Biology, Fungi

Raven Biology 13th edition, Fungi Ch31

Defining Fungi, Mycologists believe there may be as many as 1.5 million fungal species,
Fungi are

single-celled or multicellular

sexual or asexual

exhibit unusual mitosis

specialized to extract and absorb nutrients from surroundings

Defining Fungi, Animal and fungi last shared a common ancestor

460 million years ago

Phylogenetic relationships have been debated, Mycologists agreed on 6 major monophyletic phyla

Blastocladiomycota

Neocallimastigomycota

Chytridiomycota

Glomeromycota

Basidiomycota

Ascomycota

Phylogenetic relationships have been debated, There is 1 paraphyletic phylum

Zygomycota; Microsporidia are sometimes included

General features of the Fungi, Multicellular fungi consist of long slender filaments called hyphae

some hyphae are continuous, others divided by septa

General features of the Fungi, Cytoplasm flows throughout hyphae

allows rapid growth under good conditions

Mycelia and Cell Walls, Mycelium is

a mass of connected hyphae that grows through and digests its substrate

Mycelia and Cell Walls, Fungal cell walls include chitin

also found in hard shells (exoskeletons) of arthropods

Spores, Spores are the most common means of reproduction among fungi

may form from sexual or asexual processes; most are dispersed by wind

Nutrition, Fungi obtain food by secreting digestive enzymes into surroundings

then absorb the organic molecules from external digestion; great surface area-to-volume ratio

Nutrition, Fungi can break down cellulose and lignin

decompose wood; some fungi are carnivorous

Interactions with Other Species, Fungi symbioses types

obligate symbiosis (essential), facultative symbiosis (nonessential)

Interactions with Other Species, Interactions include

pathogens (harm host by disease), parasites (harm host no disease), commensal (benefit one partner, no harm), mutualistic (benefit both partners)

Endophytic fungi, Live in the intercellular spaces inside plants

some parasites, some commensals or mutualists

Endophytic fungi, Some fungi protect their hosts from herbivores by producing toxins

perennial rye grass more resistant to aphid feeding with endophytes

Lichens, Symbiotic associations between a fungus and a photosynthetic partner

cyanobacteria, green algae, or both; most mutualistic (some parasitic)

Lichens, Ascomycetes are found in

all but about 20 of the 15,000 lichen species

Lichen Biology, Fungi in lichens are unable to grow normally without their photosynthetic partners

fungi protect partners from strong light and desiccation

Lichen Biology, Lichens have invaded the harshest habitats

striking colors protect photosynthetic partner; sensitive to pollutants

Mycorrhizae, Mutualistic relationships between fungi and plants

found on roots of ~90% of all known vascular plant species; function as root system extensions increasing absorption

Mycorrhizae, Two principal types are

arbuscular mycorrhizae and ectomycorrhizae

Ectomycorrhizae, Most hosts are forest trees (pines, oaks)

hosts are important carbon sinks; fungal partners mostly basidiomycetes; at least 5000 species involved

Ectomycorrhizae, Hyphae surround but do not penetrate root cells

extract nitrogen and other nutrients from soil and pass to host

Animal mutual symbioses, Ruminant animals host Neocallimastigomycete fungi in their gut

leaf-cutter ants have domesticated basidiomycete fungi kept in underground gardens

Animal mutual symbioses, Leaf-cutter ants provide fungi with leaves

fungi are food for the ants

Fungal Parasites and Pathogens, Cause health issues in humans

allergens trigger immune responses; fungal spores cause allergic reactions and illness in high numbers

Fungal Parasites and Pathogens, Mycoses are

direct infections (skin and nails)

Fungal Parasites and Pathogens, Ingested toxins produced by fungi

cause illness

Fungal toxins, Fungi may secrete mycotoxins making food unpalatable, carcinogenic, or poisonous

example: Aspergillus flavus produces aflatoxin

Fungal toxins, Ustilago maydis (corn smut)

harms plants but not animals that eat the plants

Diseases Caused by Fungi, Fungi cause human and animal diseases

athlete's foot, ringworm, nail fungus; difficult to treat due to close phylogenetic relationship

Diseases Caused by Fungi, Batrachochytrium dendrobatidis causes chytridiomycosis

associated with worldwide decline in amphibian populations

Fungal Plant Diseases, Fungal species cause many diseases in plants

among most harmful pests of living plants; can spoil harvested or stored food

Basidiomycota, Basidiomycetes are some of the most familiar fungi

include mushrooms, toadstools, puffballs, shelf fungi; also important plant pathogens like rusts and smuts

Basidiomycota, "Club fungi" named for

basidium – club-shaped sexual reproductive structure

Ascomycota, Contain about 75% of known fungi

includes bread yeasts, common molds, cup fungi, truffles, morels; serious plant pathogens

Ascomycota, Penicillin-producing fungi are in the genus Penicillium

"Sac fungi" named for ascus – microscopic saclike reproductive structure

Reproduction in the Ascomycota, Karyogamy occurs within asci

only diploid nucleus of life cycle; asci differentiate in ascocarp

Reproduction in the Ascomycota, Meiosis and mitosis follow producing

8 haploid nuclei that become walled ascospores

Yeast, Single-celled ascomycetes

most reproduce asexually by cell fission or budding

Yeast, Yeasts can ferment carbohydrates

break down glucose into ethanol and CO2; used to make bread, beer, wine; example Saccharomyces cerevisiae

Yeast as a Model in Genetic Research, Yeast is a long-standing model system

first eukaryotes genetically engineered; Saccharomyces cerevisiae first eukaryote to have genome sequenced in 1996

Yeast as a Model in Genetic Research, Coccidioides species can cause disease

endemic in soil of SW USA; cause coccidioidomycosis (Valley Fever)

Glomeromycota, Glomeromycetes are a tiny group of fungi

form intracellular associations with plant roots called arbuscular mycorrhizae

Glomeromycota, Cannot survive in absence of host plant

probably key for plant colonization of land; no evidence of sexual reproduction

Zygomycota, Zygomycetes are incredibly diverse

not monophyletic – still under research; include common bread molds and few human pathogens

Chytridiomycota, Chytridiomycetes or chytrids

aquatic, flagellated fungi; closely related to ancestral fungi; have motile zoospores

Chytridiomycota, Batrachochytrium dendrobatidis

implicated in amphibian die-offs

Blastocladiomycetes, Aquatic and terrestrial

parasites of plants, animals, algae and fungi; have uniflagellated zoospores

Blastocladiomycetes, Allomyces example

water mold; haplodiplontic life cycle (alternation of haploid and diploid generations in multicellular forms)

Neocallimastigomycota, Digest plant biomass in mammalian herbivore rumens

sheep, cows, kangaroos, elephants; mammal depends on fungi for sufficient calories

Neocallimastigomycota, Greatly reduced mitochondria lack cristae

zoospores have multiple flagella; horizontal gene transfer brought cellulase gene from bacteria

Neocallimastigomycota, Might be useful for

biofuel production

Microsporidia, Encephalitozoon cuniculi commonly cause disease in immunosuppressed patients

infect hosts with spores containing a polar tube

Microsporidia, Infects intestinal and neuronal cells

leading to diarrhea and neurodegenerative diseas