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Fungi

Ch 14.

General Characteristics• Eukaryotic• Nuclear envelope does not break down during mitosis &

meiosis.• Heterotrophic absorbers• Primary storage carb is glycogen.• Chitin in cell walls• Chitin in cell walls.• Grow in filaments called hyphae.

– Large clusters of hyphae = mycelium• Distinctive fruiting bodies

– Used for identification• Make spores asexually.• Zygotic life cycle.• Symbiotic relationships with plants.

Great diversity

• 70,000 species.• 1,700 new species

discovered each year.F i 2 d l t• Fungi 2nd only to insects in diversity.

• Armillaria ostoyaeencompasses nearly 900 ha. in Oregon.– Largest living

organism on Earth?

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Importance of Fungi

• Ecologically important– Function as decomposers

• Medical & economical importance as:P t th & d f t i– Pests, pathogens, & producers of certain chemicals.

• Form symbiotic relationships– Mainly in plant roots.

Fungi as decomposers

• Principle decomposers in the biosphere.• Releases CO2, returns N to soil.• Top 20cm of fertile soil – 5 metric tons of

f i & b t ifungi & bacteria.• Attack foodstuffs, decreasing palatability

– Toxic substances known as mycotoxins.

Fungi as pathogens

• Most important causal agent of plant diseases.

• Most common in tropical regions.40% f h it l d th i 80’ d t• 40% of hospital deaths in 80’s due to fungi.Chytrid Red Fungus Rhizopus

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Beneficial fungi

Saccharomyces cerevisiae

Penicillium roquefortiiConidia of the fungus

(spores)

Fungi as symbionts

• 80% of plants form mutualisms– Mycorrhizae (between roots & fungi)

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Types of mycorrhizae

• Ectomycorrhizal– Usually a gymnosperm (pines)

E d hi l• Endomycorrhizal– Usually orchids & ericoids

(rhododendrons)– Also, citrus, coffee, & rubber

Fungi Phyla

A closer look!!!!!

Four major phyla of fungi

• Chytridiomycota– Chytrids

• Zygomycota– ZygomycetesZygomycetes

• Ascomycota– Ascomycetes

• Basidiomycota– Classes Basidiomycetes, Teliomycetes, &

Ustomycetes

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Major Characteristics of Fungal Phyla

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Hyphae

• Hyphae – fungal filaments• Mycelium – mass of hyphae

– Individual fungus may produce > 1 km of new hyphae within 24 hrshyphae within 24 hrs.

• Septa – divide hyphae (crosswalls)• Such hyphae are called ‘septate’.• Hyphae lacking septa are called ‘aseptate

or coenocytic’.

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Heterotrophic absorbers

• Absorb b/c cell walls are rigid.• Occurs near growing tips of hyphae.• Function as:

– Saprophytes (living on organic materials) have rhizoids.

– Parasites - haustoria– Mutualists

Mitosis & Meiosis

• Nuclear envelope does not disintegrate & re-form.

• Form spindle pole bodiesSPB’ d t i l f ti i t b l– SPB’s and centrioles function as microtubule organizing centers during mitosis & meiosis.

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Reproduction

• Both sexual & asexual• Asexual

– Spores• Sporangia or conidiogenous cellsSpo a g a o co d oge ous ce s

• Sexual– 3 phases

• Plasmogamy (fusion of protoplasts)• Karyogamy (fusion of nuclei)• Meiosis

The Chytrids: Chytridiomycota

• Predominantly aquatic (790 spp.)

• Chitin • Store glycogen• Store glycogen• Coenocytic• Motile cells (zoospores &

gametes)• Infect a number of hosts

Batrachochytrium dendrobatidis(Bd)

© Forrest Brem

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Allomyces arbusculus –Alteration of isomorphic generations

Bd life cycle

Zygomycetes: Zygomycota

• Mostly parasites & mutualist (~ 1060 spp.)• Coenocytic hyphae• Usually have profuse, rapidly growing

h hhyphae:– Hyphae called ‘stolons’ form rhizoids

• Named for sexually produced ‘zygospores’.

• Form endomycorrhizal associations

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Rhizopus stolonifer

Gametangia – fusing to produce zygospore

Zygospore developingwithin zygosporangium

Ascomycetes: Ascomycota• Blue-green, red, and brown molds (~32,00

spp.)• Unicellular or filamentous growth• Conidia borne at tips of modified hyphae p yp

called “conidiophores”.• Asexual spores are produced externally as

conidia.• Sexual reproduction involves the formation of

an ascus which ascospores are produced.

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Two asci Ascoma Ascoma

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• Asci develop on inner surface of ascomacalled hymenium.

• Antheridia “male gametangia”• Ascogonia “female gametangia”

Basidiomycetes, Teliomycetes, & Ustomycetes: Basidiomycota

• Most familiar fungi (~ 22,000 spp.)• Mushrooms, toadstools, puffballs, shelf

fungi.P d b idi b t id l b• Produce basidiospores borne outside club-shaped basidium.

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Class Basidiomycetes

• Includes Hymenomycetes & Gasteromycetes.• Edible & poisonous mushrooms, coral fungi,

tooth fungi, and shelf & bracket fungi.R f d h t b• Referred as hymenomycetes because basidiospores are produced on the hymenium.

• Gasteromycetes have no distinct hymenium is visible.– False puffballs, bird’s nest fungi, and puffballs.

Hymenomycetes

• Toadstools usually recognized– Pileus (cap)

Stipe (stalk)– Stipe (stalk)– Gills

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Mycelium spreads and dies in center

Gasteromycetes

• Form peridium (outer covering)– Opens naturally, spores not expelled

• Some cases spores need to be liberated by external source (i.e., animal or tree falling etc…)( g )

Puffballs Netted Stinkhorn

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Teliomycetes

• Referred to as rusts– Billions of dollars in

crop damage• Heteroecious• Heteroecious

– Two hosts to complete life cycle

• Autoecious– One host

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Ustomycetes

• Parasites to flowering plants – a.k.a smuts

Autoecious• Autoecious

Yeasts

• Unicellular fungus• Saccharomyces

cerevisiae

Conidial Fungi

• a.k.a Anamorphs• Medically important

– Penicillium (penicillin-producing fungi)A ill ( i t di )– Aspergillus (respiratory diseases)

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Symbiotic relationships

• Mutualisms or parasitisms• Lichens

– Mycobiont + Photobiont98% b l t A t• 98% belong to Ascomycota

• Remaining belong to Basidiomycota

Mycorrhizae

• “Fungus roots”• Endomycorrhizae

– Penetrate root cellsOft ll d “V i l b l ”– Often called “Vesicular-arbuscular” mycorrhizae

• Ectomycorrhizae– Surround root cells

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Endomycorrhizae

Ectomycorrhizae

Summary • Ecologically & Economically important• Most composed of hyphae• Absorb & produce spores• 4 distinct phyla• Chytrids form flagellated, motile cells.• Zygomycota form zygospores in zygosporangia• Zygomycota form zygospores in zygosporangia.• Ascomycota form ascospores internally in asci.• Basidiomycota form basidiospores externally on basidia.• Mushrooms, rusts, & smuts represent 3 classes of Basidiomycota.• Yeasts are unicellular.• Fungi with no sexual state are Conidial Fungi.• Lichens = Mycobionts + Photobionts• Mycorrhizae = mutualistic associations between Fungi & Roots.