1 of 65

Chapter 31

Fungi

2 of 65

Figure 31.1

Overview: Mighty Mushrooms
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

Figure 31.1

3 of 65

Concept 31.1: Fungi are multi-cellular, heterotrophs that feed by absorption
Despite their diversity

Fungi share some key traits

4 of 65

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

5 of 65

Fungi exhibit diverse lifestyles

Decomposers
Parasites
Mutualistic symbionts

6 of 65

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 continuous network of hyphae.}

^{Reproductive structure.�The mushroom produces� tiny cells called spores.}

^{Spore-producing �structures}

^{20 m}

^Mycelium

Figure 31.2

7 of 65

Fungi consist of

Mycelia, networks of branched hyphae adapted for absorption

Most fungi

Have cell walls made of chitin

8 of 65

Nuclei

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

Figure 31.3a, b

9 of 65

Nematode

Some unique fungi

Have specialized hyphae that allow them to penetrate the tissues of their host

Nematode

^Hyphae

^{25 m}

(a) Hyphae adapted for trapping and killing prey

(b) Haustoria

Fungal hypha

Plant �cell �wall

Haustorium

Plant cell �plasma �membrane

Plant cell

Figure 31.4a, b

10 of 65

Mycorrhizae

Are mutually beneficial relationships between fungi and plant roots

11 of 65

For Review

1) The cell wall of a fungus cell is composed of

a. cellulose

b. lignin

c. starch

d. fatty acids

e. chitin

12 of 65

For Review

2) The tiny filaments that comprise the body of fungi are known as

a. hyphae

b. mycelium

c. chitin

d. mycorrhizae

e. basidium

13 of 65

For Review

3) ALL fungi share which of the following characteristics?

a. pathogenic

b. saprobic

c. flagellated

d. symbiotic

e. eukaryotic

14 of 65

For Review

4) Which of the following is a mutualistic association between plant roots and fungi?

a. mold

b. yeast

c. lichen

d. mychorrhizae

e. deuteromycete

15 of 65

Concept 31.2: Fungi produce spores through sexual or asexual life cycles
Fungi propagate themselves

By producing vast numbers of spores, either sexually or asexually

16 of 65

Key

The generalized life cycle of fungi

Key

Haploid (n)

Heterokaryotic

(unfused nuclei from

different parents)

Diploid (2n)

PLASMOGAMY

(fusion of cytoplasm)

Heterokaryotic

stage

KARYOGAMY

(fusion of nuclei)

SEXUAL

REPRODUCTION

Spore-producing

structures

Spores

ASEXUAL

REPRODUCTION

Zygote

Mycelium

GERMINATION

MEIOSIS

Spore-producing

structures

Spores

Figure 31.5

17 of 65

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

18 of 65

The diploid phase following karyogamy

Is short-lived and undergoes meiosis, producing haploid spores

19 of 65

Asexual Reproduction

Many fungi can reproduce asexually

20 of 65

^{2.5 m}

Many fungi that can reproduce asexually

Grow as mold, sometimes on fruit, bread, and other foods

^{2.5 m}

Figure 31.6

21 of 65

^{10 m}

Other asexual fungi are yeasts (unicellular)

That inhabit moist environments
Which produce by simple cell division

^{10 m}

^{Parent cell}

^Bud

Figure 31.7

22 of 65

Many molds and yeasts have no known sexual stage

Mycologists have traditionally called these deuteromycetes, or imperfect fungi

23 of 65

For Review

5) During fungal reproduction, what is formed when two haploid hyphae mate but their nuclei do not fuse?

a. diploid zygote

b. haploid spores

c. dikaryotic hyphae

d. diploid spores

e. haploid zygote

24 of 65

For Review

6) Which of the following types of asexual reproduction occurs when a small cell forms and gets pinched off as it grows, eventually forming an entirely new fungi?

a. budding

b. spore production

c. deutormycete

d. dikaryotic reproduction

e. meiosis

25 of 65

For Review

7) Which of the following is a group of fungi with unknown sexual stages?

a. mold

b. yeast

c. lichen

d. mycorrhizae

e. deuteromycetes

26 of 65

Concept 31.3: 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

27 of 65

The Origin of Fungi

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

28 of 65

^{50 m}

The oldest undisputed fossils of fungi

Are only about 460 million years old

^{50 m}

Figure 31.8

29 of 65

The Move to Land

Fungi were among the earliest colonizers of land

Probably as symbionts with early land plants

30 of 65

Concept 31.4: 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

31 of 65

Chytrids

The phylogeny of fungi

Chytrids

Zygote �fungi

Arbuscular �mycorrhizal �fungi

Sac �fungi

Club �fungi

Chytridiomycota

Zygomycota

Glomeromycota

Ascomycota

Basidiomycota

Figure 31.9

32 of 65

In the 7^th edition: see review page 624

FUNGI CHART (Chapter 31)

In the 7^th edition: see review page 624

33 of 65

Chytrids

Fungi classified in the phylum Chytridiomycota, or chytrids

Are found in freshwater and terrestrial habitats
Can be saprobic or parasitic

34 of 65

^{25 m}

Chytrids are unique among fungi

In having flagellated spores, called zoospores

^{25 m}

^{4 m}

^Hyphae

Flagellum

Figure 31.10

35 of 65

^{Some �chytrids}

Until recently, systematists thought that

Fungi lost flagella only once in their history

Molecular data

Indicate that some “chytrids” are actually more closely related to another fungal group, the zygomycetes

^{Some �chytrids}

^{Zygomycetes and other chytrids}

^{Glomeromycetes, �ascomycetes, and�basidiomycetes}

^{Common ancestor}

^Key

^{Loss of �flagella}

Figure 31.11

36 of 65

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
Coenocytic and land-dwelling

37 of 65

^Rhizopus^{�growing �on bread}

The life cycle of Rhizopus stolonifer

Is fairly typical of zygomycetes

^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

^{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.}

Figure 31.12

38 of 65

^{0.5 mm}

Some zygomycetes, such as Pilobolus

Can actually “aim” their sporangia toward conditions associated with good food sources

^{0.5 mm}

Figure 31.13

39 of 65

Zygosporangia, which are resistant to freezing and drying

Are capable of persisting through unfavorable conditions
Can undergo meiosis when conditions improve

40 of 65

Microsporidia

Microsporidia

Are unicellular parasites of animals and protists
Are now classified as zygomycetes

^{10 m}

Host cell �nucleus

Developing �microsporidian

Spore

Figure 31.14

41 of 65

Glomeromycetes

Fungi assigned to the phylum Glomeromycota

Were once considered zygomycetes
Are now classified in a separate clade

42 of 65

^{2.5 m}

All glomeromycetes

Form a distinct type of endomycorrhizae called arbuscular mycorrhizae (penetrate plant roots).

^{2.5 m}

Figure 31.15

43 of 65

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
Saprobic, form symbiotic association with algae to form lichens

44 of 65

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

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 as�a mold on bread and other �food (SEM).

^{10 m}

Figure 31.16a–d

45 of 65

Ascomycetes reproduce

Asexually by producing enormous numbers of asexual spores called conidia

46 of 65

Dispersal

The life cycle of Neurospora crassa, an ascomycete

Dispersal

ASEXUAL�REPRODUCTION

Germination

Mycelium

Conidiophore

Germination

Dispersal

Mycelia

Asci

Eight�ascospores

Ascocarp

Four�haploid�nuclei

MEIOSIS

KARYOGAMY

PLASMOGAMY

SEXUAL�REPRODUCTION

Diploid nucleus�(zygote)

Ascogonium

Ascus�(dikaryotic)

Dikaryotic�hyphae

Mating�type ()

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 the�ascus, producing a�diploid nucleus.�

3

The diploid nucleus�divides by meiosis, yielding�four haploid nuclei.�

4

The developing asci� are contained in an �ascocarp. The ascospores� are discharged forcibly�from the asci through an�opening in the ascocarp.� Germinating ascospores�give rise to new mycelia.

6

5

Each haploid nucleus divides�once by mitosis, yielding eight�nuclei. Cell walls develop around�the nuclei, forming ascospores (LM).�

Figure 31.17

47 of 65

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
Love to decompose wood (“They like pina coladas and getting caught in the rain..”)

48 of 65

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

Basidiomycetes

(a) Fly agaric (Amanita muscaria), a�common 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

Figure 31.18a–d

49 of 65

Figure 31.19

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

Figure 31.19

50 of 65

PLASMOGAMY

The life cycle of a mushroom-forming basidiomycete

PLASMOGAMY

Dikaryotic�mycelium

Basidiocarp�(dikaryotic)

KARYOGAMY

Key

MEIOSIS

Gills lined�with basidia

SEXUAL�REPRODUCTION

Mating�type ()

Mating�type ()

Haploid�mycelia

Dispersal�and�germination

Basidiospores

Basidium with�four appendages

Basidium containing�four haploid nuclei

Basidia�(dikaryotic)

Diploid�nuclei

Basidiospore

1 m

Basidium

Haploid (n)

Dikaryotic (n  n)

Diploid (2n)

Each diploid nucleus yields four haploid �nuclei. Each basidium�grows four appendages, and one haploid nucleus�enters each appendage and develops into a basidiospore (SEM).

6

Two haploid mycelia of different mating types�undergo plasmogamy.

1

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

2

3

Environmental cues such as rain or�temperature changes induce the dikaryotic�mycelium to form�compact masses that�develop into�basidiocarps�(mushrooms, in this�case).

The basidiocarp�gills are lined with�terminal dikaryotic�cells called basidia.

4

Karyogamy in the �basidia produces diploid�nuclei, which then�undergo meiosis.

5

When mature,�the basidiospores�are ejected, fall�from the cap, and�are dispersed by�the wind.

7

In a suitable�environment, the�basidiospores �germinate and�grow into�short-lived�haploid mycelia.

8

Figure 31.20

51 of 65

Concept 31.5: Fungi have a powerful impact on ecosystems and human welfare

52 of 65

Decomposers

Fungi are well adapted as decomposers of organic material

Performing essential recycling of chemical elements between the living and nonliving world

53 of 65

Symbionts

Fungi form symbiotic relationships with

Plants, algae, and animals

54 of 65

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.

Figure 31.21

RESULTS

55 of 65

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

56 of 65

Figure 31.22

Many species of ants and termites

Take advantage of the digestive power of fungi by raising them in “farms”

Figure 31.22

57 of 65

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

Figure 31.23a–c

58 of 65

Ascocarp of fungus

The fungal component of a lichen (protects, H₂0)

Is most often an ascomycete

Algae (chlorophyta) or cyanobacteria (sugar)

Occupy an inner layer below the lichen surface

Ascocarp of fungus

Fungal

hyphae

Algal

layer

Soredia

Algal cell

Fungal hyphae

^{10 m}

Figure 31.24

59 of 65

Pathogens

About 30% of known fungal species

Are parasites, mostly on or in plants
Ergot (St. Anthony’s fire, Salem witches, LSD)

(a) Corn smut on corn

(b) Tar spot fungus on maple leaves

(c) Ergots on rye

Figure 31.25a–c

60 of 65

Some of the fungi that attack food crops

Are toxic to humans

61 of 65

Practical Uses of Fungi

Humans eat many fungi

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

62 of 65

Staphylococcus

Antibiotics produced by fungi

Treat bacterial infections

Staphylococcus

Penicillium

Zone of �inhibited �growth

Figure 31.26

63 of 65

Genetic research on fungi

Is leading to applications in biotechnology

64 of 65

Table 31.1

A review of fungal phyla

Table 31.1

65 of 65

For Review

8) Which of the following is NOT a fungus or caused by a fungus?

a. yeast

b. tetanus

c. mold

d. mushrooms

e. all of the above are fungi