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3/21/11 I. Mycology: Mushrooms, molds, and yeasts. General Characteristics FUNGI • Eukaryotes. • Predominant stage haploid. • Both multicellular (hyphae made up of filaments) and unicellular (yeasts). • Not photosynthetic, all heterotrophic by absorption. Fruiting body Mycelium • Key points: • Heterotrophs that obtain nutrition by absorption. • Shared common ancestor of animal-like protists with Animalia. • Vital symbionts of plants. • Classification based on reproductive modes. Hyphae made up of filaments are organized into mushroom body (mycelium and fruiting body) • m 0 a by 40 Share common ancestor with animals and some Protists (to the exclusion of other Protista and Plants). Ancient, fossils associated with earliest land plants, ca. 400mya. 1 • Five lineages of Fungi (Chytrids paraphyletic) ya I. Mycology: Mushrooms, molds, and yeasts. Evolutionary History – Molecular data suggests the split between the lineage leading to fungi and the lineage leading to animals occurred ca. 1 bya. • Have diversified into five main lineages I. Mycology: Mushrooms, molds, and yeasts. The Absorptive Mode of Nutrition – Most plants depend on mutualist relationship with fungi. • Vegetative (nonreproductive) body. • Basic units are hyphae – Filaments of cells with a wall of chitin. – Septate cells (most common) – Aseptate & coenocytic cells • Hyphae form interwoven mat called the mycelium – 10 cm3 of soil can contain 1 km of hyphae. • Haustoria are specialized hyphae of parasitic fungi that penetrate plant cells. Mycelium • Enzymes decompose organic materials. • Saprobes decompose and absorb nutrients from non-living organic matter. • Parasitic fungi absorb nutrients from cells of living hosts, some are pathogenic. • Mutualistic fungi also absorb from host organism, but reciprocate with beneficial functions, e.g. uptake of nutrients, minerals. II. Structure: The mycelium 1 3/21/11 II. Structure: Reproductive body • Varies with taxonomic group • All reproduce by haploid spores in specialized structures peculiar to each group. • Evolution of fungi toward larger, more specialized sporebearing structures. II. Structure: Other Life Styles • Molds: Rapidly growing asexual stage. – May develop sexual stage as fruiting body distinctive of one of 5 phyla. – Some without known sexual stage, called imperfect fungi or deuteromycetes. – Important molds, e.g. Penicillium (penicillin, cheese) Zygomycete Basidiomycete Ascomycete Mutualistic Symbioses II. Structure: Other Life Styles II. Structure: Other Life Styles • Mycorrhizae: “fungus roots” • Yeasts: Unicellular fungi in liquids or moisture including sap and animal tissue. – Important mutualism. – Increases surface area for absorption and exchange of nutrients. – Important in global Phosphorus cycle. – Over 95% of plants have mycorrhizae. – Ectomycorrhizae: Hyphal sheath covers root and hartig net surrounds individual plant root cells. – Asexual cell division, or budding; but some sexual ascomycetes and basidiomycetes are yeasts. – Saccharomyces: baker’s yeast, brewer’s yeast; active metabolically, release CO2 causes dough to rise, also ferments sugars to alcohol. – Candida: pathogenic yeast (vaginal, oral). • Species of Zygomycetes, Ascomycetes, Basidiomycetes. – Arbuscular mycorrhizae: Hyphae enter plant cells via invagination of plant cell membrane (do not enter protoplast--the interior of the cell). • Only and all species of Glomeromycota. Mutualistic Symbioses Mutualistic Symbioses II. Structure: Other Life Styles • Endophytes live within plant tissues. – Provide fungi with protection, nutrients, water. – May receive from fungi chemical protection from insects, protists, bacteria, other fungi. – May receive ability to tolerate stressful environmental conditions. – Found in every plant studied to date (do not know role of all). – Primarily Ascomyceta. – Taxol, effective anti-cancer drug derived from endophyte of the Pacific Yew. II. Structure: Other Life Styles • Lichens are mutualisms between fungi and photosynthetic organisms. 1. 2. 3. 4. Green Algae Cyanobacteria Yellow-Green Algae† Brown Alga (1 known case)† • Rarely three-fold: Fungus + photosynthetic green alga + nitrogen-fixing cyanobacteria. • Fungi provide mineral nutrients and water, algae provide carbohydrates via photosynthesis. • Ascomyceta (mostly), Basidiomyceta (a few), Glomeromyceta (1) 2 3/21/11 Mutualistic Symbioses II. Structure: Other Life Styles • • • Insect cultivation: Fungi are cultivated by insects, provided with protection, fungi break down cellulose in plant tissue. Internal cultivation: Termites External cultivation: – – Leaf-cutter ants: cultivate underground fungus gardens. Fungi break down cellulose in leaf tissue, ants eat fungus. Bark and ambrosia beetles: colonize new trees and inoculate carved galleries with ascomycete fungus. Fungi break down cellulose in wood, beetles consume fungus. III. Growth & Reproduction: Generalized life cycle 1. 2. 3. 4. 5. Plasmogamy: fusion of cytoplasm of haploid hyphae. Dikaryon: cells with two haploid unfused nuclei. Karyogamy: fusion of nuclei, diploid stage; followed immediately by: Meiosis in haploid spore producing structures. Spores are released as haploid and germinate into filaments. A. Chytridiomycota (chytrids) • ~1,000 species, paraphyletic. • Only fungi with flagellated (spore) stage. • A link between ancestral protists and true fungi? • Once excluded from Fungi, but share biochemical characters, cell walls of chitin, absorptive mode of nutrition. • Mainly aquatic saprobes, some parasitic on plants and animals. III. Growth & Reproduction • Growth not in bulk, but by proliferation of hyphae growing into resource (e.g. giant fairy ring) • Reproduction mostly asexual by spores or simple cloning, only chytrids with flagellar stage. • Spores dispersed by wind, water, animals. IV. Diversity A. Chytridiomycota (chytrids) B. Zygomycota (zygote fungi) C. Glomeromycota (arbuscular mycorrhizae) D. Ascomycota (sac or cup fungi) E. Basidiomycota (club fungi) B. Zygomycota (zygote fungi) • ~1,000 species • Terrestrial, soil, decaying plant/animal tissue. • Mycorrhizae: mutualistic association with plant roots. • Hyphae coenocytic. • Zygosporangia are the reproductive structures that give the name. • E.g. Rhizopus stolonifer, black bread mold. 3 3/21/11 C. Glomeromycota (arbuscular mycorrhizae) • 160 species, once considered Ascomycota, but now recognized as distinct. • Nearly all form arbuscular mycorrhizae with plants--ecologically important. – Ca. 90% of all plant species have them as mutualists! D. Ascomycota (sac or cup fungi) • Include such tasties as truffles and morels. • Unicellular to complex multicellularity. • Some extreme plant pathogens; other important saprobes. • Half symbiotic with Chlorophyta: lichens. • Karyogamy in an ascocarp; sexual spore in asci. • Asexual: spores (conidia) come from specialized structures (conidiophores), wind dispersed. E. Basidiomyceta (club fungi) • Include the commonly encountered mushrooms, shelf fungi, puffballs. • Basidium (“little pedestal”) transient diploid stage. • Most important plant (wood) decomposers. • Karyogamy in basidiocarp (sexual); puff balls release spores explosively. • Most complex of fungi: longlived dikaryotic mycelium. • Fairy rings; giant ring in Michigan ~40 acres (!); genetically uniform mycelium. 4