Kingdom Fungi Chapter 26

Learning Objective 1 What are the distinguishing characteristics of kingdom Fungi?

Fungi Eukaryotic heterotrophs Secrete digestive enzymes onto food then absorb predigested food Cell walls with chitin

KEY CONCEPTS Fungi are eukaryotic heterotrophs that absorb nutrients from their surroundings

Learning Objective 2 What is the body plan of a fungus?

Fungi Structures Fungi include Most multicellular fungi unicellular yeast filamentous, multicellular mold Most multicellular fungi have long, threadlike filaments (hyphae) branch and form a tangled mass (mycelium)

Insert “Mycelium” mycelium.swf

Learn more about mycelium by clicking on the figure in ThomsonNOW.

Hyphae In most fungi In some fungi perforated septa (cross walls) divide hyphae into individual cells In some fungi zygomycetes and glomeromycetes hyphae are coenocytic (form elongated, multinuclear cell)

Fungus Body Plan

Hyphae Figure 26.1: Fungus body plan. 25 µm Fig. 26-1 (a-b), p. 557

Figure 26.1: Fungus body plan. Fig. 26-1 (c-e), p. 557

KEY CONCEPTS A fungus may be a unicellular yeast or a filamentous, multicellular mold consisting of long, branched hyphae that form a mycelium

Learning Objective 3 What is the life cycle of a typical fungus, including sexual and asexual reproduction?

Reproduction Most fungi reproduce sexually and asexually by spores produced on aerial hyphae land in suitable spot and germinate

Germination of a Spore

Spore Hypha Mycelium Fig. 26-2, p. 557 Figure 26.2: Germination of a spore to form a mycelium. Mycelium Fig. 26-2, p. 557

Asexual Reproduction

Bud development Fig. 26-3a, p. 558 Figure 26.3: Yeasts are unicellular fungi. Bud development Fig. 26-3a, p. 558

Figure 26.3: Yeasts are unicellular fungi. Fig. 26-3b, p. 558

Plasmogamy Fungi of two different mating types meet, hyphae fuse cytoplasm fuses nuclei remain separate Fungi enter dikaryotic (n + n) stage each new cell has one nucleus of each type

Karyogamy Fusion of nuclei takes place in hyphal tip results in diploid (2n) zygote nucleus

Genetic Divisions Meiosis Mitosis produces 4 different haploid (n) nuclei each nucleus becomes part of a spore Mitosis forms new mycelia when spores germinate

Asexual Spores Can be produced by mitosis When these spores germinate genetically similar When these spores germinate they also develop into mycelia

Fungal Life Cycles

Dikaryotic stage (n + n) 7 8 Spore germinates and forms mycelium by mitosis. Large numbers of haploid (n) spores are produced by mitosis. Asexual reproduction Mycelia of two different mating types fuse at their tips, and plasmogamy (fusion of cytoplasm) occurs. Spores germinate and form mycelia by mitosis. 1 2 Mycelia 6 Sexual reproduction Spores are released. Spores Haploid stage (n) Plasmogamy Dikaryotic stage (n + n) 5 Diploid stage (2n) Meiosis results in four genetically different haploid ( n ) nuclei. Spores develop around nuclei. Figure 26.4: The basic sequence of events in most fungal life cycles. 3 Dikaryotic (n + n) mycelium develops. Zygote nucleus (2n) Dikaryotic mycelium Meiosis Karyogamy Karyogamy (fusion of nuclei) occurs, forming a diploid (2 n ) zygote nucleus. 4 Fig. 26-4, p. 559

KEY CONCEPTS Most fungi reproduce both asexually and sexually by means of spores

Learning Objective 4 Support the hypothesis that fungi are opisthokonts, more closely related to animals than to plants

Flagellate Cells Animals and fungi have flagellate cells Example: chytrid gametes and spores Flagellate cells propel themselves with single posterior flagellum

Platelike Cristae Like animal cells, fungal cells have platelike cristae in their mitochondria

Opisthokonts Fungi are opisthokonts along with animals and choanoflagellates based on chemical and structural characters

Fungal Evolution

Evolution of ascospores Glomeromycetes Basidiomycetes Zygomycetes Ascomycetes Chytrids Evolution of ascospores Evolution of basidiospores Evolution of dikaryotic stage Figure 26.5: Fungal evolution: cladogram of major phyla of fungi. This cladogram shows phylogenetic relationships among living fungi, based on comparisons of ribosomal and nuclear gene sequence data for many species. The chytrids were the lineage that branched off first during fungal evolution. Note that ascomycetes and basidiomycetes are sister clades. Remember that the phylogeny of fungi is a work in process. Loss of flagellum Common flagellate ancestor Fig. 26-5, p. 560

Learning Objective 5 Support the hypothesis that chytrids may have been the earliest fungal group to evolve from the most recent common ancestor of fungi

Chytrids (Chytridiomycetes) Produce flagellate cells during life cycle no other fungi have flagella Probably earliest fungi to evolve from flagellate protist common ancestor of all fungi

Chytrid

5 µm Fig. 26-6, p. 561 Figure 26.6: Chytrid. Nomarski differential interference micrograph of a common chytrid (Chytridium convervae). Many chytrids have a microscopic body form consisting of a rounded, coenocytic thallus and branched rhizoids that superficially resemble roots. The rhizoids may anchor the chytrid thallus and absorb predigested food. 5 µm Fig. 26-6, p. 561

Learning Objective 6 List distinguishing characteristics, describe a typical life cycle, and give examples of each of these fungal groups: chytridiomycetes zygomycetes glomeromycetes ascomycetes basidiomycetes

Chytrids 1 Reproduce both asexually and sexually Gametes and zoospores are flagellate Allomyces part of life is multicellular haploid thallus part is multicellular diploid thallus

Chytrids 2 Haploid thallus produces 2 types of flagellate gametes that fuse Both plasmogamy and karyogamy occur producing flagellate zygote

Chytrids 3 Diploid thallus bears zoosporangia produce diploid zoospores, resting sporangia in which haploid zoospores form by meiosis Haploid zoospores form new haploid thalli

Chytrid Life Cycle

Common flagellate ancestor Glomeromycetes Basidiomycetes Zygomycetes Ascomycetes Chytrids Figure 26.7: Life cycle of Allomyces arbuscula, a chytrid. Allomyces alternates between haploid and diploid stages, which are similar in appearance. Common flagellate ancestor Fig. 26-7a, p. 562

HAPLOID (n) GENERATION DIPLOID (2n) GENERATION Mature haploid thallus Haploid thallus produces two types of gametes by mitosis. Sporangium 2 1 Haploid zoospore Gamete type A Haploid zoospore grows into haploid thallus. Gamete type B 6 Haploid zoospores are produced by meiosis. SEXUAL REPRODUCTION HAPLOID (n) GENERATION Gametes fuse and their nuclei fuse, producing flagellate zygote. Resting sporangium 3 DIPLOID (2n) GENERATION Plasmogamy and karyogamy Meiosis 5 Resting sporangium Motile zygote Meiosis occurs in resting sporangia. Figure 26.7: Life cycle of Allomyces arbuscula, a chytrid. Allomyces alternates between haploid and diploid stages, which are similar in appearance. Zoosporangium 4 Zygote germinates and develops into diploid thallus. Zoosporangia produce flagellate diploid zoospores by mitosis. Zoospores give rise to new diploid thalli. ASEXUAL REPRODUCTION (by mitosis) 7 Diploid zoospore Fig. 26-7b, p. 562

Zygomycetes 1 Rhizopus (black bread mold) Asexual spores germinate forms haploid thallus produces asexual spores and sexual spores Asexual spores germinate form new thalli

Zygomycetes 2 In sexual reproduction Plasmogamy occurs hyphae of 2 different haploid mating types form gametangia Plasmogamy occurs as gametangia fuse

Zygomycetes 3 Karyogamy occurs Meiosis diploid zygote forms from which zygospore develops Meiosis produces recombinant haploid zygospores

Zygomycetes 4 When zygospores germinate Spores are released each hypha develops a sporangium at its tip Spores are released develop into new hyphae

Zygomycete Life Cycle

Common flagellate ancestor Glomeromycetes Basidiomycetes Zygomycetes Ascomycetes Chytrids Figure 26.9: Life cycle of the black bread mold (Rhizopus stolonifer), a zygomycete. Common flagellate ancestor Fig. 26-9a, p. 564

Figure 26.9: Life cycle of the black bread mold (Rhizopus stolonifer), a zygomycete. Fig. 26-9b, p. 564

Insert “Zygomycete life cycle” rhizopus_life_cycle.swf

Microsporidia Microsporidia (now zygomycetes) are opportunistic pathogens penetrate and infect animal cells with long, threadlike polar tubes

Infection by Microsporidium

Spore of microsporidium has coiled Microsporidian cell Polar tube Host cell Figure 26.10: Infection by microsporidium. 1 Spore of microsporidium has coiled polar tube. 2 Spore ejects its polar tube and penetrates host cell. 3 Infective cytoplasm is injected into host cell. Fig. 26-10, p. 565

1. Spore of microsporidium has coiled Microsporidian cell Polar tube 1. Spore of microsporidium has coiled polar tube. 2. Spore ejects its polar tube and penetrates host cell. 3. Infective cytoplasm is injected into host cell. Host cell Figure 26.10: Infection by microsporidium. Stepped Art Fig. 26-10, p. 565

Glomeromycetes 1 Phylum Glomeromycota Endomycorrhizal fungi symbionts that form intracellular associations (mycorrhizae) with plant roots Endomycorrhizal fungi extend hyphae into root cells

Glomeromycetes 2 Arbuscular mycorrhizae Glomeromycetes most common endomycorrhizae hyphae inside root cells form branched, tree-shaped structures (arbuscules) Glomeromycetes have coenocytic hyphae reproduce asexually with large, multinucleate spores (blastospores)

Arbuscular Mycorrhizae

Cells of root cortex Root epidermis Soil Vesicle Root hair Arbuscule Spore Figure 26.11: Arbuscular mycorrhizae. This mycelium has grown into the root. Its hyphae branch between the cells of the root. Hyphae have penetrated through the cell walls of two root cells and have branched extensively to form arbuscules. The tip of one hypha between root cells has enlarged and serves as a vesicle that stores food. The tip of a hypha in the soil has enlarged, forming a spore. The spaces between the root cells have been magnified. Cortex cell Hyphae of fungus Fig. 26-11, p. 565

Ascomycetes 1 Produce asexual spores (conidia) Produce sexual spores (ascospores) in asci Asci line a fruiting body (ascocarp)

Conidia Ascocarp Asci

Ascomycetes 2 Haploid mycelia of opposite mating types produce septate hyphae Plasmogamy occurs, nuclei exchanged Dikaryotic n + n stage occurs hyphae form, produce asci and ascocarp

Ascomycetes 3 Karyogamy occurs Recombinant nuclei divide by mitosis followed by meiosis Recombinant nuclei divide by mitosis produce 8 haploid nuclei that develop into ascospores When ascospores germinate can form new mycelia

Ascomycetes 4 Ascomycetes include Some ascomycetes form mycorrhizae yeasts cup fungi morels truffles pink, brown, and blue-green molds Some ascomycetes form mycorrhizae others form lichens

Ascomycete Life Cycle

Common flagellate ancestor Glomeromycetes Basidiomycetes Zygomycetes Ascomycetes Chytrids Figure 26.13: Life cycle of a typical ascomycete. Sexual reproduction requires haploid mycelia of different mating types. Note the dikaryotic stage and the separation of plasmogamy and karyogamy. Steps ●5 – ●8 take place within an ascus in the ascocarp. Common flagellate ancestor Fig. 26-13a, p. 567

ASEXUAL REPRODUCTION (by conidia) 10 Germinating conidium In asexual reproduction, hyphae produce haploid conidia that can develop into new mycelia. ASEXUAL REPRODUCTION (by conidia) Haploid (n) Conidiophore When released, ascospores germinate and form new haploid mycelia. 9 (+) mating type Haploid mycelia of opposite mating types both produce coenocytic sexual hyphae. 1 (–) mating type 2 Plasmogamy 8 Plasmogamy occurs as hyphae of the two mating types fuse and nuclei are exchanged. Nuclei migrate Each nucleus becomes incorporated into an ascospore. SEXUAL REPRODUCTION 3 HAPLOID ( n ) STAGE Dikaryotic hyphae form and produce asci. Mitosis produces eight haploid nuclei. DIKARYOTIC STAGE (n + n) 7 Mature ascus has eight haploid ascospores Hyphae form an ascocarp. First meiotic division 4 DIPLOID (2n) STAGE Figure 26.13: Life cycle of a typical ascomycete. Sexual reproduction requires haploid mycelia of different mating types. Note the dikaryotic stage and the separation of plasmogamy and karyogamy. Steps ●5 – ●8 take place within an ascus in the ascocarp. Developing ascus with n + n nuclei Second meiotic division Nuclei fuse Zygote Meiosis Ascocarp 6 Meiosis occurs, forming four haploid nuclei. Karyogamy 5 Mycelium Karyogamy occurs in each ascus. Two haploid nuclei fuse, forming a diploid zygote nucleus. Fig. 26-13b, p. 567

Insert “Sac fungi” sac_fungi_m.swf

Basidiomycetes 1 Produce sexual spores (basidiospores) Basidia develop on outside of basidium Basidia develop on surface of gills in mushrooms a type of basidiocarp (fruiting body) Hyphae in this phylum have septa

Basidiomycete Fruiting Bodies

Basidiomycetes 2 Plasmogamy occurs Dikaryotic secondary mycelium forms fusion of 2 hyphae of different mating types Dikaryotic secondary mycelium forms Basidiocarp develops basidia form

Basidiomycetes 3 Karyogamy occurs Meiosis produces 4 haploid nuclei producing diploid zygote nucleus Meiosis produces 4 haploid nuclei become basidiospores When basidiospores germinate form haploid primary mycelia

Basidium with Basidiospores

Basidiospore Basidium 5 µm Fig. 26-16, p. 570 Figure 26.16: SEM of a basidium. Each basidium produces four basidiospores. 5 µm Fig. 26-16, p. 570

Basidiomycetes 4 Basidiomycetes include mushrooms puffballs bracket fungi rusts smuts

Basidiomycete Life Cycle

Basidiospore Basidium 5 µm Fig. 26-16, p. 570 Figure 26.16: SEM of a basidium. Each basidium produces four basidiospores. 5 µm Fig. 26-16, p. 570

Insert “Club fungus life cycle” club_fungus_life_v2.swf

Explore fungus life cycles by clicking on the figures in ThomsonNOW.

KEY CONCEPTS According to current hypotheses, fungi evolved from a unicellular, flagellate protist and diverged into five main groups

Learning Objective 7 What is the ecological significance of fungi as decomposers?

Decomposers Most fungi are decomposers break down organic compounds dead organisms, leaves, garbage, wastes into simpler nutrients that can be recycled

Learning Objective 8 What is the important ecological role of mycorrhizae?

Mycorrhizae 1 Mutualistic relationships between fungi and roots of plants Fungus supplies water and nutrient minerals to plant Plant secretes organic compounds needed by fungus

Mycorrhizae 2 Glomeromycetes form endomycorrhizal associations with roots Ascomycetes and basidiomycetes form ectomycorrhizae with tree roots do not penetrate root cells

Mycorrhizal Associations

Learning Objective 9 What is the unique nature of a lichen?

Lichen Symbiotic combination of fungus and photoautotroph (alga or cyanobacterium) Photoautotroph provides fungus with organic compounds, shelter, water, minerals Lichens have 3 main growth forms: crustose, foliose, fruticose

Lichens

Fungal hyphae interwoven with photoautotroph Soredia Surface layer (fungal hyphae) Fungal hyphae interwoven with photoautotroph Figure 26.20: Lichens. Loosely woven hyphae Bottom layer (fungal hyphae) Rock or other surface to which lichen is attached Fig. 26-20a, p. 573

Fruticose liche (Ramalina) Crustose lichens (Bacidia, Lecanora) Figure 26.20: Lichens. Foliose lichen (Parmelia) Fig. 26-20b, p. 573

Insert “Lichens” lichens.swf

Learn more about lichens by clicking on the figure in ThomsonNOW.

Learning Objective 10 How do fungi impact humans economically?

Useful Fungi Fungi are used as foods (mushrooms, morels, truffles) in production of beer, wine, bread (yeasts) to produce cheeses and soy sauce to make citric acid and other industrial chemicals

Edible Ascomycetes

Learning Objective 11 What is the importance of fungi to biology and medicine? How do fungi infect plants and humans? Identify at least three fungal plant diseases and three fungal animal diseases

Research Fungi are model organisms for molecular biology and genetics yeast Saccharomyces cerevisiae other fungi Biological control of insects such as mosquitoes that transmit malaria

Medications Fungi are used to make medications penicillin, other antibiotics

Pathogens Fungi are opportunistic pathogens in humans ringworm athlete’s foot candidiasis histoplasmosis

Toxins Some fungi produce mycotoxins such as aflatoxins cause liver damage and cancer

Fungal Plant Diseases Fungal hyphae infect plants through stomata hyphal branches (haustoria) penetrate plant cells obtain nourishment from cytoplasm Include wheat rust Dutch elm disease chestnut blight

Fungal Infection of Plants

Spore Hypha Epidermis Stoma Airspace Leaf Haustoria Fig. 26-23, p. 576 Figure 26.23: How a fungus parasitizes a plant. In this example, the hypha enters the leaf through a stoma. The hypha grows, branching extensively through the internal air spaces, and penetrates plant cells with specialized hyphal extensions called haustoria. Haustoria Fig. 26-23, p. 576

Fungal Plant Diseases

KEY CONCEPTS Fungi are of major ecological, economic, biological, and medical importance