1 chapter 24 lecture outline copyright © mcgraw-hill education. permission required for...

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Chapter 24Lecture Outline

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A 460 million year old fossil fungus –one of the oldest known

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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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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Critical innovations

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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.


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


(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


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.


© 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

Fungi convert inexpensive organic compounds into citric acid, glycerol, and antibiotics

Distinctive flavor of blue cheese

Saccharomyces cerevisiae for bread, beer and wine

Replace chemical procedures that generate harmful waste products Wood pulp bleaching

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BiotechnologicalApplications of Fungi

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