Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 31

Defining Fungi Mycologists believe there may be as many as 1.5 million fungal species Single-celled or multicellular Specialized to extract and absorb nutrients from surroundings 2

7 monophyletic phyla –Microsporidia –Blastocladiomycota –Neocallismastigamycota –Chytridiomycota –Glomeromycota –Basidiomycota –Ascomycota 3

4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MicrosporidiaBlastocladiomycotaZygomycotaNeocallimastigomycotaChytridiomycotaGlomeromycotaBasidiomycota Fungi Ascomycota Dikarya 10 µm520 µm333 µm312 µm300 µm160 µm a: © Dr. Ronny Larsson; b: Contributed by Don Barr, Mycological Society of America; c: © Carolina Biological Supply Company/Phototake; d: Contributed by Don Barr, Mycological Society of America; e: © Dr. Yuuji Tsukii; f: © Yolande Dalpe, Agriculture and Agri-Food Canada; g:© inga spence/Alamy; h: © Michael&Patricia Fogden

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General Biology of the Fungi Multicellular fungi consist of long, slender filaments called hyphae –Some hyphae are continuous –Others are divided by septa Cytoplasm flows throughout hyphae –Allows rapid growth under good conditions 6

Mycelium – mass of connected hyphae –Grows through and digests its substrate Fungal cell walls include chitin –Also found in the hard shells (exoskeletons) of arthropods 7

Spores are the most common means of reproduction among fungi –May form from sexual or asexual processes –Most are dispersed by wind 8

Nutrition Obtain food by secreting digestive enzymes into surroundings Then absorb the organic molecules produced by this external digestion –Great surface area-to-volume ratio Fungi can break down cellulose and lignin –Decompose wood –Some fungi are carnivorous 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. 370 µm Fungus Nematode Fungal loop © Carolina Biological Supply Company/Phototake b. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © L. West/ Photo Researchers, Inc.

Microsporidia Obligate, intracellular, animal parasites Long thought to be protists Lack mitochondria –Ancestors lost them 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neocallimastigomycota Zygomycota Chytridiomycota GlomeromycotaBasidiomycota Ascomycota Blastocladiomycota Microsporidia Fungi

Encephalitozoon cuniculi –Commonly cause disease in immunosuppressed patients –Infect hosts with their spores, which contain a polar tube –Infects intestinal and neuronal cells, leading to diarrhea and neurodegenerative disease 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0.5 µm Polar tube Spore (left): © Daniel P. Fedorko

Chytridiomycota Chytridiomycetes or chytrids Aquatic, flagellated fungi Closely related to ancestral fungi Have motile zoospores Batrachochytrium dendrobatidis has been implicated in amphibian die-offs 12 NeocallimastigomycotaZygomycotaChytridiomycota GlomeromycotaBasidiomycota Ascomycota Blastocladiomycota Microsporidia Fungi Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Zoospore Contributed by Daniel Wubah, Mycological Society of America Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chytrid Oedogonium filament Contributed by Don Barr, Mycological Society of America

Blastocladiomycetes Uniflagellated zoospores Allomyces example –Water mold –Haplodiplontic life cycle –Female gametes secrete pheromone to attract male gametes –Giant mitochondria in its zoospores 14

15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 100 µm Female gametangium Male gametangium Haploid gametes (n) Sporophyte(2n) Gametophyte (n) Mature sporophyte (2n) Asexual sporangium Sporophyte Sporangium (2n) n 2n a.b. Young gametophyte (n) Haploid zoospore (n) Young sporophyte (2n) Young sporophyte (2n) Asexual reproduction Diploid zoospores (2n) Mature gametophyte (n) FERTILIZATION MEIOSIS MITOSIS a: © Carolina Biological Supply Company/Phototake

Neocallimastigamycota Digest plant biomass in mammalian herbivore rumens –Mammal depends on fungi for sufficient calories Greatly reduced mitochondria lack cristae Zoospores have multiple flagella Horizontal gene transfer brought cellulase gene from bacteria into Neocallimastix genome 16

Zygomycota Zygomycetes are incredibly diverse Not monophyletic – still under research Include the common bread molds A few human pathogens 17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neocallimastigomycota ZygomycotaChytridiomycota GlomeromycotaBasidiomycota Ascomycota BlastocladiomycotaMicrosporidia Fungi

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Glomeromycota Glomeromycetes are a tiny group of fungi Form intracellular associations with plant roots called arbuscular mycorrhizae –Cannot survive in absence of host plant No evidence of sexual reproduction 19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neocallimastigomycota Zygomycota ChytridiomycotaGlomeromycotaBasidiomycota Ascomycota Blastocladiomycota Microsporidia Fungi

Basidiomycota Basidiomycetes are some of the most familiar fungi Mushrooms, toadstools, puffballs, shelf fungi, etc. Also important plant pathogens like rusts and smuts 20 Neocallimastigomycota Zygomycota ChytridiomycotaGlomeromycotaBasidiomycota Ascomycota Blastocladiomycota Microsporidia Fungi Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Ascomycota Contain about 75% of the known fungi Includes bread yeasts, common molds, cup fungi, truffles, and morels Serious plant pathogens – cause of chestnut blight and Dutch elm disease Penicillin-producing fungi are in the genus Penicillium 22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neocallimastigomycota Zygomycota ChytridiomycotaGlomeromycota Basidiomycota Ascomycota Blastocladiomycota Microsporidia Fungi

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Yeast Unicellular ascomycetes Most reproduce asexually by budding Yeasts can ferment carbohydrates –Break down glucose into ethanol and CO 2 –Used to make bread, beer, and wine –Saccharomyces cerevisiae 24

Yeast is a long-standing model system for genetic research –First eukaryotes to be manipulated extensively –Saccharomyces cerevisiae first eukaryote to have genome sequenced 25

Ecology of Fungi Fungi, together with bacteria, are the principal decomposers in the biosphere Break down cellulose and lignin from wood –Release carbon, nitrogen, and phosphorus 26

Endophytic fungi –Live in the intercellular spaces inside plants –Some parasitic, some commensalistic –Some fungi protect their hosts from herbivores by producing toxins 27

Italian rye grass is more resistant to aphid feeding in the presence of endophytes 28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fungal endophyteNo endophyte Fungal EndophyteNo Endophyte Aphids after 36 days aphids SCIENTIFIC THINKING Hypothesis: Endophytic fungi can protect their host from herbivory. Prediction: There will be fewer aphids (Rhopalosiphum padi, an herbivore) on perennial ryegrass (Lolium perenne) infected with endophytic fungi than on uninfected ryegrass. Test: Place five adult aphids on each pot of 2-week-old grass plants with and without endophytic fungi. Place pots in perforated bags and grow for 36 days. Count the number of aphids in each pot. Result: Significantly more aphids were found on the uninfectedgrass plants. Conclusion: Endophytic fungi protect host plants from herbivory. Further Experiments: How do you think the fungi protect the plants from herbivory? If they secrete chemical toxins, could you use this basic experimental design to test specific fungal compounds? (left): © Nigel Cattlin/Alamy; (right): © B. Borrell Casal/Frank Lane Picture Agency/Corbis

Lichens –Symbiotic associations between a fungus and a photosynthetic partner Cyanobacteria, green algae, or sometimes both –Most are mutualistic –Ascomycetes are found in all but about 20 of the 15,000 lichen species 29

Fungi in lichens are unable to grow normally without their photosynthetic partners Fungi protect their partners from strong light and desiccation Lichens have invaded the harshest habitats Striking colors play a role in protecting photosynthetic partner Sensitive to pollutants 30 Fungus Nematode Fungal loop

Mycorrhizae –Mutualistic relationships between fungi and plants –Found on the roots of about 90% of all known vascular plant species –Function as extensions of root system Increase soil contact and absorption –Two principal types Arbuscular mycorrhizae Ectomycorrhizae 31

Arbuscular mycorrhizae –By far the most common –Fungal partners are glomeromycetes –No aboveground fruiting structures –Potentially capable of increasing crop yields with lower phosphate and energy inputs 32 Hyphae penetrate the root cell wall but not plant membranes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Root 3.7 µm Arbuscular Mycorrhizae © Eye of Science/Photo Researchers, Inc.

Ectomycorrhizae –Most hosts are forest trees (pines, oaks) –Fungal partners are mostly basidiomycetes –At least 5000 species of fungi are involved in ectomycorrhizal relationships 33 Hyphae surround but do not penetrate the root cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b. 50 µm Ectomycorrhizae © Dr. Gerald Van Dyke/Visuals Unlimited

Animal mutual symbioses –Ruminant animals host neocallimastigamycete fungi in their gut –Leaf-cutter ants have domesticated fungi which they keep in underground gardens Ants provide fungi with leaves Fungi are food for the ants 34

Fungal Parasites and Pathogens Fungal species cause many diseases in plants –Among most harmful pests of living plants –Can also spoil harvested or stored food products 35

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Fungi may secrete substances making food unpalatable, carcinogenic, or poisonous Fusarium – vomitoxin Aspergillus flavus – aflatoxin 37

Fungi also cause human and animal diseases –Candida – thrush; vaginal infections –Pneumocystis jiroveci – pneumonia in AIDS –Athlete’s foot, ringworm, and nail fungus Fungal diseases are difficult to treat because of the close phylogenetic relationship between fungi and animals 38

39 Batrachochytrium dendrobatidis causes chytridiomycosis – Responsible for the worldwide decline in amphibian populations