Lecture #4
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Transcript of Lecture #4
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
Basid
iom
ycot
a
Asco
myc
ota
Glom
erom
ycot
a
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)SEXUAL
REPRODUCTION
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
KARYOGAMY Zygosporangium(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
KeyHaploid (n)Dikaryotic (n + n)Diploid (2n)
SEXUALREPRODUCTION KARYOGAMY
Fourhaploidnuclei MEIOSIS
Dikaryotic Hyphae
ASEXUALREPRODUCTION
Diploid nucleus(zygote)
Dispersal Germination
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
KeyHaploid (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
KeyHaploid (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)
DiploidnucleiBasidiospore
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
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)
DiploidnucleiBasidiospore
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
SorediaAlgallayer
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