Fungi
Fungi Fungi • Fleshy fungi • Yeasts • Molds – Hyphae (long filaments of joined cells) – Mycelium (intertwined mass of hyphae) 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 Mushrooms 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 A General Look at Fungi - Flash Animation Note to self: may need to right chick to get to play or rewind. May need to advance slide using arrows at bottom left. Fungal lifestyles –Decomposers –Parasites –Mutualistic symbionts Body Structure • The morphology of multicellular fungi – Enhances their ability to absorb nutrients from their surroundings Reproductive structure. The mushroom produces tiny cells called spores. Hyphae. The mushroom and its subterranean mycelium are a network of hyphae. Spore-producing structures 20 m Mycelium Structure • Fungi consist of – Mycelia, networks of branched hyphae adapted for absorption • Most fungi – Have cell walls made of chitin Structure • 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 Septate Septum (a) Septate hypha Coenocytic Nuclei (b) Coenocytic hypha Structure • 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 Haustorium (b) Haustoria – specialized hyphae that can penetrate the cell walls of plants Plant cell Plant cell plasma membrane Mycorrhizae – Are mutually beneficial relationships between fungi and plant roots • Ectomycorrhizal fungi (surface) • Endomycorrhizal fungi (penetrate plant cell wall) Reproduction/propagation Fungi produce spores through sexual or asexual life cycles (Some fungi do both, some are either sexual or asexual) • The generalized life cycle of fungi Key Heterokaryotic stage Haploid (n) Heterokaryotic (unfused nuclei from different parents) PLASMOGAMY (fusion of cytoplasm) Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Spores SEXUAL REPRODUCTION ASEXUAL REPRODUCTION Zygote Mycelium MEIOSIS GERMINATION GERMINATION Spore-producing structures Spores 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 • The diploid phase following karyogamy – Is short-lived and undergoes meiosis, producing haploid spores Asexual Reproduction • Many fungi can reproduce asexually • Many fungi that can reproduce asexually – Grow as mold, sometimes on fruit, bread, and other foods Penicillium (common saprobe on food) 2.5 m Conidia (asexual) Asexual Reproduction • Other asexual fungi are yeasts – That inhabit moist environments – Which produce by simple cell division 10 m Parent cell Bud Asexual Reproduction • Many molds and yeasts have no known sexual stage – Mycologists have traditionally called these deuteromycetes, or imperfect fungi Evolution/Origin of Fungi • 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 • 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 Origin of Fungi • The oldest undisputed fossils of fungi are only about 460 million years old 50 m Fossil hyphae and spores • Fungi were among the earliest colonizers of land. -Probably as symbionts with early land plants Arbuscular mycorrhizal fungi Sac fungi Club fungi Ascomycota Basidiomycota Zygomycota – 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 Zygote fungi Chytrids Chytridiomycota • Fungi have radiated into a diverse set of lineages • The phylogeny of fungi Glomeromycota Phylogeny/Classification Phylogeny/Classification Five Phyla of Fungi Chytrids • Fungi classified in the phylum Chytridiomycota, or chytrids – Are found in freshwater and terrestrial habitats – Can be saprobic or parasitic Chytrids • Chytrids are unique among fungi – In having flagellated spores, called zoospores Hyphae 25 m Flagellum 4 m Chytrids • Until recently, systematists thought that – Fungi lost flagella only once in their history • Molecular data – Indicate that some “chytrids” are closely related to another fungal group, the zygomycetes Some chytrids Zygomycetes and other chytrids Glomeromycetes, ascomycetes, and basidiomycetes Key Common ancestor Loss of flagella 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 Zygomycetes - Life Cycle • The life cycle of Rhizopus stolonifer (fairly typical of zygomycetes) 2 Mycelia have various mating types (here designated +, with red nuclei, and , 1 Neighboring mycelia of different mating types form hyphal extensions called gametangia, each walled off around several haploid nuclei by a septum. Key Haploid (n) with blue nuclei). Heterokaryotic (n + n) Diploid 3 PLASMOGAMY Rhizopus growing on bread Mating type (+) Mating type () A heterokaryotic zygosporangium forms, containing multiple haploid nuclei from the two parents. Gametangia with haploid nuclei 100 m 8 The spores Young germinate and zygosporangium grow into new (heterokaryotic) mycelia. SEXUAL REPRODUCTION 9 Mycelia can also reproduce asexually by forming sporangia that produce genetically identical haploid spores. Dispersal and germination Sporangia 7 The sporangium KARYOGAMY disperses genetically diverse, haploid spores. Sporangium ASEXUAL REPRODUCTION Zygosporangium (heterokaryotic) Diploid nuclei MEIOSIS Dispersal and germination 50 m 4 This cell develops a rough, thick-walled coating that can resist dry environments and other harsh conditions for months. Mycelium When conditions are favourable, karyogamy occurs, followed by meiosis. 5 6 The zygosporangium then breaks dormancy, germinating into a short sporangium. Zygomycetes • Some zygomycetes, such as Pilobolus – Can actually “aim” their sporangia toward conditions associated with good food sources This decomposer of animal dung bends toward bright light and shoots its sporangia up to 2 meters 0.5 mm Spore dispersal movie Zygomycetes • Zygosporangia, which are resistant to freezing and drying – Are capable of persisting through unfavorable conditions – Can undergo meiosis when conditions improve Microsporidia • Microsporidia 10 m – Are unicellular parasites of animals and protists – A taxonomic mystery…Are now classified as zygomycetes (But that could change at any time!) Host cell nucleus Developing microsporidian Spore This cell is infected with the parasitic fungus Encephalitozoon intestinalis Glomeromycetes • Fungi assigned to the phylum Glomeromycota – Were once considered zygomycetes – Are now classified in a separate clade Glomeromycetes • All glomeromycetes – Form a distinct type of endomycorrhizae called arbuscular mycorrhizae 2.5 m Picture shows cytoplasm removed to show the arbuscule (branched structure) inside plant cell. 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 – Have asexual reproduction by producing enormous numbers of asexual spores called conidia Ascomycetes • Ascomycetes – Vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels (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 as a mold on bread and other food (SEM). Ascomycetes – Life Cycle • The life cycle of Neurospora crassa Ascomycete mycelia can also reproduce asexually by producing haploid conidia. 7 Conidia; mating type () Neurospora can reproduce sexually by producing specialized 1 hyphae. Conidia of the opposite mating type fuse to these hyphae. Key Haploid (n) Dikaryotic (n n) Diploid (2n) Dispersal Germination ASEXUAL REPRODUCTION Mating type () Mycelium PLASMOGAMY Ascogonium Mycelia Conidiophore The developing asci are contained in an 6 ascocarp. The ascospores are discharged forcibly from the asci through an opening in the ascocarp. Germinating ascospores give rise to new mycelia. 2 A dikaryotic ascus develops. Ascus (dikaryotic) Dikaryotic hyphae SEXUAL REPRODUCTION Germination KARYOGAMY Dispersal Asci Diploid nucleus (zygote) Eight ascospores Four haploid nuclei 3 Karyogamy occurs within the ascus, producing a diploid nucleus. MEIOSIS Ascocarp 5 Each haploid nucleus divides once by mitosis, yielding eight nuclei. Cell walls develop around the nuclei, forming ascospores (LM). 4 The diploid nucleus divides by meiosis, yielding four haploid nuclei. 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 Basidiomycetes (b) Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat (a) Fly agaric (Amanita muscaria), a common species in conifer forests in the northern hemisphere (d) Puffballs emitting spores (c) Shelf fungi, important decomposers of wood Basidiomycetes • 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 Fairy rings can appear overnight. A very large mycelium is growing underneath this ring of fruiting structures Basidiomycetes • The life cycle of a mushroom-forming basidiomycete 2 1 Two haploid mycelia of different mating typesundergo plasmogamy. A dikaryotic mycelium forms, growing faster then, and ultimately crowding out, the haploid parental mycelia. In a suitable the basidiospores germinate and grow into short-lived haploid mycelia. 8environment, 7 3 Environmental cues such as rain or temperature changes induce the dikaryotic mycelium to form compact masses that develop into basidiocarps (mushrooms, in this case). Dikaryotic mycelium PLASMOGAMY Mating type () Mating type () Haploid mycelia SEXUAL REPRODUCTION Gills lined with basidia Basidiocarp (dikaryotic) Dispersal and germination When mature, the basidiospores are ejected, fall from the cap, and are dispersed by the wind. Basidiospores Basidia (dikaryotic) Basidium with four appendages Basidium containing four haploid nuclei Basidium 4 KARYOGAMY MEIOSIS 1 m Basidiospore 6 Each diploid nucleus yields four haploid nuclei. Each basidium grows four appendages, and one haploid nucleus enters each appendage and develops into a basidiospore (SEM). Key Diploid nuclei 5 Karyogamy in the basidia produces diploid nuclei, which then undergo meiosis. Haploid (n) Dikaryotic (n n) Diploid (2n) The basidiocarp gills are lined with terminal dikaryotic cells called basidia. Fungi have a powerful impact on ecosystems and human welfare Decomposers • Fungi are well adapted as decomposers of organic material – Performing essential recycling of chemical elements between the living and nonliving world Symbionts • Fungi form symbiotic relationships with – Plants, algae, and animals Mycorrhizae • Mycorrhizae – Are enormously important in natural ecosystems and agriculture – Increase plant productivity 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 RESULTS RESULTS 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. 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 Many species of ants and termites – Take advantage of the digestive power of fungi by raising them in “farms” Leaf cutter ant movie Lichens • Lichens – Are a symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae (a) A fruticose (shrub-like) lichen (b) A foliose (leaf-like) lichen (c) Crustose (crust-like) lichens Lichen • The fungal component of a lichen – Is most often an ascomycete • Algae or cyanobacteria – Occupy an inner layer below the lichen surface Ascocarp of fungus Soredia Fungal hyphae Algal layer Algal cell 10 m Fungal hyphae Pathogens • About 30% of known fungal species – Are parasites, mostly on or in plants. • Some of the fungi that attack food crops – Are toxic to humans (a) Corn smut on corn (b) Tar spot fungus on maple leaves (c) Ergots on rye Practical Uses of Fungi • Humans eat many fungi – And use others to make cheeses, alcoholic beverages, and bread • Genetic research on fungi – Is leading to applications in biotechnology • Antibiotics produced by fungi-treat bacterial infections Staphylococcus Penicillium Zone of inhibited growth Fungi: Wrap-up video clip The End
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