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Fungi

1. General characteristics of fungi

2. Ecological roles of fungi

3. The fungus life cycle

4. The four fungal phyla

Some major episodes in the history of life

Figure 31.9 Phylogeny of fungi

Learn to match structures in these groups to the stages ofthe generalized fungus life cycle

Traits of fungi:1. Eukaryotic2. Heterotrophic, with absorptive nutrition (exoenzymes)3. Body made of hyphae—thin, long strands of cells

-interwoven net of hyphae is called amycelium-cell walls usually composed of chitin

4. Dispersal via asexual and/or sexual spores5. Unique life cycle, including a heterokaryotic stage

Septate hyphae (left) and nonseptate (or coenocytic) hyphae (right)

Figure 31.2 Fungal structureThe mycelium: How is its structurerelated to the absorptive nutrition of thefungus?

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Mycelia

• Highly branched, have very high surfacearea:volume ratio– 1 cm3 of soil may contain 1 km of hyphae

• All parts of fungal body (exceptreproductive structures) in close contactwith environment

• Interior of any cell is in close contact withenvironment

Figure 31.3-31.4 Examples of fungal hyphae

Fungal ecology

• Most fungi are decomposers• Many fungi are parasites, causing

diseases in plants or animals• A very few fungi are predators - eat very

small animals (nematodes) in the soil• Fungi are always heterotrophs, but…• Fungi are involved in important

mutualisms with plants and algae

One ecological role of fungi:mycorrhizae

• Some fungi attach to plant roots, forming a“mycorrhiza”

• These fungi obtain nutrients from the soil and passsome of them along to the plant

• In return, the fungus receives carbon (sugars) fromthe plant

• One type of mycorrhiza, the ectomycorrhiza, isusually a basidiomycete fungus on the roots ofconifers, oaks, eucalypts, and a few other trees

• Many of the mushrooms you see in the forest arethe basidiocarps or sexual fruiting bodies ofmycorrhizal fungi

“Mycorrhiza” = Fungus/root(plural: mycorrhizae)

Plant

Fungus

SugarsSoil Nutrients

2 main types:1. Ectomycorrhizae(pictured here;mostly Basidio-,some Ascomycota)and2. ArbuscularMycorrhizae(formerly “endo-”,all areGlomeromycetes)

Two main types of mycorrhizae

• Ectomycorrhizae form sheaths over theouter surface of a root, and may grow intothe extracellular spaces of the root cortex,but do not penetrate cell walls

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Figure 37.12 Ectomycorrhizae and endomycorrhizae.

Two main types of mycorrhizae

• Ectomycorrhizae form sheaths over theouter surface of a root, and may grow intothe extracellular spaces of the root cortex,but do not penetrate cell walls

• Endomycorrhizae (arbuscularmycorrhizae) extend into the interiors ofroot cells

Figure 37.12 Ectomycorrhizae and endomycorrhizae. Figure 31.123 Lichens: a symbiosis between a fungus (usually an ascomycete)and a photosynthetic organism (alga or cyanobacterium). Usually presumed tobe a mutualism. Grow very slowly, can live for a very long time.

Figure 31.24 Anatomy of a lichen Figure 31.5 Generalized life cycle of fungi (Layer 3)

**Notice the lack of a multicellular diploid stage

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Fungi

1. General characteristics of fungi

2. Ecological roles of fungi

3. The fungus life cycle

4. The four fungal phyla

Figure 31.9 Phylogeny of fungi

Learn to match structures in these groups to the stages ofthe generalized fungus life cycle

Flagellated zoospores

Zygosporangia(sporangium)

Ascocarps

Basidiocarps

Figure 31.11 Phylogeny of fungi

Chytrids and Zygomycetesmay be paraphyletic

Chytridiomycota• ‘early’ fungi: flagellated spores, zoospores• Lakes, ponds, soil• Some are saprobes, some parasitic• Some single celled, most have coenocytic

hyphae• A ‘link’ to animal evolution? 1.5 billion years

animals and fungi diverged, but fossil evidenceis sparse!

Chytrid ecology

• Mostly unicellular, some species formcolonies with hyphae

• Mostly saprobes (eat dead organisms),some parasites

• Disease caused by a chytrid fungusappears responsible for many cases ofamphibian decline

Zygomycota• Form a zygospore: resistant structures during sexual reproduction• About 1,000 species - variable life histories! Including molds,

parasites and commensal symbionts• Coenocytic hyphae, with septa only where reproductive cells are

found• Asexual phase: haploid spores develop in sporangia at the tips of

upright hyphae• When conditions get bad: sexual reproduction and the zygospore• Zygosporangium is a resistant multinucleate structure where

heterokaryotic nuclei fuse to form diploid nuclei that undergomeiosis

• When conditions improve: meiosis and the release of haploid spores

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Figure 31.12 The life cycle of the zygomycete Rhizopus (black bread mold)

Notice the lack of aheterokaryoticmycelial stage

Glomeromycota: AMF• This is a ‘phylum?’ currently grouped

with the zygomycota

• They are classified as arbuscularMycorrhizal Fungi (AMF)

• All (?) are asexual

• They are symbionts - over half ofliving fungi in soil are probably these!

• Important commercially

Figure 37.12 Glomeromycota are arbuscular mycorrhizae (endomycorrhizae).

Ascomycota: sac fungi• 35,000 species! Marine, freshwater , terrestrial habitats• Produce sexual spores in saclike asci• Fruiting bodies: ascocarps• Variety of morphologies and life histories from single celled yeasts

to morels• Many are plant pathogens, many are saprobes, many live with algae

as lichens (about 40%)• Produce conidia - naked spores on conidiophores (asexual

reproduction)• Extensive heterokaryotic stage

Figure 31.16 Ascomycetes (sac fungi): Scarlet cup (top left), “true” truffles(bottom left), morel (right)

Figure 31.17 The life cycle of an ascomycete

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Figure 31.17 The life cycle of an ascomycete Figure 31.18 Basidiomycota (club fungi)

•30,000 species•Long liveddikaryotic mycelia•Basidium: transientdiploid stage•Important saprobes(can decomposelignin)•Fruiting bodies arebasidiocarps•Asexualreproduction not ascommon

Figure 31.20 The life cycle of a mushroom-forming basidiomyceteaka fruiting body,basidioma

hymenial layer

Basidiomycete Gills, and their attached basidia and basidiospores.Basidiomycetes are named after their basidia.

False truffles: spherical, underground,mammal-dispersed basidiomycetefruiting bodies evolved from mushroomancestors

Figure 31.19 A fairy ring

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Table 31.1 Review of Fungal Phyla

Not always!Always hasmicroscopicbasidia