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  • 1. Chapter 31 Fungi
  • 2.
    • Overview: Mighty Mushrooms
    • Fungi
      • Are diverse and widespread
      • Are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients
    Figure 31.1
  • 3.
    • Concept 31.1: Fungi are heterotrophs that feed by absorption
    • Despite their diversity
      • Fungi share some key traits
  • 4. Nutrition and Fungal Lifestyles
    • Fungi are heterotrophs
      • But do not ingest their food
    • Fungi secrete into their surroundings exoenzymes that break down complex molecules
      • And then absorb the remaining smaller compounds
  • 5.
    • Fungi exhibit diverse lifestyles
      • Decomposers
      • Parasites
      • Mutualistic symbionts
  • 6. Body Structure
    • The morphology of multicellular fungi
      • Enhances their ability to absorb nutrients from their surroundings
    Hyphae. The mushroom and its subterranean mycelium are a continuous network of hyphae. Reproductive structure. The mushroom produces tiny cells called spores. Spore-producing structures 20  m Mycelium Figure 31.2
  • 7.
    • Fungi consist of
      • Mycelia, networks of branched hyphae adapted for absorption
    • Most fungi
      • Have cell walls made of chitin
  • 8.
    • Some fungi
      • Have hyphae divided into cells by septa, with pores allowing cell-to-cell movement of materials
    • Coenocytic fungi
      • Lack septa
    Nuclei Cell wall Septum Pore (a) Septate hypha (b) Coenocytic hypha Cell wall Nuclei Figure 31.3a, b
  • 9.
    • Some unique fungi
      • Have specialized hyphae that allow them to penetrate the tissues of their host
    Nematode Hyphae 25  m (a) Hyphae adapted for trapping and killing prey (b) Haustoria Fungal hypha Plant cell wall Haustorium Plant cell plasma membrane Plant cell Figure 31.4a, b
  • 10.
    • Mycorrhizae
      • Are mutually beneficial relationships between fungi and plant roots
  • 11.
    • Concept 31.2: Fungi produce spores through sexual or asexual life cycles
    • Fungi propagate themselves
      • By producing vast numbers of spores, either sexually or asexually
  • 12.
    • The generalized life cycle of fungi
    Key Haploid ( n ) Heterokaryotic (unfused nuclei from different parents) Diploid (2 n ) PLASMOGAMY (fusion of cytoplasm) Heterokaryotic stage KARYOGAMY (fusion of nuclei) SEXUAL REPRODUCTION Spore-producing structures Spores ASEXUAL REPRODUCTION Zygote Mycelium GERMINATION GERMINATION MEIOSIS Spore-producing structures Spores Figure 31.5
  • 13. Sexual Reproduction
    • The sexual life cycle involves
      • Cell fusion, plasmogamy
      • Nuclear fusion, karyogamy
    • An intervening heterokaryotic stage
      • Occurs between plasmogamy and karyogamy in which cells have haploid nuclei from two parents
  • 14.
    • The diploid phase following karyogamy
      • Is short-lived and undergoes meiosis, producing haploid spores
  • 15. Asexual Reproduction
    • Many fungi can reproduce asexually
  • 16.
    • Many fungi that can reproduce asexually
      • Grow as mold, sometimes on fruit, bread, and other foods
    2.5  m Figure 31.6
  • 17.
    • Other asexual fungi are yeasts
      • That inhabit moist environments
      • Which produce by simple cell division
    10  m Parent cell Bud Figure 31.7
  • 18.
    • Many molds and yeasts have no known sexual stage
      • Mycologists have traditionally called these deuteromycetes, or imperfect fungi
  • 19.
    • Concept 31.3: Fungi descended from an aquatic, single-celled, flagellated protist
    • Systematists now recognize Fungi and Animalia as sister kingdoms
      • Because fungi and animals are more closely related to each other than they are to plants or other eukaryotes
  • 20. The Origin of Fungi
    • Molecular evidence
      • Supports the hypothesis that fungi and animals diverged from a common ancestor that was unicellular and bore flagella
    • Fungi probably evolved
      • Before the colonization of land by multicellular organisms
  • 21.
    • The oldest undisputed fossils of fungi
      • Are only about 460 million years old
    Figure 31.8  50  m
  • 22. The Move to Land
    • Fungi were among the earliest colonizers of land
      • Probably as symbionts with early land plants
  • 23.
    • Concept 31.4: Fungi have radiated into a diverse set of lineages
    • The phylogeny of fungi
      • Is currently the subject of much research
    • Molecular analysis
      • Has helped clarify the evolutionary relationships between fungal groups, although there are still areas of uncertainty
  • 24.
    • The phylogeny of fungi
    Chytrids Zygote fungi Arbuscular mycorrhizal fungi Sac fungi Club fungi Chytridiomycota Zygomycota Glomeromycota Ascomycota Basidiomycota Figure 31.9
  • 25.
    • A review of fungal phyla
    Table 31.1
  • 26. Chytrids
    • Fungi classified in the phylum Chytridiomycota, or chytrids
      • Are found in freshwater and terrestrial habitats
      • Can be saprobic or parasitic
  • 27.
    • Chytrids are unique among fungi
      • In having flagellated spores, called zoospores
    25  m 4  m Hyphae Flagellum Figure 31.10
  • 28.
    • Until recently, systematists thought that
      • Fungi lost flagella only once in their history
    • Molecular data
      • Indicate that some “chytrids” are actually more closely related to another fungal group, the zygomycetes
    Some chytrids Zygomycetes and other chytrids Glomeromycetes, ascomycetes, and basidiomycetes Common ancestor Key Loss of flagella Figure 31.11
  • 29. Zygomycetes
    • Fungi in the phylum Zygomycota, the zygomycetes
      • Exhibit a considerable diversity of life histories
      • Include fast-growing molds, parasites, and commensal symbionts
      • Are named for their sexually produced zygosporangia
  • 30.
    • The life cycle of Rhizopus stolonifer
      • Is fairly typical of zygomycetes
    Figure 31.12 Rhizopus growing on bread ASEXUAL REPRODUCTION Mycelium Dispersal and germination MEIOSIS KARYOGAMY PLASMOGAMY Key Haploid ( n ) Heterokaryotic ( n + n ) Diploid Sporangium Diploid nuclei Zygosporangium (heterokaryotic) 100  m Young zygosporangium (heterokaryotic) SEXUAL REPRODUCTION Dispersal and germination Mating type (+) Mating type (  ) Gametangia with haploid nuclei 50  m Sporangia Mycelia have various mating types (here designated +, with red nuclei, and  , with blue nuclei). 1 Neighboring mycelia of different mating types form hyphal extensions called gametangia, each walled off around several haploid nuclei by a septum. 2 A heterokaryotic zygosporangium forms, containing multiple haploid nuclei from the two parents. 3 The sporangium disperses genetically diverse, haploid spores. 7 4 This cell develops a rough, thick-walled coating that can resist dry environments and other harsh conditions for months. 5 When conditions are favourable, karyogamy occurs, followed by meiosis. 6 The zygosporangium then breaks dormancy, germinating into a short sporangium. The spores germinate and grow into new mycelia. 8 9 Mycelia can also reproduce asexually by forming sporangia that produce genetically identical haploid spores.
  • 31.
    • Some zygomycetes, such as Pilobolus
      • Can actually “aim” their sporangia toward conditions associated with good food sources
    0.5 mm Figure 31.13
  • 32.
    • Zygosporangia, which are resistant to freezing and drying
      • Are capable of persisting through unfavorable conditions
      • Can undergo meiosis when conditions improve
  • 33. Microsporidia
    • Microsporidia
      • Are unicellular parasites of animals and protists
      • Are now classified as zygomycetes
    10  m Host cell nucleus Developing microsporidian Spore Figure 31.14
  • 34. Glomeromycetes
    • Fungi assigned to the phylum Glomeromycota
      • Were once considered zygomycetes
      • Are now classified in a separate clade
  • 35.
    • All glomeromycetes
      • Form a distinct type of endomycorrhizae called arbuscular mycorrhizae
    2.5  m Figure 31.15
  • 36. Ascomycetes
    • Fungi in the phylum Ascomycota
      • Are found in a variety of marine, freshwater, and terrestrial habitats
      • Are defined by the production of sexual spores in saclike asci, which are usually contained in fruiting bodies called ascocarps
  • 37.
    • Ascomycetes
      • Vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels
    (a) The cup-shaped ascocarps (fruiting bodies) of Aleuria aurantia give this species its common name: orange peel fungus. (b) The edible ascocarp of Morchella esculenta, the succulent morel, is often found under trees in orchards. (c) Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open. (d) Neurospora crassa feeds as a mold on bread and other food (SEM). 10  m Figure 31.16a–d
  • 38.
    • Ascomycetes reproduce
      • Asexually by producing enormous numbers of asexual spores called conidia
  • 39.
    • The life cycle of Neurospora crassa, an ascomycete
    Figure 31.17 Dispersal ASEXUAL REPRODUCTION Germination Mycelium Conidiophore Germination Dispersal Mycelia Asci Eight ascospores Ascocarp Four haploid nuclei MEIOSIS KARYOGAMY PLASMOGAMY SEXUAL REPRODUCTION Diploid nucleus (zygote) Ascogonium Ascus (dikaryotic) Dikaryotic hyphae Mating type (  ) Conidia; mating type (  ) Key Haploid ( n ) Dikaryotic ( n  n ) Diploid (2 n ) Ascomycete mycelia can also reproduce asexually by producing haploid conidia. 7 Neurospora can reproduce sexually by producing specialized hyphae. Conidia of the opposite mating type fuse to these hyphae. 1 A dikaryotic ascus develops. 2 Karyogamy occurs within the ascus, producing a diploid nucleus. 3 The diploid nucleus divides by meiosis, yielding four haploid nuclei. 4 The developing asci are contained in an ascocarp. The ascospores are discharged forcibly from the asci through an opening in the ascocarp. Germinating ascospores give rise to new mycelia. 6 5 Each haploid nucleus divides once by mitosis, yielding eight nuclei. Cell walls develop around the nuclei, forming ascospores (LM).
  • 40. Basidiomycetes
    • Fungi in the phylum Basidiomycota
      • Include mushrooms and shelf fungi
      • Are defined by a clublike structure called a basidium, a transient diploid stage in the life cycle
  • 41.
    • Basidiomycetes
    (a) Fly agaric ( Amanita muscaria ), a common species in conifer forests in the northern hemisphere (b) Maiden veil fungus ( Dictyphora ), a fungus with an odor like rotting meat (c) Shelf fungi, important decomposers of wood (d) Puffballs emitting spores Figure 31.18a–d
  • 42.
    • The life cycle of a basidiomycete
      • Usually includes a long-lived dikaryotic mycelium, which can erect its fruiting structure, a mushroom, in just a few hours
    Figure 31.19
  • 43.
    • The life cycle of a mushroom-forming basidiomycete
    Figure 31.20 PLASMOGAMY Dikaryotic mycelium Basidiocarp (dikaryotic) KARYOGAMY Key MEIOSIS Gills lined with basidia SEXUAL REPRODUCTION Mating type (  ) Mating type (  ) Haploid mycelia Dispersal and germination Basidiospores Basidium with four appendages Basidium containing four haploid nuclei Basidia (dikaryotic) Diploid nuclei Basidiospore 1  m Basidium Haploid ( n ) Dikaryotic ( n  n ) Diploid (2 n ) Each diploid nucleus yields four haploid nuclei. Each basidium grows four appendages, and one haploid nucleus enters each appendage and develops into a basidiospore (SEM). 6 Two haploid mycelia of different mating types undergo plasmogamy. 1 A dikaryotic mycelium forms, growing faster then, and ultimately crowding out, the haploid parental mycelia. 2 3 Environmental cues such as rain or temperature changes induce the dikaryotic mycelium to form compact masses that develop into basidiocarps (mushrooms, in this case). The basidiocarp gills are lined with terminal dikaryotic cells called basidia. 4 Karyogamy in the basidia produces diploid nuclei, which then undergo meiosis. 5 When mature, the basidiospores are ejected, fall from the cap, and are dispersed by the wind. 7 In a suitable environment, the basidiospores germinate and grow into short-lived haploid mycelia. 8
  • 44.
    • Concept 31.5: Fungi have a powerful impact on ecosystems and human welfare
  • 45. Decomposers
    • Fungi are well adapted as decomposers of organic material
      • Performing essential recycling of chemical elements between the living and nonliving world
  • 46. Symbionts
    • Fungi form symbiotic relationships with
      • Plants, algae, and animals
  • 47. Mycorrhizae
    • Mycorrhizae
      • Are enormously important in natural ecosystems and agriculture
      • Increase plant productivity
    RESULTS RESULTS Researchers grew soybean plants in soil treated with fungicide (poison that kills fungi) to prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed mycorrhizae in the soybean plants’ roots. EXPERIMENT The soybean plant on the left is typical of the experimental group. Its stunted growth is probably due to a phosphorus deficiency. The taller, healthier plant on the right is typical of the control group and has mycorrhizae. CONCLUSION These results indicate that the presence of mycorrhizae benefits a soybean plant and support the hypothesis that mycorrhizae enhance the plant’s ability to take up phosphate and other needed minerals. Figure 31.21
  • 48. Fungus-Animal Symbiosis
    • Some fungi share their digestive services with animals
      • Helping break down plant material in the guts of cows and other grazing mammals
  • 49.
    • Many species of ants and termites
      • Take advantage of the digestive power of fungi by raising them in “farms”
    Figure 31.22
  • 50. Lichens
    • Lichens
      • Are a symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae
    (a) A fruticose (shrub-like) lichen (b) A foliose (leaf-like) lichen (c) Crustose (crust-like) lichens Figure 31.23a–c
  • 51.
    • The fungal component of a lichen
      • Is most often an ascomycete
    • Algae or cyanobacteria
      • Occupy an inner layer below the lichen surface
    Ascocarp of fungus Fungal hyphae Algal layer Soredia Algal cell Fungal hyphae 10  m Figure 31.24
  • 52. Pathogens
    • About 30% of known fungal species
      • Are parasites, mostly on or in plants
    (a) Corn smut on corn (b) Tar spot fungus on maple leaves (c) Ergots on rye Figure 31.25a–c
  • 53.
    • Some of the fungi that attack food crops
      • Are toxic to humans
  • 54. Practical Uses of Fungi
    • Humans eat many fungi
      • And use others to make cheeses, alcoholic beverages, and bread
  • 55.
    • Antibiotics produced by fungi
      • Treat bacterial infections
    Staphylococcus Penicillium Zone of inhibited growth Figure 31.26
  • 56.
    • Genetic research on fungi
      • Is leading to applications in biotechnology