Fungi

Fungi

• Fleshy fungi

• Yeasts

• Molds– Hyphae (long filaments of joined cells)– Mycelium (intertwined mass of

hyphae)

Fungi– Are diverse and widespread

» Are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients

Mushrooms

Nutrition and Fungal Lifestyles

• Fungi are heterotrophs– But do not ingest their food

• Fungi secrete into their surroundings exoenzymes that break down complex molecules– And then absorb the remaining

smaller compounds

A General Look at Fungi - Flash Animation

Note to self: may need to right chick to get to play or rewind. May need to advance slide using arrows at bottom left.

Fungal lifestyles–Decomposers–Parasites–Mutualistic symbionts

Body Structure• The morphology of multicellular fungi

– Enhances their ability to absorb nutrients from their surroundings

Hyphae. The mushroom and its

subterranean mycelium are a

network of hyphae.

Reproductive structure.

The mushroom produces

tiny cells called spores.

Spore-producing

structures

20 m

Mycelium

Structure

• Fungi consist of– Mycelia, networks of branched

hyphae adapted for absorption

• Most fungi– Have cell walls made of chitin

Structure

• Some fungi– Have hyphae divided into cells by

septa, with pores allowing cell-to-cell movement of materials

• Coenocytic fungi– Lack septa

Nuclei

Cell wall

Septum

Pore

(a) Septate hypha (b) Coenocytic hypha

Cell wall

Nuclei

Septate Coenocytic

Structure• Some unique fungi

– Have specialized hyphae that allow them to penetrate the tissues of their hostNematode Hyphae 25 m

(a) Hyphae adapted for trapping and killing prey

(b) Haustoria – specialized hyphae that can penetrate the cell walls of plants

Fungal hypha Plant cell wall

Haustorium

Plant cell plasma membrane

Plant cell

Mycorrhizae

– Are mutually beneficial relationships between fungi and plant roots• Ectomycorrhizal fungi (surface)• Endomycorrhizal fungi (penetrate plant cell

wall)

Reproduction/propagation Fungi produce spores through sexual or asexual life cycles (Some fungi do both, some are either sexual or asexual)• The generalized life cycle of fungiKey

Haploid (n)

Heterokaryotic(unfused nuclei fromdifferent parents)

Diploid (2n)

PLASMOGAMY(fusion of cytoplasm)

Heterokaryoticstage

KARYOGAMY(fusion of nuclei)

SEXUALREPRODUCTION

Spore-producingstructures

SporesASEXUALREPRODUCTION

Zygote

Mycelium

GERMINATION GERMINATION

MEIOSIS

Spore-producingstructures

Spores

Sexual Reproduction• The sexual life cycle involves

– Cell fusion, plasmogamy– Nuclear fusion, karyogamy

• An intervening heterokaryotic stage– Occurs between plasmogamy and

karyogamy in which cells have haploid nuclei from two parents

• The diploid phase following karyogamy– Is short-lived and undergoes meiosis,

producing haploid spores

Asexual Reproduction• Many fungi can reproduce

asexually• Many fungi that can reproduce

asexually– Grow as mold, sometimes on fruit,

bread, and other foods

2.5 m

Penicillium (common saprobe on food)

Conidia (asexual)

Asexual Reproduction• Other asexual fungi are yeasts

– That inhabit moist environments– Which produce by simple cell

division 10 m

Parent cell

Bud

Asexual Reproduction

• Many molds and yeasts have no known sexual stage– Mycologists have traditionally

called these deuteromycetes, or imperfect fungi

Evolution/Origin of Fungi

• Fungi descended from an aquatic, single-celled, flagellated protist

• Systematists now recognize Fungi and Animalia as sister kingdoms– Because fungi and animals are more

closely related to each other than they are to plants or other eukaryotes

• Molecular evidence– Supports the hypothesis that fungi and

animals diverged from a common ancestor that was unicellular and bore flagella

• Fungi probably evolved– Before the colonization of land by

multicellular organisms

Origin of Fungi

50 m

 

• The oldest undisputed fossils of fungi are only about 460 million years old

• Fungi were among the earliest colonizers of land.

-Probably as symbionts with early land plants

Fossil hyphae and spores

Phylogeny/Classification• Fungi have

radiated into a diverse set of lineages

• The phylogeny of fungi– Is currently the

subject of much research

– Molecular analysis has helped clarify the evolutionary relationships between fungal groups, although there are still areas of uncertainty

ChytridsZygote

fungiArbuscular mycorrhizal

fungi

Sac fungi

Club fungi

Ch

ytrid

iom

yco

ta

Zyg

om

yco

ta

Glo

me

rom

yco

ta

Asc

om

yco

ta

Ba

sid

iom

yco

ta

Phylogeny/Classification

Five Phyla of Fungi

Chytrids

• Fungi classified in the phylum Chytridiomycota, or chytrids– Are found in freshwater and

terrestrial habitats– Can be saprobic or parasitic

Chytrids• Chytrids are unique among fungi

– In having flagellated spores, called zoospores

25 m

4 m

Hyphae

Flagellum

Chytrids• Until recently, systematists thought

that– Fungi lost flagella only once in

their history

• Molecular data– Indicate that some “chytrids” are

closely related to another fungal group, the zygomycetes

Some

chytrids

Zygomycetes and other chytrids

Glomeromycetes,

ascomycetes, and

basidiomycetes

Common ancestor

Key

Loss of

flagella

Zygomycetes• Fungi in the phylum Zygomycota,

the zygomycetes– Exhibit a considerable diversity of

life histories– Include fast-growing molds,

parasites, and commensal symbionts– Are named for their sexually

produced zygosporangia

Rhizopus

growing

on bread

ASEXUAL

REPRODUCTION

Mycelium

Dispersal and

germination

MEIOSIS

KARYOGAMY

PLASMOGAMY

Key

Haploid (n)

Heterokaryotic (n + n)

Diploid

Sporangium

Diploid

nuclei

Zygosporangium

(heterokaryotic)

100 m

Young

zygosporangium

(heterokaryotic)SEXUAL

REPRODUCTION

Dispersal and

germination

Mating

type (+)Mating

type ()

Gametangia with

haploid nuclei

50 m

Sporangia

Zygomycetes - Life Cycle

• The life cycle of Rhizopus stolonifer (fairly typical of zygomycetes)

Mycelia have

various mating types

(here designated +,

with red nuclei, and ,

with blue nuclei).

1

Neighboring mycelia of different

mating types form hyphal extensions

called gametangia, each walled off

around several haploid nuclei by a septum.

2

A heterokaryotic

zygosporangium

forms, containing

multiple haploid

nuclei from the two

parents.

3

The sporangium

disperses genetically

diverse, haploid spores.

7

4

This cell develops a

rough, thick-walled

coating that can resist

dry environments and

other harsh conditions

for months. 5

When conditions are favourable,

karyogamy occurs, followed by

meiosis.6

The zygosporangium

then breaks dormancy,

germinating into a

short sporangium.

The spores

germinate and

grow into new

mycelia.

8

9 Mycelia can also reproduce

asexually by forming sporangia

that produce genetically identical haploid spores.

Zygomycetes• Some zygomycetes, such as

Pilobolus– Can actually “aim” their sporangia

toward conditions associated with good food sources

0.5 mm

This decomposer of animal dung bends toward bright light and shoots its sporangia up to 2 meters

Spore dispersal movie

Zygomycetes

• Zygosporangia, which are resistant to freezing and drying– Are capable of persisting through

unfavorable conditions– Can undergo meiosis when

conditions improve

Microsporidia

• Microsporidia– Are unicellular parasites of animals and protists– A taxonomic mystery…Are now classified as

zygomycetes (But that could change at any time!)

10

m

Host cell nucleus

Developing microsporidian

Spore

This cell is infected with the parasitic fungus

Encephalitozoon intestinalis

Glomeromycetes

• Fungi assigned to the phylum Glomeromycota– Were once considered zygomycetes– Are now classified in a separate

clade

Glomeromycetes

• All glomeromycetes– Form a distinct type of

endomycorrhizae called arbuscular mycorrhizae2.5 m

Picture shows cytoplasm removed to show the arbuscule (branched structure) inside plant cell.

Ascomycetes

• Fungi in the phylum Ascomycota– Are found in a variety of marine,

freshwater, and terrestrial habitats– Are defined by the production of

sexual spores in saclike asci, which are usually contained in fruiting bodies called ascocarps

– Have asexual reproduction by producing enormous numbers of asexual spores called conidia

Ascomycetes• Ascomycetes

– Vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels

(a) The cup-shaped ascocarps (fruiting bodies) of Aleuria aurantia give this species its common name: orange peel fungus.

(b) The edible ascocarp of Morchella esculenta, the succulent morel, is often found under trees in orchards.

(c) Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open.

(d) Neurospora crassa feeds asa mold on bread and other food (SEM).

10 m

Ascomycetes – Life Cycle• The life cycle of Neurospora crassa

Dispersal

ASEXUALREPRODUCTION

Germination

Mycelium

Conidiophore

Germination

Dispersal

Mycelia

AsciEightascospores

Ascocarp

Fourhaploidnuclei

MEIOSIS

KARYOGAMY

PLASMOGAMY

SEXUALREPRODUCTION

Diploid nucleus(zygote)

Ascogonium Ascus(dikaryotic)

Dikaryotichyphae

Matingtype ()

Conidia;mating type ()

Key

Haploid (n)

Dikaryotic (n n)

Diploid (2n)

Ascomycete mycelia can also reproduce asexually by producing haploid conidia.

7

Neurospora can reproduce sexually by producing specialized hyphae. Conidia of the opposite mating type fuse to these hyphae.

1

A dikaryotic ascus develops.

2

Karyogamy occurs within theascus, producing adiploid nucleus.

3

The diploid nucleusdivides by meiosis, yieldingfour haploid nuclei.

4

The developing asci are contained in an

ascocarp. The ascospores

are discharged forciblyfrom the asci through anopening in the ascocarp. Germinating ascosporesgive rise to new mycelia.

6

5 Each haploid nucleus dividesonce by mitosis, yielding eightnuclei. Cell walls develop aroundthe nuclei, forming ascospores (LM).

Basidiomycetes

• Fungi in the phylum Basidiomycota– Include mushrooms and shelf

fungi– Are defined by a clublike structure

called a basidium, a transient diploid stage in the life cycle

Basidiomycetes

(a) Fly agaric (Amanita muscaria), acommon species in conifer forests in the northern hemisphere

(b) Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat

(c) Shelf fungi, important decomposers of wood

(d) Puffballs emitting spores

Basidiomycetes• The life cycle of a

basidiomycete– Usually includes a long-lived

dikaryotic mycelium, which can erect its fruiting structure, a mushroom, in just a few hours

Fairy rings can appear overnight. A very large mycelium is growing underneath this ring of fruiting structures

PLASMOGAMY Dikaryoticmycelium

Basidiocarp(dikaryotic)

KARYOGAMY

Key

MEIOSIS

Gills linedwith basidiaSEXUAL

REPRODUCTION

Matingtype ()

Matingtype ()

Haploidmycelia

Dispersalandgermination

Basidiospores

Basidium withfour appendages

Basidium containingfour haploid nuclei

Basidia(dikaryotic)

Diploidnuclei

Basidiospore1 m

Basidium

Haploid (n)

Dikaryotic (n n)

Diploid (2n)

Basidiomycetes• The life cycle of a mushroom-

forming basidiomycete

Each diploid nucleus yields four haploid nuclei. Each basidiumgrows four appendages, and one haploid nucleusenters each appendage and develops into a basidiospore (SEM).

6

Two haploid mycelia of different mating typesundergo plasmogamy.

1

A dikaryotic mycelium forms, growing faster then, and ultimately crowding out, the haploid parental mycelia.

2

3 Environmental cues such as rain ortemperature changes induce the dikaryoticmycelium to formcompact masses thatdevelop intobasidiocarps(mushrooms, in thiscase).

The basidiocarpgills are lined withterminal dikaryoticcells called basidia.

4

Karyogamy in the basidia produces diploidnuclei, which thenundergo meiosis.

5

When mature,the basidiospores

are ejected, fallfrom the cap, andare dispersed by

the wind.

7

In a suitableenvironment, the

basidiospores germinate and

grow intoshort-lived

haploid mycelia.

8

Fungi have a powerful impact on ecosystems and human welfare

Decomposers

• Fungi are well adapted as decomposers of organic material– Performing essential recycling of

chemical elements between the living and nonliving world

Symbionts

• Fungi form symbiotic relationships with– Plants, algae, and animals

Mycorrhizae• Mycorrhizae

– Are enormously important in natural ecosystems and agriculture

– Increase plant productivity

RESULTS

Researchers grew soybean plants in soil treated with fungicide (poison that kills fungi) to prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed mycorrhizae in the soybean plants’ roots.

EXPERIMENT

The soybean plant on the left is typical of the experimental group. Its stunted growth is probably due to a phosphorus deficiency. The taller, healthier plant on the right is typical of the control group and has mycorrhizae.

CONCLUSION These results indicate that the presence of mycorrhizae benefits a soybean plant and support the hypothesis that mycorrhizae enhance the plant’s ability to take up phosphate and other needed minerals.

RESULTS

Fungus-Animal Symbiosis• Some fungi share their

digestive services with animals– Helping break down plant

material in the guts of cows and other grazing mammals

Many species of ants and termites– Take advantage of the digestive

power of fungi by raising them in “farms”

Leaf cutter ant movie

Lichens• Lichens

– Are a symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae

(a) A fruticose (shrub-like) lichen

(b) A foliose (leaf-like) lichen (c) Crustose (crust-like) lichens

Lichen• The fungal component of a lichen

– Is most often an ascomycete

• Algae or cyanobacteria– Occupy an inner layer below the

lichen surfaceAscocarp of fungus

Fungalhyphae

Algallayer

Soredia

Algal cell

Fungal hyphae

10

m

Pathogens• About 30% of known fungal species

– Are parasites, mostly on or in plants.• Some of the fungi that attack food crops

– Are toxic to humans

(a) Corn smut on corn (b) Tar spot fungus on maple leaves (c) Ergots on rye

Practical Uses of Fungi• Humans eat many fungi

– And use others to make cheeses, alcoholic beverages, and bread

• Genetic research on fungi– Is leading to applications in biotechnology

• Antibiotics produced by fungi-treat bacterial infections

Staphylococcus

Penicillium

Zone of inhibited growth

Fungi: Wrap-up video clip

The End