Fungi

Fungal Characteristics: Eukaryotic Multicellular Kingdom Feed by Absorptive Nutrition Tubular cell shape, called Hyphae –Septate or aseptate hyphae Chitin cell walls Store sugar alcohols Divisions determined by sexual reproduction Reproduce by making spores

Nutrition and Habits Saprobes- decomposers – exoenzymes Parasitic fungi- Mutualistic Fungi-

Hyphae Structure Mycelium: whole extensive organism Hyphae- tubular, typical fungal cell –Septate hyphae have internal walls with pores that allow smaller organelles to migrate

Most fungi are multicellular Septate have have incomplete cell wall divisions with pores Coenocytic fungi, or aspetate are multinucleate with free flowing cytoplasm –repeated mitosis without cytokinesis. Hyphae types Septum

Structure of hyphae Nuclei Cell wall Septum Pore (a) Septate hypha(b) Coenocytic hypha Cell wall Nuclei

Hyphae Growth Rapid growth by Cytoplasmic streaming. Mycelia grow in length not girth, with branching Most Fungi are nonmotile Mitosis: Nuclear envelope remains intact with the spindle apparatus inside. Nuclei can migrate –n+n pairs Produce chemicals

Antibiotics Staphylococcus Penicillium Zone of inhibited growth

Anti-fungal drugs Fungi have ergosterol in their membranes for fluidity ( animals have cholesterol) Target for drug activity – binds up and makes membrane porous.

Haustoria in plants modified hyphae that grow into plant cell walls without piercing plasma membrane Allow for nutrient exchange May persist without killing host cell Common in parasitic, and mutualistic fungi like mycorrhizae

Spores of all types !!!! Spore= A haploid cell for dispersal. Grows into a new fungus. Trillions released from a single fruiting body- from a Sporangia Sexual spores are meiospores. Asexual spores are mitospores. May be produced endogenously or exogenously. Carried by wind, water.

Figure 31.5 Generalized life cycle of fungi (layer 1) Key Haploid (n) Heterokaryotic (unfused nuclei from different parents) Diploid (2n) PLASMOGAMY (fusion of cytoplasm) Heterokaryotic stage KARYOGAMY (fusion of nuclei) SEXUAL REPRODUCTION Zygote Mycelium

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

Generalized fungal lifecycle Spore-producing structures Spores ASEXUAL REPRODUCTION GERMINATION Zygote Mycelium GERMINATION MEIOSIS Spore-producing structures Spores Key Haploid (n) Heterokaryotic (unfused nuclei from different parents) Diploid (2n) PLASMOGAMY (fusion of cytoplasm) Heterokaryotic stage KARYOGAMY (fusion of nuclei) SEXUAL REPRODUCTION Zygote Mycelium

General fungal lifecycle 1.Spore germinates, grows into mycelium. 2.Mitospores may be produced 3.Plasmogamy Hyphae of different mating types grow together, exchange nuclei and become n+n (dikaryotic). 4.Dikarytotic state may live for many years. 5.In hyphal tips, karyogamy followed by meiosis. 6.Meiospores are produced

More than 100,000 species of fungi Chytrids are the aquatic ancestral group to the other divisions Divisions by sex Fungal Diversity

Phylogeny of fungi Chytrids Zygote fungi Arbuscular mycorrhizal fungi Sac fungi Club fungi Chytridiomycota Zygomycota Glomeromycota Ascomycota Basidiomycota

Fungal Divisions Chytridyomycota – Aquatic, with flagellated zoospores Zygomycota = zygospores. Resistant zygote sporangium Glomeromycota= zygospores arbuscular mycorrhizae. Ascomycota = ascospores Endogenous meiospores Basidiomycota = basidiospores Exogenous meiospores Deuteromycetes – imperfect, no sexual reproduction

Molds – rapidly growing, asexually reproducing fungi Most also have non-mold sexual stages The mycelia of these fungi grow as saprobes or parasites on a variety of substrates

Yeasts- unicellular fungi growing in liquid substrates Form new cells by budding Some can sexually reproduce, many form asci Some can ferment sugar to alcohol

Mycorrhizae Mutualism of Tree root and fungus. Gives tree water and minerals (desert plants) and fungus gets carbohydrates.

Plant growth without mycorrhizae is often stunted

Mycorrhizae

Pathogenic Fungi Attack plants –Rusts -red spores on multiple hosts –Smuts –yeast like fungi rot plant –Aflatoxins, Ergot –on rye. Attack People – Mycosis –Ringworm, athlete’s foot –San Joaquin Valley Fever –Yeast, lung infections Attack insects, fish, etc.

Figure Examples of fungal diseases of plants (a) Corn smut on corn (b) Tar spot fungus on maple leaves (c) Ergots on rye

Commercial Roles Fermentors: Fungi Are Eukaryotes –Baking and Alcohol formation –Sugar conc. above 5% inhibit aerobic enzymes, switch to fermentation. Biotechnology Decomposers- Nutrient cycles in ecosystems Antibiotics Storage spoilers – –10- 50% of fruit harvest is lost to fungi Cheeses, edible mushrooms, truffles, morels

Lichens Symbiosis of –Phycobiont, algae / cyanobacteria –Mycobiont - fungi. Not individual organisms Primary colonizers of new land in succession, and in tundra areas Soredia asexually reproduce lichen –Fungi often reproduce on their own.

Fig

Three growth forms: 1.Crustose – flat on stones 2.Foliose- leaf-like as in picture 3.Fruticose- upright growing Phycobiont in inner layers protected by fungi on top and bottom

(a) A fruticose (shrub-like) lichen (b) A foliose (leaf-like) lichen (c) Crustose (crust-like) lichens

Chytridiomycota Chytrids use an absorptive mode of nutrition and have chitin cell walls. There are a few unicellular chytrids, but most form ceonocytic hyphae. Chytrids share key enzymes and metabolic pathways with other fungal groups, but not with the slime molds Ancestral to other three groups on land Forms flagellated zoospores

Zygomycetes: Form resistant (Zygote) Zygosporangia Zygosporangia are resistant to freezing and drying. They are also ceonocytic. When conditions improve, the zygosporangia release haploid spores that colonize new substrates. They can make both asexual and sexual spores –Pilobolus, can actually aim their asexual sporangia and shoot them off. Many molds are zygomycetes Have different mating types, often labeled +, - Have ceonocytic hyphae

Zygomycete lifecycle #8 #10

Zygosporangium formation +, - suspensor hyphae grow together. Each tip cuts off a gametangia with complete septa. Gametangia fuse into one large heterokaryont. Nuclei pair up form many diploid nuclei. Resistant wall forms on Zygosporangium Before germination meiosis takes place Forms sporangia, releasing haploid spores

Asexual Spore formation Haploid nuclei migrate to swollen hyphal tip. Hyphal tip forms complete septum, now a sporangium. Each nucleus forms a spore around itself with cytoplasm, endospores. Sporangium wall breaks. Spores blow away.

Glomeromycota Has some characteristics similar to zygomycetes. DNA comparisons show then to be their own group Form Arbscular endomycorrhizae

Arbuscular mycorrhizae 2.5  m Plant cell wall

Mycologists have described over 60,000 species of ascomycetes, or sac fungi. They range in size and complexity from unicellular yeasts to elaborate cup fungi and morels. Ascomycota: Sac fungi produce sexual spores in saclike asci

Ascomycetes are characterized by an extensive heterokaryotic stage during the formation of ascocarps. Fig

Ascus formation Hyphal tip makes complete septum, Nuclei fuse – a single 2n nucleus Meiosis – 4 haploid nuclei One mitotic division – 8 haploid nuclei Each nucleus cuts off some cytoplasm and forms new wall, inside original hyphae wall. 8 ascospores are forcibly ejected by osmotic pressure. Different forms of ascocarp have evolved.

Ascospore formation Zygote Meiosis Mitosis Spore wall N+N

Conidia Many Ascomycetes reproduce asexually by producing enormous numbers of Conidia, asexual spores, (exogenous mitospores) which are usually dispersed by the wind. Conidiophore continuously divides forming more spores at tip.

Basidiomycota Typical Mushroom Almost no asexual reproduction Many mycorrhizae species Oldest organism ? Mushrooms caps have basidia on gills. The spores drop beneath the cap and are blown away.

The life cycle of a Basidiomycete usually includes a long-lived dikaryotic mycelium. Fig

Basidia formation