9/23/2013
Fungi
• Diverse and widespread
• Heterotrophic
• About 100,000 described species
• It is estimated there are actually 1.5 million species of fungi
Fungi are heterotrophs that feed by
absorption
• The versatility of enzymes contributes to fungi’s ecological
success
• Decomposers
• Parasites
• Mutualists
Body Structure
• Single celled (yeast)
Reproductive structure
• Multicellular filaments
• Morphology with large Hyphae
surface area to volume
ratios
Spore-producing
• Fungi consist of
structures
mycelia, networks of
branched hyphae
• Cell walls contain chitin
60 m
Mycelium
Specialized
Hyphae
Hypha
Nematode
Hyphae
25 m
• Most divided into cells by septa, with pores allowing cell-tocell movement of organelles
• Coenocytic fungi lack septa and have a continuous
cytoplasmic mass with hundreds or thousands of nuclei
(a) Hyphae adapted for trapping and killing prey
Nuclei
Cell wall
Cell wall
Fungal hypha
Plant
cell
wall
Pore
Septum
Nuclei
Plant cell
(a) Septate hypha
(b) Coenocytic hypha
Haustorium
(b) Haustoria
Plant cell
plasma
membrane
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Mycorrhizae
Ectomycorrhizae
• Mutually beneficial relationships between fungi and plant
roots
Endomycorrhizae
Fungi produce spores through sexual or
asexual life cycles
• Arbuscular mycorrhizal fungi
Sexual Reproduction
• Transient diploid stages formed during the sexual life cycles
• Fusion of hyphae from different mating types
• Plasmogamy is the union of cytoplasm from two parent
mycelia
• In most fungi, the haploid nuclei from each parent do not fuse
right away
• In some fungi, the haploid nuclei pair off two to a cell; such a
mycelium is said to be dikaryotic
• Hours, days, or even centuries may pass before the occurrence
of karyogamy, which is nuclear fusion
• Karyogamy and meiosis produce genetic variation
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Asexual Reproduction
Yeast
• Molds produce haploid spores by mitosis and form
visible mycelia
• Bud
• Some fungi can grow as yeasts and as filamentous
mycelia
10 m
1.5 m
Parent
cell
Bud
The ancestor of fungi was an aquatic,
single-celled, flagellated protist
Deuteromycetes
Animals (and their close
protistan relatives)
UNICELLULAR,
FLAGELLATED
ANCESTOR
Nucleariids
Fungi
Chytrids
Opisthokonts
• No known sexual stage
• This is not a sound taxonomic group; fungi are
reclassified once their sexual stage is discovered
Other fungi
• Fungi are most closely related to unicellular nucleariids
• Animals are most closely related to unicellular choanoflagellates
• This suggests that multicellularity arose separately in animals and
fungi
Hyphae
Fungi have
radiated into
a diverse set
of lineages
25 m
Chytrids (1,000 species)
Chytrids
Zygomycetes (1,000 species)
Fungal hypha
25 m
Glomeromycetes (160 species)
• Decomposers, parasites, or mutualists in freshwater and
terrestrial habitats
• Chytrids are unique among fungi in having flagellated
spores, called zoospores
Hyphae
25 m
Ascomycetes (65,000 species)
Basidiomycetes (30,000 species)
Chytrids (1,000 species)
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Zygomycota
PLASMOGAMY
• Zygomycetes include fastgrowing molds, parasites,
and commensal
symbionts
• Hyphae are coenocytic
• Asexual sporangia
produce haploid spores
Mating
type ()
Mating
type ()
Gametangia with
haploid nuclei
100 m
Rhizopus
growing
on bread
Young
zygosporangium
(heterokaryotic)
SEXUAL
REPRODUCTION
Dispersal and
germination
Sporangium
ASEXUAL
REPRODUCTION
Zygomycetes (1,000 species)
Key
50 m
• The site of karyogamy and meiosis
• Zygosporangia, which are resistant to freezing and drying, can
survive unfavorable conditions
Diploid
nuclei
MEIOSIS
Dispersal and
germination
• Zygomycetes are named for their sexually produced
zygosporangia
Zygosporangium
KARYOGAMY
Flagellum
Sporangia
Mycelium
Haploid (n)
Heterokaryotic (n  n)
Diploid (2n)
Glomeromycota
• The glomeromycetes were once considered zygomycetes and
are now classified in a separate clade
• Glomeromycetes form arbuscular mycorrhizae
0.5 mm
2.5 m
Ascomycota (Sac fungi)
• Ascomycetes live in marine, freshwater, and terrestrial
habitats and are plant pathogens, decomposers and symbionts
• Ascomycetes produce sexual spores in saclike asci contained in
fruiting bodies called ascocarps
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Conidia;
mating type ()
• Ascomycetes reproduce asexually by enormous numbers of
asexual spores called conidia
• Conidia are not formed inside sporangia; they are produced
asexually at the tips of specialized hyphae called
conidiophores
Key
Dispersal
Germination
Haploid (n)
Dikaryotic (n  n)
Diploid (2n)
Mating
type ()
ASEXUAL
REPRODUCTION Hypha
PLASMOGAMY
Ascus
(dikaryotic)
Conidiophore
Mycelia
Dikaryotic
hyphae
Mycelium
SEXUAL
REPRODUCTION
Germination
KARYOGAMY
Dispersal
Asci
Ascocarp
Diploid nucleus
(zygote)
Eight
ascospores
Four
haploid
nuclei
MEIOSIS
Shelf fungi
Basidomycota (Club Fungi)
Life cycle of basidiomycete
• Basidomycetes include
mushrooms, puffballs, and
shelf fungi, mycorrhizae,
and plant parasites
• Usually includes a long-lived dikaryotic mycelium
• In response to environmental stimuli, the mycelium
reproduces sexually by producing elaborate fruiting bodies
called basidiocarps
• Many are wood
decomposers
• Have a clublike structure
called a basidium, a
transient diploid stage in
the life cycle
Puffballs emitting
spores
Maiden veil fungus
(Dictyphora)
Key
Basidiocarp
Dikaryotic
mycelium
PLASMOGAMY
Haploid (n)
Dikaryotic (n  n)
Diploid (2n)
Mating
type ()
Mating
type ()
• The numerous basidia in a basidiocarp are sources of sexual
spores called basidiospores
Haploid
mycelia
Gills lined
with basidia
SEXUAL
REPRODUCTION
Basidiocarp
(n  n)
Dispersal
and
germination
Basidiospores
(n)
Basidium with
four basidiospores
Basidium
Basidia
(n  n)
Basidium containing
four haploid nuclei
KARYOGAMY
MEIOSIS
1 m
Basidiospore
Diploid
nuclei
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Basidiocarps are quickly produced
Decomposers
Fungi play key roles in
nutrient cycling,
ecological interactions,
and human welfare
Mutualists
• Efficient decomposers of
organic material including
cellulose and lignin
• Perform essential recycling of
chemical elements between
the living and nonliving world
• Fungi form mutualistic relationships with plants, algae,
cyanobacteria, and animals
• Mycorrhizae are enormously important in natural
ecosystems and agriculture
Fungi-Animal Symbiosis
• Fungi help break down plant material in the guts of cows and
other grazing mammals
• Leaf-cutter ants use the digestive power of fungi by raising
them in “farms”
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Lichens
• A lichen is a symbiotic
association between a
photosynthetic microorganism
(algae or cyanobacteria) and a
fungus (usually an ascomycete)
• Millions of photosynthetic cells
are held in a mass of fungal
hyphae
Ascocarp of fungus
Soredia
50 m
Fungal
hyphae Algal
layer
Fungi as Pathogens
• About 30% of known fungal species are parasites or
pathogens, mostly on or in plants
• Each year, 10% to 50% of the world’s fruit harvest is lost due
to fungi
• Some fungi that attack food crops are toxic to humans
Fungal hyphae
Algal cell
The chytrid Batrachochytrium dendrobatidis might
be the cause of the recent decline in amphibians
worldwide
• Ergotism is characterized
by gangrene, nervous
spasms, burning
sensations, hallucinations,
and temporary insanity
California
Sixty
Lake
Basin
Yellow-legged frogs
killed by B. dendrobatidis
infection
N
(b)Tar spot
fungus
on maple
leaves
Key
Boundary of chytrid spread
Lake status in 2009:
Frog population extinct
(a) Corn smut on corn
2007
Treatment lake: frogs
treated with fungicides
and released
(c) Ergots on rye
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Practical Fungi Use
• Humans eat many fungi and use others to make cheeses, alcoholic
beverages, and bread
• Some fungi (e.g., penicillin) are used to produce antibiotics for the
treatment of bacterial infections
Penicillium
Zone of
inhibited
growth
When does meiosis occur in
fungi?
Ascomycota
(ascomycetes, or
sac fungi)
Sexual spores (ascospores)
borne internally in sacs
called asci; vast numbers
of asexual spores (conidia)
produced
Basidiomycota
(basidiomycetes,
or club fungi)
Elaborate fruiting body
(basidiocarp) containing
many basidia that
produce sexual spores
(basidiospores)
Which phylogenetic tree represents the
evolutionary history of the fungi based on the
most recent data?
A. A
25%
25%
25%
B. B
C. D
D. C
25%
op
...
fu
. ..
Arbuscular mycorrhizae
formed with plants
fu
s io
n
of
rt
fte
ya
el
iat
C
D
B
A
at
er
.. .
tr.
.
an
d
ck
s
ro
st
ag
in
in
g
gr
ow
na
n
on
et
th
ee
n
tw
tf
re
sh
w
oe
s
fv
as
cu
la
rp
la
of
so
...
nt
s
25% 25% 25% 25%
ro
ot
so
tri
do
m
Ch
y
A. the roots of
vascular plants
B. between the toes of
someone with
athlete's foot
C. growing on rocks
and tree bark
D. in stagnant
freshwater ponds
be
25%
yc
ot
a
ot
a
yc
As
co
m
yc
Zy
go
m
Glomeromycota
(arbuscular
mycorrhizal
fungi)
af
te
25%
ot
a
25%
ot
a
yc
io
m
Ba
sid
Resistant zygosporangium
as sexual stage
cy
t
he
of
ed
im
m
lo
w
fo
l
25%
Zygomycota
(zygote fungi)
You have been given the task of finding living
members of the phylum Glomeromycota. Where is
the best place to look for these fungi?
Your parents are coming to visit so you immediately run to the
pantry to throw away the loaf of bread with the black fuzzy
stuff on it. What phylum of fungi did you probably just trash?
A. Basidiomycota
B. Zygomycota
C. Ascomycota
D. Chytridomycota
Flagellated spores
rt
he
ep
lr
gt
he
xu
a
in
as
e
fu
s io
n
ro
du
c
tio
n.
..
n
25% 25% 25% 25%
du
r in
g
A. during asexual
reproduction
B. following the fusion
of nuclei
C. immediately after the
fusion of two fungal
cells
D. after the fusion of
cytoplasm but before
the fusion of nuclei
Distinguishing Features of
Morphology and Life Cycles
Chytridiomycota
(chytrids)
th
e
Staphylococcus
Fungal
Phylum
8