fungus - any of those plants without leaves, flowers or green
coloring matter, growing on other plants or on decaying
matter and including mushrooms, toadstools and molds.
Oxford American Dictionary, 1980
fungus - any chemoheterotrophic eukaryote that reproduces
with spores and has cell walls at some stage of life.
Plant Biology 2nd Ed. (2006) Rost, Barbour, Stocking, Murphy
chemoheterotrophic - an organism that obtains both energy and
carbon from organic sources.
Some fungi obtain nutrition from living organisms such as
mycorrhizae and lichens. Others are saprobes - organisms that
feed on dead organic material.
Main differences between plants and fungi: 1) both have cell
walls but the fungi use chitin for cell walls while plants use
cellulose; 2) plants are photoautotropic, fungi are
chemoheterotrophic.
Because fungi have a rigid cell wall, that cannot engulf food as
animal cells can. They secrete digestive enzymes and transport
the products (sugars, amino acids, peptides) through the plasma
membrane.
polymer of an N-acetylglucosamine
Kingdom Fungi - monophyletic group of eukaryotic heterotrophs with
chitinous cell walls.
dikaryomycete - has a dikaryotic mycelium stage with pairs of haploid
nuclei in each septate compartment.
coenomycetes - lack a dikaryotic stage and have aseptate hyphae.
dikaryomycetes
coenomycetes
Ascomycota
Glomeromycota
Zygomycota and
Chytridiomycota
Basidiomycota
Fungal septa
present in
dikaryomycetes
Septa of Ascomycetes
Dolipore septa of Basidiomycetes
Phyla in Kingdom Fungi
Chytridiomycota - artificial (non monophyletic) phylum containing all
fungi that have swimming reproductive cells.
Zygomycota - fungi with zygospores, aseptate hyphae, mitosporangia
and lack of swimming cells.
dikaryomycetes
Glomeromycota monophyletic,
members engage in
arbuscular
endomycorrhizae
zygospore
coenomycetes
Ascomycota
Glomeromycota
Zygomycota and
Chytridiomycota
Basidiomycota
Phyla (continued)
Ascomycota - monophyletic phylum, fungi that produce sexual spores
in asci, mycelia have septate hyphae, there is a dikaryotic stage in
sexual reproduction, and they spread primarily by releasing conidia
(asexual mitospores).
Basidiomycota - all members extrude myospores from a basidium,
mycelia are septate and a dikaryotic stage is present.
ascospores in asci
basidium
most fungi develop a mycelium composed of branching hyphae
septate
aseptate
Mycelium - branching network of hyphae
Hyphae allow the fungus to grow towards food sources by
chemotropism (remember that a tropism is oriented
growth in response to a directional signal).
proteins, starch
Hyphae grow by tip growth
enzymes
amino acids,
sugar, etc.
water
solutes
flow
PRESSURE
growth
septum
tip of hypha
Some fungi live as single cells (yeasts)
Some are dimorphic consisting of hyphae or yeasts
budding cell
yeasts
Fungi compete with bacteria for food and bacteria existed for
1 billion years before fungi. So how do fungi compete?
Although fungal cell division is slower (90 minutes for yeast,
20 minutes for bacteria). Fungi are able to grow toward food
sources. Also they are able to redistribute the acquired
nutrients through the mycelium and produce spores above
the surface for dispersal.
Fungi secrete acid (H+) that inhibits bacterial growth.
Fungi secrete antibiotics including alcohol that inhibit or kill
bacteria.
Most fungi produce asexual spores to multiply,
such as these mitospores from Penicillium
conidia
conidiophore
and sexual spores for diversity,
Are fungi closer to animals or plants?
The original kingdom
Fungi contained slime molds
and oomcyetes (egg fungi).
But this classification is not
monophyletic and therefore
does not make sense.
Oomycetes
kingdom
Fungi
Acrasids
kingdom
Animalia
Mycetozoa
Original kingdom Fungi
kingdom
Plantae
Within the kingdom Fungi the phyla (or division) names end with
mycota as in Basidiomycota or Ascomycota. Within phyla the class
names end with mycetes such as Hymenomycetes the largest
class in the Basidiomycota.
In the Basidiomycota, basidiospores are
exuded from the basidium
In the Ascomcota,
ascospores are
contained in a cell
called the ascus.
basidium
Sexual reproduction in the dikaryomcetes
In the Zygomycota, compatible hyphae fuse together to form a
large cell that becomes the zygospore.
zygospore
One problem with using the morphology of sexual structures to
classify fungi is that sexual reproduction has never been
observed for thousands of species of fungi.
95% of named fungal species are dikaryomycetes, what makes them
sucessful? 1) a dikaryotic stage 2) septate hyphae.
coenomycetes
(lower fungi)
Chytridiomycota
Zygomycota
dikaryomycetes
(higher fungi)
Glomeromycota Ascomycota Basidiomycota
dikaryotic stage
septate hyphae
5% of named
fungal species
95% of named
fungal species
Fig. 20-11, p. 344
Sexual life cycle of a dikaryomycetes with a dikaryotic stage.
By having 2 different nuclei in each cell, the number of meiotic
events can be huge leading to high diversity of progeny.
karyogamy
zygote
nuclei
diploid
dikaryotic stage
n+n
2n
n + n mycelium n + n
meiosis
1n
spores
plasmogamy
1n mating
mycelia
haploid
Septate hyphae may be an advantage in producing more complex
fungal structures. It may facilitate differentiation (different tissues
need different genetic programs). The septum may also help in
damage control.
proteins, starch
enzymes
amino acids,
sugar, etc.
water
solutes
flow
PRESSURE
growth
septum
tip of hypha
plasmogamy - fusion of protoplasts, not accompanied by nuclear
fusion
karyogamy - the fusion of two nuclei
haploid - 1n, having one complete set of
chromosomes.
diploid - 2n
This example is from the zygomycota
Phylum Chytridiomycota - swimming reproductive cells
mitosporangium
c
mitospores
(zoospores)
asexual
loop
d
gametes
e
plasmogamy
rhizoids
zygote
meiospores
(zoospores)
karyogamy
and meiosis
resting
meiosporangium
Phylum Chytridiomycota
1000 named species.
none cause human diseases except for “swimmers
itch” there are amphibian diseases caused by chytrids
Here is a chytrid sporangium growing on
pollen grains
Phylum Zygomycota - fungi with zygospores, aseptate hyphae,
mitosporangia and lack of swimming cells.
1100 zygomycete species
a few human diseases - zygomycosis occurs mainly in
immunocompromised individuals. Transmission is usually by
inhalation of spores.
Phylum Zygomycota - life cycle of Rhizopus stolonifer
Some common features of both zygomyces and chytridiomyces
both meiospores and mitospores are made in sporangia
the meiosporagium is a resting phase
both make aseptate hyphae
Differences:
in the Zygomycota neither meiospores nor mitospores are motile
Spore fusion takes place in the Chytridiomycota
but is replaced by fusing hypha in the Zygomycota.
Phylum Glomeromycota - form mycorrhizae
157 species
80% of plants make symbiotic mycorrhizal interactions with
glomeromycetes
form endomycorrhizae - fungal interactions “within the cell”
arbuscules - “little trees”, hyphal proliferations within the cell wall of
plant cells but not within the plasma membrane
vesicles - swollen hyphal tips that store nutrients
The fungus contributes water, nutrients such as phosphate to the plant
and may make other - yet to be discovered - contributions.
Sexual reproduction is unknown in glomeromycetes, they make huge
mitospores (up to 1mm).
Phylum Glomeromycota
cortex
root tissues
epidermis
soil
root hair
spore
vesicle
arbuscule
hypha
cortex
cell
fungal
mycelium
Ascomycota and Basidiomycota
Ascomycota
32,000 named species
Many human diseases: athelete’s foot, jock itch, ringworm
Many plant diseases: apple scab, corn leaf blight, Dutch elm
disease, powdery mildew
Many benefits to humans also: bread, wine, beer, penicillin,
morels (Morchella), truffles (Tuber), soy sauce, bleu cheese.
ascospores
(meiospores)
mitospores are
produced in the haploid
generation
both mating types
make antheridia and
ascogonia
meiosporangia are
called asci
b
n
ascus
conidia
(mitospores)
m
conidiophore
ascogonium
a
mycelia
c
l
Meiosis
antheridium
d
karyogamy and
meiosis occur in the
ascus
zygote Diploid (2n)
Haploid (1n)
Plasmogamy
Dikaryotic (n + n)
1n hypha
meiospores are
produced in the ascus
and released
k
Karyogamy
ascogenous
ascus crozier hypha
g
j
i
e
f
h
ascoma
n+n
hypha
Single dikaryotic hyphae can lead to multiple asci
1
ascogenous
hypha (n + n)
fertilized
ascogonium
3
etc.
b
a
c
d
e
2
1
2
h
g
f
Different fruiting bodies (ascoma) of the Ascomycota
Apothecia
Perithecia
Cleistothecia
hymenium
ascospores
asci
asci
perithecial
wall
asci
Ascomycetes and symbiosis
The vast majority of lichens are
composed of an ascomycete + either
a cyanobacteria or an algae.
crustose - flat and crusty
foliose - leaflike
fruiticose - branching
crustose lichens
Most lichens reproduce asexually by releasing soredia (singular is
soredium).
Soredia are a few hyphae wrapped around photosynthetic cells.
Lichens also reproduce asexually through isidia (singular is
isidium).
isidia are fragments of lichens
isidia
sterigma
Basidiomycota
life cycle
a
basidium
1n
mycelia
g
Meiosis
b
basidioma is
dikaryotic
karyogamy and
meiosis occur in
the basidium
basidiospores
are not enclosed
in a cell
i
h
no mitospores!
Basidiomycetes
use meiospores
to reproduce
and diversify
basidiospores
(meiospores)
Diploid (2n)
zygote
f
Haploid (1n)
Dikaryotic (n + n)
Plasmogamy
n + n fusion cell
Karyogamy
c
basidium
n+n
mycelium
gill
e
basidioma
d
Poisonous mushrooms (Basidiomycetes)
The Destroying Angel (Amanita bisporigera). It is an ectomycorrhizal fungus, so it
can be found near trees. It makes amatoxin and as little as 1/2 of a mushroom cap
can be fatal. Symptoms appear 5 to 24 hours after ingestion, symptoms include
vomiting, cramps, diarrhea, delirium, and convulsions. By the time symptoms
appear, liver and kidney damage has occurred.
The volva or surrounding
membrane of developing
mushrooms is discintive.
Fly agaric (Amanita muscaria)
It is poisonous and psychoactive (produces muscimol). It was used as an
intoxicant in Siberia, and as an insecticide in Europe. It is ectomycorrhizal
with many trees. A toxic dose for an adult is one cap and a fatal dose is 15
caps. The toxins are muscimol and ibotenic acid.
There is no antidote.
If properly prepared (detoxified) it can be safely consumed and there are
traditions in Siberia, Japan and the Americas of eating Amanita.
btw, morels are also toxic if not
cooked properly.
The death cap (Amanita phalloides), produces α-amanitin and
there is no known antidote. Native to Europe. Especially
associated with beeches, birches, pines, chestnuts, spruces. It is
highly toxic and responsible for the majority of fungal poisonings
worldwide. Toxicity is not reduced by cooking or drying, 1/2 of a
cap is fatal for an adult. Initial symptoms are gastrointestinal and
resolve within 2-3 days. Death occurs 6 to 16
days after ingestion due to liver and kidney
damage.
α-amanitin
Deadly webcap (Cortinarius rubellus formerly speciosissimus)
Cortinarius mushrooms produce orellanine. If ingested, the first symptoms usually do not
appear for 2–3 days and can in some cases take as long as 3 weeks. The first symptoms
are similar to the common flu (nausea, vomiting, stomach pains, headaches, myalgia, etc),
these symptoms are followed by early stages of renal failure (immense thirst, frequent
urination, pain on and around the kidneys) and eventually decreased or nonexistent urine
output and other symptoms of renal failure occur. If left untreated death will follow.
orellanine
Jack o’Lantern mushroom (Omphalotus olearius) looks similar to a
chanterelle. Not fatal but causes cramps vomiting and diarrhea. The
gills are bioluminescent due to luciferase and luciferin. The gills
glow (hence the name). It glows blue-green.
Maintaining the dikaryotic stage: at each cell division two nuclei need to be
sorted into each cell. This is done either by making the septum in the plane
of the spindle fibers (left) or a clamp connection is formed (right).
A more complex septum may also permit basidiomycetes to have more
complicated structures.
septum
hyphal wall
dolipore
parenthesome
ER
Basidioma have many forms
brackets
Puff balls
pore
Coral fungi
Basidiomyctes make huge
numbers of spores
example a shelf fungus can make
3 billion spores per day for 6
months.
How are they released from the
basidioma?
droplet
sterigma
a
compression
By ballistospore release - the
projection secretes sugars,
attracting water from the air. When
the droplet spreads around the
b
spore it compresses the sterigma rebound
which acts as a spring to launch
the spore.
water film
spore
In addition to the Hymenomycetes, the Basidiomycota contains classes
Ustilagomycetes (smuts) and Urediniomycetes (rusts) that do not make large
fruiting structures. These include some of the most destructive fungal pathogens.
Corn smut