Fungi
Fungi
• Fleshy fungi
• Yeasts
• Molds
– Hyphae (long filaments of joined cells)
– Mycelium (intertwined mass of hyphae)
Fungi
– Are diverse and widespread
» Are essential for the well-being of most terrestrial
ecosystems because they break down organic
material and recycle vital nutrients
Mushrooms
Nutrition and Fungal Lifestyles
• Fungi are heterotrophs
– But do not ingest their food
• Fungi secrete into their surroundings
exoenzymes that break down complex
molecules
– And then absorb the remaining smaller
compounds
A General Look at Fungi - Flash Animation
Note to self: may need to right chick to
get to play or rewind. May need to
advance slide using arrows at bottom
left.
Fungal lifestyles
–Decomposers
–Parasites
–Mutualistic symbionts
Body Structure
• The morphology of multicellular fungi
– Enhances their ability to absorb nutrients
from their surroundings
Reproductive structure.
The mushroom produces
tiny cells called spores.
Hyphae. The mushroom and
its subterranean mycelium
are a network of hyphae.
Spore-producing
structures
20 m
Mycelium
Structure
• Fungi consist of
– Mycelia, networks of branched hyphae
adapted for absorption
• Most fungi
– Have cell walls made of chitin
Structure
• Some fungi
– Have hyphae divided into cells by septa, with
pores allowing cell-to-cell movement of
materials
• Coenocytic fungi
– Lack septa
Cell wall
Cell wall
Nuclei
Pore
Septate
Septum
(a) Septate hypha
Coenocytic
Nuclei
(b) Coenocytic hypha
Structure
• Some unique fungi
– Have specialized hyphae that allow them to
penetrate the tissues of their host
Nematode
Hyphae
25 m
(a) Hyphae adapted for
trapping and killing prey
Plant
cell
wall
Fungal hypha
Haustorium
(b) Haustoria – specialized hyphae
that can penetrate the cell walls of plants
Plant cell
Plant cell
plasma
membrane
Mycorrhizae
– Are mutually beneficial relationships between
fungi and plant roots
• Ectomycorrhizal fungi (surface)
• Endomycorrhizal fungi (penetrate plant cell wall)
Reproduction/propagation
Fungi produce spores through sexual or asexual life
cycles (Some fungi do both, some are either sexual or asexual)
• The generalized life cycle of fungi
Key
Heterokaryotic
stage
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
PLASMOGAMY
(fusion of cytoplasm)
Diploid (2n)
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Spores
SEXUAL
REPRODUCTION
ASEXUAL
REPRODUCTION
Zygote
Mycelium
MEIOSIS
GERMINATION
GERMINATION
Spore-producing
structures
Spores
Sexual Reproduction
• The sexual life cycle involves
– Cell fusion, plasmogamy
– Nuclear fusion, karyogamy
• An intervening heterokaryotic stage
– Occurs between plasmogamy and karyogamy in which
cells have haploid nuclei from two parents
• The diploid phase following karyogamy
– Is short-lived and undergoes meiosis, producing
haploid spores
Asexual Reproduction
• Many fungi can reproduce asexually
• Many fungi that can reproduce asexually
– Grow as mold, sometimes on fruit, bread,
and other foods
Penicillium
(common
saprobe on
food)
2.5 m
Conidia
(asexual)
Asexual Reproduction
• Other asexual fungi are yeasts
– That inhabit moist environments
– Which produce by simple cell division
10 m
Parent cell
Bud
Asexual Reproduction
• Many molds and yeasts have no known
sexual stage
– Mycologists have traditionally called these
deuteromycetes, or imperfect fungi
Evolution/Origin of Fungi
• Fungi descended from an aquatic, single-celled,
flagellated protist
• Systematists now recognize Fungi and Animalia
as sister kingdoms
– Because fungi and animals are more closely related
to each other than they are to plants or other
eukaryotes
• Molecular evidence
– Supports the hypothesis that fungi and animals
diverged from a common ancestor that was
unicellular and bore flagella
• Fungi probably evolved
– Before the colonization of land by multicellular
organisms
Origin of Fungi
• The oldest
undisputed fossils
of fungi are only
about 460 million
years old
50 m
Fossil hyphae
and spores
• Fungi were
among the earliest
colonizers of land.
-Probably as
symbionts with
early land
plants
Arbuscular
mycorrhizal
fungi
Sac
fungi
Club
fungi
Ascomycota
Basidiomycota
Zygomycota
– Is currently the
subject of much
research
– Molecular analysis
has helped clarify the
evolutionary
relationships
between fungal
groups, although
there are still areas of
uncertainty
Zygote
fungi
Chytrids
Chytridiomycota
• Fungi have radiated
into a diverse set of
lineages
• The phylogeny of
fungi
Glomeromycota
Phylogeny/Classification
Phylogeny/Classification
Five Phyla of
Fungi
Chytrids
• Fungi classified in the phylum
Chytridiomycota, or chytrids
– Are found in freshwater and terrestrial
habitats
– Can be saprobic or parasitic
Chytrids
• Chytrids are unique among fungi
– In having flagellated spores, called zoospores
Hyphae
25 m
Flagellum
4 m
Chytrids
• Until recently, systematists thought that
– Fungi lost flagella only once in their history
• Molecular data
– Indicate that some “chytrids” are closely
related to another fungal group, the
zygomycetes
Some
chytrids
Zygomycetes and other chytrids
Glomeromycetes,
ascomycetes, and
basidiomycetes
Key
Common ancestor
Loss of
flagella
Zygomycetes
• Fungi in the phylum Zygomycota, the
zygomycetes
– Exhibit a considerable diversity of life histories
– Include fast-growing molds, parasites, and
commensal symbionts
– Are named for their sexually produced
zygosporangia
Zygomycetes - Life Cycle
• The life cycle of Rhizopus stolonifer (fairly typical of
zygomycetes)
2
Mycelia have
various mating types
(here designated +,
with red nuclei, and ,
1
Neighboring mycelia of different
mating types form hyphal extensions
called gametangia, each walled off
around several haploid nuclei by a
septum.
Key
Haploid (n)
with blue nuclei).
Heterokaryotic (n + n)
Diploid
3
PLASMOGAMY
Rhizopus
growing
on bread
Mating
type (+)
Mating
type ()
A heterokaryotic
zygosporangium
forms, containing
multiple haploid
nuclei from the two
parents.
Gametangia with
haploid nuclei
100 m
8 The spores
Young
germinate and
zygosporangium
grow into new
(heterokaryotic)
mycelia.
SEXUAL
REPRODUCTION
9 Mycelia can also reproduce
asexually by forming sporangia
that produce genetically identical haploid spores.
Dispersal and
germination
Sporangia
7 The sporangium
KARYOGAMY
disperses genetically
diverse, haploid spores.
Sporangium
ASEXUAL
REPRODUCTION
Zygosporangium
(heterokaryotic)
Diploid
nuclei
MEIOSIS
Dispersal and
germination
50 m
4 This cell develops a
rough, thick-walled
coating that can resist
dry environments and
other harsh conditions
for months.
Mycelium
When conditions are favourable,
karyogamy occurs, followed by
meiosis.
5
6 The zygosporangium
then breaks dormancy,
germinating into a
short sporangium.
Zygomycetes
• Some zygomycetes, such as Pilobolus
– Can actually “aim” their sporangia toward
conditions associated with good food sources
This
decomposer
of animal
dung bends
toward bright
light and
shoots its
sporangia up
to 2 meters
0.5 mm
Spore dispersal movie
Zygomycetes
• Zygosporangia, which are resistant to
freezing and drying
– Are capable of persisting through
unfavorable conditions
– Can undergo meiosis when conditions
improve
Microsporidia
• Microsporidia
10 m
– Are unicellular parasites of animals and protists
– A taxonomic mystery…Are now classified as zygomycetes (But
that could change at any time!)
Host cell
nucleus
Developing
microsporidian
Spore
This cell is
infected with the
parasitic fungus
Encephalitozoon
intestinalis
Glomeromycetes
• Fungi assigned to the phylum
Glomeromycota
– Were once considered zygomycetes
– Are now classified in a separate clade
Glomeromycetes
• All glomeromycetes
– Form a distinct type of endomycorrhizae
called arbuscular mycorrhizae
2.5 m
Picture
shows
cytoplasm
removed to
show the
arbuscule
(branched
structure)
inside plant
cell.
Ascomycetes
• Fungi in the phylum Ascomycota
– Are found in a variety of marine, freshwater,
and terrestrial habitats
– Are defined by the production of sexual
spores in saclike asci, which are usually
contained in fruiting bodies called ascocarps
– Have asexual reproduction by producing
enormous numbers of asexual spores called
conidia
Ascomycetes
• Ascomycetes
– Vary in size and complexity from unicellular
yeasts to elaborate cup fungi and morels
(a) The cup-shaped ascocarps (fruiting bodies)
of Aleuria aurantia give this species its
common name: orange peel fungus.
(b) The edible ascocarp of
Morchella esculenta, the
succulent morel, is often
found under trees in orchards.
10 m
(c) Tuber melanosporum is a truffle, an ascocarp that grows
underground and emits strong odors. These ascocarps
have been dug up and the middle one sliced open.
(d) Neurospora crassa feeds as
a mold on bread and other
food (SEM).
Ascomycetes – Life Cycle
• The life cycle of Neurospora crassa
Ascomycete mycelia can
also reproduce asexually by
producing haploid conidia.
7
Conidia;
mating type ()
Neurospora can
reproduce sexually by
producing specialized
1 hyphae. Conidia of the
opposite mating type
fuse to these hyphae.
Key
Haploid (n)
Dikaryotic (n  n)
Diploid (2n)
Dispersal
Germination
ASEXUAL
REPRODUCTION
Mating
type ()
Mycelium
PLASMOGAMY
Ascogonium
Mycelia
Conidiophore
The developing asci
are contained in an
6 ascocarp. The
ascospores
are discharged forcibly
from the asci through an
opening in the ascocarp.
Germinating ascospores
give rise to new mycelia.
2 A dikaryotic
ascus develops.
Ascus
(dikaryotic)
Dikaryotic
hyphae
SEXUAL
REPRODUCTION
Germination
KARYOGAMY
Dispersal
Asci
Diploid nucleus
(zygote)
Eight
ascospores
Four
haploid
nuclei
3
Karyogamy
occurs within
the
ascus,
producing a
diploid
nucleus.
MEIOSIS
Ascocarp
5 Each haploid nucleus divides
once by mitosis, yielding eight
nuclei. Cell walls develop around
the nuclei, forming ascospores (LM).
4
The diploid nucleus
divides by meiosis, yielding
four haploid nuclei.
Basidiomycetes
• Fungi in the phylum Basidiomycota
– Include mushrooms and shelf fungi
– Are defined by a clublike structure called a
basidium, a transient diploid stage in the life
cycle
Basidiomycetes
(b) Maiden veil fungus (Dictyphora),
a fungus with an odor like rotting
meat
(a) Fly agaric (Amanita muscaria), a
common species in conifer forests in
the northern hemisphere
(d) Puffballs emitting spores
(c) Shelf fungi, important decomposers of
wood
Basidiomycetes
• The life cycle of a basidiomycete
– Usually includes a long-lived dikaryotic
mycelium, which can erect its fruiting
structure, a mushroom, in just a few hours
Fairy rings can appear overnight. A very large mycelium is
growing underneath this ring of fruiting structures
Basidiomycetes
• The life cycle of a mushroom-forming
basidiomycete
2
1
Two haploid mycelia of different
mating typesundergo plasmogamy.
A dikaryotic mycelium forms,
growing faster then, and ultimately
crowding out, the haploid parental
mycelia.
In a suitable
the
basidiospores
germinate and
grow into
short-lived
haploid mycelia.
8environment,
7
3 Environmental cues such as rain or
temperature changes induce the
dikaryotic
mycelium to form
compact masses that
develop into
basidiocarps
(mushrooms, in this
case).
Dikaryotic
mycelium
PLASMOGAMY
Mating
type ()
Mating
type ()
Haploid
mycelia
SEXUAL
REPRODUCTION
Gills lined
with basidia
Basidiocarp
(dikaryotic)
Dispersal
and
germination
When mature,
the basidiospores
are ejected, fall
from the cap, and
are dispersed by
the wind.
Basidiospores
Basidia
(dikaryotic)
Basidium with
four appendages
Basidium containing
four haploid nuclei
Basidium
4
KARYOGAMY
MEIOSIS
1 m
Basidiospore
6 Each diploid nucleus
yields four haploid
nuclei. Each basidium
grows four appendages,
and one haploid nucleus
enters each appendage
and develops into a
basidiospore (SEM).
Key
Diploid
nuclei 5
Karyogamy in the
basidia produces diploid
nuclei, which then
undergo meiosis.
Haploid (n)
Dikaryotic (n  n)
Diploid (2n)
The basidiocarp
gills are lined with
terminal dikaryotic
cells called basidia.
Fungi have a powerful
impact on ecosystems
and human welfare
Decomposers
• Fungi are well adapted as decomposers of
organic material
– Performing essential recycling of chemical
elements between the living and nonliving
world
Symbionts
• Fungi form symbiotic relationships with
– Plants, algae, and animals
Mycorrhizae
• Mycorrhizae
– Are enormously important in natural ecosystems and
agriculture
– Increase plant productivity
EXPERIMENT Researchers grew soybean plants in soil treated with fungicide (poison that kills fungi) to
prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed
mycorrhizae in the soybean plants’ roots.
The soybean plant on the left is typical of the experimental group. Its
RESULTS
RESULTS
stunted growth is probably due to a phosphorus deficiency. The taller, healthier plant on
the right is typical of the control group and has mycorrhizae.
CONCLUSION
These results indicate that the presence of mycorrhizae benefits a soybean
plant and support the hypothesis that mycorrhizae enhance the plant’s ability to take up
phosphate and other needed minerals.
Fungus-Animal Symbiosis
• Some fungi share their digestive services
with animals
– Helping break down plant material in the guts
of cows and other grazing mammals
Many species of ants and termites
– Take advantage of the digestive power of
fungi by raising them in “farms”
Leaf cutter ant movie
Lichens
• Lichens
– Are a symbiotic association of millions of
photosynthetic microorganisms held in a
mass of fungal hyphae
(a) A fruticose (shrub-like) lichen
(b) A foliose (leaf-like) lichen
(c) Crustose (crust-like) lichens
Lichen
• The fungal component of a lichen
– Is most often an ascomycete
• Algae or cyanobacteria
– Occupy an inner layer below the lichen surface
Ascocarp of fungus
Soredia
Fungal
hyphae
Algal
layer
Algal cell
10 m
Fungal hyphae
Pathogens
• About 30% of known fungal species
– Are parasites, mostly on or in plants.
• Some of the fungi that attack food crops
– Are toxic to humans
(a) Corn smut on corn
(b) Tar spot fungus on maple leaves
(c) Ergots on rye
Practical Uses of Fungi
• Humans eat many fungi
– And use others to make cheeses, alcoholic beverages, and bread
• Genetic research on fungi
– Is leading to applications in biotechnology
• Antibiotics produced by fungi-treat bacterial infections
Staphylococcus
Penicillium
Zone of
inhibited
growth
Fungi: Wrap-up video clip
The End