Fungi

Basic Information: Fungi are... - eukaryotes - mostly multicellular - sometimes unicellular (yeast) - very diverse with an estimated 1.5 million species - widely spread, having colonized most terrestrial habitats

- Fungi likely evolved from an aquatic, unicellular, flagellated protist 1.5 billion years ago. - All the oldest fungi Evolutionary History: fossils are 460 million years old. Perhaps microscopic fungal ancestors fossilized poorly.

- Systematists recognize Fungi and Anamalia as sister kingdoms - Animals, fungi, and their closest common ancestor are opisthokonts - Most fungal diversity may have come from adaptive radiation with land colonization.

Body Structures: - Hyphae are a network of tiny filaments composed of tubular cell walls. - Mycelia are interwoven hyphae that surround and penetrate nutrient sources. - Hyphae are made of chitin. - Specialized hyphae for penetrating hosts called haustoria.

Body Structures: - Septa are cross walls with pores large enough to allow nuclei through that divide the hyphae into cells. - A fungus with septa is septic and one without is coenocytic. - In coenocytic fungi hyphae are continuous plasma with up to thousands of nuclei.

Reproduction: Asexual - Some fungi (molds) can reproduce with spores, which are carried from the parent by air/water. - Molds grow quickly as mycelia, making spores. - Fungi like yeasts can reproduce by mitosis. - If a fungus has no known sexual stage, it is called a deuteromycete.

Reproduction: Sexual Sporing - Cells are haploid with transient diploid stages. - Begins when hyphae from two different mycelia release pheramones, which bind to receptors. - Hyphae extend toward each other and fuse. - Combining the cytoplasm is called plasmogamy. - Nuclei do not fuse instantly, so the mycelia contain genetically different, coexisting nuclei. - This makes it heterokaryotic. When nuclei pair off two to a cell, it is dikaryotic.

- The amount of time between plasmogamy and karyogamy can be hours or centuries. - In karyogamy, nuclei fuse to form diploid cells, which then go through meiosis. - The mycelia then produce structures that disperse the new spores.

Chytrids (Chytridiomycota) - Live in soil and lakes. - Both saprobes (decomposers) and parsites of protists, plants, and animals. - Unicellular, but occasionally form colonies with hyphae. - Have flagellated spores (zoospores)

Zygomycetes (Zygomycota) - Phylum includes fast growing molds, parasites, and commensal symbionts of animals. - Coenozoic, with the exception of reproductive cells (mostly asexual). - If sexual reproduction occurs, a sturdy structure called zygosporangium is produced. This is a zygote that is multinucleate. - Zygosporangia are resistant to many harsh conditions (i.e. freezing, dry). If conditions become better, they undergo meiosis and germinate.

- Mutualistic relationships between plants and fungi where phosphate ions are exchanged for nutrients are called mycorrhizae. - Ectomycorrhizal fungi surround a root with hyphae and grow into the extracellular spaces of the root cortex. - Endomycorrihizal fungi grow into the cells of the root. Mutualistic Symbionts

- All glomeromycetes take part in a special type of endomycorrhizae called arbuscular mycorrhizae. - Hyphae extend into tiny tree-like structures in the plant called arbuscules. Glomeromycetes (Glomeromycota)

- Some are deadly plant pathogens, many are saprobes, others are mutualistic symbionts, and some are even pesticides. - Defining feature of phylum is sexual spores in saclike asci. - Sexual stages are in fruiting bodies called ascocarps. - Usually reproduce asexually using large numbers of spores called conidia. Ascomycetes (Ascomycota)

- Named for basidium, a cell in which there is a transient diploid stage. - Saprobes, and mostly sexual reproducers. - Exists for long periods of time as a dikaryotic mycelium, until as a result of environmental stimuli, produces fruiting bodies basidiocarps. Basidiomycetes (Basidiomycota)

-Lichens come from symbiotic bonds between fungi and unicellular photosynthetic organisms like green algae or cyanobacteria. - The fungi often reproduce sexually, but lichen can produce asexually as a unit, by either fragmentation or soredia. - Soredia are clusters of hyphae full of algae. Lichens

- Saprobes cycle nutrients. - Many fungi are plant pathogens, but a couple protect plants from insects. - Some fungal ailments effect animals (mycosis) - Many plants could not grow without the mutualistic relationships they share with fungi. Ecological Significance

Picture Citations: Works Cited: Cummings, Benjamin, 7th edition. Campbell Biology. New York: Pearson, "Ecological Roles". Tanelorn. Accessed 11/16/11. Available [Online]