Chapter 23 Fungi

1. Chapter 23Fungi

2. 23.1 High-Flying Fungi • Dust carries spores of fungi long distances – even across oceans • Puccinia graminis is the fungal pathogen that causes wheat stem rust, a disease that destroys food crops worldwide • Plant breeding programs have developed rust-resistant strains of wheat – but a mutant form of the fungus (Ug99) is now infecting rust-resistant wheat

3. 23.2 Fungal Traits and Classification • Fungiare heterotrophs that obtain nutrition from their environment by extracellular digestion • They have walled cells, spend their lives fixed in place, and disperse by producing spores • Most are free-living saprobes that live on the remains of other organisms; others live on or in other organisms

4. Ecology of Fungi • Some fungi decompose organic wastes and remains, which helps recycle nutrients in ecosystems • Some form beneficial partnerships with plants, photosynthetic cells (lichen), or herbivores • Some are parasites or pathogens

5. Structure of Fungi • Some fungi live as single cells (yeasts) • Most are a multicelled (molds, mushrooms) • Multicelled fungi grow as a mesh of branching filaments (mycelium) – each filament is one hypha

6. Multicelled Fungi

7. Hyphae • In the oldest fungal lineages (chytrids, zygomycetes, and glomeromycetes) hyphae do not have cross-walls • Hyphae divided into compartments by cross-walls (septae) evolved in the common ancestor of sac fungi and club fungi • Cross-walls made hyphae stronger, allowing the evolution of larger, more elaborate spore-producing bodies • Septate hyphae also are more resistant to desiccation than nonseptate hyphae

8. Hyphae in a Mycelium one cell (part of one hypha of the mycelium)

9. Life Cycles • Asexually produced spores form by mitosis in sporangia at the tips of specialized haploid hyphae • Sexual reproduction begins with cytoplasmic fusion of haploid hyphae to produce a dikaryoticstage having two genetically distinct types of nuclei (n+n) in each cell • Fusion of two haploid nuclei produces a diploid zygote that undergoes meiosis, restoring the haploid state

10. Table 23-1 p381

11. Take-Home Message:What are characteristics of fungi? • Fungi are heterotrophs that absorb nutrients from their environment • Some live as single cells; others live as a multicelled mycelium • They disperse by producing spores

12. 23.3 The Flagellated Fungi • Chytrids are the only modern fungi with a life cycle that includes flagellated cells • Some feed on organic wastes and remains • Some live in guts of herbivores and help digest cellulose • Some are parasites

13. A Parasitic Chytrid • Frog populations are threatened by Batrachochytrium dendrobatidis, a parasitic chytrid that causes chytridiomycosis • A mycosis is a disease caused by a fungus • Outbreaks of B. dendrobatididis have far-reaching ecological effects because frogs help control populations of insects and serve as food for many other animals

14. Zygote Fungi • Rhizopus species • Include black bread mold, molds that spoil foods, and the fungus that causes zygomycosis • Pilobolus • Produces specialized spore-bearing hyphae with fluid-filled sacs that blast spores up to 2 meters

15. mature zygospore Diploid (2n) Fusion of nuclei Meiosis Dikaryotic (n+n) Haploid (n) spores young zygospore between hyphae of its parents mycelium Cytoplasmic fusion asexual reproduction gametangia Figure 23-5 p382

16. Spore Bearing Structures of Pilobolus

17. Microsporidia – Intracellular Parasites • Microsporidia are single-celled intracellular parasites • Most infect animals, usually fish and insects • A microsporidium spore has a tough coat enclosing a long coiled tube that uncoils and perforates a host cell • One microsporidium (Nosema ceranae) has been implicated in honeybee colony collapse disorder

18. Glomeromycetes – Partners of Plants • Glomeromycetes take part in plant root–fungus partnerships called mycorrhizae • A glomeromycete hypha grows into a root and branches inside the wall of a root cell • The fungus shares nutrients from the soil with its host

19. sporangium plant root hypha branching inside a plant cell wall Figure 23-8a p383

20. Take-Home Message: What are zygote fungi and their relatives? • Zygote fungi form a thick-walled diploid spore when they reproduce sexually • Some spoil food or cause disease • Microsporidia are single-celled parasites that invade an animal cell by way of a polar tube • Glomeromycetes are mycorrhizal fungi; they partner with plants

21. 23.5 Sac Fungi—Ascomycetes • Sac fungi are the most diverse fungal group • Some are single cells (yeasts), but in most a haploid mycelium dominates the life cycle • The hyphae have cross-walls at regular intervals and often form elaborate spore-producing bodies • Sac fungi are the group that most often causes diseases in humans

22. Asexual Reproduction • Sac fungi commonly reproduce by asexual mechanisms • Yeasts usually reproduce asexually by binary fission or by budding • Multicelled sac fungi grow as a haploid mycelium that produces spores by mitosis at the tips of specialized hyphae

23. Asexual Reproduction in Sac Fungi

24. Sexual Reproduction • Two haploid hyphae undergo cytoplasmic fusion – the dikaryotic cell divides by mitosis to produce dikaryotic hyphae • Dikaryotic hyphae intertwine with haploid hyphae to form a spore-producing structure called an ascocarp • Spores form by meiosis inside a saclike cell called an ascus • Meiosis of the ascus produces spores

25. Ascocarp: Scarlet Cup Fungus

26. Human Uses of Sac Fungi • Food and beverages • Morels and truffles • Baking yeast and fermentation (Saccharomyces, Aspergillus), blue cheese (Penicillium) • Drugs • Antibiotics (Penicillium, Cephalosporium) • Statins (Aspergillus) • Natural herbicides and pesticides • Arthrobotrys

27. Morels

28. Truffles

29. part of one hypha that forms a nooselike ring roundworm Figure 23-12 p385

30. Take-Home Message:What are sac fungi? • Sac fungi are the most diverse group of fungi; some are yeasts, but a haploid mycelium dominates most life cycles • Sac fungi that reproduce sexually typically form spores inside an ascus • Yeasts reproduce asexually by budding, and multicelled species by formation of conidia • We use sac fungi as sources of food and beverages, as drugs, and as control agents for pests

31. 23.6 Club Fungi—Basidiomycetes • Club fungi make the largest and most elaborate fruiting bodies of all fungi • They are typically multicelled fungi in which a dikaryotic mycelium dominates the life cycle • They form sexual spores inside club-shaped cells that develop on a fruiting body (basidiocarp) composed of interwoven dikaryotic hyphae

32. Diploid (2n) stage Nuclear fusion Meiosis Dikaryotic (n+n) stage Haploid (n) stage spore (n) gill cap stalk Cytoplasmic fusion Hyphae of mycelium Sexual spore (n) at gill margin Figure 23-13 p386

33. Ecology and Diversity • Club fungi are the only decomposers capable of breaking down lignin in plants and trees (e.g. shelf fungus, honey mushroom) • Jelly fungi form a parasitic gelatinous fruiting body that taps into the mycelia of other fungi that feed on wood • Other club fungi include edible mushrooms (chanterelles, puffballs), poisonous mushrooms (death cap), and hallucinogenic psilocybin-containing mushrooms

34. Club Fungus Diversity

35. Take-Home Message:What are club fungi? • Club fungi are a group of mostly multicelled fungi. Multicelled species spend most of their life cycle as a dikaryotic mycelium and have the largest, most complex spore-bearing structures of all fungi • Club fungi are the only fungi that can break down lignin, and they are important in forests both as decomposers and as pathogens of trees

36. 23.7 Fungal Partners and Pathogens • Fungi form partnerships with plants and with single-celled photosynthetic species • Lichens • Fungal endophytes • Mycorrhizae • Other fungi are pathogens of other species

37. Lichens • A lichen is a composite organism consisting of a sac fungus and a photosynthetic cyanobacteria or green algae • A lichen may be a mutualism that benefits both partners, or the fungus may be parasitically exploiting captive cells • Lichens disperse by fragmentation, or the fungus alone can release spores • Lichens break down rock by releasing acids, and colonize hostile such as bedrock

38. Leaflike and Pendant Lichens

39. Encrusting Lichen

40. Lichen Structure dispersal fragment (cells of fungus and of photosynthetic species) outer layer of fungal cells photosynthetic species inner layer of loosely woven hyphae outer layer of fungal cells

41. Mycorrhizae • Mycorrhizaeare a partnership between fungi and plant roots • Some hyphae form a dense net around roots but do not penetrate them (sac fungi and club fungi) • Some hyphae penetrate root cells (glomeromycetes) • Hyphae increase the absorptive surface area of their partner • Both partners benefit • Fungus concentrates nutrients for plant • Plant supplies sugars to the fungus

42. without fungus with fungus Figure 23-16b p389

43. Fungal Pathogens • Some fungi are plant pathogens • Wheat stem rust • Powdery mildew • Ergotism (alkaloid poisoning, Claviceps) • A minority of fungi are human pathogens • Athlete’s foot • “Ringworm” • Vaginal yeast infection (Candida)

44. Rye with Ascocarps of Claviceps

45. Athlete’s Foot

46. Table 23-2 p391

47. Take-Home Message: What close relationships do fungi have with other species? • Fungi form mutually beneficial partnerships with plants, cyanobacteria, and green algae • Some ants, termites, and beetles farm fungus and rely on them for food • Some fungi are pathogens that invade the tissues of plants and animals