25 Kingdom Fungi Lecture Outline

Дата канвертавання19.04.2016
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25 Kingdom Fungi
Lecture Outline

  1. Most fungi have a filamentous body plan

A.Although some fungi are unicellular (yeasts), most are filamentous (molds)

1.Filaments of a fungal body are hyphae, forming an aggregation called a mycelium

2.Hyphae may have cross walls, called septa, separating individual cells or may be coenocytic, lacking cross walls

B.Cytoplasm and even organelles often stream between hyphae via pores in the septa

C.Most have chitinous cell walls

D.The yeast Saccharomyces cerevisiae is a model eukaryotic organism for molecular biologists

1.Its genome has been sequenced

2.6,000 genes encoding proteins have been sequenced

  1. Most fungi reproduce by spores

E.Spores are nonmotile reproductive cells that are dispersed by animals or wind

F.Spores are typically produced on structures that project up into the air, referred to as fruiting bodies

G.Fungi produce spores sexually or asexually

1.In sexual reproduction, hyphae of 2 different mating types come together and fuse, forming a diploid zygote

a)In the ascomycetes and basidiomycetes, the hyphae fuse, but the nuclei do not and remain distinct—the dikaryotic (n+n) condition

b)Hyphae with 1 nuclei per cell are monokaryotic

2.Gametangia are structures where gametes are formed

3.Sporangia are structures where asexual spores are formed

4.Conidiophores are structures where sexual spores (conidia) are formed

  1. Fungi are diverse!

H.Fungi have evolved a variety of spores and fruiting bodies

I.Classically, fungi were divided into taxa based on sexual spores and fruiting bodies, but recently molecular data (DNA and RNA sequences) is providing more information

1.5 phyla are often identified

2.4 true phyla exist; the Deuteromycota (imperfect fungi) contains the fungi that don’t fit into the other phyla

a)Sexual stages are necessary to correctly classify fungi

b)Deutoromycetes have no sexual stages observed to date

J.Chytridiomycetes are the most primitive fungi

1.The members of phylum Chytridiomycota were previously classified as protists as they are similar to water molds

2.Chytrids are the only fungi with flagella, and this is considered to be a primitive character (the remainder of the fungi have lost this character)

3.Chytrids are typically freshwater parasites or decomposers

4.Allomyces is a common genus, but unusual, as it exhibits alternation of generation (common in plants, rare in fungi)

5.In 1998, a chytrid was identified as a pathogen causing some of the amphibian declines dating back to the 1970s in many parts of the world

K.Zygomycetes reproduce sexually by forming zygospores

1.The 3000 members of phylum Zygomycota produce sexual spores, called zygospores

2.Zygomycetes have coenocytic hyphae, and most are decomposers found in the soil; others are parasitic, and some are mycorrhizal

3.Rhizopus stolonifer, the black bread mold, is a common zygomycete

a)The black spots that appear on bread are the sporangia, which hold the asexual spores

b)Sexual reproduction occurs when different mating types grow together

c)Rhizopus is heterothallic; mating can only occur between 2 different mating types (a + strain and a - strain)

d)The diploid zygote is formed within the zygospore, which may remain dormant under adverse conditions (protected by the zygosporangium)

e)Meiosis occurs near germination, and an aerial hypha develops with a sporangium at the tip, which forms haploid spores by mitosis

f)The haploid hypha of the bread mold develops from these spores (may be all +, all -, or a mixture of + and - strains)

L.Ascomycetes reproduce sexually by forming ascospores

1.The approximately 30,000 members of phylum Ascomycota are called sac fungi because their sexual spores are produced in sacs called asci

2.Ascomycete hyphae are septate, but perforate

3.Most yeasts, powdery mildews and many blue-green, pink and brown molds, as well as cup fungi, morels and truffles are ascomycetes

4.Some plant diseases such as Dutch elm disease, chestnut blight, rye ergot, and powdery mildews are caused by ascomycetes

5.Asexual reproduction involves production of conidia produced on conidiophores

6.Some ascomycetes are heterothallic (different mating strains); others are homothallic (self fertile)

a)In sexual reproduction, 2 gametangia grow together and fuse

b)Nuclei from the parent hyphae do not fuse, but the cytoplasm mixes

c)The resulting n + n hyphae form the ascocarp, in which the asci develop

d)The nuclei within the asci fuse forming a diploid nucleus, the zygote

e)The zygote undergoes meiosis and mitosis to form 8 haploid nuclei

f)Each nucleus develops into an ascospore, released when the ascus breaks open, and they are usually wind dispersed

7.Most yeasts are ascomycetes

a)Yeasts primarily reproduce by budding, which is an asexual mode of reproduction

b)In sexual reproduction, a sac of spores is formed, which is functionally an ascus

M.Basidiomycetes (club fungi) reproduce sexually by forming basidiospores

1.Members of phylum Basidiomycota (approximately 25,000 species) include mushrooms, bracket fungi, puff balls, wheat rust, and corn smut

2.Basidiomycetes are called club fungi as their reproductive structures are club-shaped basidia

a)Each basidia is an enlarged hyphal cell, the outer surface of which are 4 basidiospores

3.A basidiospore gives rise to a primary mycelium, which is composed of monokaryotic cells

4.When the hypha of a primary mycelium of 1 mating strain meets the hypha of a different strain, the hyphae fuse, but the nuclei remain distinct

5.The secondary mycelium develops from this dikaryotic cell

6.The secondary mycelium forms buttons, which develop into the fruiting bodies we call mushrooms (basidiocarps)

7.The basidia develop on the gills of the mushroom, forming diploid zygotes

a)The zygotes undergo meiosis forming basiodiospores

8.Asexual reproduction is less common in this group

N.Imperfect fungi are fungi with no known sexual stage

1.Fungi with no known sexual stage are classified in this form phylum, phylum Deuteromycota

a)The form phylum is polyphyletic, but classified together for convenience

b)There are still about 25,000 species of fungi remaining in this grouping

2.Most reproduce with conidia and are closely related to the ascomycetes; others are more closely related to the basidiomycetes

3.If a sexual stage is discovered, mycologists assign it to the appropriate group

4.DNA and RNA sequencing aid in taxonomy as well

  1. Lichens are dual "organisms"

O.Lichens are a symbiosis between a phototroph and a fungus

1.Although each lichen is composed of 2 distinct species, it is assigned a scientific name as well—about 14,000 species have been identified

2.The phototroph is a green alga or a cyanobacterium

3.The fungus is typically an ascomycete, or a basidiomycete in some tropical species

P.When grown separately, the phototroph grows more rapidly, suggesting that the lichen phototroph relationship may be more accurately described as a controlled parasitism of the phototroph, as opposed to a mutualistic relationship (the traditional view)

Q.Lichens are crustose (flat), foliose (flat, with leaf-like lobes), or fruticose (erect or shrub-like)

1.Reindeer moss is a fruticose lichen (not a moss) that serves as food for caribou

R.Lichens tolerate dry and cold climates, but are sensitive to pollution

1.Lichens are often the first organisms to appear in denuded or bare areas such as bare rock or tree bark

a)They are important in forming soil from rock; starting the process where plants may later begin to grow

2.Lichens grow very slowly and are long lived

3.Lichens absorb minerals from the air, rainwater, and the surface they are growing on and cannot excrete many of the elements they absorb, so they are sensitive to toxins such as sulfur dioxide

4.Lichens are very important bioindicators, particularly of air pollution

S.Lichens reproduce asexually by fragmentation in which soredia break off

1.Soredia contain both algal and fungal cells

  1. Fungi are ecologically important

T.As saprotrophs, along with bacteria, fungi are essential in carrying out and speeding decomposition and recycling of organic compounds

U.Parasitic fungi are harmful to the host that they live on or in

V.Mycorrhizae are mutualistic relationships between fungi and the roots of many plants

1.The fungi facilitate the uptake of minerals and water by the roots

2.The roots may supply organic compounds to the fungus

3.Mycorrhizae have been demonstrated to be essential to the growth of some orchids and many pine trees

  1. Fungi are economically and medically important

W.As decomposers, fungal enzymes destroy many grains and other stored goods and building materials, and cause many diseases in animals and plants

X.Fungi provide beverages and food

1.In fermentation, yeast produce ethyl alcohol and carbon dioxide, which are utilized in the production of bread, wine, and beer

2.Fungi are used in the production of cheeses such as Roquefort, Brie, and Camembert

3.Aspergillus is used to produce soy sauce

4.Many basidiomycete (Agaricus brunnescens) and ascomycete fruiting bodies are eaten as "mushrooms"

5.Some mushrooms contain toxins that may be fatal (such as Amanita); others cause hallucinations

Y.Fungi produce useful drugs and chemicals

1.In 1928, Alexander Fleming discovered that bacterial growth was inhibited by molds, which led to the discovery of penicillin from the ascomycete Penicillium notatum

2.Cephalosporin (an antibiotic), cyclosporine (an immunosuppressant after organ transplants), and statins (lower cholesterol) are important drugs derived from fungi

3.Claviceps purpurea infects rye and other cereal plants, forming an ergot, which contains toxins, including lysergic acid

a)Consumption of bread contaminated by ergot causes ergotism, which caused many deaths during the Middle Ages

b)Some of the compounds of ergot are now used to treat migraine headaches and high blood pressure, and to induce labor

Z.Fungi cause many important plant diseases, which commonly spread rapidly and can cause complete crop failure

1.Plants may become infected when hyphae enter through stomata or wounds, or by dissolving away the cuticle with cutinase

2.Parasitic fungi produce specialized hyphae, called haustoria, which penetrate plant cells and absorb nutrients

3.Ascomycetes cause Dutch elm disease, powdery mildews, chestnut blight, and various scabs and rots

4.Basidiomycetes cause smuts and rusts, which have very complicated life cycles, often including more than one host plant

AA.Fungi cause certain animal diseases

1.Superficial infections such as ringworm, athlete’s foot, and candidiasis that infect the skin, hair, or nails are caused by fungi (primarily the imperfect fungi)

2.Histoplasmosis is an example of a systemic fungal infection

3.Persons at high risk for developing fungal infections include HIV infected persons, cancer patients, and those with organ transplants (because of immunosuppression), and normally simply aggravating infections may become extremely serious

4.Some fungi produce mycotoxins

a)Aflatoxins are produced by some species of Aspergillus and are potent carcinogens, often growing on peanut and corn products

b)These may also cause liver damage, as do many of the toxins produced by fungi (e.g. poisonous mushrooms)

5.Fungi contribute to "sick building" syndrome, which may have acute adverse health affects on the occupants

a)Mold spores, fragments of hyphae, and mold products can cause harm by direct skin contact and inhalation

b)This has been linked to decreased immune function and various ailments, ranging from allergic reactions such as sinusitis and dermatitis to very serious medical problems

Research and Discussion Topics

  • It has been suggested that the Salem, Massachusetts witch trials were caused by ergot poisoning of women, who were believed to be "bewitched." Investigate the causes and symptoms of ergotism.

  • Investigate the role of yeast in the production of beer and wine. What are the functions of the various components of beer: hops, malt, yeast, and barley? How is wine made? Explain the difference between champagne and still wine. What does the term residual sugar mean? Why is fine wine aged in wooden casks?

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