I. Overview of Fungi
1. most are multicellular with major haploid life stage. Unicellular fungi are called yeast.
2. nutrition: all heterotrophs; feed by absorption
3. All produce spores
4. Only one phylum (Chytridiomycota) has flagella (gametes).
5. ecology: majority of fungi are saprobes. Other fungi are parasites, including mutual symbionts-especially mycorrhizae (ectomycorrhizae vs. endomycorrhizae) and lichens; others are pathogens. Some are active predators.
6. cell walls contain chitin
7. The kingdom Fungi consists of four major plus one extraneous phyla
8. Fossil evidence: fungi have been present for at least 600 million years.
1. hyphae: Coenocytic hyphae vs. septate hyphae. Septate hyphae can be monokaryotic, or dikaryotic.
2. vegetative body called the mycelium.
3. haustoria: tissue penetrating feeding hyphae of parasitic fungi.
4. Rhizoids are modified hyphae, which anchor Chytridiomycota to a substrate.
5. Fungal parasites of plants invade at wounds on plants and grow mycelium throughout the plant and their fruit.
C. Basics of reproduction: asexual and sexual
reproduction are common.
1. asexual reproduction often via spore production. Cell division by unicellular fungi and simple breakage of mycelium are also asexual.
2. Sexual reproduction: fusion between different mating types.
a. Often zygote nuclei are the only diploid nuclei of fungi life cycle.
b. These nuclei undergo meiosis.
c. Haploid spores divide mitotically to form haploid hyphae.
3. syngamy (fertilization) = plasmogamy (fusion of cells)+ karyogamy (fusion of nuclei)
A.
D. Chytridiomycota (chytrids)
1. earliest diverging fungal lineage.
2. currently classed with fungi because of chitin in cell walls.
3. Only fungal taxon with flagella
4. Most live in fresh water or moist soil; some live in marine environments: Chytrids either parasitic (on aquatic plants or invertebrates) or saprobic. Some live as mutual symbionts in many herbivore guts
5. reproduce both sexually and asexually.
6. one of the few fungi with alternating generations (both a haploid and diploid life cycle).
B.
D. Zygomycota (zygomycotes)
1. named for sexually produced zygosporangia
2. Zygomycetes have coenocytic hyphae (no regular septa); produce no motile cells and only one diploid cell, the zygote
3. Almost 1100 species described. Include fungal species in the most common mycorrhizal associations. Endomycorrhizae: live with 80% of all vascular plants
4. Most are terrestrial decomposers
5. eg. Rhizopus sp. (black bread molds) and Pilobolus sp.
C.
D. Ascomycota (ascomycetes or sac fungi)
1. ascomycetes are a large and diverse group distinguished from other fungi by the production of asci (singular ascus). The ascus contains the products of meiosis.
2. Most abundant and diverse taxon of fungi, includes about 30,000 species
3. Conidia: spores produced for asexual reproduction; characteristic to some taxons and endow them with characteristic colors.
4. Ascomycete hyphae: haploid and septated
5. Ecological diversity: saprobes (truffles, Penicillium sp.), parasites (Dutch elm disease, ergot, Candida sp. and chestnut blight), mutual symbionts (ectomycorrhizae-morels and lichens)
6. Diversity of ascomycetes:
a. Baker's or brewer's yeast (Saccharomyces cerevisiae); make ethanol and CO2 from glucose. Bubbles of CO2 responsible for making bread rise. The alcohol and bubbles in beer are produced by this yeast.
b. yeasts reproduce asexually by budding or fission, or sexually when two haploid cells of opposite mating types fuse
c. Many are plant parasites. Chestnut blight and Dutch elm disease. Powdery mildews infect cereals, lilacs, roses, and other plants.
d. Cup fungi: Morels are edible cup fungi. Truffles grow underground, on the roots of some species of oak.
e. Penicillium: genus of green molds. Some produce the antibiotic penicillin. P. roquefortii and P. camembertii.
f. Brown molds of the genus Aspergillus are used in food preparation, including soy sauce and sake. Some Aspergillus species contaminate peanuts and pecans; produce powerful mutagens called aflatoxins.
D.
D. Basidiomycota (club fungi)
1. About 25,000 species of basidiomycetes have been described.
2. produce a wide variety of sexual fruiting structures, called basidiocarps: puffballs, mushrooms, stinkhorns, and giant bracket fungi. Fairy rings
3. Basidiomycetes: usually septated and monokaryotic.
4. Ecology: decomposers; plant parasites-rusts and smuts; ectomycorrhizal mutualists
5. Some representative basidiomycetes:
a. Agaricus bisporus is the common edible one; some Amanita mushrooms are deadly poisonous
b. Bracket fungi are tree parasites
c. Smut fungi parasitize cereal grains and corn
A. molds: any fast growing fungus
B. yeasts: any unicellular fungus; usually ascomycetes, but some basidiomycetes
C. Lichens: usually ascomycotes; symbionts-chlorophytes and/or cyanobacteria; asexual soredia; sensitive to air pollution
D. mycorrhizae: zygo, asco, or basidiomycetes