“The Mighty Mushroom”

• take a walk through a forest • mushrooms are truly are the largest

organisms in the forest• Kingdom Fungi:

– not just mushrooms!– approximately 100,000 species now described– may be as many as 1.5 million species– range from unicellular to complex multicellular

organisms– just about every terrestrial and aquatic

environment– essential decomposers in ecosystems

• critical for the release of nutrients into the ecosystem

– included with animals and plants in the Clade Opisthokonta• diverged about a billion years ago

Nutrition

• like animals, fungi are heterotrophs– cannot make their own food like algae and plants– must go and find it

• unlike animals – they do not ingest their food (i.e. eat)

• fungi decompose & absorb nutrients from its environment

• digestion of both living and dead sources

Body StructureReproductive structure

Hyphae

Spore-producingstructures

Mycelium

20 µm

• most common body structures of a fungus are:– 1. multicellular filaments =

mycelium– 2. yeasts

• mycelium made up of multicellular filaments called hyphae (hypha – singular)

The Mycelium• mycelium body structure:

– the mycelium is a haploid (n) multi-cellular organism

– hyphae enhances the ability to absorb nutrients

– a mycelium infiltrates the material on which it feeds

– the emphasis is on increasing mycelium length NOT width

Reproduction• fungus reproduce asexually & sexually through the production of spores• spores are haploid• spores are carried by wind or water• germination upon exposure to moisture to produce a new mycelium

Haploid (n)

Key

Heterokaryotic(unfused nuclei fromdifferent parents)Diploid (2n)

PLASMOGAMY(fusion of cytoplasm)

Heterokaryoticstage

KARYOGAMY(fusion of nuclei)

Mycelium

SEXUALREPRODUCTION

Zygote

Spores

GERMINATIONMEIOSIS

Spore-producingstructures

ASEXUALREPRODUCTION

Spores

GERMINATION

Spore-producingstructures

• definitions:– karyogamy: fusion of two

haploid nuclei in fungi• production of a diploid

zygote– plasmogamy: fusion of the

cytoplasm NOT the nuclei– plasmogamy produces a

heterokaryotic stage – means different nuclei

• fungal asexual reproduction: through the production of haploid spores by mitosis– the mycelium is haploid and so are the spores = MITOSIS– single-celled yeasts don’t produce a mycelium or spores but simply divide by mitosis or form

progeny by budding

Asexual Reproduction

Haploid (n)

Key

Heterokaryotic(unfused nuclei fromdifferent parents)Diploid (2n)

ASEXUALREPRODUCTION

Spores

GERMINATION

Spore-producingstructures

Mycelium

10 m

Parentcell

Bud

Sexual Reproduction

• fungal sexual reproduction: consists of three stages – plasmogamy karyogamy meiosis– two hyphae of opposite mating type meet and fuse– two cytoplasms fuse = plasmogamy– the two nuclei do not fuse right away – hypha is now called a heterokaryon (different nuclei)

Haploid (n)

Key

Heterokaryotic(unfused nuclei fromdifferent parents)

Diploid (2n)

PLASMOGAMY(fusion of cytoplasm)

Heterokaryoticstage

KARYOGAMY(fusion of nuclei)

Mycelium

SEXUALREPRODUCTION

Zygote

Spores

GERMINATION

MEIOSIS

Spore-producingstructures

ASEXUALREPRODUCTION

Spores

GERMINATION

Spore-producingstructures

Sexual Reproduction

The mycelium is a HAPLOIDmulti-cellular organism

Haploid (n)

Key

Heterokaryotic(unfused nuclei fromdifferent parents)

Diploid (2n)

PLASMOGAMY(fusion of cytoplasm)

Heterokaryoticstage

KARYOGAMY(fusion of nuclei)

Mycelium

SEXUALREPRODUCTION

Zygote(2n)

Spores (n)

GERMINATION

MEIOSIS

Spore-producingstructures

ASEXUALREPRODUCTION

Spores

GERMINATION

Spore-producingstructures

• sexual reproduction: – hours or decades later (!) the nuclei will fuse inside the hypha = karyogamy– production of a diploid zygote (2n)– zygote develops into a spore producing structure called a sporangium– MEIOSIS takes place in the sporangium - producing haploid spores (n)– spores are dispersed to germinate and form a new mycelium

Fungal Diversity

ChytridsZygotefungi

Arbuscularmycorrhizal

fungi

Sacfungi

Clubfungi

• fungi are thought to be descended from a unicelluar, aquatic flagellated protist

• then moved to land – fossils of the earliest vascular land plants

have fungal associations (mycorrhizea)• radiated into 5 Phyla:

– 1. Chytridiomycota– 2. Zygomycota– 3. Glomeromycota– 4. Ascomycota– 5. Basidiomycota

Molds• 1,100 known species in Phylum Zygomycota• diverse in lifestyles• fast-growing molds• e.g. Rhizopus stolonifer – black bread mold

– typical of a zygomycete– mycelium forms as a spread of horizontal hyphae over the food – penetrates it and absorb the

nutrients– spore dispersal through the air eventually passes it onto other substrates for continued growth

Rhizopusgrowingon bread

Matingtype (+) Mating

type (–)

PLASMOGAMY

KeyHaploid (n)Heterokaryotic (n + n)Diploid (2n)

100 µmYoungzygosporangiumSEXUAL

REPRODUCTION

KARYOGAMYZygosporangium

Diploidnuclei

MEIOSISSporangium

Mycelium

Dispersal andgermination

Dispersal andgermination

ASEXUALREPRODUCTION

Sporangia

50 µm

– sexual reproduction: “parents” are mycelia with hyphae or two mating types: “-” and “+”• fusion of two “parental” mycelia with “+” and “-” hyphae• plasmogamy produces a unique structure called a zygosporangium

– heterokaryotic – no nuclear fusion yet!!– zygosporangium can remain dormant for months

Rhizopusgrowingon bread

Matingtype (+) Mating

type (–)

PLASMOGAMY

KeyHaploid (n)Heterokaryotic (n + n)Diploid (2n)

100 µmYoungzygosporangiumSEXUAL

REPRODUCTION

KARYOGAMYZygosporangium(heterokaryotic)

Diploidnuclei

MEIOSISSporangium

Mycelium

Dispersal andgermination

Dispersal andgermination

ASEXUALREPRODUCTION

Sporangia

50 µm

– sexual reproduction:• under favorable conditions – the nuclei in the zygosporangium fuse to make

diploid (2n) nuclei (karyogamy)• zygosporangium starts to make haploid spores (n) via Meiosis• these spores are contained in and released by a sporangium that “sprout” from

the zygosporangium– this is what you see as the fluffy black stuff in black mold

• spores are released to land and germinate into new mycelia on a new substrate

Mushrooms

• club fungus – Phylum Basidiomycota

• 30,000 species• includes the mushrooms, shelf

fungi, molds and mycorrizhae, rusts and smuts

• important decomposers of wood• saprophoric (decomposing) and

parasitic species (rusts and smuts)Fly agaric (Amanita muscoria), a common species in conifer forests in the northern hemisphere

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

Shelf fungi, important decomposers of wood

Puffballs emitting spores

The Common Mushroom

pileus

stipe

stipe

gills

basidiocarp

• basidium = “little pedestal”– spore forming part of the

mushroom• the part of the mushroom we

see is a reproductive structure called a basidiocarp

• basidiocarp = cap (pileus) with the gills on the underside + the supporting stalk = stipe

• the basidiocarp is actually a large aggregation of hyphae forming the mushroom

• underground is the actual mycelium

• sexual reproduction: • two haploid mating types ‘+’ and ‘–’ undergo plasmogamy and a heterokaryotic

mycelium made of two different nuclei per cell forms • rain or temperature changes induce the mycelium to form many basidiocarps

(mushroom) that poke up above the ground

PLASMOGAMY

Key

Haploid (n)Dikaryotic (n + n)Diploid (2n)

SEXUALREPRODUCTION

KARYOGAMY

MEIOSIS

Mycelium

Basidium containingfour haploid nuclei

Dispersal andgermination

Basidium

1 µm

Matingtype (+)

Matingtype (–)

Haploidmycelia

Gills linedwithbasidia

Basidiocarp

Basidia(dikaryotic)

Diploidnuclei

Basidiospore

Basidiospores

• sexual reproduction cont…..: • the gills of the basidiocarp are lined with spore-producing structures (i.e. sporangia) called

basidia (basidium = singular)• within each basidium the 2 nuclei fuse to make a diploid parental cell (i.e. karyogamy)• the parental cell undergoes meiosis 4 haploid nuclei total per basidium• each haploid nuclei develops into a basidiospore (4 basidiospores per basidium)• basidiospores are released and are carried by the wind – germinate into new mycelia which

rapidly undergo more sexual reproduction

4 basidiospores on a basidium

PLASMOGAMY

Key

Haploid (n)Dikaryotic (n + n)Diploid (2n)

SEXUALREPRODUCTION

KARYOGAMY

MEIOSIS

Dikaryoticmycelium

Basidium containingfour haploid nuclei

Dispersal andgermination

Basidium

1 µm

Matingtype (+)

Matingtype (–)

Haploidmycelia

Gills linedwithbasidia Basidiocarp

(dikaryotic)

Basidia

Diploidnuclei

Basidiospore

Basidiospores

Yeasts

• 1500 species of unicellular fungi– not a single taxonomic or phylogenic grouping– divided up between Phylum Ascomycota & Phylum

Basidiomycota• often a synonym for the species Saccharomyces

cerevisiae– but there are several species of yeasts

Yeasts

• are chemotrophs – convert carbohydrates into CO2 and alcohol (fermentation)– yeasts are either obligate aerobes (for cellular

respiration) or anaerobic (fermentation)• naturally occurring on skins of fruits & berries –

even on the skin or epithelial linings of humans– Candida albicans - yeast infections or athlete’s foot

• also found in guts of mammal and insects– e.g. bees and ants

• even in deep sea environments• most reproduce asexually through budding or

fission (mitosis)

Fungal Associations: Lichens

• Lichens: 25,000 species– fungus + green algae (or cyanobacteria)– algae provide organic compounds, the

cyanobacteria fix nitrogen – algae nestle among the fungal hyphae and are

protected

• types of lichens:– 1. Crustose lichens – grow as a crust on a

surface– 2. Foliose lichens – leafy in appearance– 3. Fructicose lichens – shrublike with

branching and intertwined fibrous parts

A fruticose (shrub-like) lichen

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

Fungal hyphae

Algal cell

Soredia

Algallayer

Fungalhyphae

Ascocarp of fungus

10 µ

m

Lichens• most reproduce asexually:

– either through fragmentation – or by the formation of soredia – small clusters

of hyphae with embedded algae - may be carried by the wind to new locations