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 Hyphae. The mushroom and its subterranean mycelium are a network of hyphae. Reproductive structure. The mushroom produces tiny cells called spores. Spore-producing structures 20 m Mycelium

Structure Fungi consist of Most fungi Mycelia, networks of branched hyphae adapted for absorption Most fungi Have cell walls made of chitin

Structure Some fungi Coenocytic 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 Coenocytic Septum Nuclei (a) Septate hypha (b) Coenocytic hypha

Structure Some unique fungi Have specialized hyphae that allow them to penetrate the tissues of their host Nematode Hyphae 25 m Hyphae adapted for trapping and killing prey Fungal hypha Plant cell wall Plant cell Plant cell plasma membrane Haustorium (b) Haustoria – specialized hyphae that can penetrate the cell walls of plants

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) Key Haploid (n) Heterokaryotic (unfused nuclei from different parents) Diploid (2n) PLASMOGAMY (fusion of cytoplasm) stage KARYOGAMY (fusion of nuclei) SEXUAL REPRODUCTION Spore-producing structures Spores ASEXUAL Zygote Mycelium GERMINATION MEIOSIS The generalized life cycle of fungi

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 2.5 m Penicillium (common saprobe on food) 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 Fungi were among the earliest colonizers of land. -Probably as symbionts with early land plants 50 m Fossil hyphae and spores  

Phylogeny/Classification Fungi have radiated into a diverse set of lineages The phylogeny of fungi 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 Chytrids Zygote fungi Arbuscular mycorrhizal fungi Sac fungi Club fungi Chytridiomycota Zygomycota Glomeromycota Ascomycota Basidiomycota

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 25 m 4 m Hyphae Flagellum

Zygomycetes and other 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 Glomeromycetes, ascomycetes, and basidiomycetes Some chytrids Zygomycetes and other chytrids 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) Neighboring mycelia of different mating types form hyphal extensions called gametangia, each walled off around several haploid nuclei by a septum. 2 Mycelia have various mating types (here designated +, with red nuclei, and , with blue nuclei). 1 Rhizopus growing on bread ASEXUAL REPRODUCTION Mycelium Dispersal and germination MEIOSIS KARYOGAMY PLASMOGAMY Key Haploid (n) Heterokaryotic (n + n) Diploid Sporangium Diploid nuclei Zygosporangium (heterokaryotic) 100 m Young zygosporangium (heterokaryotic) SEXUAL REPRODUCTION Mating type (+) Mating type () Gametangia with haploid nuclei 50 m Sporangia A heterokaryotic zygosporangium forms, containing multiple haploid nuclei from the two parents. 3 The spores germinate and grow into new mycelia. 8 9 Mycelia can also reproduce asexually by forming sporangia that produce genetically identical haploid spores. The sporangium disperses genetically diverse, haploid spores. 7 4 This cell develops a rough, thick-walled coating that can resist dry environments and other harsh conditions for months. 5 When conditions are favourable, karyogamy occurs, followed by meiosis. 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 0.5 mm This decomposer of animal dung bends toward bright light and shoots its sporangia up to 2 meters

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 Are unicellular parasites of animals and protists A taxonomic mystery…Are now classified as zygomycetes (But that could change at any time!) 10 m 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. (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). 10 m

Ascomycetes – Life Cycle The life cycle of Neurospora crassa Neurospora can reproduce sexually by producing specialized hyphae. Conidia of the opposite mating type fuse to these hyphae. 1 Ascomycete mycelia can also reproduce asexually by producing haploid conidia. 7 Dispersal ASEXUAL REPRODUCTION Germination Mycelium Conidiophore Mycelia Asci Eight ascospores Ascocarp Four haploid nuclei MEIOSIS KARYOGAMY PLASMOGAMY SEXUAL REPRODUCTION Diploid nucleus (zygote) Ascogonium Ascus (dikaryotic) Dikaryotic hyphae Mating type () Conidia; mating type () Key Haploid (n) Dikaryotic (n  n) Diploid (2n) A dikaryotic ascus develops. 2 Karyogamy occurs within the ascus, producing a diploid nucleus. 3 The developing asci are contained in an ascocarp. The ascospores are discharged forcibly from the asci through an opening in the ascocarp. Germinating ascospores give rise to new mycelia. 6 5 Each haploid nucleus divides once by mitosis, yielding eight nuclei. Cell walls develop around the nuclei, forming ascospores (LM). The diploid nucleus divides by meiosis, yielding four haploid nuclei. 4

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 (a) Fly agaric (Amanita muscaria), a common species in conifer forests in the northern hemisphere (b) Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat (c) Shelf fungi, important decomposers of wood (d) Puffballs emitting spores

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 A dikaryotic mycelium forms, growing faster then, and ultimately crowding out, the haploid parental mycelia. 2 Two haploid mycelia of different mating typesundergo plasmogamy. 1 PLASMOGAMY Dikaryotic mycelium Basidiocarp (dikaryotic) KARYOGAMY Key MEIOSIS Gills lined with basidia SEXUAL REPRODUCTION Mating type () Mating type () Haploid mycelia Dispersal and germination Basidiospores Basidium with four appendages Basidium containing four haploid nuclei Basidia (dikaryotic) Diploid nuclei Basidiospore 1 m Basidium Haploid (n) Dikaryotic (n  n) Diploid (2n) 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). In a suitable environment, the basidiospores germinate and grow into short-lived haploid mycelia. 8 When mature, the basidiospores are ejected, fall from the cap, and are dispersed by the wind. 7 The basidiocarp gills are lined with terminal dikaryotic cells called basidia. 4 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). 6 Karyogamy in the basidia produces diploid nuclei, which then undergo meiosis. 5

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 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. EXPERIMENT The soybean plant on the left is typical of the experimental group. Its 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. RESULTS RESULTS

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 Algae or cyanobacteria Is most often an ascomycete Algae or cyanobacteria Occupy an inner layer below the lichen surface Ascocarp of fungus Fungal hyphae Algal layer Soredia Algal cell Fungal hyphae 10 m

(b) Tar spot fungus on maple leaves 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

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