Kingdom Fungi Biology 108 Fall 2024 PDF

Topic 18: Kingdom Fungi BIOL 108 A1 Fall 2024 © 2024 Neil Harris Kingdom Fungi are more closely...

Topic 18: Kingdom Fungi BIOL 108 A1 Fall 2024 © 2024 Neil Harris Kingdom Fungi are more closely Fungi are diverse and widespread. related to Animalia than to Plantae. − ~145,000 described species; est. − Molecular phylogeny places fungi in ~2.2-3.8 million fungal species. the Opisthokonts (Unikonta protist − Fungi play crucial roles in nutrient supergroup), which also includes cycling and decomposition processes, animals. making them indispensable for  Fungi and animals may have a shared ecosystem function. common protist ancestor that was single- − Most fungi are found in soil, where celled and had posterior flagella (opistho = posterior, kont = pole). they decompose organic material. The fruiting body of coral tooth fungus (Hericium coralloides), a wood-decomposing basidiomycete. NH Red Deer, AB 1 Characteristics shared by most fungal taxa BIOL 108 A1 Fall 2024 © 2024 Neil Harris Common structural features: Key functional characteristics: 1. Hyphae and mycelium 3. Absorptive nutrition − Fungi typically grow as long, thread-like − Fungi are absorptive chemoheterotrophs. filaments called hyphae that collectively  Fungi absorb nutrients directly from their form a network, the mycelium, which environment. increases surface area for nutrient  They secrete enzymes that break down absorption. complex organic materials into simpler molecules, which are then absorbed into their 2. Chitinous cell wall cells. − The majority of fungi have cell walls  c.f. animals are phagotrophic made of chitin, a strong, flexible chemoheterotrophs that feed by engulfing food particles and digesting them internally. carbohydrate that provides structural support and protection. 4. Spore production − Fungi reproduce by producing spores, Exceptions to these shared characteristics are which can be generated through asexual observed in early-diverging fungal lineages (mitosis) or sexual (meiosis) reproduction. 2 Fungal absorptive nutrition BIOL 108 A1 Fall 2024 © 2024 Neil Harris Fungi are chemoheterotrophic − Fungi secrete enzymes (exoenzymes) eukaryotes that obtain nutrients by to break down a large variety of complex molecules into smaller absorbing dissolved organic organic compounds (external compounds directly from the digestion). external environment (absorptive  Once broken down into simpler organic heterotrophs). molecules, such as sugars and amino acids, these nutrients are absorbed by the − i.e. utilize organic compounds for fungal body. both carbon and energy.  The versatility of these enzymes contributes to the ecological success of fungi.  Fungi can digest cellulose and lignin from plant tissues, and chitin and keratin from animal tissues. Severe athlete’s foot fungal infection (WC) 3  Fig 31.7 The yeast Saccharomyces cerevisiae in several Fungal body structure stages of budding (SEM) BIOL 108 A1 Fall 2024 © 2024 Neil Harris Fungi are non-motile: they use Most fungi are characterized by growth to find and acquire numerous cylindrical, branched, nutrients in their environment. multicellular filaments (hyphae) that absorb nutrients. − When fungi encounter a food source, their hyphae form a branching filamentous network of hyphae (mycelium), adapted for nutrient absorption. − Not all fungi produce hyphae.  Early-diverging fungal lineages lack hyphae.  Single-celled fungi (yeasts) live in moist, nutrient-rich environments. Yeasts descended from hyphae- forming ancestors; yeasts evolved independently several times Fig 31.2 Structure of a (convergent evolution). multicellular fungus 4  Human hair and Sordaria fimicola hyphae http://hdl.handle.net/10214/6161 Fungal body structure BIOL 108 A1 Fall 2024 © 2024 Neil Harris The multicellular hyphal − The filamentous structure of a morphology enhances fungi's mycelium maximizes its surface area- to-volume ratio, facilitating more ability to absorb nutrients. efficient enzyme secretion and − Hyphae are thin, tubular cells (single- nutrient absorption. cell diameter, 2-10 µm Ø) filled with − Thin hyphae are protected by strong, cytoplasm and organelles. flexible cell walls composed of chitin,  Hyphae grow at their tips, elongating in length, not width. a glucosamine polymer.  Chitin is a nitrogenous polysaccharide, a  Some fungi grow rapidly, adding up to 1 structural component that has evolved km of hyphae per day in some species. independently in some invertebrates. Chitin is a long-chain polymer of N-acetylglucosamine (WC) Microscopic view of Oyster mushroom mycelium a mycelium (WC) growing on coffee grounds (WC) 5 Fungal body structure BIOL 108 A1 Fall 2024 © 2024 Neil Harris Coenocytic fungi: Septate fungi: − The earliest fungal lineages exhibit a − In later evolving groups, nuclear coenocytic (aseptate) structure, divisions are accompanied by the lacking septa or dividing walls within formation of septa (cross-walls) that their hyphae. divide the cytoplasm into separate  The hyphae of coenocytic fungi form a cells. continuous compartment containing  Most fungal species are septate. numerous nuclei but no dividing cell walls.  Pores allow cell-to-cell movement of  Continuous cytoplasmic mass with water/solutes, cytoplasm, and small thousands of nuclei dispersed throughout. organelles. Fig 31.3 Two forms of hyphae  Septate fungi have single nuclei per cell. Coenocytic hyphae Septate hyphae George Barron, www.uoguelph.ca 6 Fungi produce spores through sexual or asexual reproduction BIOL 108 A1 Fall 2024 © 2024 Neil Harris Fungi reproduce and disperse by − Many fungi use sexual and asexual producing vast numbers of spores. reproduction at different stages of their life cycle, while others exclusively rely − Spores can be produced asexually (by on asexual reproduction. mitosis) or sexually (by cell fusion and meiosis). − Fungal mycelia are haploid (1n) that  Fungal spores differ from plant spores: produce haploid (1n) spores that grow plant spores are produced only by to produce hyphae. meiosis; fungal spores are produced by  Spores are the dispersal stage, as they are mitosis and meiosis. resistant to desiccation and can be carried by wind, water, or animals. − During sexual reproduction, many fungi produce spores within multicellular fruiting bodies, specialized organs for spore production and dispersal. Puffball releasing spores (WC) 7 Generalized life cycle of fungi BIOL 108 A1 Fall 2024 © 2024 Neil Harris Fig 13.6 Sexual life The fungal life cycle is similar to cycle of most fungi and some protists haploid-dominant life cycles observed in many eukaryotic organisms. Except fungi have a unique separation of plasmogamy (cell fusion) and karyogamy (nuclear fusion). − Between plasmogamy and karyogamy Asexual spores Haploid (n) is a heterokaryotic stage where (genetically identical) genetically distinct haploid nuclei coexist within a single cell. Fig 31.5 Generalized life cycle of fungi Sexual spores (genetically distinct) 8 Sexual reproduction BIOL 108 A1 Fall 2024 © 2024 Neil Harris Fungal nuclei are haploid (1n), except for transient diploid stages formed during the sexual life cycles. − Hyphae and spores carry haploid nuclei. − Septate hyphae are monokaryotic (single, identical nuclei). − Coenocytic hyphae are homokaryotic (multiple, identical nuclei). 9 Sexual reproduction BIOL 108 A1 Fall 2024 © 2024 Neil Harris Sexual reproduction involves the fusion of hyphae from different mating types. − Fungi use sexual signalling molecules (pheromones) to communicate their mating type. Plasmogamy, the merging of cytoplasm from two parental mycelia, initiates the process. − In most fungi, the haploid nuclei of each parent coexist in the resulting mycelium, termed a heterokaryon, where multiple genetically distinct haploid nuclei cohabit. 10 Sexual reproduction BIOL 108 A1 Fall 2024 © 2024 Neil Harris In septate fungi, haploid nuclei pair off during mitosis to form a dikaryotic mycelium, containing two nuclei per cell. The interval between plasmogamy and karyogamy can vary widely, ranging from hours to centuries. − During karyogamy, haploid nuclei fuse to form a diploid cell (zygote). − The formation of dikaryotic mycelia enables multiple karyogamy events, yielding numerous diploid zygotes. 11 Sexual reproduction BIOL 108 A1 Fall 2024 © 2024 Neil Harris The diploid zygote is short-lived, immediately undergoing meiosis to yield haploid spores. − This separation of plasmogamy and karyogamy ensures mating and spore production occur at optimal times. − Fungi lack diploid multicellular stages.  i.e. fungi do not exhibit alternation of generations. − Karyogamy and meiosis generate genetic diversity within fungal populations. − Fungi do not produce gametes; the zygote arises from the fusion of regular haploid nuclei. 12 Asexual reproduction BIOL 108 A1 Fall 2024 © 2024 Neil Harris Fungi employ various methods for − Asexual spores: moulds (or molds) asexual reproduction: form visible mycelia and generate haploid asexual spores via mitosis − Fragmentation: fragments of hyphae during dispersal. grow into new mycelia. − Many moulds and yeasts have no − Budding: unicellular yeasts reproduce known sexual stage. asexually by budding. Fig 31.6 Penicillium, a mould commonly  Asymmetric mitosis is where a small bud encountered as a decomposer of food cell emerges from the parent cell.  Some fungi can grow both as budding Conidia, asexual yeasts and filamentous mycelia. spore-producing structures Fig 31.7 The yeast Saccharomyces cerevisiae in several stages of budding (SEM) 13  Fig 31.8 Fungi and their close relatives Origin of fungi BIOL 108 A1 Fall 2024 © 2024 Neil Harris Fungi, along with animals and related − Fungi are most closely related to protists form the opisthokonts clade. unicellular nucleariids.  cf. animals are most closely related to − The opisthokont ancestor of fungi was an unicellular choanoflagellates. aquatic, single-celled, flagellated protist.  This suggests that multicellularity evolved Molecular analyses indicate: independently in animals and fungi. − Kingdom Fungi is monophyletic, − Nucleariids are characterized as non- suggesting a common evolutionary flagellated, spherical or flat amoebae, ancestor with radiating filopodia.  Nucleariids are aquatic − Ancestors of both animals and fungi phagotrophs that feed on diverged from a shared opisthokont bacteria and unicellular algae. ancestor ~1 bya. Fig 31.9 Fossil hyphae from the fungus  Unlike plants and animals, the early fossil Tortotubus (440 mya). The central record of fungi is sparse due to the ease filament is surrounded by two partially overlapping filaments (LM). with which fungal bodies degrade and the difficulty in resolving microscopic fungal structures in fossils. 14 Fungi have radiated into a diverse set of lineages BIOL 108 A1 Fall 2024 © 2024 Neil Harris Other than animals, fungi are the most diverse group of eukaryotic organisms. − While ~145k fungal species have been classified, it’s estimated that the actual diversity may be around 2.2-3.8 million species. − Fungi played a crucial role as early colonizers of land, likely forming mutualistic relationships with the earliest plants. Phylogenetic analysis has identified nine major lineages, including: − An early-diverging, basal fungal lineage (clade Opisthosporidia) − Chytrids (phylum Chytridiomycota) [ myco = fungus ] − Zoopagomycetes (phylum Zoopagomycota) − Mucoromycetes (phylum Mucoromycota) − Ascomycetes (phylum Ascomycota) − Basidiomycetes (phylum Basidiomycota) Fig 31.10 Phylogenetic hypothesis for the major clades of extant fungi (dotted lines indicate uncertain evolutionary relationships) 15 Fungal diversity BIOL 108 A1 Fall 2024 © 2024 Neil Harris Unicellular Kingdom Fungi (most unicellular) Coenocytic Septate Septate hyphae Complex, multicellular fruiting bodies 16 Basal fungi lineage Clade Opisthosporidia BIOL 108 A1 Fall 2024 © 2024 Neil Harris Cryptomycetes and Microsporidians form a sister group and are a basal fungal lineage. − More data are needed to resolve the phylogeny of this lineage. Cryptomycetes (phylum Cryptomycota) are found in marine and freshwater communities, as well as soils. − ~30 identified species, but environmental DNA sequencing suggests cryptomycetes are likely diverse. − Cryptomycetes are unicellular, have flagellated spores, and lack chitinous cell walls.  Chitin deposition has only been observed in the spore walls of some cryptomycete species. − Many identified cryptomycetes are parasites of protists and other fungi. Fig 31.11 The cryptomycete Rozella allomycis parasitizing another fungus 17 Basal fungi lineage Clade Opisthosporidia BIOL 108 A1 Fall 2024 © 2024 Neil Harris Microsporidians (phylum Microsporidia) are spore-forming, unicellular parasites. − Microsporidia parasitize animal hosts; most infect insects.  e.g. Nosema ceranae is a parasite of honeybees and may contribute to Colony Collapse Disorder of honeybee colonies (see Figure 30.17).  Microsporidians lack flagellated spores; instead, they produce unique spores that infect host cells via an infection organelle, the polar tube.  Microsporidia can form resistant spores with chitin-rich cell walls, capable of surviving outside their host for several years. Fig 31.12 A spore of the microsporidian Fibrillanosema crangonycis that parasitizes crustaceans (TEM) 18 Chytrids BIOL 108 A1 Fall 2024 © 2024 Neil Harris Chytrids, (phylum Chytridiomycota) are low diversity (~1k species), ubiquitous inhabitants of aquatic ecosystems. − Chytrids predominantly inhabit aquatic or moist environments.  Some species are found in soil, estuaries, or within the digestive tracts of animals. − Most chytrids are unicellular, while others form colonies with hyphae. − Nearly all chytrids have flagellated asexual spores, known as zoospores. − Like other fungi, chytrids have chitin cell walls and utilize external digestion. Fig 31.13 Flagellated chytrid zoospore (TEM) 19 Chytrids BIOL 108 A1 Fall 2024 © 2024 Neil Harris Chytrids have diverse ecological roles: − Many are free-living decomposers. − Certain species are cellulose-digesting mutualists within the WC digestive systems of ruminants like sheep and cattle. − Some chytrids are parasitic, targeting hosts such as plants, animals, or other fungi.  The parasitic chytrid Batrachochytrium dendrobatidis causes severe skin infections in many amphibian species, contributing to the global decline of amphibians. Magnified frog skin infected with chytrid fungus https://tinyurl.com/y6d9pl7g The life cycle of the amphibian chytrid https://www.pnas.org/content/110/23/9193 20 Zoopagomycetes BIOL 108 A1 Fall 2024 © 2024 Neil Harris Zoopagomycetes (phylum Zoopagomycota) are a low diversity (~900 species) group with: − Chitinous cell walls. − Coenocytic (nonseptate) filamentous hyphae that form simple, branched or unbranched bodies. − Reproduce asexually by producing non-flagellated spores. Fig 31.14 A fly covered with hyphae of parasitic zoopagomycete Entomophthora muscae  Basal fungal lineages have flagellated spores that disperse through water.  Zoopagomycetes, along with mucoromycetes, ascomycetes, and basidiomycetes, are terrestrial fungi that have non-flagellated spores, which are dispersed by wind. − During karyogamy (sexual reproduction), zoopagomycetes form diploid zygotes enclosed in a protective covering, the zygosporangium, which can survive unfavourable conditions.  Zygosporangia are the site of karyogamy and then meiosis. − Zoopagomycetes are typically parasites of other fungi, soil microbes, or animals.  Some are commensal (neutral) symbionts of animals. 21 Mucoromycetes BIOL 108 A1 Fall 2024 © 2024 Neil Harris Mucoromycetes (phylum Mucoromycota; ~750 species). − Mucoromycetes include fast-growing decomposers (moulds) of plant tissues, parasites or pathogens of plants, a mutualists (including some mycorrhizae). − The life cycle of black bread mould (Rhizopus stolonifer) is typical of a WC decomposer mucoromycete. Rhizopus sporangia and spores  Asexual sporangia produce haploid spores that are dispersed through the air. − Some mucoromycetes, such as Pilobolus, “aim” and shoot their sporangia toward bright light sources. https://youtu.be/T8OAmcUnm4g Rhizopus fruit rot on strawberry Fig 31.16 Pilobolus aiming its sporangia 22 Mucoromycetes BIOL 108 A1 Fall 2024 © 2024 Neil Harris Mucoromycetes reproduce sexually through the formation of zygosporangia, which form after the fusion of specialized hyphae. − Karyogamy (the fusion of nuclei) and meiosis occur within zygosporangia. − Zygosporangia are resistant to harsh conditions such as freezing and drying, enabling them to survive unfavourable environments. Fig 31.15 The life cycle of the mucoromycete Rhizopus stolonifer (black bread mould) 23 Mucoromycetes BIOL 108 A1 Fall 2024 © 2024 Neil Harris Mucoromycota includes glomeromycetes, a clade of fungi that form mycorrhizae, mutually beneficial symbiotic relationships between fungi and plant roots. − Glomeromycetes play a significant ecological role by establishing arbuscular mycorrhizae (endomycorrhizae) with ~85% of plant species.  Mycorrhizae facilitate the exchange of minerals https://dx.doi.org/10.1038/ncomms1046 Fig 31.4 Fungal mycorrhizae and nutrients, enhancing the overall health and growth of plants.  Specialized hyphae that push into plant root cells branch into tiny treelike arbuscules.  Glomeromycetes reproduce via asexual soil spores; no evidence of sexual reproduction. 24 Dikarya fungi BIOL 108 A1 Fall 2024 © 2024 Neil Harris Fig 31.10 Phylogenetic hypothesis for the major clades of extant fungi (dotted lines indicate uncertain evolutionary relationships) Most fungi belong to the subkingdom Dikarya, which is characterized by the formation of septate hyphae and the development of dikaryotic hyphae after plasmogamy. − ~98% of fungal diversity is found in Dikarya, encompassing a wide array of species including edible mushrooms, yeast strains utilized in bread, beer, and cheese production, significant wood- decaying fungi, as well as various Dikarya pathogens affecting both crops and Septate humans. hyphae Complex, multicellular fruiting bodies 25  Septate hyphae Dikarya fungi Dikarya BIOL 108 A1 Fall 2024 © 2024 Neil Harris Complex, multicellular fruiting bodies Dikarya form two clades: During the heterokaryotic stage, − Ascomycetes and Basidiomycetes. these fungi produce dikaryotic cells  Both are named for the cell structures (n + n) containing two haploid where karyogamy and meiosis occur. nuclei, each contributed by a different parental strain. − Ascomycetes typically exhibit a brief dikaryotic stage, with plasmogamy and karyogamy occurring in relatively rapid succession. − Basidiomycetes often maintain a prolonged dikaryotic phase, where dikaryotic hyphae frequently dominate the mycelium structure. Fig 31.5 Generalized life cycle of fungi 26 Ascomycetes BIOL 108 A1 Fall 2024 © 2024 Neil Harris Ascomycetes (phylum Ascomycota, “sac-fungi”) are the most diverse fungi (~90k species) and are found in a variety of marine, freshwater, and terrestrial habitats. − Range in size from unicellular yeasts to those forming complex, multicellular structures, such as cup fungi, truffles, and morels. NH − Ascomycetes include wood-decaying fungi crucial for False morel in black spruce forest, decomposition, numerous ectomycorrhizal species forming Northwest of Bruderheim Natural Area, AB symbiotic relationships with plants, pathogens affecting both plants and animals, the fungal component of most lichens, and yeasts essential for baking and brewing. Fig 31.17 Ascomycetes (sac fungi) 27 Ascomycetes BIOL 108 A1 Fall 2024 © 2024 Neil Harris Ascomycetes produce sexual spores within sac-like structures called asci, which are contained in specialized fruiting bodies known as ascocarps (carp = fruit). Ascomycetes reproduce asexually via the production of vast quantities of asexual spores termed conidia. − Conidia are not formed within sporangia; instead, conidia are produced at the tips of specialized hyphae called conidiophores. Fig 31.18 The life cycle of Neurospora crassa, an ascomycete 28 Basidiomycetes BIOL 108 A1 Fall 2024 © 2024 Neil Harris Basidiomycetes include a range of familiar fungi, including toadstools, puffballs, shelf fungi, ectomycorrhizae, and the plant pathogens smuts and rusts. Fig 31.19 Basidiomycetes (club fungi) − They play crucial roles as decomposers, particularly in breaking down lignin-rich wood. Typically, the life cycle of basidiomycetes involves a prolonged phase of dikaryotic mycelium, where two different nuclei coexist within the same hyphal compartment. A defining feature of Basidiomycetes is their club-shaped structures called basidia, transient diploid stages in their life cycle (“club fungi”). − Singular: basidium = pedestal 29 Basidiomycetes BIOL 108 A1 Fall 2024 © 2024 Neil Harris Toadstool basidiocarps (WC) In response to environmental cues, Within a short-lived basidiocarp Basidiomycete mycelia undergo (cap), thin vertical sheets of sexual reproduction by generating mycelia called gills are lined with elaborate, multicellular fruiting millions of basidia. bodies known as basidiocarps. − Young basidia start as dikaryotic cells − Basidiocarps include classic (n + n), which undergo karyogamy to mushrooms and toadstools. become diploid (2n) nuclei. − At maturity, diploid basidia undergo meiosis to produce four basidiospores, each containing a Basidium Gills single haploid nucleus. − A single mushroom cap can release up to a billion basidiospores. Basidiospores 30 Basidiomycetes BIOL 108 A1 Fall 2024 © 2024 Neil Harris Fig 31.20 The life cycle of a mushroom-forming basidiomycete 31