Lecture 6

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Transcript Lecture 6

Fall 2008
Lecture 6
Tuesday October 7
Chapter 14, Fungi (part II)
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
• “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)
• 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
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
• 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
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
www.sasionline.org/ attafldtrp/Atta0.html
www2.thu.edu.tw/~biodiver/ variety/fungus/3-29.htm
Left, Termitomyces; above, the fungus
garden of an attine ant colony
Fungal Predators of Bacteria
Photo: G.L. Barron