Fungi

Decomposers,

Mutualists,

and

Killers

Fungi

• Fungi

– (most) degrade dead organic matter

– form nutritional partnerships with most vascular plants & some algae

– are pathogens of some plants & animals

parasitic fungiFigure 31.1

Fungi

• Fungi

– are absorptive heterotrophs

• saprobic

• mutalistic

• parasitic

• predatory (rarely)

predatory fungusFigure 31.5

fungal hyphaeFigure 31.3

Fungi

• Fungal growth forms– yeasts are unicellular– most fungi produce multinucleate hyphae

• high surface area for absorption• coenocytic or septate• chitinous cell walls

– mycelia are massed hyphae

conidIa

Figure 31.12

budding yeastFigure 31.2

Fungi

• Fungal reproduction

– asexual reproduction

• sporangia - chambers producing haploid spores

• conidia - naked spores on hyphal tips

• binary fission or budding

• fragmentation

Fungi• Fungal reproduction

– sexual reproduction– between haploid hyphae of different mating

types– fusion of haploid hyphae (plasmogamy)

produces dikaryotic (n+n) hyphae (heterokaryon)

– dikaryotic nuclei eventually fuse (karyogamy) to produce zygote

– meiosis produces haploid spore nuclei

Fungi• Phylogeny

– four phyla differ in

• presence of septa in hyphae

• sexual reproductive structures

• methods of sexual spore formation

– DNA sequencing agrees that the four phyla are monophyletic

Fungi• Phylogeny

• deuteromycetes are fungi without sexual reproductive data

– a polyphyletic “holding category”

– new techniques are assigning deuteromycetes to the four phyla

fungal phylogenyFigure 31-6

fungal classificationTable 31.1

Fungi

• Phylum Chytridiomycota

– earliest diverging fungal group

– aquatic

– parasitic or saprobic (rarely mutualistic)

– unicellular or mycelial

– haploid or diploid, none dikaryotic

Fungi

• Phylum Chytridiomycota– reproduction in Allomyces

• haploid zoospore germinates to produce haploid body

• haploid body produces male and female gametangia

• gametangia produce haploid gametes• [flagellated gametes and zoospores is a unique (ancestral?) character]

Fungi

• Phylum Chytridiomycota– reproduction in Allomyces

• pheromone attracts male gamete to female• fusion of gamete nuclei produces zygote• zygote grows into diploid body• diploid body produces many diploid zoospores

– diploid zoospores produce more diploid bodies

Fungi

• Phylum Chytridiomycota– reproduction in Allomyces

• diploid bodies produce resting sporangia• meiosis within resting sporangia produces haploid zoospores

– alternation of generations

Allomyces sp.

gametangia forming haploid gametes

Figure 31.7

Fungi

• Phylum Zygomycota

– mostly coenocytic

– haploid except zygote

– entirely nonmotile

– some participate in mycorrhizal association with plants

– familiar example: Rhizopus stolonifer

Pilobolus sp.sporangiophores

topped with sporangia

Figure 31.8

sporangium shedding

sporesFigure 31.9

Fungi

• Phylum Zygomycota

– reproduction

• asexual spores are produced on stalked sporangiophores bearing single or multiple sporangia

• sexual reproduction occurs between hyphae of different mating types

Fungi

• Phylum Zygomycota

– reproduction

• sexual reproduction

–pheromones cause hyphae to grow toward each other

–gametangia are produced and fuse into a zygosporangium

–gametes (1n) fuse into a zygote (2n)

Fungi• Phylum Zygomycota

– reproduction

• sexual reproduction

–meiosis produces zygospores (1n) inside the resistant zygosporangium

–after dormancy, zygosporangium releases zygospores

–zygospores germinate to produce haploid hyphae

Zygomycete life cycle

Figure 31.9

Fungi• Phylum Ascomycota

– large diverse group (~30,000 spp.)

– saprobes, parasites, mutualistic symbionts

– hyphae segmented by porous septa

– produce sexual spores in asci (sacs)

Fungi• Phylum Ascomycota

– two major subgroups

• Hemiascomycetes

–mostly unicellular (yeasts) or microscopically multicellular

–asexual reproduction by fission or budding

Fungi

• Phylum Ascomycota– Hemiascomycetes

• sexual reproduction–fusion of haploid cells of different

mating types• [+/- mitotic population growth]• meiosis produces four haploid nuclei• [+/- mitosis to produce eight]• ascospores in the original cell = ascus

Fungi

• Phylum Ascomycota– Hemiascomycetes

• familiar example = Saccharomyces cerevisiae (baker’s, brewer’s yeast)

Fungi

• Phylum Ascomycota– Euascomycetes

• mycelia of septate hyphae

• multicellular sexual fruiting bodies: ascocarps

• asexual reproduction by conidia

Fungi

• Phylum Ascomycota– Euascomycetes

• sexual reproduction

–mating structures form on two compatible mating types

–haploid nuclei from the “male” enter the female mating structure

–the dikaryotic mating structure produces ascogenous hyphae

Fungi

• Phylum Ascomycota– Euascomycetes

• sexual reproduction

–tips of n+n hyphae form asci

–in asci, haploid nuclei fuse

–meiosis produces four haploid nuclei

–[+/- mitosis to form 8 haploid nuclei]

–spores are formed and released

characteristic ascomycete reproductive

sacsFigure 31.10

Ascomycete life cycle

Figure 31.13

Fungi• Phylum Ascomycota

– Euascomycetes• familiar examples

–Neurospora crassa bread mold used by Beadle and Tatum

–brightly colored cup fungi–morels & truffels–Penecillium spp.–Aspergillus spp.

Figure 31.11

Fungi• Phylum Basidiomycota

– large diverse group (~25,000 spp.)

– saprobes, parasites, mutualistic symbionts

– produce sexual spores on basidia

Fungi• Phylum Basidiomycota

– familiar examples• puffballs• bracket fungi• mushrooms and toadstools, edible and toxic

• bird’s nest fungi• jelly fungi• smut and rust fungi

BasidiomycetesFigure 31.14

Fungi

• Phylum Basidiomycota

– sexual reproduction

• basidiospores germinate to produce haploid, septate hyphae

• hyphae of different mating types fuse to form dikaryotic hyphae

• dikaryotic hyphae eventually produce a characteristic basidiocarp

Fungi• Phylum Basidiomycota

– sexual reproduction

• basidiocarp bears surfaces covered with basidia

• two nuclei in n+n basdium fuse to form 2n zygote

• meiosis produces four basidiospores

• basidiospores are displayed on tip of basidium and released

basidiomycete life cycle

Figure 31.15

Fungi

• Fungal Mutualisms with plants

– mycorrhizae

• endomycorrhizal fungi are within the root

• ectomycorrhizal fungi are outside the root

– fungal symbiont enhances absorption of water and some nutrients by photosymbiont

– photosymbiont provides carbohydrate to fungal symbiont

Fungi• Fungal mutualisms with plants

– lichens (~13,500 spp.)

• partnerships between fungi and green algae or cyanobacterium

• fungal symbionts are usually ascomycetes

• lichen are classified as distinct organisms

• among the hardiest organisms

Fungi

• Fungal mutualisms with plants

– lichens

• critical primary producers in arctic ecosystems

• fungal symbiont provides mineral nutrients

• photosymbiont provides fixed carbon

• among the most environmentally sensitive organisms

Fungi

• Fungal mutualisms with plants

– lichens

• three general growth forms

–crustose - crust-like

–foliose - “leafy”

–fruticose - “shrubby”

crustose, foliose, fruticose lichensFigure 31.17

Fungi

• Fungal mutualisms with plants

– lichens

• reproduction

–fragmentation of thallus

–some fungal symbionts produce ascospores or basidiospores

Fungi

• Fungal mutualisms with plants

– lichens

• reproduction

–fragmentation of thallus

–some fungal symbionts produce ascospores or basidiospores

–soredia

reproduction by sorediaFigure 31-18