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Chapter 24Lecture Outline
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Chapter 24
Fungi
Evolutionary Relationships of the Kingdom Fungi
Fungal Bodies and Feeding
Fungal Asexual and Sexual Reproduction
The Importance of Fungi in Ecology and Medicine
Biotechnological Applications of Fungi
Chapter Outline:
Eukaryote supergroup Opisthokonta Includes certain protists, Kingdom Animalia, and Kingdom
Fungi
Fungi are most closely related to animals, but diverged over a billion years ago Fungi arose from protists related to Nuclearia – an amoeba
that feeds by engulfing cells
True fungi are a monophyletic group of over 100,000 species Does not include slime molds or oomycetes
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Evolutionary Relationshipsof the Kingdom Fungi
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Met
azo
a(a
nim
al k
ing
do
m)
Ch
oan
ofl
agel
late
s(p
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sts)
Nu
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)
Ch
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Mic
rosp
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dia
Cry
pto
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Zyg
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AM
fu
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Asc
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Bas
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Critical innovations
KEY
Single flagellum
Rigid chitincell wall,osmotrophicnutrition
Primarily terrestrial habitat
Beneficial associations withphotosynthetic organisms
Septate hyphae,dikaryotic hyphae,fruiting bodies
Supergroup Opisthokonta
Kingdom Fungi
BIOLOGY PRINCIPLE
All species (past and present) are related by an evolutionary history
There are more than 15 fungal phyla, but their relationships and names are still being determined.
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Fungal cell walls
Rigid cell walls are composed of chitin A tough, nitrogen-containing carbohydrate Except for the cryptomycota which lack cell walls
Benefit Allows cells to resist high osmotic pressure resulting
from feeding by absorption of small organic molecules
Drawbacks Cells cannot engulf food due to rigid cell walls Restricts mobility of nonflagellated cells
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Seven main groups of fungi
Cryptomycota Chytrids Microsporidia Zygomycetes AM fungi Ascomycetes Basidiomycetes
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Cryptomycota
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The earliest-diverging fungi
Occur in soil and water
Can produce flagella for reproduction
Only fungi to lack a cell wall
Chytrids
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Microscopic aquatic species
Have cell walls made of chitin
Produce reproductive cells with flagella Only found in chytrids and cryptomycota Loss of flagella linked to ecological transition from
aquatic habitats to land
Zygomycetes
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Several lineages of terrestrial fungi
Have distinctive large zygotes called zygospores
ex: Common black bread molds
Microsporidia
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Pathogens that can only reproduceinside the cells of an animal host. Linked to honeybee decline
Very small size (1–4 μm)
Single-celled, chitin-walled spores Strong chitin wall helps survival in the environment
until they enter the bodies of animals
AM fungi
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Arbuscular mycorrhizal fungi
Close symbiotic associations with plant roots Fungus provides plant with minerals Plant provides food for the fungus
Fossils suggest that even early plants may have depended on these AM fungal associations
Ascomycetes
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Asci – unique reproductive structures
Some ascomycetes cause disease
Ecologically important as decomposers
example: Edible truffles and morels
Basidiomycetes
Basidia – club-shaped reproductive cells
Very important decomposers and plant symbionts ~30,000 species
Varied reproductive structures Mushrooms, puffballs, stinkhorns, shelves, rusts, smuts
Fungi are most closely related to animals and share several opisthokont features
Both heterotrophic – cannot produce their own food
Both use absorptive nutrition – secrete enzymes and absorb small organic molecules
Both store surplus food as the carbohydrate glycogen
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Fungal Bodies and Feeding
Unique body form
Most have mycelia composed of hyphae Most of the mycelium is diffuse and inconspicuous
Fruiting bodies – visible reproductive structures Mushrooms are one type Fruiting bodies produce spores
Spores Chitin-walled reproductive cells An adaptation to the terrestrial environment Transported by wind or by animals 18
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Region where hyphae mate,forming a fruiting body
Myceliumwithin substrate
(such as soil)
Unmated mycelium Different unmated mycelium
Mated hyphae
Fruiting body above the substrate
Spores
BIOLOGY PRINCIPLE
Living organisms grow and develop
After a mating process occurs, mated hyphae produce fruiting bodieswhose form fosters spore productionand dispersal.
In suitable sites, sporesmay germinate, producingnew mycelia.
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Distinctive growth processes
Mycelia grow quickly when food is plentiful Grow from the edges as hyphae extend their tips
Narrow dimensions and extensive branching provides high surface area for absorption
Osmosis important in growth – entry of water produces force for tip extension
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Mycelium shape depends on substrate Long extensions in soil to reach food-rich areas Spherical in liquid medium Flat disk in petri dish
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(a) Mycelium growing in liquid medium
(b) Mycelium growing on flat, solid medium
a: © Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, London ON; b: CDC
Many fungi reproduce by microscopic spores that grow into a new organism Spores may be asexual clones Or from sexual reproduction with new allele
combinations
Asexual reproduction is ideal for rapid spread No need to find a mate No fruiting body No meiosis
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Fungal Asexual and Sexual Reproduction
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Conidia Asexual spores grown
at the tips of hyphae
Aspergillus versicolor Causes skin and lung
infections in vulnerable patients
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69 µm
© Dr. Dennis Kunkel Microscopy/ Visuals Unlimited
Medically important fungi that reproduce primarily by asexual means include Athlete’s foot fungus (Epidermophyton floccosum) Infectious yeast (Candida albicans)
Budding yeast, Saccharomyces cerevisiae Can reproduce
either sexuallyor by asexual budding
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Daughtercell (bud)
Mother cell
© Medical-on-Line/Alamy
Sexual reproduction
Involves union of gametes, zygote formation and meiosis
Gametes of most fungi are cells from hyphal branches Mating types differ biochemically Hyphal branches fuse between compatible
mating types
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Most sexual organisms have plasmogamy (fusion of gametes’ cytoplasm) followed by karyogamy (fusion of gametes’ nuclei)
In fungi, after plasmogamy, nuclei may remain separate for a long time Mycelium is dikaryotic or heterokaryotic
Some fungi persist as dikaryons, producing clones that can live for hundreds of years Dikaryotic mycelia are functionally diploid Eventually, dikaryotic mycelia produce fruiting
bodies, the next stage of reproduction
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Fruiting bodies
Mated mycelia will produce a fleshy fruiting body when conditions are right Fruiting structure disperse haploid spores that grow
into mycelia If a haploid mycelium meets a compatible mating
type, they fuse (mate) and the cycle repeats
Fruiting body structures aid spore dispersal Puffballs puff spores out onto wind currents Stinkhorns stink, and attract flies that carry off spores Truffles are underground – but their scent attracts
animals that dig them up 29
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(a) Fruiting bodies adapted for dispersal of spores by wind
(b) Fruiting body adapted for dispersal of spores by insects
Sporesin astickymatrix
a: © Felix Labhardt/Taxi/Getty Images; b: © Bob Gibbons/ardea.com
Many fungi produce substances in the fruiting body to deter consumption Toxins can cause liver failure requiring a transplant Hallucinogenic or psychoactive substances
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© David Q. Cavagnaro/Getty Images
Ergot
Decomposer fungi are essential components of the Earth’s ecosystems
Work with bacteria
Only certain bacteria and fungi can break down cellulose
Release minerals to the soil and water
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The Importance of Fungiin Ecology and Medicine
Some fungi are predators trapping tiny soil nematodes
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Nematode
Hyphal loop
© N. Allin & G.L. Barron/Biological Photo Service
Fungal pathogens
Crop diseases caused by 5000 species Rust spores can be spread on the wind
Human diseases Dermatophytes – athlete’s foot, ringworm Pneumocystis jiroveci and Cryptococcus neoformans infect
people with weakened immune systems (as in AIDS) Blastomyces dermatitidis, Coccidioides immitis, and
Histoplasma capsulatum infect the lungs
In nature, fungal pathogens play important ecological role in controlling other species
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Pucciniagraminisspores
Wheat leaf tissue
0.1 mm
(left): © Nigel Cattlin/Photo Researchers, Inc.; (right): © Herve Conge/ISM/Phototake
BIOLOGY PRINCIPLE
Biology affects our society
Recent analyses indicate that environmental changes linked to human activities correlate with increases in the incidence of new fungal pathogen infestations that threaten human health and agricultural sustainability.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Nigel Cattlin/Photo Researchers, Inc.
Beneficial fungal associations
Fungal associations with photosynthetic partners can be mutualistic Symbioses where both partners benefit
Some animal species farm fungus for food Leaf-cutter ants, termites, beetles, salt marsh snail
Mycorrhizal fungi associate with plant roots
Lichens are partnerships between fungi and photocynthetic algae or bacteria
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Mycorrhizae
Association between the hyphae of certain fungi and the roots of most seed plants
More than 80% of terrestrial plants have mycorrhizae
Plants receive increased supply of water and mineral nutrients
Fungi get organic food molecules from the plants
Two most common types are endomycorrhizae (within roots) and ectomycorrhizae (on roots)
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© Dr. D.P. Donelley and Prof. J.R. Leake, University of Sheffield, Department of Animal & Plant Sciences
Seedlingroot
Mycorrhizalhyphae
Endomycorrhizae Fungal hyphae penetrate the spaces between root
cell walls and plasma membranes and grow along the outer surface of the plasma membrane
Arbuscular mycorrhizae (AM) form highly branched structures with high surface area
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a: © Mark Brundrett
Hyphae
Arbuscules
Cell wall
Plasmamembrane
Root cells49 µm
(a) Micrograph of arbuscular mycorrhizae (b) Hyphae growing between cell wallsand plasma membranes
Ectomycorrhizae Coat root surface and grow between cells of roots Some species of oak, beech, pine, and spruce trees
will not grow unless their ectomycorrhizal partners are also present
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(b) SEM of ectomycorrhizal hyphae (c) Hyphae invading intercellular spaces(a) Ectomycorrhizal fruiting body
Ectomycorrhizalhyphae coatinga root tip
Rootcells
Ectomycorrhizalhyphae
a: © Jacques Landry, Mycoquebec.org; b: © Courtesy of Larry Peterson and Hugues Massicotte
Comparison of genomes reveals how basidiomycete metabolism diversified
Basidiomycete genomes show diverse metabolic pathways that help utilize organic carbon from plants
Some decompose cellulose and lignin Break down dead trees, woody debris, leaf litter Some break down similar materials from animal dung
Other species evolved ectomycorrhizal associations with living plants
What genes are different to give species different capabilities?
EVOLUTIONARY CONNECTIONS
White rot fungi – decompose both cellulose and lignin Complex enzymatic pathways to break down the many types of
chemical bonds Energetically expensive but give access to cellulose
White rot fungal metabolism arose 300 mya during the Carboniferous This new set of enzymes is why there are no major
plant carbon deposits since then!
Brown rot fungi – break down cellulose, leave lignin Evolved from white-rot fungi but lost genes to degrade lignin,
saving energy by not producing those enzymes
Ectomycorrhizal fungi evolved in turn from the brown-rot fungi
EVOLUTIONARY CONNECTIONS
Lichens
Partnerships of particular fungi and certain photosynthetic green algae and/or cyanobacteria
25,000 lichen species Not all descended from a common ancestor At least five separate fungal lineages
Three major forms – crustose, foliose, fruticose
Photosynthetic partner provides organic food molecules and oxygen
Fungal partner provides carbon dioxide, water, and minerals
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(a) Crustose lichen (b) Foliose lichen
(c) Fruticose lichen (d) Microscopic view of a crosssection of a lichen
a: © Joe McDonald/Corbis; b: © Lee W. Wilcox; c: © Ed Reschke/Getty Images; d: © Lee W. Wilcox