The Diverse World of Fungi: From Decomposers to Mutualistic Symbionts

1. Chapter 31 Fungi

2. Figure 31.1 • 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

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. Reproductive structure.The mushroom produces tiny cells called spores. Hyphae. The mushroom and its subterranean mycelium are a continuous network of hyphae. Spore-producing structures 20 m Mycelium Figure 31.2 Body Structure • The morphology of multicellular fungi • Enhances their ability to absorb nutrients from their surroundings

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 Cell wall Cell wall Nuclei Pore Septum Nuclei (a) Septate hypha (b) Coenocytic hypha 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 Plant cell wall Fungal hypha Plant cell Plant cell plasma membrane (b) Haustoria Haustorium 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. Key Heterokaryotic stage Haploid (n) Heterokaryotic (unfused nuclei from different parents) PLASMOGAMY (fusion of cytoplasm) Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Zygote SEXUAL REPRODUCTION Spores ASEXUAL REPRODUCTION Mycelium MEIOSIS GERMINATION GERMINATION Spore-producing structures Spores Figure 31.5 • The generalized life cycle of fungi

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. 2.5 m Figure 31.6 • Many fungi that can reproduce asexually • Grow as mold, sometimes on fruit, bread, and other foods

17. 10 m Parent cell Bud Figure 31.7 • Other asexual fungi are yeasts • That inhabit moist environments • Which produce by simple cell division

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. 50 m • The oldest undisputed fossils of fungi • Are only about 460 million years old Figure 31.8 

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. Arbuscular mycorrhizal fungi Zygote fungi Club fungi Sac fungi Chytrids Zygomycota Ascomycota Basidiomycota Glomeromycota Chytridiomycota Figure 31.9 • The phylogeny of fungi

25. Table 31.1 • A review of fungal phyla

26. Chytrids • Fungi classified in the phylum Chytridiomycota, or chytrids • Are found in freshwater and terrestrial habitats • Can be saprobic or parasitic

27. 25 m Hyphae Flagellum 4 m Figure 31.10 • Chytrids are unique among fungi • In having flagellated spores, called zoospores

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 Glomeromycetes, ascomycetes, andbasidiomycetes Zygomycetes and other chytrids Some chytrids Key Figure 31.11 Common ancestor Loss of flagella

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. 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 Key Haploid (n) Heterokaryotic (n + n) Diploid 3 A heterokaryoticzygosporangiumforms, containingmultiple haploidnuclei from the twoparents. PLASMOGAMY Rhizopusgrowing on bread Mating type (+) Gametangia with haploid nuclei Mating type () 100 m The spores germinate and grow into new mycelia. 8 Young zygosporangium (heterokaryotic) Mycelia can also reproduce asexually by forming sporangia that produce genetically identical haploid spores. 9 SEXUAL REPRODUCTION Dispersal and germination Sporangia 7 The sporangium disperses genetically diverse, haploid spores. Zygosporangium (heterokaryotic) KARYOGAMY Diploid nuclei 4 Sporangium This cell develops a rough, thick-walled coating that can resist dry environments and other harsh conditions for months. ASEXUAL REPRODUCTION MEIOSIS Dispersal and germination 50 m Mycelium 5 When conditions are favourable, karyogamy occurs, followed by meiosis. The zygosporangium then breaks dormancy, germinating into a short sporangium. 6 • The life cycle of Rhizopus stolonifer • Is fairly typical of zygomycetes Figure 31.12

31. Figure 31.13 0.5 mm • Some zygomycetes, such as Pilobolus • Can actually “aim” their sporangia toward conditions associated with good food sources

32. Zygosporangia, which are resistant to freezing and drying • Are capable of persisting through unfavorable conditions • Can undergo meiosis when conditions improve

33. 10 m Host cell nucleus Developing microsporidian Spore Figure 31.14 Microsporidia • Microsporidia • Are unicellular parasites of animals and protists • Are now classified as zygomycetes

34. Glomeromycetes • Fungi assigned to the phylum Glomeromycota • Were once considered zygomycetes • Are now classified in a separate clade

35. 2.5 m Figure 31.15 • All glomeromycetes • Form a distinct type of endomycorrhizae called arbuscular mycorrhizae

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. (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. 10 m (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 asa mold on bread and other food (SEM). Figure 31.16a–d • Ascomycetes • Vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels

38. Ascomycetes reproduce • Asexually by producing enormous numbers of asexual spores called conidia

39. Key Neurospora can reproduce sexually by producing specialized hyphae. Conidia of the opposite mating type fuse to these hyphae. Ascomycete mycelia can also reproduce asexually by producing haploid conidia. Conidia;mating type () 1 7 Haploid (n) Dikaryotic (n n) Diploid (2n) Dispersal Germination Matingtype () ASEXUALREPRODUCTION Mycelium PLASMOGAMY A dikaryotic ascus develops. 2 Ascogonium Ascus(dikaryotic) Mycelia Conidiophore Dikaryotichyphae SEXUALREPRODUCTION KARYOGAMY Germination Dispersal Karyogamy occurs within theascus, producing adiploid nucleus. 3 Diploid nucleus(zygote) Eightascospores The developing asci are contained in an ascocarp. The ascospores are discharged forciblyfrom the asci through anopening in the ascocarp. Germinating ascosporesgive rise to new mycelia. Asci 6 Fourhaploidnuclei MEIOSIS Ascocarp The diploid nucleusdivides by meiosis, yieldingfour haploid nuclei. Each haploid nucleus dividesonce by mitosis, yielding eightnuclei. Cell walls develop aroundthe nuclei, forming ascospores (LM). 4 5 • The life cycle of Neurospora crassa, an ascomycete Figure 31.17

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. (b) Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat (a) Fly agaric (Amanita muscaria), acommon species in conifer forests in the northern hemisphere (d) Puffballs emitting spores Figure 31.18a–d (c) Shelf fungi, important decomposers of wood • Basidiomycetes

42. Figure 31.19 • 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

43. A dikaryotic mycelium forms, growing faster then, and ultimately crowding out, the haploid parental mycelia. 2 Two haploid mycelia of different mating typesundergo plasmogamy. 1 Environmental cues such as rain ortemperature changes induce the dikaryoticmycelium to formcompact masses thatdevelop intobasidiocarps(mushrooms, in thiscase). Dikaryoticmycelium 3 PLASMOGAMY In a suitableenvironment, thebasidiospores germinate andgrow intoshort-livedhaploid mycelia. Matingtype () 8 Matingtype () Haploidmycelia Gills linedwith basidia SEXUALREPRODUCTION Basidiocarp(dikaryotic) Dispersalandgermination When mature,the basidiosporesare ejected, fallfrom the cap, andare dispersed bythe wind. 7 Basidiospores Basidia(dikaryotic) Basidium withfour appendages Basidium containingfour haploid nuclei Basidium The basidiocarpgills are lined withterminal dikaryoticcells called basidia. 4 KARYOGAMY MEIOSIS Each diploid nucleus yields four haploid nuclei. Each basidiumgrows four appendages, and one haploid nucleusenters each appendage and develops into a basidiospore (SEM). 6 Key Diploidnuclei Karyogamy in the basidia produces diploidnuclei, which thenundergo meiosis. Haploid (n) 5 Dikaryotic (n n) 1 m Basidiospore Diploid (2n) • The life cycle of a mushroom-forming basidiomycete Figure 31.20

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. EXPERIMENT 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. 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 Mycorrhizae • Mycorrhizae • Are enormously important in natural ecosystems and agriculture • Increase plant productivity RESULTS RESULTS

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. Figure 31.22 • Many species of ants and termites • Take advantage of the digestive power of fungi by raising them in “farms”

50. (a) A fruticose (shrub-like) lichen Figure 31.23a–c (b) A foliose (leaf-like) lichen (c) Crustose (crust-like) lichens Lichens • Lichens • Are a symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae