Lecture #4

Fungi

“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

• unlike animals – they do not ingest their food• fungi 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 are:– 1. multicellular filaments– 2. yeasts

• relatively few species grow as yeasts– those that do inhabit moist environments

• most grow as multicellular filaments called hyphae (hypha – singular)– cell wall is strengthened by chitin

(not cellulose = plants)– chitin - nitrogen containing polysaccharide– strong yet flexible

Body Structure

Nuclei

Septate hypha

Septum

Pore

Cell wallCell wall

Nuclei

Coenocytic hypha

Reproductive structure

Hyphae

Spore-producingstructures

Mycelium

20 µm

• body structure:– hyphae enhances the ability to absorb

nutrients– hyphae form an interwoven mass called

a mycelium (mycelia plural)– a mycelium infiltrates the material on

which it feeds– mycelia grow very fast – nutrients for

growth are carried rapidly via cytoplasmic streaming to the growing hyphae

– the emphasis is on increasing mycelium length NOT width

Fungal Hyphae

Nuclei

Septate hypha

Septum

Pore

Cell wallCell wall

Nuclei

Coenocytic hypha

• septate hyphae are divided into individual cells by walls called septa– septa have relatively large pores to allow for the

passage of ribosomes, mitochondria and nuclei between cells

• those that lack septa are called ceonocytic fungi

Mycorrhizal Fungus

Fungal hypha

Haustorium

Plant cell

Haustoria

Plant cellplasmamembrane

Plant cellwall

• mycorrhizal fungi: fungi with mutually beneficial relationships between the fungus and plant roots– mycorrhiza = symbiotic relationship between a

fungus and the root of a vascular plant– the hyphae are specialized = form haustoria that

project into a plant cell• but do not penetrate it• haustoria remain separated from the plant by

the plant’s plasma membrane!– very common type - ectomycorrhizal fungi= sheaths

of hyphae grow over the root

Reproduction• fungus reproduce through the production of spores• 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– produces a heterokaryotic

stage – means different nuclei

Sexual Reproduction

• fungal sexual reproduction: consists of three stages – plasmogamy karyogamy meiosis– two hyphae of different mating type extends towards each other – production of

pheromones– the hyphae meet and fuse– two cytoplasms fuse = plasmogamy– nuclei from these two “parental” fungi do not fuse right away – fungus is now called a

heterokaryon

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

Sexual Reproduction

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

The mycelium is a HAPLOIDmulti-cellular organism

• sexual reproduction: – hours or decades later (!) the nuclei will fuse = karyogamy– production of a diploid zygote (2n)– formation of 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

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

10 m

Parentcell

Bud

• fungal asexual reproduction: most fungi can reproduce sexually and asexually depending on nutrient availability– some fungi (molds) reproduce asexually through their mycelium making haploid spores (by

mitosis) – other reproduce asexually by binary fission or budding - single-celled yeasts

• yeasts don’t produce spores

Fungal Diversity

ChytridsZygotefungi

Arbuscularmycorrhizal

fungi

Sacfungi

Clubfungi

Basi

diom

ycot

a

Asco

myc

ota

Glo

mer

omyc

ota

Zygo

myc

ota

Chyt

ridio

myc

ota

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

• earliest lineages of fungus thought to possess flagella– some still have flagella – called

chytrids• 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

1. Phylum: Chytridiomycota

• known as the chytrids• most primitive of the fungi - diverged the earliest in fungal evolution• unique in that they have flagellated spores called zoospores• some exist as single cells, others form colonies with hyphae• do not have a true mycelium – fungal body is called a thallus• are considered a coenocytic fungus – no septa in their hyphae• extensions off the hyphae produce digestive enzymes for decomposition of their

substrate

Hyphae

2. Phylum: Zygomycota• 1,100 known species• 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– hyphae are mainly coenocytic – spore dispersal through the air eventually passes it onto other substrates for continued growth

Rhizopusgrowingon bread

Matingtype (+) Mating

type (–)

Gametangia withhaploid nuclei

PLASMOGAMY

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

100 µmYoungzygosporangium(heterokaryotic)

SEXUALREPRODUCTION

KARYOGAMYZygosporangium(heterokaryotic)

Diploidnuclei

MEIOSISSporangium

Mycelium

Dispersal andgermination

Dispersal andgermination

ASEXUALREPRODUCTION

Sporangia

50 µm

– sexual reproduction: “parents” are mycelia with hyphae or two mating types: “-” and “+”• + and – hypha extend toward one another (pheromones)• two gametangia form between these hyphae – each contains multiple haploid nuclei

that are similar to gametes• two gametangia undergo plasmogamy to produce a zygosporangium

– said to be heterokaryotic – no nuclear fusion yet!!

• zygosporangium thickens and forms a “cyst” – remains resistant and dormant for months

Rhizopusgrowingon bread

Matingtype (+) Mating

type (–)

Gametangia withhaploid nuclei

PLASMOGAMY

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

100 µmYoungzygosporangium(heterokaryotic)SEXUAL

REPRODUCTION

KARYOGAMYZygosporangium(heterokaryotic)

Diploidnuclei

MEIOSISSporangium

Mycelium

Dispersal andgermination

Dispersal andgermination

ASEXUALREPRODUCTION

Sporangia

50 µm

– sexual reproduction: • under favorable conditions – karyogamy occurs in the zygosporangium => diploid nuclei

inside the zygosporangium (parental cells for meiosis)• followed by meiosis into haploid spores

– from the cyst arises a sporangium (called a fruiting body) for the production of haploid spores

– this is what we see as the black fuzziness on bread– spores germinate into new + and - mycelia

- http://academic.kellogg.edu/herbrandsonc/bio111/animations/0120.swf

3. Phylum Ascomycota• cup fungus• 60,000 species

• red, blue and green molds• also includes mildews

• defined by the formation of a cup-like ascocarp

– a sac-like reproductive structure containing asci that produce haploid spores edible portion of this fungus

– e.g. morels and truffles

• half the species associate with algae to form lichens

• most are septate within their hyphae

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

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

10 µm

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.

Neurospora crassa feeds as a mold on bread and other food (SEM).

3. Phylum Ascomycota

• mildews: general term of mildew means dicolorations and odors created by fungus

• mildews are actually are parasitic fungi of plants

• white powdery appearance

PLASMOGAMY

Key

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

SEXUALREPRODUCTION KARYOGAMY

Fourhaploidnuclei

MEIOSIS

Dikaryotic Hyphae

ASEXUALREPRODUCTION

Diploid nucleus(zygote)

DispersalGermination

Mycelium

MyceliaConidiophore

Conidia;mating type (–) or (+)

fusion of (+) and (-) hyphae

Ascus(dikaryotic)

EightascosporesAsci

Ascocarp

Germination

Dispersal

• sexual reproduction: – fusion of the hyphae from opposite mycelia mating types produces a new mycelium

where the touching hyphae undergo plasmogamy (just like in the zygomycotes)– this new mycelium is made up of dikaryotic hyphae (2 unfused nuclei inside)– at the tip of each of some of these hyphae a dikaryotic ascus forms (plural = asci)

• sexual reproduction: – within each individual ascus – karyogamy unites the 2 nuclei and meiosis follows to form 4 haploid

nuclei– each of these 4 nuclei divide by mitosis ONCE to form a total of 8 ascospores each with a single

nuclei– multiple asci become surrounded by a protective ascocarp (aggregation of hyphae) – that sprouts

above the soil– ascospores are ejected from this ascocarp to germinate and form new mycelia

PLASMOGAMY

Key

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

SEXUALREPRODUCTION KARYOGAMY

Fourhaploidnuclei MEIOSIS

Hyphaeextending fromascogonium

Diploid nucleus(zygote)

Mycelia

fusion of (+) and (-) hyphae

Ascus(dikaryotic)

EightascosporesAsci

Ascocarp

Germination

Dispersal

PLASMOGAMY

Key

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

SEXUALREPRODUCTION KARYOGAMY

Fourhaploidnuclei

MEIOSIS

Dikaryotic hyphaeextended fromascogonium

ASEXUALREPRODUCTION

Diploid nucleus(zygote)

Dispersal Germination

Mycelium

MyceliaConidiophore

Conidia;mating type (–)

Matingtype (+)

Ascus(dikaryotic)

EightascosporesAsci

Ascocarp

GerminationDispersal

e.g. Neurospora crassa conidiophore( green bread mold)

• asexual reproduction: fungus produces a powdery structures called conidiophores at the tip of their hyphae– conidiophore is equivalent to a asexual sporangium– mitosis within the conidiophore produces spores called conidia– conidia carried by air currents to new locations– germination leads to specialized hyphae formation called haustoriae – penetrate the epidermis of

leaves and absorb nutrients– eventual production of a new mycelium with new conidiophores

4. Phylum: Basidiomycota

• club fungus• 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

4. Phylum: Basidiomycota

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

• all are characterized by the formation of a basidium (plural = basidia) – club-shaped structure which is diploid and produces basidiospores

• basidia are located on the visible mushroom called the basidiocarp and are the structures we call mushrooms, puffballs, toadstools, bracket fungus

• beneath the basidiocarp are extensive mats of mycelia that feed on decaying vegetation – very long lived and dikaryotic

• hyphae of the mycelium are septate and coenocytic at specific stages during their reproduction

The Common Mushroom

pileus

stipe

stipe

gills

basidiocarp

• the basidiomycotes include the common mushroom

• basidium = “little pedestal”• note the cap (pileus) with the

gills on the underside• the supporting stalk = stipe• fruiting body or basidiocarp =

cap + stalk• as in the ascomycotes and its

ascocarp – the basidiocarp is an aggregation of hyphae

PLASMOGAMY

KeyHaploid (n)Dikaryotic (n + n)Diploid (2n)

SEXUALREPRODUCTION

KARYOGAMYMEIOSIS

Dikaryoticmycelium

Basidium containingfour haploid nuclei

Dispersal andgermination

Basidium

1 µm

Matingtype (+)

Matingtype (–)

Haploidmycelia

Gills linedwithbasidia Basidiocarp

(dikaryotic)

Basidia(dikaryotic)

Diploidnuclei

Basidiospore

Basidiospores

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

mycelium forms made up many dikaryotic hyphae • rain or temperature changes induce the dikaryotic mycelium to form a

basidiocarp (mushroom)• the hyphae of the mushroom are still dikaryotic – no nuclear fusion yet

(nuclei are still separated and are haploid)

• sexual reproduction: • the gills of the basidiocarp are made of dikaryotic hyphae • their tips are called called basidia (basidium = singular)• within each basidium karyogamy occurs - two nuclei fuse • followed by meiosis 4 haploid nuclei total per basidium• at the tip of the basidium - each haploid nuclei develops into a basidiospore• basidiospores are released when mature and are carried by the wind – germinate into new

mycelia which rapidly undergo more sexual reproduction

basidiospores

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(dikaryotic)

Diploidnuclei

Basidiospore

Basidiospores

Fungi as Decomposers

• fungi are well-adapted decomposers of organic material

• very good at decomposing the polysaccharides cellulose and lignin (plants & wood)

• their decomposition makes available to ecosystems inorganic nutrients such as carbon, nitrogen and phosphate ions

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)– most species are either obligate aerobes (for cellular

respiration) or anaerobic (fermentation)– are no species of obligate anaerobes

• 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• exist as either diploid or haploid forms

Yeasts

• asexual reproduction through budding or mitosis – occurs in both haploid and diploid cells

• sexual reproduction through the production of pheromones by two mating types – two yeast cells of opposite mating types meet and

fuse – karyogamy results in a diploid yeast cell– this yeast cell can reproduce asexually by budding– when stressed– the diploid cells undergo meiosis to

form spores of two haploid mating types- “alpha” and “a”

Haploid

Diploid

alphaa

Fungal Associations

• fungi can form mutualistic relationships with plants, algae and animals

• Fungal-Plant associations: formation of mycorrhizal associations with the roots of vascular plants– these fungi are called mycorrhizal– all plant species harbor symbiotic fungi called

endophytes– these live harmlessly inside the leaves of

plants– benefit certain grasses and other non-woody

plants by making toxins to deter herbivores– can also increase the plants tolerance to heat,

drought or heavy metals

leaf cutter ants depend on fungi to convertplant material into something these ants can digest

Fungal Associations• Fungal-Animal associations: some

fungus share their digestive services with animals– assist in the breakdown of plant

material– guts of cattle and other grazing

mammals– some insects (termites and ants) can

raise “farms” of fungi to aid in digestion – called farmer insects

leaf cutter ants depend on fungi to convertplant material into something these ants can digest

Fungal Associations: Lichens

• Lichens: 25,000 species– fungus + green algae (or cyanobacteria)– each requires one another to colonize areas

they wouldn’t be able to alone– algae provide organic compounds, the

cyanobacteria fix nitrogen– algae nestle among the fungal hyphae– found from the arctic to the tropics– most reproduce asexually

• 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• asexual reproduction:

– 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

– some sexual reproduction can occur through the formation of basidiocarps or ascocarps