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3/21/11 FUNGI • 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. I. Mycology: Mushrooms, molds, and yeasts. General Characteristics Fruiting body • Eukaryotes. • Predominant stage haploid. • Both multicellular (hyphae made up of filaments) and unicellular (yeasts). • Not photosynthetic, all heterotrophic by absorption. Mycelium Hyphae made up of filaments are organized into mushroom body (mycelium and fruiting body) • m 0 by a 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 • 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 1 3/21/11 Five lineages of Fungi (Chytrids paraphyletic) I. Mycology: Mushrooms, molds, and yeasts. The Absorptive Mode of Nutrition • 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. – Most plants depend on mutualist relationship with fungi. II. Structure: The mycelium • 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 Mycelium – 10 cm3 of soil can contain 1 km of hyphae. • Haustoria are specialized hyphae of parasitic fungi that penetrate plant cells. 2 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. Zygomycete Basidiomycete Ascomycete 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) II. Structure: Other Life Styles • Yeasts: Unicellular fungi in liquids or moisture including sap and animal tissue. – 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). 3 3/21/11 Mutualistic Symbioses II. Structure: Other Life Styles • Mycorrhizae: “fungus roots” – 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. • 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 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. Mutualistic Symbioses 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) 4 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 • 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. 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. 5 3/21/11 IV. Diversity A. Chytridiomycota (chytrids) B. Zygomycota (zygote fungi) C. Glomeromycota (arbuscular mycorrhizae) D. Ascomycota (sac or cup fungi) E. Basidiomycota (club fungi) 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. 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. 6 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. 7