Overview: Mighty Mushrooms

1. Overview: Mighty Mushrooms • Fungi are diverse and widespread • They are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients

2. Concept 31.1: Fungi are heterotrophs that feed by absorption Despite their diversity, fungi share key traits, most importantly the way in which they derive nutrition • The fungi live by absorptive nutrition, secreting digestive enzymes (exoenzymes) that break down large food molecules and absorbing the breakdown products. • Some are saprobes (feeding on dead matter) and are decomposers; others are parasites, pathogens and predators. • A few have mutually beneficial (symbiotic) relationships with other organisms.

3. Practical Uses of Fungi Humans eat many fungi and use others to make cheeses, alcoholic beverages, and bread Some fungi are used to produce antibiotics for the treatment of bacterial infections, for example the ascomycete Penicillium Genetic research on fungi is leading to applications in biotechnology For example, insulin-like growth factor can be produced in the fungus Saccharomyces cerevisiae

4. Fig. 31-26 Staphylococcus Penicillium Zone of inhibited growth

5. Fungal pathogens are a major cause of death among people with compromised immune systems. The general term for a fungal infection in animals is mycosis • Most patients with AIDS die of fungal diseases such as Pneumocystis carinii. • Candida albicans and other yeasts also cause severe diseases in those with AIDS. • Other less severe and common diseases include ringworm and athlete’s foot. • Plant diseases include black stem rust and others.

6. Fig. 31-25 (b) Tar spot fungus on maple leaves (a) Corn smut on corn (c) Ergots on rye

7. Lichens are symbiotic associations of a fungus with a cyanobacterium, a unicellular photosynthetic eukaryote, or both. • Mycorrhizae are mutualistic associations of fungi and plant roots. • The fungus obtains organic compounds, while the plant is provided with water and soil minerals.

8. Body Structure • The most common body structures are multicellular filaments (hyphae) but single cells Fungi also exist (yeasts) • Some species grow as either filaments or yeasts; others grow as both Animation: Fungal Reproduction and Nutrition

9. Fungal Morphology • The morphology of multicellular fungi enhances their ability to absorb nutrients • The vegetative body of the Fungi consist of mycelia, networks of branched hyphae adapted for absorption • Most fungi have cell walls made of chitin

10. Fig. 31-2 Reproductive structure Hyphae Spore-producing structures 20 µm Mycelium

11. Some fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement of organelles • Coenocytic fungi lack septa

12. Fig. 31-3 Cell wall Cell wall Nuclei Pore Septum Nuclei (a) Septate hypha (b) Coenocytic hypha

13. The hyphae may be widely dispersed to forage for nutrients (increase the surface area) or they may be clumped together in a cottony mass to exploit a rich nutrient source. • Sometimes the mycelium becomes reorganized into a fruiting (reproductive) structure, such as a mushroom. • Rhizoids are modified hyphae, which serve to anchor the fungus to a substrate. • These rhizoids are not homologous to the rhizoids of plants because they are not specialized to absorb water and nutrients.

14. Specialized Hyphae in Mycorrhizal Fungi • Some unique fungi have specialized hyphae called haustoria that allow them to penetrate the tissues of their host • Most predatory fungi secrete sticky substances from the hyphae. Trapped prey are penetrated by hyphae and eventually killed. • Some species form a ring with modified hyphae that constricts around nematodes. • The crawling nematode triggers these rings to swell and trap the worm. Hyphae quickly invade and digest the worm.

15. Fig. 31-4 Hyphae Nematode 25 µm (a) Hyphae adapted for trapping and killing prey Plant cell wall Fungal hypha Plant cell Plant cell plasma membrane Haustorium (b) Haustoria

16. The mycelium has a very high surface area-to-volume ratio. • Throughout the mycelium (except in fruiting structures), all the hyphae are very close to their environmental food source. • Fungi are tolerant to highly hypertonic environments. • Many can tolerate temperatures as low as 5–6°C below freezing. Some can tolerate temperatures as high as 50 °C or more.

17. 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 • Fungi can produce spores from different types of life cycles

18. Fig. 31-5-1 Key Haploid (n) Heterokaryotic (unfused nuclei from different parents) Diploid (2n) Spore-producing structures Spores ASEXUAL REPRODUCTION Mycelium GERMINATION

19. Fig. 31-5-2 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 GERMINATION

20. Fig. 31-5-3 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 Spores

21. Sexual Reproduction • Fungal nuclei are normally haploid, with the exception of transient diploid stages formed during the sexual life cycles • Sexual reproduction requires the fusion of hyphae from different mating types • Fungi use sexual signaling molecules called pheromones to communicate their mating type

22. Plasmogamy is the union of two parent mycelia • In most fungi, the haploid nuclei from each parent do not fuse right away; they coexist in the mycelium, called a heterokaryon • In some fungi, the haploid nuclei pair off two to a cell; such a mycelium is said to be dikaryotic

23. Hours, days, or even centuries may pass before the occurrence of karyogamy, nuclear fusion • During karyogamy, the haploid nuclei fuse, producing diploid cells • The diploid phase is short-lived and undergoes meiosis, producing haploid spores

24. Asexual Reproduction • In addition to sexual reproduction, many fungi can reproduce asexually • Molds produce haploid spores by mitosis and form visible mycelia

25. Fig. 31-6 2.5 µm

26. Other fungi that can reproduce asexually are yeasts, which inhabit moist environments • Instead of producing spores, yeasts reproduce asexually by simple cell division and the pinching of “bud cells” from a parent cell

27. Many molds and yeasts have no known sexual stage • Mycologists have traditionally called these deuteromycetes, or imperfect fungi

28. Concept 31.3: The ancestor of fungi was an aquatic, single-celled, flagellated protist • Fungi and animals are more closely related to each other than they are to plants or other eukaryotes. The production of chitin is a shared derived trait for fungi, choanoflagellates, and animals. • The presence of chitin in fungi is evidence that all fungi are more closely related to animals than to plants.

29. The Origin of Fungi • Fungi, animals, and their protistan relatives form the opisthokonts clade Animals (and their close protistan relatives) UNICELLULAR, FLAGELLATED ANCESTOR Opisthokonts Nucleariids Fungi Chytrids Other fungi Fig. 31-8

30. DNA evidence suggests that fungi are most closely related to unicellular nucleariids while animals are most closely related to unicellular choanoflagellates • This suggests that fungi and animals evolved from a common flagellated unicellular ancestor and multicellularity arose separately in the two groups • The oldest undisputed fossils of fungi are only about 460 million years old

31. Fig. 31-9 50 µm

32. Concept 31.4: Fungi have radiated into a diverse set of lineages • Molecular analyses have helped clarify evolutionary relationships among fungal groups, although areas of uncertainty remain

33. Fig. 31-11 Hyphae 25 µm Chytrids (1,000 species) Zygomycetes (1,000 species) Fungal hypha Glomeromycetes (160 species) Ascomycetes (65,000 species) Basidiomycetes (30,000 species)

34. Chytrids • Chytrids (phylum Chytridiomycota) are found in freshwater and terrestrial habitats • They can be decomposers, parasites, or mutualists • Molecular evidence supports the hypothesis that chytrids diverged early in fungal evolution • Chytrids are unique among fungi in having flagellated spores, called zoospores Video: Allomyces Zoospore Release Video: Phlyctochytrium Zoospore Release

35. Fig. 31-12 Flagellum 4 µm

36. Zygomycetes • The zygomycetes (phylum Zygomycota) exhibit great diversity of life histories • They include fast-growing molds, parasites, and commensal symbionts • The zygomycetes are named for their sexually produced zygosporangia • Zygosporangia, which are resistant to freezing and drying, can survive unfavorable conditions

37. Fig. 31-13-4 Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) PLASMOGAMY Mating type (+) Gametangia with haploid nuclei Mating type (–) 100 µm Young zygosporangium (heterokaryotic) Rhizopus growing on bread SEXUAL REPRODUCTION Dispersal and germination Zygosporangium KARYOGAMY Sporangia Spores Diploid nuclei Sporangium ASEXUAL REPRODUCTION MEIOSIS • The life cycle of black bread mold (Rhizopus stolonifer) is fairly typical of the phylum Dispersal and germination Mycelium 50 µm

38. Fig. 31-14 0.5 mm

39. Glomeromycetes • The glomeromycetes (phylum Glomeromycota) were once considered zygomycetes • They are now classified in a separate clade • Glomeromycetes form arbuscular mycorrhizae

40. Fig. 31-15 2.5 µm

41. Ascomycetes • Ascomycetes (phylum Ascomycota) live in marine, freshwater, and terrestrial habitats • The phylum is defined by production of sexual spores in saclike asci, usually contained in fruiting bodies called ascocarps • Ascomycetes are commonly called sac fungi • Ascomycetes vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels

42. Fig. 31-16 Morchella esculenta, the tasty morel Tuber melanosporum, a truffle

43. Ascomycetes include plant pathogens, decomposers, and symbionts • Ascomycetes reproduce asexually by enormous numbers of asexual spores called conidia • Conidia are not formed inside sporangia; they are produced asexually at the tips of specialized hyphae called conidiophores • Neurospora is a model organism with a well-studied genome

44. Fig. 31-17-4 Conidia; mating type (–) Key Haploid spores (conidia) Haploid (n) Dikaryotic (n + n) Diploid (2n) Dispersal Germination Mating type (+) ASEXUAL REPRODUCTION Hypha PLASMOGAMY Ascus (dikaryotic) Conidiophore Dikaryotic hyphae Mycelia Mycelium SEXUAL REPRODUCTION Germination KARYOGAMY Dispersal Diploid nucleus (zygote) Eight ascospores Asci Ascocarp Four haploid nuclei MEIOSIS

45. Basidiomycetes • Basidomycetes (phylum Basidiomycota) include mushrooms, puffballs, and shelf fungi, mutualists, and plant parasites • The phylum is defined by a clublike structure called a basidium, a transient diploid stage in the life cycle • The basidiomycetes are also called club fungi

46. Fig. 31-18 Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat Puffballs emitting spores Shelf fungi, important decomposers of wood

47. The life cycle of a basidiomycete usually includes a long-lived dikaryotic mycelium • In response to environmental stimuli, the mycelium reproduces sexually by producing elaborate fruiting bodies call basidiocarps • Mushrooms are examples of basidiocarps • The numerous basidia in a basidiocarp are sources of sexual spores called basidiospores

48. Fig. 31-19-4 Dikaryotic mycelium PLASMOGAMY Haploid mycelia Mating type (–) Mating type (+) Gills lined with basidia Haploid mycelia SEXUAL REPRODUCTION Basidiocarp (n+n) Dispersal and germination Basidiospores (n) Basidium with four basidiospores Basidia (n+n) Basidium Basidium containing four haploid nuclei KARYOGAMY MEIOSIS Key Haploid (n) Dikaryotic (n+n) Diploid nuclei Diploid (2n) Basidiospore 1 µm

49. Fig. 31-20

50. Fungi as Decomposers • Fungi are efficient decomposers • They perform essential recycling of chemical elements between the living and nonliving world • Fungi form mutualistic relationships with plants, algae, cyanobacteria, and animals • All of these relationships have profound ecological effects