Chapter 31 Fungi

Mighty Mushrooms 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 Figure 31.1

Characteristics of Fungi Fungi are heterotrophs that feed by absorption 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 Fungi exhibit diverse lifestyles Decomposers Parasites Mutualistic symbionts

The morphology of multicellular fungi 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 continuous network of hyphae. Reproductive structure. The mushroom produces tiny cells called spores. Spore-producing structures 20 m Mycelium Figure 31.2

Body Structure Except for yeasts, ALL fungi are multi-cellular and composed of tiny filaments called hyphae. The bodies of multicellular fungi are composed of many hyphae tangled together into a thick mass called a mycelium. The mycelium is well suited to absorb food. The fruiting body is a reproductive structure that develops from a mycelium that grows below the surface of the ground. Most fungi have cell walls made of chitin

Body 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 Septum Nuclei Figure 31.3a, b (a) Septate hypha (b) Coenocytic hypha

(a) Hyphae adapted for trapping and killing prey Body 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 Fungal hypha Plant cell wall Plant cell Plant cell plasma membrane (b) Haustoria Haustorium Figure 31.4a, b

Mycorrhizae Mycorrhizae Are mutually beneficial relationships between fungi and plant roots A symbiotic associations of plant roots and fungi. Fungi increases the surface area of the plants roots. Its presence is often necessary for the growth of many plants.

Fungi produce spores through sexual or asexual life cycles Life Cycles of Fungi Fungi produce spores through sexual or asexual life cycles Fungi propagate themselves By producing vast numbers of spores, either sexually or asexually

The Generalized Life Cycle of Fungi 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 Figure 31.5

Sexual Reproduction in Fungi 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 in Fungi Many fungi that can reproduce asexually Grow as mold, sometimes on fruit, bread, and other foods 2.5 m Figure 31.6

Yeasts Other asexual fungi are yeasts that inhabit moist environments which produce by simple cell division Many molds and yeasts have no known sexual stage Mycologists have traditionally called these deuteromycetes, or imperfect fungi 10 m Parent cell Bud Figure 31.7

Evolution 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

Fungi were among the earliest colonizers of land The Move to Land Fungi were among the earliest colonizers of land Probably as symbionts with early land plants 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

Arbuscular mycorrhizal fungi The Phylogeny of Fungi Chytrids Zygote fungi Arbuscular mycorrhizal fungi Sac fungi Club fungi Chytridiomycota Zygomycota Glomeromycota Ascomycota Basidiomycota Figure 31.9

Classification of Fungi Fungi are classified according to their structure and method of reproduction The 5 main groups of fungi are: Chytridiomycota (spore fungi) Motile spores with flagella Zygomycota (common molds) Bread molds Ascomycota (sac fungi) Club fungi, yeasts Basidiomycota (club fungi) mushrooms Deuteromycota (imperfect fungi) “catch all”, penicillium 17

Chytrids Fungi classified in the phylum Chytridiomycota, or chytrids are found in freshwater and terrestrial habitats Can be saprobic or parasitic Chytrids are unique among fungi in having flagellated spores, called zoospores 25 m 4 m Hyphae Flagellum Figure 31.10

Zygomycota – The Common Molds Zygomycetes are the familiar molds that grown on meat, cheese, and bread. Ex: Rhizopus stolonifer (black bread mold). 3 Types of Hyphae: Stolons: Stem like hyphae - run along top of food source Rhizoids: Root like hyphae – Penetrate & release digestive enzymes, absorb organic matter Sporangiophores : hyphae that push up in air…release spores into the air 19

The Life Cycle of Rhizopus stolonifer Is fairly typical of zygomycetes Mycelia have various mating types (here designated +, with red nuclei, and , with blue nuclei). 1 Neighboring mycelia of different mating types form hyphal extensions called gametangia, each walled off around several haploid nuclei by a septum. 2 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. Figure 31.12

Some zygomycetes, such as Pilobolus Can actually “aim” their sporangia toward conditions associated with good food sources 0.5 mm Figure 31.13

Ascomycota – The Sac Fungi The phylum Ascomycota is named for the ascus, a reproductive structure that contains spores. Ascomycetes are the largest phyum in the kingdom Fungi Some are large and some are microscopic. Examples: cup fungi (large) and yeasts (microscopic). 22

Phylum Ascomycota - Sac Fungi Named for the Ascus (reproductive structure that contains spores) Visible and microscopic Sexual and Asexual Reproduction Conidia – tiny spore; name means “dust” Formed at tips of specialized Hyphae called Conidiophore. In suitable conditions form new haploid organisms. 23

Life Cycle of Neurospora crassa – an Ascomycete 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) Neurospora can reproduce sexually by producing specialized hyphae. Conidia of the opposite mating type fuse to these hyphae. 1 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 Figure 31.17

Phylum Ascomycota - Yeast Yeasts are Unicellular fungi Have ascus and produce ascospores Dry granules are ascospores! Activate in moist conditions Can see asexual reproduction Baking Yeast – called Saccharomyces Means “sugar fungi” use alcohol fermentation to obtain energy Sugar used as food, give off alcohol, CO2 CO2 is why bread rises 25

Sac Fungi - Ascomycota CUP FUNGI (visible to the eye) YEASTS (microscopic) 26

Basidiomycota – The Club Fungi The phylum Basidiomycota gets its name from a specialized reproductive structure (called a basidium) that resembles a club. Includes: Mushrooms Shelf fungi Puffballs Earthstars Jelly fungi Plant rusts Bird’s nest fungi 27

Diversity of Club Fungi PUFFBALL EARTH STAR MUSHROOM SHELF FUNGI BIRD’S NEST FUNGI JELLY FUNGI 28

Phylum Basidiomycota - Club Fungi Reproductive Structure looks like a club Fruiting Body Common Mushrooms Edible, Medicinal, Poisonous Very complex life cycle Mycelium underground grow very large and survive a long time Largest organism in the world is a club fungi 29

Life Cycle Fruiting bodies are the visible mushrooms Produced by vast underground networks of mycelium (bundles of hyphae) when ready to reproduce Gills – part on mushroom which contain Basidia Basidia have 2 nuclei fuse to make 2N zygote cell Zygote undergoes meiosis making Basidiospores which are scattered Mating types (+) and (-) can fuse sexually to make secondary mycelium network 30

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 types undergo 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 Figure 31.20

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 Figure 31.19

Deuteromycota – The Imperfect Fungi Deuteromycota is an extremely varied phylum composed of those fungi that are not placed in other phyla. The term imperfect implies that these fungi do not appear to have sexual reproduction. Ex: Penicillium notatum – the source of antibiotic penicillin. 33

Phylum Deuteromycota - Imperfect Fungi Extremely varied Phylum Grab Bag – whatever does not fit in others NEVER have observed Sexual Life Cycle Reproduce Asexually by Conidia spores Like Ascomycetes Ex: Penicillium notatum Grows on fruit Source of antibiotic penicillin 34

Fungi are heterotrophic decomposers Ecology of Fungi Fungi are heterotrophic decomposers Saprobes – fungi that obtain food by breaking down dead and decaying orgs Can be decomposers – good for nutrient cycle Need this to maintain life! Can be “predators” Some fungi poison and decompose worms which feed on them 35

Ecology of Fungi - Symbiosis Lichens A symbiotic associations between a fungus and a photosynthetic organism. Lichen can grow on dry, bare rock and are often the first organisms to inhabit an area (pioneer species). The lichen break down the bare rock, allowing other plants to grow. Mycorrhizae A symbiotic associations of plant roots and fungi. Fungi increases the surface area of the plants roots. Its presence is often necessary for the growth of many plants. 36

Symbiotic Fungi lichen mycorrhizae 37

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 Figure 31.23a–c

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. Figure 31.21 RESULTS RESULTS

Disease: Some Fungi are Pathogenic Ecology of Fungi Some produce antibiotics – Penicillium makes penicillin (discovered by Alexander Fleming) Disease: Some Fungi are Pathogenic Plant diseases – “Rusts”, Root Rot Animal diseases - Ringworm, Yeast infections, Athlete’s Foot 40

Fungi as Heterotrophs ALL FUNGI ARE HETEROTROPHS – BUT THEY OBTAIN NUTRIENTS IN VARIOUS WAYS: Many are saprobes, organisms that obtain food from decaying organic matter. Some are parasites which harm other organisms. Some are symbionts that live in close and mutually beneficial association with other species. 41

Fungi as Decomposers Fungi are found in every ecosystem, where they recycle nutrients by breaking down the bodies and wastes of other organisms. Without decay, the energy-rich compounds that organisms accumulate during their lifetime would be lost forever. 42

Parasitic fungi cause serious plant and animal diseases: Fungi as Parasites Parasitic fungi cause serious plant and animal diseases: wheat rust mildew on fruit athlete’s foot 43

Fungal Impact on Ecosystems Fungi have a powerful impact on ecosystems and human welfare Fungi are well adapted as decomposers of organic material Performing essential recycling of chemical elements between the living and nonliving world Fungi form symbiotic relationships with Plants, algae, and animals Some fungi share their digestive services with animals Helping break down plant material in the guts of cows and other grazing mammals

(b) Tar spot fungus on maple leaves Pathogens About 30% of known fungal species Are parasites, mostly on or in plants (a) Corn smut on corn (b) Tar spot fungus on maple leaves (c) Ergots on rye Figure 31.25a–c

Practical Uses of Fungi Humans eat many fungi And use others to make cheeses, alcoholic beverages, and bread

Fungi and Antibiotics Antibiotics produced by fungi can be used to treat bacterial infections Staphylococcus Penicillium Zone of inhibited growth Figure 31.26

A Review of Fungal Phyla Table 31.1