-cancer
drug derived from endophyte of
the Pacific Yew.
Mutualistic Symbioses
II. Structure:
Other Life Styles
•  Lichens are mutualisms between
fungi and photosynthetic
organisms.
1. 
2. 
3. 
4. 
Green Algae
Cyanobacteria
Yellow-Green Algae†
Brown Alga (1 known case)†
•  Rarely three-fold: Fungus +
photosynthetic green alga +
nitrogen-fixing cyanobacteria.
•  Fungi provide mineral nutrients and
water, algae provide carbohydrates
via photosynthesis.
•  Ascomyceta (mostly),
Basidiomyceta (a few),
Glomeromyceta (1)
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Mutualistic Symbioses
II. Structure:
Other Life Styles
• 
• 
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Insect cultivation: Fungi are cultivated by
insects, provided with protection, fungi
break down cellulose in plant tissue.
Internal cultivation: Termites
External cultivation:
– 
– 
Leaf-cutter ants: cultivate underground fungus
gardens. Fungi break down cellulose in leaf
tissue, ants eat fungus.
Bark and ambrosia beetles: colonize new trees
and inoculate carved galleries with ascomycete
fungus. Fungi break down cellulose in wood,
beetles consume fungus.
III. Growth & Reproduction
•  Growth not in bulk, but by
proliferation of hyphae
growing into resource
(e.g. giant fairy ring)
•  Reproduction mostly
asexual by spores or
simple cloning, only
chytrids with flagellar
stage.
•  Spores dispersed by
wind, water, animals.
III. Growth & Reproduction:
Generalized life cycle
1. 
2. 
3. 
4. 
5. 
Plasmogamy: fusion of
cytoplasm of haploid hyphae.
Dikaryon: cells with two
haploid unfused nuclei.
Karyogamy: fusion of nuclei,
diploid stage; followed
immediately by:
Meiosis in haploid spore
producing structures.
Spores are released as
haploid and germinate into
filaments.
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IV. Diversity
A.  Chytridiomycota (chytrids)
B.  Zygomycota (zygote fungi)
C.  Glomeromycota (arbuscular
mycorrhizae)
D.  Ascomycota (sac or cup fungi)
E.  Basidiomycota (club fungi)
A. Chytridiomycota (chytrids)
•  ~1,000 species,
paraphyletic.
•  Only fungi with flagellated
(spore) stage.
•  A link between ancestral
protists and true fungi?
•  Once excluded from Fungi,
but share biochemical
characters, cell walls of
chitin, absorptive mode of
nutrition.
•  Mainly aquatic saprobes,
some parasitic on plants and
animals.
B. Zygomycota (zygote fungi)
•  ~1,000 species
•  Terrestrial, soil, decaying
plant/animal tissue.
•  Mycorrhizae: mutualistic
association with plant
roots.
•  Hyphae coenocytic.
•  Zygosporangia are the
reproductive structures
that give the name.
•  E.g. Rhizopus stolonifer,
black bread mold.
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C. Glomeromycota
(arbuscular mycorrhizae)
•  160 species, once
considered
Ascomycota, but now
recognized as distinct.
•  Nearly all form
arbuscular
mycorrhizae with
plants--ecologically
important.
–  Ca. 90% of all plant
species have them as
mutualists!
D. Ascomycota (sac or cup fungi)
•  Include such tasties as truffles
and morels.
•  Unicellular to complex
multicellularity.
•  Some extreme plant pathogens;
other important saprobes.
•  Half symbiotic with Chlorophyta:
lichens.
•  Karyogamy in an ascocarp;
sexual spore in asci.
•  Asexual: spores (conidia) come
from specialized structures
(conidiophores), wind
dispersed.
E. Basidiomyceta (club fungi)
•  Include the commonly
encountered mushrooms, shelf
fungi, puffballs.
•  Basidium (“little pedestal”)
transient diploid stage.
•  Most important plant (wood)
decomposers.
•  Karyogamy in basidiocarp
(sexual); puff balls release
spores explosively.
•  Most complex of fungi: longlived dikaryotic mycelium.
•  Fairy rings; giant ring in
Michigan ~40 acres (!);
genetically uniform mycelium.
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