Ch.22

Question 1

Kingdom Fungi

Answer 1

• Monophyletic group
─ descended from a unicellular, marine protist that likely had a flagellum (Opisthokonta)

• Approx. 100,000 species described

• Molecular data place Fungi much closer to Animalia
— Common ancestor: aquatic, single celled, flagellated protist. (From opisthokonts)

• 5 recognized phyla
—Chytrids
—Zygomycetes (zygote fungi)
—Glomeromycetes (endomycoeehizal fungi)
— Ascomycetes (sac fungi)
—Basidomycetes (club fungi)

• Evolution of novel modes for absorbing nutrients from a wide array of food sources drove the fungal diversification

Overview of Characteristics

• Both unicellular (considered primitive) and multicellular
– “yeasts” and “moulds” respectively

• Cell walls made of chitin

• Occupy marine, freshwater and terrestrial habitats

• Heterotrophic (chemoheterotrophs)
– digest food externally and absorb nutrients through cell wall. (Consume food externally)

• Sessile (not able to move)

• Modular body plan constrained by the need to absorb
nutrients
– basic subunit = hypha
– mycelium = mass of hyphae
- (constrained from the ability to get food (being chemoautotrophs))

Question 2

Body Plan of Multicellular Fungi

Answer 2

• Cell walls made of chitin

• Bodies of most fungi composed of hyphae

• delicate tubes surrounding cytoplasm

• interwoven hyphal mat called mycelium (many hyphae) —> hyphae increase absorption

• mycelium acts as feeding network

• grow in direction of food sources

Two main types of hyphae:

• Septate: cross-walls (septa) dividing cells into separate chambers
— holes in walls to allow cytoplasm and even nuclei to travel through

• Coenocytic (aseptate): lack cross walls
— continuous cytoplasm with hundreds or thousands of nuclei
— allows nutrients and by products to flow through
— cytoplasmic flow —> may suggest where fungi and plants diverged.

Mycelia: networks of hyphae

• Filamentous structure
— large surface area: volume ratio*
— more area for enzyme secretion and food absorption
— a cubic cm of rich soil might have 1 km of hyphae
— can stretch to another area for food
—can dry out very easily so they adapted to find water effectively

• Hyphae can grow very quickly
— some fungi can add up to 1 km/day!
— hyphae only grow in length, not in width
— can wait to germinate till enviro conditions are favourable.

— extension of length —> Maximizes the digestion

Question 3

How Fungi feed

Answer 3

• Fungi secrete powerful enzymes (exoenzymes) outside their bodies (= absorptive nutrition or absorptive heterotrophy)
— consequence is they must consistently grow and find new places for food. Must be very competitive or reduce competition

• External digestion (saprophytes)
─ break down large complex organic molecules→absorb small simple ones
— also make them available for other organisms to use —> could lead to beneficial relationships or more competition

• Digests cellulose and lignin from plant tissues, and chitin and keratin from animal tissues

• Simple organic molecules absorbed by body of fungus:
— decomposers – break down & absorb nonliving organic matter
— parasites – absorb nutrient from cells of living hosts
— mutualists – absorb nutrient from hosts, but give something back

Question 4

Overview of Fungi Reproduction

Answer 4

• Fungi produce spores asexually or sexually

• Spores always haploid (n), and produce hyphae

• ‘Spore’ of fungi is different from the ‘spore’ of plantae in that they are produced by both mitosis and meiosis, not just by meiosis as they are in plants

• Some do both at different times
— depends if enviro conditions

• Other species only asexually

• Spores: resistant to desiccation(no water available) & act as dispersal stages

•if sessile they must repro asexually

Question 5

Fungal life cycle

Answer 5

• different from most haploid dominant species

Meiosis —> haploid cell —> mitosis —> haploid adult —> mitosis —> haploid Gametes (2 of them) —> fertilization (= plasmogamy + karyogamy) —> fungi delay karyogamy = heterokaryotuc —> diploid cell —> haploid egg —> meiosis

Question 6

Why do fungi delay karyogamy?

Answer 6

Has to do with:
1. Fertilization (maintain genetic diversity)
• By delaying karyogamy, fungi can maintain a heterokaryotic state → more time for exchange of genetic material

2. Dispersal (ensure survival and dispersal of offspring)
   • By controlling the timing of sexual reproduction → ensure there are ideal environmental conditions for growth and development of fungal offspring
   • ensure survival if the spores = new individuals

Question 7

Generalized fungal life cycle (reproduction)

Answer 7

Haploid = n
Diploid = 2n
Heterokaryotic cell

•spend most of life as a haploid

Asexual cycle
Mycelium (n)—> Spores (propagate via asexual spores)(n) —> dispersal and germination (n) —> mycelium (n)

Sexual
Mycelium (n)—> plasmogamy (fusion of cytoplasm) (n)—> heterokaryotic cell (unfused nuclei from diff parents) “different nuclei” —> karyogamy (fusion of nuclei) (2n)—> zygote (2n) —> meiosis(2n) —> spores (propagate via sexual spores)(n) —> dispersal and germination (n)—> mycelium (n)

Question 8

Generalized fungal life cycle (just another cycle tbh)

Answer 8

Haploid (n)
Diploid (2n)

• Facultative sexuality

• Most fungi spend most of their lives haploid

• Fungi do not have gametes

• no sexes, only compatible/incompatible mating types

Asexual

Mycelium (n) —> spore- producing structures (sporangia)(n) —> spores(n) —> germination (propagate via asexual spores) (n) —> mycelium (n)

Sexual

Mycelium (n)—> plasmogamy (fusion of cytoplasm)(n) —> heterokaryotic stage “diff nuclei” —> karyogamy (fusion of nuclei) (2n) —> meiosis (2n) —> spore-producing structures (sporangia)(n) —> spores (n) —> germination (propagate via sexual spores)(n) —> mycelium (n)

Question 9

Classification

Answer 9

• Colonized land around the same time as plants or possibly before!

• Maybe even as (mycorrhizal) symbionts of plants

• Five phyla: (myco = fungus)

• Phylum Chytridiomycota

• Phylum Zygomycota

• Phylum Glomeromycota

• Phylum Ascomycota

• Phylum Basidiomycota

Question 10

Phylum Chytridiomycota

Answer 10

• Mainly freshwater, some in soil, estuaries, or on/inside guts of animals

• Free-living chytrids digest dead organic matter

• Parasitic chytrids digest tissues of living hosts

• Depending on chytrid species, host is plant, animal, or other fungus

• Chytrids implicated in global decline of amphibians

Question 11

Phylum Zygomycota

Answer 11

• Live in soil and organic remains

• Few are parasites or predators

• Morphologically rather monotonous
─ most are like Rhizopus stolonifer, black bread-mold

Question 12

Zygomycota: Life cycle

Answer 12

Haploid = n
Diploid = 2n
Dikaryotic

•can be dormant for a long time if enviro not favourable

•mating types realize pheromones

•most reproduce sexual but can asexually

1. Hyphae of 2 mating strains, + & -, make contact. A septum forms behind each hyphal tip, isolating haploid nuclei into gametangia. (N) (sexual)
2. The gametangia fuse, and plasmogamy takes place. (N) (sexual)
3. The cell wall thickens as a dikaryotic zygospore develops. (Dikaryotic stage) (sexual)
4. Karyogamy occurs. + & -, nuclei pair and fuse, forming diploid nuclei. Further development produces a single multinucleate zygospore or zygote. (2n) (sexual)
5. After months or years, the zygospore germinates and splits open, producing sporangium. Meiosis produces haploid spores of each mating type. (N) (sexual)
6. New mycelia develop from germinating spores. (N) (sexual)
7. Mycelia may reproduce asexually when sporangia give rise to haploid spores that are genetically alike. (N) (asexual)

Question 13

Heterokaryotic ≠ Dikaryotic

Answer 13

• Heterokaryosis is an intermediate stage that precedes the formation of dikaryotic cells in many fungi.

• During sexual reproduction, two haploid nuclei from different parents fuse to form a heterokaryotic cell. The heterokaryotic cell then undergoes mitosis to produce a mycelium containing many cells with genetically different nuclei.
In some fungi, these nuclei may then fuse to form dikaryotic cells.

• Heterokaryotic cells contain multiple genetically different nuclei within a single cytoplasm, while dikaryotic cells contain two genetically distinct nuclei that have fused to form a dikaryon.

Question 14

Phylum Glomeromycota

Answer 14

• All species engage in symbiotic relationships with roots of plants

• 90% of vascular plant species involved

• Supply minerals, nutrients + H2O to roots in exchange for sugar
(photosynthates)

• Only asexual reproduction

Question 15

Phylum Ascomycota

Answer 15

• Called “Sac fungi”
• Largest phylum of fungi (~65,000 species)
• Range in size from single-celled yeasts to fist-sized truffles
• Defining feature is production of sexually produced spores in sac-like asci (sing. ascus)

Question 16

Phylum Ascomycota life cycle

Answer 16

Haploid = n
Diploid = 2n
Dikaryotic

•can reproduce sexually but dominant way is asexually.

•produce conidia spores (sexually) on tip of hyphae

1. Type + conidia or mycelium fragments serve as gametes. (n) (sexual)
2. Extension of ascogonium (trichogyne) fuses with conidium and grows dikaryotic hyphae within developing ascocarp. (n) (sexual)
3. The tips of the dikaryotic hyphae develop into asci. (Sexual)
4. In each ascus, the 2 nuclei fuse, producing a diploid zygote. (2n) (sexual)
5. Meiosis in the diploid nucleus produces 4 haploid nuclei. (n) (sexual)
6. The 4 nuclei now divide by mitosis; then the cell walls form around each of the resulting eight nuclei. These cells are ascospores. Asci develop inside an ascocarp, which began to form soon after sexual repro began. (n) (sexual)
7. Asci release their ascospores through an opening In the ascocarp. (N) (Sexual)

8.when ascospore germinates, it gives rise to a new mycelium. (N) (sexual)

Then it may go into asexual cycle

9. Haploid conidia (spores) develop on coindiophores by mitosis.
10. Spores may germinate and give rises to a new mycelium of the same mating type.

Then back to 1.

Question 17

Phylum Basidiomycota

Answer 17

• ‘Club fungi’ (~ 30 000 species)

• Sexual structures the classic mushrooms and toadstools
— basidium = pedestal

• Very important decomposers of dead plant matter (especially lignin)

• Many parasites of plants • e.g., smuts and rusts

• Cap contains thin vertical sheets of tissue called gills

• Gills lined with millions of basidia (spore production)

• Single mushroom can release a billion spores

Question 18

Phylum Basidiomycota life cycle

Answer 18

• Mostly sexual reproduction

• Few species can also reproduce asexually

Question 19

Ecological Roles of Fungi

Answer 19

• Saprotrophs
– acquire organic carbon from nonliving
sources
– essential component of nutrient cycles (decomposers)

• Symbionts
– acquire organic carbon from living sources
– Parasites
– Mutualists
▪ Mycorrhizae
▪ Lichens
▪ With animals

Question 20

Role in Decomposition

Answer 20

• Decomposers break down complex organic compounds into inorganic (mineral) forms

• Nutrient and CO2 cycling
─ releases carbon & nitrogen from dead tissues

• Most soil-dwelling fungi make their living by decomposing plant matter
─ fungi more important than bacteria in breaking down lignin (wood)

Question 21

Fungi Speed Up the Carbon Cycle:

Answer 21

•break down dead trees in terrestrial ecosystems

• The carbon cycle on land has two basic components:

1. The fixation of carbon by land plants
2. The release of CO2 from plants, animals, and fungi as the result of cellular respiration

• For most carbon atoms, fungi connect the two components

Question 22

Saprotrophs and Nitrogen Cycle

Question 23

Plant-parasitic Fungi

Answer 23

• 2nd most important pests of plants
─ 10 - 50% world’s fruit harvest lost annually

• ‘Blights’, ‘cankers’, ‘scabs’ are necroses caused by fungi digesting plant tissues

• Other fungi cause wilt when hyphae block xylem

• Powdery mildews are fungi that coat leaves and fruits
─ Penetrate surface cells with special hyphae

Question 24

Fungi as Pathogens (Disease-
causing organisms)

Question 25

Fungi that parasitize invertebrates

Answer 25

• Many fungi attack insects and arachnids

• It’s a very slow death…

• Produce spores inside host

• Or fruiting structure may burst through host’s body

Question 26

Fungi that parasitize vertebrates
mycosis = fungal disease of animals (including humans)

Answer 26

• Terrestrial and aquatic vertebrate hosts

• Cutaneous: infection occurs on outer layers of skin ─ ex: digest keratin & dead tissue
▪ cause skin diseases called ringworm
▪ ring-shaped growth pattern of hyphae

• Localized subcutaneous: infection due to wounds

• Systemic: infection widely spread inside host body

Question 27

Fungi as Mutualists: Fungi-Plant Mutualism

Answer 27

•Extomycorrhizae
— Fungus provides defensive compounds to deter herbivory
— hyphae do not penetrate root cells
— Ascomycota, Basidiomycota, Zygomycota

•endomycorrhizae
—Fungus provides water and mineral nutrient
— hyphae penetrate root cells
— Only Glomeromycota

Mutualisms with Plants (Mycorrhizae)

• Mycorrhizae represent mutualistic symbioses of plant roots and fungi
— Mycorrhiza = fungus + root, not just fungus
— helped plants colonize land

• Fungus helps plant absorb minerals from soil, plant gives fungus carbohydrates

• Almost all vascular plant species have mycorrhizal associates

• Glomero-, zygo-, asco- and basidiomycotans involved

Question 28

Mutualisms with other organisms: Lichens

Answer 28

• Lichen = symbiotic mixture of fungal hyphae and photosynthetic partner.
— green algae (chlorophyta) or cyanobacteria→carbon, organic nitrogen — fungi→place to grow, protection, retains water & minerals

• > 90% of fungal partners are asco-, basidio-

Question 29

Soil Formation - Lichens

Answer 29

• Break down solid rock, volcanic flows,
burned forests
— hyphae get into cracks
— swelling of hyphae when wet can further split rock
— trap windblown soil

• Aid the colonization of land plants

Question 30

Lichen as Indicators of Pollution

Answer 30

• Like fungi, lichen absorb nutrients, minerals and water through their surface

• Any pollution in the air will be absorbed too

Question 31

Mutualisms with Animals

Answer 31

• Guts of cattle and other herbivores

• “Farmed” by leaf-cutter ants (50 million years)

• The processing workers reduce the leaf fragments to a mulch which is used to feed the ant colony’s fungus garden.

Question 32

Fungi as… molds!

Answer 32

• Molds (or ‘moulds’) are rapidly growing and asexually reproducing fungi
— zygo-, asco- or basidiomycota

• Often produces fuzzy growth of hyphae on the surface of organic substrates

Question 33

Fungi as… yeasts!

Answer 33

• Unicellular fungi that inhabit liquid or moist habitats

• Reproduce asexually by pinching off bud cells from parent cell

• Some fungi can live as yeast or as hyphae depending on availability of nutrients

Question 34

Importance to Humans

Answer 34

Fungi as Human Food
• Most commonly cultivated mushroom: ✓button/white mushroom, Agaricus bisporus (basidio-)

• Domesticated in France in 17th century

• Annual world production ~ 1 million tons

• Other species of mushrooms also mass-produced
✓oyster, shiitake

Fungi as food-making agents
• Saccharomyces cereviseae
✓yeast form of an asco-

• Brewer’s and baker’s yeast

• Produces CO2 and ethanol by breaking down sugars
✓CO2 leavens (raises) dough
✓ethanol in wine, beer, hard liquors
✓sparkling wine, like champagne, uses both products

• Soft cheese: moulds make white mycelial mat that coats curd, and enzymes make inside soft and flowing (e.g., Camembert & Brie)

• Hard blue cheese: pressed curd drilled with holes, and bread-crumbs with spores introduced

Fungal Medications
• Yeast as health supplement
✓B-vitamins, chromium

• First antibiotic from Penicillium chrysogenum (asco-)fungus
✓the compound penicillin kills bacteria
✓P. chrysogenum typically feeds on dead plant matter
✓This fungus produce antibiotics naturally… why?

Question 35

Hallucinogenic & Toxic Fungi

Answer 35

• Psilocybe and three related genera (basidio-) contain hallucinogen psilocybin
✓“magic mushrooms”
✓‘flesh of the gods’ to the Aztecs

• Pleasant hallucinations at low doses

• Paranoia at high doses

• Children susceptible to high fever and convulsions

Question 36

Toxic mushrooms

Answer 36

• Even button mushroom dangerous if eaten raw and in large amounts
✓contains carcinogen destroyed by cooking

• Other mushrooms deadly cooked or raw

• Several species of Amanita (basidio-) highly toxic
✓evidence of illness does not appear until long after destruction of liver has begun
✓no antidote for amanitin poisoning except removal of toxin by cleaning blood

• Even if a mushroom produces no toxic effects in one person, can make another ill
✓cramps, nausea, vomiting

• If eating a species of mushroom for the first time, take only a small amount

Question 37

Major characteristics of fungal phyla table

Answer 37

Phylum: Chytridiomycota (790 species)
Representatives: Allomyces, Coelomomyces
Nature of hyphae: Aseptate, coenocytic
Method of asexual reproduction: zoospores
Type of sexual spore: none

Phylum: Zygomycota (1060 species)
Representatives: Rhizopus (common bread mold), Glomus (endomycorrhizal fungus)
Nature of hyphae: Aseptate, coenocytic
Method of asexual reproduction: nonmotile spores (sporangiospores)
Type of sexual spore: zygospore (in zygosporangium)
Common plant diseases: soft rot of various plant parts

Phylum: Ascomycota (32,300 species)
Representatives: Neurospora, powdery mildews, Morchella (edible morels), tuber (truffles)
Nature of hyphae: septate
Method of asexual reproduction: budding, conidia (nonmotile spores), fragmentation
Type of sexual spore: Ascospore

Phylum: Basidiomycota (22,244 species)
Representatives: mushrooms (amanita poisonous; agaricus, edible), stinkhorns, puffballs, shelf fungi, rusts, smuts
Nature of hyphae: septate, with dolipore in many species
Method of asexual reproduction: budding, conidia (nonmotile spores, including urediniospores), fragmentation
Type of sexual spore: Basidiospore

Question 38

Fungal phyla and distinguishing features of morphology and life cycle table

Answer 38

Fungal phylum: Chytridiomycota (Chytrids)
Distinguishing features of morphology and life cycle: Flagellated spores

Fungal phylum: Zygomycota (zygote fungi)
Distinguishing features of morphology and life cycle: resistant zygosporangium as sexual stage

Fungal phylum: Glomeromycota (arbuscular mycorrhizal fungi)
Distinguishing features of morphology and life cycle: form arbuscular mycorrhizae with plants

Fungal phylum: Ascomycota (sac fungi)
Distinguishing features of morphology and life cycle: sexual spores (ascospores) borne internally in sacs called asci; ascimycetes also produce vast numbers of asexual spores (conidia)

Fungal phylum: Basidiomycota (club fungi)
Distinguishing features of morphology and life cycle: elaborate fruiting body (basidiocarp) containing many basidia that produce sexual spores (basidiospores)