Lecture #4
Fungi
“The Mighty Mushroom”
• take a walk through a forest
• mushrooms are truly are the largest
organisms in the forest
• Kingdom Fungi:
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–
–
–
not just mushrooms!
approximately 100,000 species now described
may be as many as 1.5 million species
range from unicellular to complex multicellular
organisms
– just about every terrestrial and aquatic
environment
– essential decomposers in ecosystems
• critical for the release of nutrients into the
ecosystem
– included with animals and plants in the Clade
Opisthokonta
• diverged about a billion years ago
Nutrition
• like animals, fungi are heterotrophs
– cannot make their own food like algae and plants
• unlike animals – they do not ingest their food
• fungi absorb nutrients from its environment
• digestion of both living and dead sources
Body Structure
• most common body structures are:
– 1. multicellular filaments
– 2. yeasts
Reproductive structure
Hyphae
Spore-producing
structures
• relatively few species grow as yeasts
20 µm
– those that do inhabit moist environments
• most grow as multicellular filaments
called hyphae (hypha – singular)
– cell wall is strengthened by chitin
(not cellulose = plants)
– chitin - nitrogen containing polysaccharide
– strong yet flexible
Mycelium
Body
Structure
• body structure:
– hyphae enhances the ability to absorb
nutrients
– hyphae form an interwoven mass called
a mycelium (mycelia plural)
– a mycelium infiltrates the material on
which it feeds
– mycelia grow very fast – nutrients for
growth are carried rapidly via
cytoplasmic streaming to the growing
hyphae
– the emphasis is on increasing mycelium
length NOT width
Cell wall
Cell wall
Nuclei
Pore
Septum
Septate hypha
Nuclei
Coenocytic hypha
Reproductive structure
Hyphae
Spore-producing
structures
20 µm
Mycelium
•
septate hyphae are divided into individual cells by
walls called septa
– septa have relatively large pores to allow for the
passage of ribosomes, mitochondria and nuclei
between cells
•
those that lack septa are called ceonocytic fungi
Cell wall
Cell wall
Nuclei
Pore
Septum
Septate hypha
Nuclei
Coenocytic hypha
Fungal
Hyphae
Mycorrhizal Fungus
•
mycorrhizal fungi: fungi with mutually beneficial
relationships between the fungus and plant roots
– mycorrhiza = symbiotic relationship between a
fungus and the root of a vascular plant
– the hyphae are specialized = form haustoria that
project into a plant cell
• but do not penetrate it
• haustoria remain separated from the plant by
the plant’s plasma membrane!
– very common type - ectomycorrhizal fungi=
sheaths of hyphae grow over the root
Plant
cell
wall
Fungal hypha
Plant cell
Haustoria
Haustorium
Plant cell
plasma
membrane
•
•
•
Reproduction
fungus reproduce through the production of spores
spores are carried by wind or water
germination upon exposure to moisture to produce a new mycelium
• definitions:
– karyogamy: fusion of two
haploid nuclei in fungi
• production of a diploid
zygote
– plasmogamy: fusion of the
cytoplasm NOT the nuclei
– produces a heterokaryotic
stage – means different
nuclei
Key
Heterokaryotic
stage
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
Diploid (2n)
PLASMOGAMY
(fusion of cytoplasm)
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Zygote
Spores
ASEXUAL
REPRODUCTION
Mycelium
SEXUAL
REPRODUCTION
MEIOSIS
GERMINATION
GERMINATION
Spores
Spore-producing
structures
Sexual Reproduction
• fungal sexual reproduction: consists of three stages – plasmogamy
karyogamy  meiosis
– two hyphae of different mating type extends towards each other – production of
pheromones
– the hyphae meet and fuse
– two cytoplasms fuse = plasmogamy
– nuclei from these two “parental” fungi do not fuse right away – fungus is now called a
heterokaryon
Key
Heterokaryotic
stage
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
Diploid (2n)
PLASMOGAMY
(fusion of cytoplasm)
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Zygote
Spores
ASEXUAL
REPRODUCTION
Mycelium
SEXUAL
REPRODUCTION
MEIOSIS
GERMINATION
GERMINATION
Spores
Spore-producing
structures
Sexual Reproduction
•
sexual reproduction:
–
–
–
–
–
hours or decades later (!) the nuclei will fuse = karyogamy
production of a diploid zygote (2n)
formation of a spore producing structure called a sporangium
MEIOSIS takes place in the sporangium - producing haploid spores (n)
spores are dispersed to germinate and form a new mycelium
Key
Heterokaryotic
stage
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
Diploid (2n)
The mycelium is a HAPLOID
multi-cellular organism
PLASMOGAMY
(fusion of cytoplasm)
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Zygote
Spores
ASEXUAL
REPRODUCTION
Mycelium
SEXUAL
REPRODUCTION
MEIOSIS
GERMINATION
GERMINATION
Spores
Spore-producing
structures
• fungal asexual reproduction: most fungi can reproduce sexually and asexually
depending on nutrient availability
– some fungi (molds) reproduce asexually through their mycelium making haploid spores (by
mitosis)
– other reproduce asexually by binary fission or budding - single-celled yeasts
• yeasts don’t produce spores
10 m
Key
Heterokaryotic
stage
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
Diploid (2n)
Parent
cell
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Zygote
Spores
ASEXUAL
REPRODUCTION
Bud
PLASMOGAMY
(fusion of cytoplasm)
Mycelium
SEXUAL
REPRODUCTION
MEIOSIS
GERMINATION
GERMINATION
Spores
Spore-producing
structures
Sac
fungi
Club
fungi
Basidiomycota
Arbuscular
mycorrhizal
fungi
Ascomycota
Chytrids
Zygote
fungi
Zygomycota
Fungal Diversity
Chytridiomycota
• fungi are thought to be descended
from a unicelluar, aquatic flagellated
protist
• earliest lineages of fungus thought to
possess flagella
– some still have flagella – called
chytrids
– fossils of the earliest vascular land plants
have fungal associations (mycorrhizea)
• radiated into 5 Phyla:
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–
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–
–
1. Chytridiomycota
2. Zygomycota
3. Glomeromycota
4. Ascomycota
5. Basidiomycota
Glomeromycota
• then moved to land
•
•
•
•
•
•
•
known as the chytrids
most primitive of the fungi - diverged the earliest in fungal evolution
unique in that they have flagellated spores called zoospores
some exist as single cells, others form colonies with hyphae
do not have a true mycelium – fungal body is called a thallus
are considered a coenocytic fungus – no septa in their hyphae
extensions off the hyphae produce digestive enzymes for decomposition of their
substrate
Hyphae
1. Phylum:
Chytridiomycota
2. Phylum: Zygomycota
•
•
•
•
1,100 known species
diverse in lifestyles
fast-growing molds
e.g. Rhizopus stolonifer – black bread mold
– typical of a zygomycete
– mycelium forms as a spread of horizontal hyphae over the food – penetrates it and absorb the
nutrients
– hyphae are mainly coenocytic
– spore dispersal through the air eventually passes it onto other substrates for continued growth
– sexual reproduction: “parents” are mycelia with hyphae or two mating types: “-”
and “+”
• + and – hypha extend toward one another (pheromones)
• two gametangia form between these hyphae – each contains multiple haploid nuclei
that are similar to gametes
• two gametangia undergo plasmogamy to produce a zygosporangium
– said to be heterokaryotic – no nuclear fusion yet!!
•
zygosporangium thickens and forms a “cyst” – remains resistant and dormant for months
Key
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
Rhizopus
growing
on bread
Mating
type (+)
Mating
type (–)
PLASMOGAMY
Gametangia with
haploid nuclei
100 µm
Young
zygosporangium
(heterokaryotic)
SEXUAL
REPRODUCTION
Dispersal and
germination
Sporangia
Sporangium
MEIOSIS
ASEXUAL
REPRODUCTION
Dispersal and
germination
50 µm
Mycelium
KARYOGAMY
Diploid
nuclei
Zygosporangium
(heterokaryotic)
– sexual reproduction:
• under favorable conditions – karyogamy occurs in the zygosporangium => diploid nuclei
inside the zygosporangium (parental cells for meiosis)
• followed by meiosis into haploid spores
– from the cyst arises a sporangium (called a fruiting body) for the production of
haploid spores
– this is what we see as the black fuzziness on bread
– spores germinate into new + and - mycelia
Key
-
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
http://academic.kellogg.ed
u/herbrandsonc/bio111/ani
mations/0120.swf
Rhizopus
growing
on bread
Mating
type (+)
PLASMOGAMY
Gametangia with
Mating haploid nuclei
type (–)
Young
zygosporangium
SEXUAL (heterokaryotic)
100 µm
REPRODUCTION
Dispersal and
germination
Sporangia
ASEXUAL
REPRODUCTION
50 µm
Mycelium
Dispersal and
germination
KARYOGAMY
Sporangium
MEIOSIS
Diploid
nuclei
Zygosporangium
(heterokaryotic)
3. Phylum Ascomycota
•
•
cup fungus
60,000 species
•
•
red, blue and green molds
also includes mildews
•
defined by the formation of a
cup-like ascocarp
–
–
•
•
The cup-shaped ascocarps (fruiting
bodies) of Aleuria aurantia give this
species its common name: orange
peel fungus.
a sac-like reproductive structure
containing asci that produce haploid
spores edible portion of this fungus
e.g. morels and truffles
The edible ascocarp of
Morchella esculenta,
the succulent morel is
often found under
trees in orchards.
10 µm
half the species associate with
algae to form lichens
most are septate within their
hyphae
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.
Neurospora crassa
feeds as a mold on
bread and other food
(SEM).
3. Phylum Ascomycota
•
•
•
mildews: general term of mildew
means dicolorations and odors
created by fungus
mildews are actually are parasitic
fungi of plants
white powdery appearance
• sexual reproduction:
– fusion of the hyphae from opposite mycelia mating types produces a new mycelium
where the touching hyphae undergo plasmogamy (just like in the zygomycotes)
– this new mycelium is made up of dikaryotic hyphae (2 unfused nuclei inside)
– at the tip of each of some of these hyphae a dikaryotic ascus forms (plural = asci)
Key
Conidia;
mating type (–) or (+)
Dispersal
fusion of (+)
and (-)
hyphae
Germination
ASEXUAL
REPRODUCTIONMycelium
PLASMOGAMY
Ascus
(dikaryotic)
Mycelia
Conidiophore
Haploid (n)
Dikaryotic (n + n)
Diploid (2n)
Dikaryotic
Hyphae
SEXUAL
REPRODUCTION
Germination
Dispersal
Diploid nucleus
(zygote)
Eight
Asci ascospores
Four
haploid
nuclei
Ascocarp
KARYOGAMY
MEIOSIS
•
sexual reproduction:
– within each individual ascus – karyogamy unites the 2 nuclei and meiosis follows to form 4 haploid
nuclei
– each of these 4 nuclei divide by mitosis ONCE to form a total of 8 ascospores each with a single
nuclei
– multiple asci become surrounded by a protective ascocarp (aggregation of hyphae) – that sprouts
above the soil
– ascospores are ejected from this ascocarp to germinate and form new mycelia
Key
Haploid (n)
Dikaryotic (n + n)
Diploid (2n)
fusion of (+)
and (-)
hyphae
PLASMOGAMY
Ascus
(dikaryotic)
Mycelia
Hyphae
extending from
ascogonium
SEXUAL
REPRODUCTION
Germination
Dispersal
Asci
Diploid nucleus
(zygote)
Eight
ascospores
Four
haploid
nuclei
Ascocarp
KARYOGAMY
MEIOSIS
•
asexual reproduction: fungus produces a powdery structures called conidiophores at the
tip of their hyphae
–
–
–
–
conidiophore is equivalent to a asexual sporangium
mitosis within the conidiophore produces spores called conidia
conidia carried by air currents to new locations
germination leads to specialized hyphae formation called haustoriae – penetrate the epidermis of
leaves and absorb nutrients
– eventual production of a new mycelium with new conidiophores
Key
Haploid (n)
Dikaryotic (n + n)
Diploid (2n)
Conidia;
mating type (–)
Dispersal
Germination
ASEXUAL
Mycelium
REPRODUCTION
Mating
type (+)
PLASMOGAMY
Ascus
(dikaryotic)
Dikaryotic hyphae
extended from
ascogonium
SEXUAL
KARYOGAMY
REPRODUCTION
Dispersal
Diploid nucleus
Eight
(zygote)
Asci ascospores
Mycelia
Conidiophore
Germination
e.g. Neurospora crassa conidiophore
( green bread mold)
Four
haploid
nuclei
Ascocarp
MEIOSIS
4. Phylum:
Basidiomycota
•
•
•
•
•
club fungus
30,000 species
includes the mushrooms, shelf
fungi, molds and mycorrizhae,
rusts and smuts
important decomposers of wood
saprophoric (decomposing) and
parasitic species (rusts and smuts)
Maiden veil fungus (Dictyphora), a
fungus with an odor like rotting
meat
Fly agaric (Amanita
muscoria), a common species
in conifer forests in the
northern hemisphere
Puffballs emitting spores
Shelf fungi, important decomposers of
wood
4. Phylum:
Basidiomycota
•
all are characterized by the formation
of a basidium (plural = basidia) – clubshaped structure which is diploid and
produces basidiospores
•
basidia are located on the visible
mushroom called the basidiocarp and
are the structures we call mushrooms,
puffballs, toadstools, bracket fungus
•
beneath the basidiocarp are extensive
mats of mycelia that feed on decaying
vegetation – very long lived and
dikaryotic
•
hyphae of the mycelium are septate
and coenocytic at specific stages
during their reproduction
Maiden veil fungus (Dictyphora), a
fungus with an odor like rotting
meat
Fly agaric (Amanita
muscoria), a common species
in conifer forests in the
northern hemisphere
Puffballs emitting spores
Shelf fungi, important decomposers of
wood
The Common Mushroom
pileus
•
•
•
•
•
•
the basidiomycotes include the
common mushroom
basidium = “little pedestal”
note the cap (pileus) with the
gills on the underside
the supporting stalk = stipe
fruiting body or basidiocarp =
cap + stalk
as in the ascomycotes and its
ascocarp – the basidiocarp is an
aggregation of hyphae
stipe
gills
basidiocarp
stipe
• sexual reproduction:
• two haploid mating types ‘+’ and ‘–’ undergo plasmogamy and a dikaryotic
mycelium forms made up many dikaryotic hyphae
• rain or temperature changes induce the dikaryotic mycelium to form a
basidiocarp (mushroom)
• the hyphae of the mushroom are still dikaryotic – no nuclear fusion yet (nuclei
are still separated and are haploid)
Dikaryotic
mycelium
PLASMOGAMY
Mating
type (–)
Mating
type (+)
Haploid
mycelia
SEXUAL
REPRODUCTION
Gills lined
with
basidia
Basidiocarp
(dikaryotic)
Dispersal and
germination
Basidiospores
Basidium
Basidium containing
four haploid nuclei
Basidia
(dikaryotic)
KARYOGAMY
MEIOSIS
1 µm
Basidiospore
Diploid
nuclei
Key
Haploid (n)
Dikaryotic (n + n)
Diploid (2n)
•
•
•
•
•
•
•
sexual reproduction:
the gills of the basidiocarp are made of dikaryotic hyphae
their tips are called called basidia (basidium = singular)
within each basidium karyogamy occurs - two nuclei fuse
followed by meiosis 4 haploid nuclei total per basidium
at the tip of the basidium - each haploid nuclei develops into a basidiospore
basidiospores are released when mature and are carried by the wind – germinate into new
mycelia which rapidly undergo more sexual reproduction
Dikaryotic
mycelium
PLASMOGAMY
Mating
type (–)
Haploid
mycelia
Mating
type (+)
SEXUAL
REPRODUCTION
Gills lined
with
basidia
Basidiocarp
(dikaryotic)
Dispersal and
germination
Basidiospores
Basidium
Basidium containing
four haploid nuclei
Basidia
(dikaryotic)
KARYOGAMY
MEIOSIS
basidiospores
1 µm
Basidiospore
Diploid
nuclei
Key
Haploid (n)
Dikaryotic (n + n)
Diploid (2n)
Fungi as Decomposers
• fungi are well-adapted decomposers of
organic material
• very good at decomposing the
polysaccharides cellulose and lignin (plants &
wood)
• their decomposition makes available to
ecosystems inorganic nutrients such as
carbon, nitrogen and phosphate ions
Yeasts
• 1500 species of unicellular fungi
– not a single taxonomic or phylogenic grouping
– divided up between Phylum Ascomycota & Phylum
Basidiomycota
• often a synonym for the species Saccharomyces
cerevisiae
– but there are several species of yeasts
Yeasts
• are chemotrophs – convert carbohydrates into CO2
and alcohol (fermentation)
– most species are either obligate aerobes (for cellular
respiration) or anaerobic (fermentation)
– are no species of obligate anaerobes
• naturally occurring on skins of fruits & berries –
even on the skin or epithelial linings of humans
– Candida albicans - yeast infections or athlete’s foot
• also found in guts of mammal and insects
– e.g. bees and ants
• even in deep sea environments
• exist as either diploid or haploid forms
Yeasts
• asexual reproduction through budding or mitosis –
occurs in both haploid and diploid cells
• sexual reproduction through the production of
pheromones by two mating types
– two yeast cells of opposite mating types meet and
fuse – karyogamy results in a diploid yeast cell
– this yeast cell can reproduce asexually by budding
– when stressed– the diploid cells undergo meiosis to
form spores of two haploid mating types- “alpha”
and “a”
a
Haploid
alpha
Diploid
Fungal Associations
•
•
fungi can form mutualistic relationships
with plants, algae and animals
Fungal-Plant associations: formation of
mycorrhizal associations with the roots
of vascular plants
–
–
–
–
–
these fungi are called mycorrhizal
all plant species harbor symbiotic fungi called
endophytes
these live harmlessly inside the leaves of
plants
benefit certain grasses and other non-woody
plants by making toxins to deter herbivores
can also increase the plants tolerance to heat,
drought or heavy metals
leaf cutter ants depend on fungi to convert
plant material into something these ants can digest
Fungal Associations
•
Fungal-Animal associations: some
fungus share their digestive services
with animals
– assist in the breakdown of plant
material
– guts of cattle and other grazing
mammals
– some insects (termites and ants) can
raise “farms” of fungi to aid in digestion
– called farmer insects
leaf cutter ants depend on fungi to convert
plant material into something these ants can digest
Fungal Associations:
Lichens
•
Lichens: 25,000 species
– fungus + green algae (or cyanobacteria)
– each requires one another to colonize areas
they wouldn’t be able to alone
– algae provide organic compounds, the
cyanobacteria fix nitrogen
– algae nestle among the fungal hyphae
– found from the arctic to the tropics
– most reproduce asexually
•
A fruticose (shrub-like) lichen
types of lichens:
– 1. Crustose lichens – grow as a crust on a
surface
– 2. Foliose lichens – leafy in appearance
– 3. Fructicose lichens – shrublike with
branching and intertwined fibrous parts
A foliose (leaf-like) lichen
Crustose (crust-like) lichens
Lichens
asexual reproduction:
– either through fragmentation
– or by the formation of soredia – small clusters
of hyphae with embedded algae - may be
carried by the wind to new locations
– some sexual reproduction can occur through
the formation of basidiocarps or ascocarps
Ascocarp of fungus
Soredia
Fungal
hyphae
Algal
layer
Algal cell
Fungal hyphae
10 µm
•