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BIOLOGY 3404FEVOLUTION OF PLANTS
Fall 2008
Lecture 6Tuesday October 7
Chapter 14, Fungi (part II)Symbioses
Fungal Symbioses• With phototrophs: lichens, mycorrhizae, endophytes, disease [remember, symbiosis means living together, not necessarily happily for both partners]
• With animals: human/veterinary diseases, “diseases” (parasitoids) of arthropods, nematodes and microfauna of soil, ant-garden and termite-garden fungi
• With heterotrophic bacteria: endosymbionts, consortia, and predation
Lichens• “Lichenomycota” or “Mycophycomycota”, but are a completely fictitious group
• Lichens have evolved many times in at least 8 orders in 2 classes of Ascomycota (most species are Lecanorales of Lecanoromycetes) and 2 orders in Agaricomycetes of Basidiomycota (a few species in each of Agaricales and Aphyllophorales)
Gargas et al. (1995)
Mycorrhizae• Myco = fungus; rhiza = root; extra r as a linker
• (Usually) Mutualistic symbiosis between fungi and roots or other underground organs of plants
• Apparently identical fungi form associations with leaves and stems of some Bryophyta
• Term mycorrhiza refers to the association or the structure, not to the fungus or the plant
• We will recognize two main types: endo & ecto
Endomycorrhzae (also called Arbuscular Mycorrhizae or
AM; or Vesicular-A M, VAM)• These are formed by Glomeromycota in association
with a great diversity of green plants, predominantly herbaceous, or tropical woody plants
• Fungal hyphae penetrate cell walls (but not plasmalemma) of root cortex
• Within root cells, form shrubby arbuscules for nutrient transfer and sometimes oily vesicles for storage/survival
• Form spores in soil or dead roots – no fruiting bodies
• Particularly important in delivery of Phosphorus
Fossil endomycorrhiza from Triassic (~220 MYA) in Antarctica (when it was warmer there)
Ectomycorrhizae (ECM)
• These are formed by various groups of Basidiomycota (~90% are in Agaricomycetes) and a few Ascomycota, in association with predominantly temperate woody plants: e.g., Pinaceae, Betulaceae, Fagaceae
• Hyphae do not (usually) penetrate cell walls of plant roots, but form a mantle over the root then a network of hyphae between cortex cells called a Hartig Net
• Form large sexual fruiting bodies, above or below ground
• Particularly important in delivery of Nitrogen, but also water, and in protection from root disease
Plant Diseases
• Billions of $ losses worldwide annually
• Take Bio-318b (Mycology) or Bio-418a (Plant-Microbe Interactions)
Diseases of Animals, including Humans
• Many superficial skin disorders, but also major invasive infections of muscle, bone, lungs, and other organs
• Some are opportunistic – taking advantage of patients exposed during surgery, and with weakened immune systems; others are aggressive pathogens
• 2 of the major killers of persons with AIDS are fungal infections – of brain or lungs
• Few courses on Medical Mycology, but see http://www.doctorfungus.org/
Fungus-gardening Ants & Termites
• These two associations arose independently in South America and Africa
• In both, the arthropods harvest organic matter (leaves, twigs, fruits) and “feed” this to the fungus, which converts it to much more nutritious food for their hosts
• Neither partner can live without the other
• Fungus-gardening ants are major agricultural pests in tropical America
Left, Termitomyces; above, the fungus garden of an attine ant colony
www.sasionline.org/ attafldtrp/Atta0.html
www2.thu.edu.tw/~biodiver/ variety/fungus/3-29.htm
Fungal Predators of Bacteria
Photo: G.L. Barron
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