Funguslike protists

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Fungus-like protists
Fungi and animals share a common ancestor with
amoebozoans (amoebae slime molds)
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Fungus-like protists
1) Plasmodial slime molds (Physarum, below) 2)
Cellular slime molds (Dictyostelium, model
organism for studying
multicellularity)
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Plasmodial slime mold life cycle
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Cellular slime mold life cycle
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Fungi
Heterotrophic decomposers - feed by absorbing
nutrients Single-celled (yeasts) or
multicellular May be free-living, parasitic, or
mutualists ( symbionts) Bodies composed of
threadlike structures called hyphae Cell walls
contain chitin
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Key Terms Symbiosis two organisms (or
species) living in close association (e.g.
mycorrhizae) mutualism both
benefit parasitism the parasite benefits at
the expense of the host commensalism one
benefits, the other is unaffected Endosymbiosis
one organism (endosymbiont) living inside
another (host) Examples Plastids and
mitochondria arose through endosymbiosis Rhizob
ium bacteria living in root nodules fix
nitrogen Lichens algal symbionts within a
fungal host
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Heterotrophs ingest or absorb external source
of organic carbon - Fungi are heterotrophs that
absorb organic carbon Decomposers (saprobes)
break down complex organic molecules into
simpler organic molecules - Fungi and bacteria
are important decomposers, recycling carbon
and other nutrients Biogeochemistry the (re-)
cycling of key elements (O,C,N,P,S) -
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Basic fungal structure hyphae and mycelia
(singular mycelium)
Hyphae release digestive exoenzymes into their
surrounding - break down organic matter
into small molecules that can be
absorbed Hyphae form a web called the mycelium
that greatly increases surface area,
maximizing uptake of dissolved nutrients from
the substrate
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Hyphae release digestive exoenzymes into their
surrounding - break down organic matter
into small molecules that can be
absorbed Produce enzyme that can break
down.. 1- lignin, a complex polymer that makes
wood tough 2- cellulose, a polymer of glucose
(sugar) that animals cannot break down (hence
why termites, cows need gut symbionts) Without
fungi, carbon cycle would be interrupted
atmospheric CO2 would be stored in wood for
millenia
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Fungi grow by extending the tips of their
hyphae through cytoplasmic streaming Hyphae
can be divided into individual cells by
partitions called septa Some fungi grow by
repeated mitotic divisions of nuclei without
cell division coenocytic condition -
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Some fungi form mutualistic or parasitic
associations with plants Use special hyphae
called haustoria to penetrate cell wall of
plants -
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Fungal Life Cycle
Fungi spread by producing huge s of spores -
structures that resist harsh environmental
conditions - can disperse long distances by
wind
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Stage 1 Plasmogamy
Most hyphae contain haploid nuclei 2 hyphae of
different mating types can grow together
fuse plasmogamy
NN
2N
N
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Stage 2 Karyogamy
Eventually, 2 haploid nuclei from different
parents fuse into diploid nuclei Zygote
quickly undergoes meiosis, producing haploid
spores
NN
2N
N
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Heterokaryotic stage separate haploid nuclei
from different parents, in the same
hyphae Karyogamy the 2 haploid nuclei fuse
into 1 diploid nucleus
NN
2N
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Changes in Fungal Taxonomy
Campbell Reece 2002
Campbell Reece 2005
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Fungal Evolution
Fungi evolved from an ancestor that was an
aquatic protist, with a posterior flagellum
(like sperm cells of animals) Molecular evidence
indicates this ancestor was also
single-celled - thus, animals fungi
independently evolved multicellularity -
only primitive fungi have flagellated spores
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Fungal Phylogeny
Based on molecular evidence, fungi are now
grouped into 5 phyla
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Chytrids
May be single-celled or form multi-cellular
hyphae Only fungi w/ flagellated spores,
called zoospores Relationship to Zygomycetes is
still controversial Aquatic
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Chytrids
zoospore
Branching hyphae increase surface area for uptake
of nutrients from surrounding aquatic medium
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Phylum Zygomycota (Zygomycetes)
molds like Rhizopus sp., common bread mold
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Zygomycetes life cycle
Haploid
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1) hyphae of opposite mating type fuse to
form heterokaryotic (NN) structure, the
zoosporangium - contains many haploid
nuclei from each parent - resists bad conditions
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Zygomycetes life cycle
Haploid
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2) when conditions improve, karyogamy
occurs haploid nuclei fuse into
diploid nuclei - zygote then undergoes
meiosis, producing genetically diverse
spores - regular sporangia may form
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Zygomycetes life cycle
Haploid
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3) Regular sporangia may form and produce
spores by mitosis (asexual
reproduction)
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Phylum Zygomycota (Zygomycetes)
Pilobolus sp. dung fungus
Microsporidia - highly modified
parasites (Encephalitozoon intestinalis)
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Phylum Glomeromycota - Glomeromycetes Formerly
considered zygomycetes, now in their own
phylum Only 160 identified species, but
ecologically critical group Form
endomycorrhizae, mutualistic associations inside
of plant roots
Taiz Zeiger 2002
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Phylum Glomeromycota - Glomeromycetes Formerly
considered zygomycetes, now in their own
phylum Only 160 identified species, but
ecologically critical group
Endomycorrhizae Hyphae penetrate cell walls,
but do not puncture plasma membrane of plant
cells Instead, push inside host cell
surrounded by plants membrane
Taiz Zeiger 2002
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Phylum Ascomycota (ascomycetes)
Sac fungi produce sexual spores in saclike
asci - contained in ascocarps,
fruiting bodies Have an extended heterokaryotic
stage...
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Hyphae fuse into NN heterokaryotic
stage Septa form cells with 2 haploid nuclei
each - one of these grows into an ascus
Developing asci are housed in the ascocarp, the
fruiting body that will later eject the spores
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Hyphae fuse into NN heterokaryotic
stage Septa form cells with 2 haploid nuclei
each - one of these grows into an ascus
Karyogamy in the ascus combines parental
genomes then meiosis produces 4 haploid
cells Each undergoes mitosis to yield 8
haploid ascospores
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Penicillium sp. an ascoymycete (formerly
considered a deuteromycete) -
Why does a fungus make an antibiotic?
Campbell Reece 2005
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Saccharomyces sp. -- yeast Common disease
organisms Used by humans to ferment sugar in
dough or grains, for baking or production of
adult beverages - under anaerobic conditions,
metabolize sugar to ethanol and CO2
(makes dough rise)
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Phylum Basidiomycota - basidiomycetes
includes common mushrooms, toadstools, shelf
fungi
important decomposers of wood long-lived
heterokaryotic stage, giving rise to
basidiocarp (mushroom) in bad conditions A
single mushroom cap produces a billion
basidiospores
Campbell Reece 2005
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Phylum Basidiomycota sexual life cycle stages
heterokaryotic NN
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Basidiocarps of a basidiomycete forming a fairy
ring pop up overnight
Heterokaryotic mycelium connects individual
mushrooms underground - expands outward
digesting organic matter in soil
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Ectomycorrhizae
Freeman 2005
Many basidiomycetes form ectomycorrhizae with
plant roots - roots are completely covered in
a layer of hyphae Exoenzymes release nitrogen
from decaying matter, which is transferred to
hyphae extending in between outermost root cells,
which absorb the N
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Fungal Symbioses

• Lichens fungus alga mutualism
• - Endosymbiont is either a cyanobacterium or a
  chlorophyte
• 
  (green alga)
• - Fungus is the host
• Mycorrhizae fungus plant root mutualism
• Endomycorrhizae - glomeromycete symbiont
• (inner)
• Ectomycorrhizae - basidiomycete symbiont
• (outer)
• Various parasitic fungi (many diseases of plants
  animals)

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Lichens mutualism between fungus (usually
Ascomycete) green alga
3 growth forms of lichens - Foliose
(leaf-like) - Crustose - Fruticose
(shrub-like) This relationship evolved 3
separate times
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Lichens mutualism between fungus (usually
Ascomycete) green alga
This relationship evolved 3 separate
times Enable plants to eventually grow on what
was bare rock by eroding the rock surface,
trapping soil Are very sensitive to air
pollution, acid rain
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Ecto-mycorrhizae Endo-mycorrhizae
Taiz Zeiger 2002
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Fungi are responsible for many plant diseases
destroy 10-50 of many crops worldwide Eating
fungus-infected grains is a severe human health
issue in much of the world - contributes to
high rate of liver cancer in areas that
consume peanut meal, which supports fungi
that produce toxins Historically, eating
ergot-infected grain caused outbreaks of madness
and death, once thought to be possession
- ergot produces lysergic acid, similar to LSD