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Fungus-like protists Fungi and animals share a common

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Presentation on theme: "Fungus-like protists Fungi and animals share a common"— Presentation transcript:

1 Fungus-like protists Fungi and animals share a common
ancestor with amoebozoans (amoebae + slime molds)

2 Fungus-like protists 1) Plasmodial slime molds (Physarum, below)
2) Cellular slime molds Dictyostelium…

3 Plasmodial slime mold life cycle
spores hatch into 2 haploid forms that switch back + forth, fuse to form a zygote

4 Cellular slime mold life cycle
2 cells may fuse into a “giant cell” (2N) that eats other amoebae as it grows thousands of unrelated haploid cells aggregate to form a single “slug” fruiting body forms; some cells become non- reproductive stalk

5 Fungi Heterotrophic decomposers - feed by absorbing nutrients
Single-celled (yeasts) or multicellular May be free-living, parasitic, or mutualists (= symbionts) Bodies composed of threadlike structures called hyphae Cell walls contain chitin

6 Key Terms: Symbiosis – two organisms (or species) living in close association (e.g. mycorrhizae) mutualism – both benefit parasitism – parasite benefits, host suffers commensalism – one benefits, the other is unaffected Endosymbiosis – one organism living inside another (host) Examples: Plastids, mitochondria evolved through endosymbiosis Rhizobium bacteria living in root nodules – fix nitrogen Lichens – algal symbionts within a fungal host

7 Heterotrophs – ingest or absorb an external source of
organic carbon (molecules with CH’s) - Fungi are heterotrophs that absorb organic carbon from their surroundings Decomposers (saprobes) – break down complex organic molecules into simpler organic molecules - Fungi and bacteria are important decomposers, recycling carbon and other nutrients Biogeochemistry – the (re-)cycling of key elements O, C, N, P, S

8 Basic fungal structure: hyphae and mycelia (singular: mycelium)
Hyphae release digestive exo-enzymes into their surrounding Hyphae form a web called the mycelium that greatly increases surface area, maximizing uptake of dissolved nutrients from the substrate (= whatever the fungus is growing on)

9 Hyphae release digestive exoenzymes
into their surrounding - break down organic matter into small molecules that can be absorbed Produce enzyme that can break down.. 1- lignin, a complex polymer that makes wood tough 2- cellulose, a polymer of glucose (sugar) that animals can’t break down (hence why termites + cows need gut symbionts)

10 Fungi grow by extending
the tips of their hyphae through cytoplasmic streaming Hyphae can be divided into individual cells by partitions called septa Some fungi grow by repeated mitotic divisions of nuclei without cell division coenocytic condition - giant multi-nucleated cells, similar to slime molds

11 Some fungi form mutualistic
or parasitic associations with plants Use special hyphae called haustoria to penetrate cell wall of plants - push into cell surrounded by plant plasma membrane

12 Fungal Life Cycle Fungi spread by producing huge #’s of spores
- structures that resist harsh environmental conditions - can disperse long distances by wind Produced during both sexual and asexual phases of life cycle

13 Stage 1: Plasmogamy Most hyphae contain haploid nuclei N+N
2 hyphae of different mating types can grow together + fuse = plasmogamy N+N 2N N

14 Stage 2: Karyogamy N+N 2N N Eventually, 2 haploid nuclei from
different parents fuse into diploid nuclei Zygote quickly undergoes meiosis, producing haploid spores N+N 2N N

15 N+N 2N Heterokaryotic stage = separate haploid nuclei from different
parents, in the same hyphae Karyogamy = the 2 haploid nuclei fuse into 1 diploid nucleus (like syngamy) N+N 2N

16 Fungal Evolution Fungi evolved from an ancestor that was
an aquatic protist with a flagellum (like sperm cells of animals) Molecular evidence indicates this ancestor was also single-celled - thus, animals & fungi independently evolved multicellularity - only primitive fungi have flagellated spores

17 new phylogeny indicates flagellae were lost often phylogeny assuming
flagellae were lost once Campbell & Reece 2002

18 Chytrids May be single-celled or form multi-cellular hyphae
Only fungi w/ flagellated spores, called zoospores Relationship to Zygomycetes is still controversial Aquatic

19 Chytrids zoospore Branching hyphae increase surface area for uptake of nutrients from surrounding aquatic medium

20 Zygomycetes life cycle
Haploid 1 1) hyphae of opposite mating type fuse to form heterokaryotic (N+N) zoosporangium - contains many haploid nuclei from each parent - resists bad conditions

21 Zygomycetes life cycle
Haploid 1 2) when conditions get better, karyogamy occurs: haploid nuclei fuse into diploid nuclei - zygote then undergoes meiosis, producing genetically diverse spores - regular sporangia form

22 Zygomycetes life cycle
Haploid 1 3) Regular sporangia may form and produce spores by mitosis (asexual reproduction) 3

23 Phylum Zygomycota (Zygomycetes)
Pilobolus sp. – dung fungus Microsporidia - highly modified parasites (Encephalitozoon intestinalis)

24 Phylum Glomeromycota - Glomeromycetes
Formerly put in zygomycetes; now their own phylum Only 160 known species, but ecologically critical Form endomycorrhizae, mutualistic associations inside of plant roots >90% of plants have endomycorrhizae associated with roots Fungal partner takes up minerals like phosphate from soil, transfers them to root tissue of host plant

25 Endomycorrhizae Phylum Glomeromycota - Glomeromycetes
Formerly put in zygomycetes; now their own phylum Only 160 known species, but ecologically critical Endomycorrhizae Hyphae penetrate cell walls, but do not puncture plasma membrane of plant cells Instead, push inside host cell surrounded by plant membrane like fingers in a glove Taiz & Zeiger 2002

26 Phylum Ascomycota (ascomycetes)
“Sac fungi” produce sexual spores in saclike asci

27 Hyphae fuse into N+N heterokaryotic stage Septa form cells with 2
haploid nuclei each - one of these grows into an ascus Developing asci are housed in the ascocarp, the fruiting body that will later eject the spores

28 Hyphae fuse into N+N heterokaryotic stage Septa form cells with 2
haploid nuclei each - one of these grows into an ascus Karyogamy in the ascus combines both parental genomes  meiosis produces 4 haploid cells Each undergoes mitosis  8 haploid ascospores

29 Penicillium sp. – an ascoymycete (formerly called a deuteromycete)
- source of antibiotic penicillin Campbell & Reece 2005

30 Saccharomyces sp. -- “yeast”
Common disease organisms Used by humans to ferment sugar in dough or grains, for baking or production of adult beverages - under anaerobic conditions, metabolize sugar to ethanol and CO2 (makes dough rise) S. cerevisiae is model eukaryotic cell for molecular biologists to study - 1st fully sequenced eukaryotic genome

31 Saccharomyces sp. - “yeast”
Many yeasts have no known sexual stage Yeast cells budding (asexual reproduction)

32 Phylum Basidiomycota - basidiomycetes
includes common mushrooms, toadstools, shelf fungi important decomposers of wood long-lived heterokaryotic stage, giving rise to basidiocarp (“mushroom”) in bad conditions A single mushroom cap produces a billion basidiospores Campbell & Reece 2005

33 Phylum Basidiomycota – sexual stages
heterokaryotic N+N

34 Heterokaryotic mycelium connects mushrooms underground
Basidiocarps of a basidiomycete form a “fairy ring” overnight Heterokaryotic mycelium connects mushrooms underground - expands outward, digesting organic matter in soil

35 Ectomycorrhizae Freeman 2005 Many basidiomycetes form ectomycorrhizae with plant roots - roots are completely covered in a layer of hyphae Exoenzymes release nitrogen from decaying matter  transferred to hyphae extending in between outer-most root cells

36 Self-quiz: Know the 4 different types of reproductive structures
that are characteristic of the different fungal phyla

37 Fungal Symbioses Lichens – fungus & alga mutualism
- Endosymbiont is usually a chlorophyte (green alga) - Fungus is the host Mycorrhizae – fungus & plant root mutualism Endomycorrhizae - glomeromycete symbiont (inner) Ectomycorrhizae - basidiomycete symbiont (outer) Parasitic fungi cause many plants & animal diseases

38 Lichens – mutualism between fungus (Ascomycete) & green alga
3 growth forms of lichens: - Foliose (leaf-like) - Crustose - Fruticose (shrub-like) This relationship evolved 3 separate times

39 Lichens – mutualism between fungus (Ascomycete) & green alga
This relationship evolved 3 separate times Enable plants to eventually grow on what was bare rock by eroding the rock surface, trapping soil Are very sensitive to air pollution, acid rain

40 Ecto-mycorrhizae Endo-mycorrhizae
Taiz & Zeiger 2002


42 Fungi are responsible for many plant diseases;
destroy 10-50% of crops worldwide Eating fungus-infected grains is a severe human health issue in much of the world - contributes to high rate of liver cancer in areas that consume peanut meal, which supports fungi that produce liver toxins Historically, eating ergot-infected grain caused outbreaks of madness and death, once thought to be demon possession - ergot fungus produces lysergic acid, similar to LSD

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