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Part 2: The Sexual Fungal Life Cycle

1. formation of fruiting body = Dikaryotic hyphae grow and intertwine to form into this 2. In specialized regions of the fruiting body, karyogamy occurs: karyogamy = fusion of many haploid + and - nuclei (fertilization) -- forms many diploid zygotes 3. Zygotes undergo meiosis to produce haploid spores

Part 3: The Sexual Fungal Life Cycle

1. mature, haploid spores are released 2. Each spore grows mitotically into a genetically unique (+ or -) haploid mycelium The most familiar fungi undergo this same life cycle, though the stages vary in appearance in different taxa

- Basidium

= microscopic club shaped structure where zygotes undergo meiosis to become (basidio) spores Each basdium undergoes meiosis to produce 4 basidiospores that are shed from the gills(= pores) on the mushroom cap at maturity

6. Basidiomycota (Club Fungi)

= named after their basidium the most commonly recognized fungi, and the most commonly eaten by humans, for good or ill

- Ascus

= named after their microscopic pouch(sac) where zygotes undergo meiosis to become (asco)spores Each ascus produces 4-8 spores in the linear sac, allowing determination of mitotic chromosomal migrations

Phungal Phyla

Fungal phylogeny is in constant flux as new molecular data reveal artificial taxa in need of repair. currently accepted groups are: -- Microsporidia -- Chytridiomycota -- Zygospore Fungi -- Glomeromycota -- dycaria ---- Ascomycota ---- Basidiomycota (but don't get too attached)

Hyphae

Fungi lack true tissues thallus = fungal body is composed only of hyphae = branching, threadlike structures -- multinucleate strand of cytoplasm surrounded by a tubular cell wall fortified by chitin. -- branch into the fungal substrate (soil) -- During reproduction, hyphae clump together to form fruiting bodies.

Part 1: The Sexual Fungal Life Cycle

Fungi reproduce sexually when conditions are conducive Individuals are of 2 complementary mating types: 1. "+" hyphae or 2. "-" hyphae When + and - hyphae meet chemically under/within the soil plasmogamy occurs: plasmogamy = fusion of haploid hyphae's cytoplasm -- results in hyphae that are dikaryotic = 2 genetically different haploid nuclei ---- some from the + parent ---- some from the - parent

Hyphae: Coenocytic or Septate

Hyphae can be either: coenocytic(aseptate) = primitive form septate = derived form -- split up by septa In most species, hyphae are septate: -- Internal septa divide hypha into compartments -- Septa are ~perpendicular to the cell walls -- Septa are perforated with pores -- Small organelles (ribosomes, mitochondria) can move through pores. -- Each compartment may contain multiple nuclei. -- Nuclei can sometimes move between compartments.

Lichen: Obligate Mutualism

Lichens = a symbiotic association between a fungus and a photoautotroph (algae or cyanobacteria) fungus provides: safe habitat for the photoautotroph photoautotroph provides: photosynthates for the fungus Lichens are -- ubiquitous, but inconspicuous -- able to survive in very harsh (dry, cold) climates -- vital primary producers in harsh environments, such as tundra. -- able to absorb nutrients directly from the atmosphere -- ...so are very sensitive to air pollution Growth form may be -- crustose (encrusting) -- foliose ("leafy") -- fruticose (branching and upright) Lichens are the original source of the compound used to make litmus paper, the old-fashioned way to identify a solution as acidic or basic.

1. Microsporidia (Microsporidians)

Long believed to be apicomplexan protists, was only recently removed from Alveolata -- Molecular data revealed their fungal origins (Or at least status as an outgroup to Fungi) CHARACTERISTICS: They appear to be primitive, lacking -- mitochondria -- Golgi apparatus -- peroxisomes EATING HABIT: obligate, intracellular parasites = infect specific organs and organ systems in both vertebrates and invertebrates VERY diverse: may be more than one million species, but only 1800 have been described and named

sexual reproduction

Part 1: The Sexual Fungal Life Cycle Part 2: The Sexual Fungal Life Cycle Part 3: The Sexual Fungal Life Cycle

BONUS

Q: By definition, an organism that is a decomposer is able to A: break down dead organic matter into its inorganic components

BONUS

Q: The symbiotic relationship between a mycorrhizal fungus and its plant partner is best described as. A: obligate mutualism

BONUS

Q: View the cluster of mushrooms in the photo below. All are sprouting from the same dikaryotic hyphae below the ground. Pick the correct statement. A: The hyphae of each mushroom should contain two genetically different lineages of haploid nuclei in its hyphae. Q: In which part of the mushroom might you expect to find many cells, each of which is genetically different from the others? A: inside sporangia (basidia) on the underside of the cap

3. Zygospore Fungi

Two phyla of fungi, Mucoromycota and Zoopagomycota,were once grouped in "Zygomycota", now defunct CHARACTERISTICS: -- hyphae are coenocytic AND aseptate -- ~1060 species are mostly terrestrial, found in soil, organic detritus, or in plant or animal tissues -- held in zygosporangium -- results from fusion of nuclei -- inside diploid nucli undergo meiosis to create haploid?? daughter cells EATING HABIT: -- Some are parasites of plants or small animals (e.g., insects) -- Others form mutualistic symbioses with plants

fungal reproduction

asexual reproduction sexual reproduction

Haustoria: Parasitic Straws

haustoria = Parasitic fungi have these specialized hyphal extensions (extend from hypha) penetrate the host's cells, creating a nutrient pathway between fungus and host.

Decay Can Be Beautiful: Spalting

spalting = Wood discoloration caused by fungal decay can occur in both dead and live wood Even though spalted wood is lighter and weaker than unspalted wood, its unique colors and patterns make it a rare commodity sought after by -- wood turners -- furniture makers -- makers of musical instruments.

Fungal Forms

A fungal thallus may be either -- compacted into a solid structure -- spread diffusely into the substrate Fungal form can be either: mold = rapidly growing, asexually reproducing hyphae -- forms a solid form yeast = unicellular, usually in liquid or moist environments -- reproduce by budding Some species can alternate between the two forms

Asexual Reproduction

A fungus is haploid for most of its life cycle Fungi can reproduce asexually via: mitosis of single cells budding of single cells hyphal fragmentation asexual spores via mitosis (different among species) -- conidiospores (conidia) -- arthrospores -- chlamyhdospores -- blastospores -- sporangiospores

Fungal Nutrition

All fungi are absorptive heterotrophs = They secrete digestive enzymes onto the nutrient source and absorb the product. -- saprobe = feeds on dead, organic matter -- parasite = feeds on living tissue just like animals its main storage carbohydrate is glycogen Along with bacteria, fungi are the biosphere's most important decomposers.

Two Major Types of Mycorrhizae

Arbuscular Mycorrhizae (AM) -- Fungal hyphae form arbuscules inside root cortex cells -- These serve as water/nutrient bridges between host and symbiont -- Some AM also form storage vesicles -- more common in herbaceous and smaller plants -- formed by fungi in Phylum Glomeromycota Ectomycorrhizae -- Fungal hyphae wrap around cortex cells to form a Hartig Net -- This net serves as a water/nutrient bridge between plant and fungus -- most common in large trees -- formed by fungi in Phyla Ascomycota and Basidiomycota

2. Chytridiomycota (Chytrids)

CHARACTERISTICS: retain primitive characters that help us root fungal phylogenetic trees -- Most are aquatic , suggesting an aquatic origin of the Fungi -- Like all fungi, they have chitin in the cell walls -- One aberrant group of chytrids has cellulose in the cell walls -- only fungi to retain flagellated gametes (zoospores) --- Flagella have been lost in all other fungal species EATING HABIT: -- some are free-living saprobes -- Others are parasites of protists, plants and aquatic invertebrates, and amphibians

5. Ascomycota (Sac Fungi)

Containing about 64,000 species, Ascomycota is the most diverse fungal phylum -- About 75% of all described fungal species are ascomycetes. CHARACTERISTICS: Many have secondarily lost the sexual life cycle, and reproduce only via asexual conidiospores. This group includes many economically important species such as -- Penicillium (source of penicillin) -- Saccharomyces cereviseae (Baker's Yeast) -- Neurospora crassa (widely used as a model organism in genetic research) -- morels and truffles (widely used in fancy cooking) -- Xylaria polymorpha (Dead Man's Fingers; used in spalting hardwoods).

Lignin Decomposition

Decomposition of organic matter is arguably the most vital ecological service provided by fungi A few species of bacteria are able decompose lignin, but bacterial degradation of lignin appears to be uncommon A few species of fungi can break down lignins, and they serve as the primary decomposers of lignin

Fungi: Predator and Prey

Many animals eat fungi -- Rodents can be important spore dispersers for mycorrhizal fungi. -- Many fungi have evolved deadly toxins as protection from fungivores mycotoxins = Toxins produced by fungi Different mycotoxins have different effects: -- neurotoxicity -- nephrotoxicity -- cytotoxicity -- carcinogenicity etc.

Root Symbiosis: Mycorrhizae

Mycorrhizae = are a symbiotic relationship between plant roots and fungi. -- Most water and nutrients are taken up from the soil by mycorrhizae, not by the root hairs fungal partner receives: photosynthetically produced organic nutrients plant partner receives: a vastly expanded underground absorptive network. Mycorrhizae are arguably the most important symbiotic relationship on earth -- Without them, the plant partner cannot thrive -- Without their mycorrhizal fungal partners, plants do not thrive, and have greatly lowered Darwinian fitness

Fungi: Parasites and Parasitoids

Not all fungi wait for you to die before they begin dining. Rainforest ascomycete parasitoids infect arthropods A chytrid fungus, Batrachochytrium dendrobatidis, is responsible for recent worldwide amphibian extinctions Various dermatophytes invade living tissues Respiratory pathogen Histoplasma capsulatum causes histoplasmosis Dutch Elm disease threatens native North American elm trees Some fungal grain crop parasites produce carcinogenic mycotoxins Some Aspergillis produce highly toxic ergots which: - are sclerotia (fungal resting stage) - replace the ovaries of infected grasses - produce highly toxic alkaloids that can cause -- central nervous system damage -- severe smooth muscle spasms -- tissue necrosis -- hallucinations and temporary insanity.

Lignin, Cellulose and Wood Rot

The color of a rotting log can reveal the type of fungi decomposing it Brown Rot Fungi -- more common in cool, wet climates (e.g., Pacific NW rainforest) -- feed mainly upon cellulose, -- cannot fully break down ligin produce rotting wood that: -- is reddish-brown in color (the color of lignin) -- breaks down in large chunks (cellulose network is destroyed) White Rot Fungi -- are more common in warmer climates -- feed upon both cellulose and hemicellulose -- can hydrolyze ligin -- cellulose residues last longer (more abundant) produce rotting wood that: -- is whitish-grey in color (the color of celluloses) -- becomes uniformly spongy as it decays ("dry rot")

The Wonderful World of Fungi

mushroom is only the fruiting body of what can be a vast network of underground filaments largest single organism on earth is a parasitic fungus Fungi are partners in numerous symbiotic interactions Although relatively inconspicuous, fungi are among the most vital components of the biosphere Along with bacteria, they are the only organisms that can decompose organic matter back into its inorganic components.

Fungal Terminology

mycelium (thallus) = WHOLE vegetative body of the fungus hyphae = filaments that comprise the mycelium fruiting body = (usually) above ground reproductive structure -- tightly coiled hyphae sporangium = compartment in which spores are formed spore = haploid(most of the time) propagule may be produced: -- sexually via meiosis -- asexually via mitosis

4. Glomeromycota

the least diverse (~ 230 species) but most abundant and widespread fungal group EATING HABIT: All known species are obligate mutualistic symbionts with plants, forming arbuscular mycorrhizae (AM). Glomeromycete hyphae and spores appear in association with 450 million year old fossil plant roots, indicating that the glomeromycetes are among the most ancient fungi Because glomeromycetes cannot be grown in culture without their plant hosts, study of their nutritional requirements has been challenging.