Lecture 4 - University of Toronto Mississauga

Summary from Lecture 3:
Zygomycota (commonly called “zygomycetes”)
Key features of the Zygomycetes:
• Unlike Chytridiomycota
(called “chytrids” or chytridiomycetes)
NO zoospores at any time of life cycle. Lack of flagella
shared with ascomycetes and basidiomycetes.
• Haploid
• Filamentous or yeast vegetative state;
no regular crosswalls in hyphae (aseptate).
• Both sexual and asexual sporangia producing spores.
• Sex by fusion of sex organs (gametangial fusion) to form
zygospore that produces zygosporangium.
Lecture 4
Mushrooms, etc.- Introduction to the Basidiomycetes (Basidiomycota,
Basidiomycotina)
Reading: Text, beginning of Chapter 4, all of Chapter 5 (Lectures 4-8)
Suggested: Anderson JB & Kohn LM. 2007. Dikaryons, dipolids and
evolution. Sex in Fungi: molecular determination and evolutionary
implications. Edited by Heitman J, Casselton L, Taylor JW,& Kronstad J.
Objectives: Understand what a dikaryon is and consider its significance.
Get the basic lifecycle of mushroom-forming fungi in the Basidiomycota
and learn basic mushroom structure.
http://tolweb.org/tree?group=Basidiomycota&contgroup=Fungi
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Phylum Dikaryomycota
Subphylum - Basidiomycotina*
Subphylum - Ascomycotina Dikaryomycotan hyphae average about 5 microns in
width, but in aggregate of course they are very long
(sometimes kilometres per gram of soil).
They are also septate - they have cross-walls called
septa at regular intervals. Septa give the hyphae
some physical rigidity, and limit loss of cytoplasm if
the hyphal wall is ruptured. As a result, we find
that dikaryomycotan fungi can grow in a wider
range of conditions: they can often spread and fruit
in drier situations than zygomycetes could tolerate.
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Spore-producing
surface is called a
2
hymenium
In a dikaryon each cell has 2 nuclei
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Septal ultrastructure has provided useful phylogenetic
characters (all images from your Text):
Picture A shows what you would see if you could crawl inside a hypha and look
toward the septum at the end of a compartment. The septal pore is obvious, and you
can also see the fine fibres of which the cross-wall is made.
Picture B: Cytoplasm and nuclei can move through the septal pores of ascomycetes,
as you can see in this transmission electron micrograph of a short segment of
Neurospora crassa hypha - a nucleus is shown in the act of
squeezing through the pore.
A
B
Picture C shows a
dolipore septum typical of
many Basidiomycetes
C
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All Basidiomycotina (commonly called “basidiomycetes”)
undergo meiosis inside basidia; meiospores (specifically
called basidiospores) are produced outside the basidium
and may be forcibly shot off.
Most (not all) Basidiomycetes with basidia exposed on a hymenium
shoot their basidiospores actively from hymenia that are exposed at
maturity (surface tension catapult) - from Text.
Basidiospores which are to be forcibly discharged
are asymmetrically mounted, i.e. at an angle, on the sterigma.
Just before discharge, a droplet of fluid, enclosed within a membrane, appears at
one side of the spore base, and within seconds, the spore is shot away. HOW?
Mannitol and hexoses are secreted at the base of the spore - forms a hygroscopic
spot on which water condenses from the saturated air surrounding the basidium.
The droplet merges with a film of water on the
surface of the spore, causing a rapid displacement
of the spore's centre of gravity.
This redistribution of mass is opposed by the sterigma, which is under high turgor
pressure. The spore detaches from the sterigma, and shoots away with very high
initial acceleration, though it doesn't go very far.
• About the same mechanism is found in mushrooms, jelly fungi, rust
fungi and some yeasts. It is a strong argument for the monophyly of the
basidiomycetes.
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http://helios.bto.ed.ac.uk/bto/microbes/basidio.htm
If you see clamp
connections you’re looking
at a basidiomycete.
The basidiomycete life cycle is a modified mainly haploid one.
The “modification” is a long period of time between plasmogamy (cell fusion)
and karyogamy in the basidium.
During this period the cells are dikaryotic (1N + 1N) but NOT diploid (2N).
The function of clamp connections in Basidiomycetes
is to organize synchronous mitosis in the 2 nuclei of
each cell in growing dikaryon hyphae:
in Ascomycetes we will see croziers.
Diagram to show the role of clamp connections in maintaining a dikaryon
[From JW Deacon, 1997, Modern Mycology, Blackwell Science]
Smaller diagram shows orientation of the two mitoses (from Eric Swan, see Tree of Life site)
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Basidiospores with asymmetric
attachment to sterigma (power!)
Basidiospores with symmetric
attachment (passive discharge,
e.g. puffballs.)
Ultrastructure of sterigma - basidiospore
attachment.
The Basidiomycetes with single-celled basidia (called Holobasidiomycetes
in your Text) include mushrooms, boletes, shelf fungi and resupinates,
coral fungi, tooth fungi, stinkhorns, bird’s nest fungi, and puffballs:
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In wet weather fungi in the Agaricales (mushrooms usually with
gills) fruit to form lots of mushrooms: look for fairy rings.
Most fairy ring fungi produce only "green" rings and cause no damage to the
grass. For example, this is true of the rings caused by Hygrocybe species,
the fruitbodies of which are waxy and often brightly coloured.
Rings of Hygrocybe fruitbodies and zones of lush grass growth caused by
this fungus.
When fairy rings go bad:
home lawncare tips.
Caps are 3 cm in diam.
Marasmius oreades forms such a thick,
water-repellent mass of hyphae beneath the
soil surface that it prevents water from
penetrating the soil and therefore leads to a
ring of dead turf, with a ring of darker,
lusher grass behind this. M. oreades is known
to produce hydrogen cyanide in laboratory
culture, and HCN also has been detected in
the killing zone of rings
In fact, the simplest way of overcoming the killing action of this
fungus is to water the affected zone of turf with a dilute solution of
a surfactant such as washing-up liquid.
http://helios.bto.ed.ac.uk/bto/microbes/basidio.htm
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When we describe a Basidiomycete:
Cap (pileus):
Diameter,shape, color, texture (e.g viscid),
color and texture of cuticle,
flesh (trama).
Stalk (stipe):
Length/width, shape, texture…
Gills: attachment type, color, shape…
Latex?
Veil: Universal veil? Partial veil?
ring (annulus)?, basal cup (volva)?, patches
Of tissue on surface of cap? Also, Spores…
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Lecture 4
Mushrooms, etc.- Basidiomycotans with one-celled basidia
Reading: Text, beginning of Chapter 4, all of Chapter 5 (Lectures 4-8);
Suggested: Anderson JB & Kohn LM. 2007. Dikaryons, dipolids and
evolution. Sex in Fungi: molecular determination and evolutionary
implications. Edited by Heitman J, Casselton L, Taylor JW,& Kronstad J.
Objectives: Understand what a dikaryon is and consider its significance.
In lecture and lab get the basic lifecycle of mushroom-forming fungi in
the Basidiomycota and learn basic mushroom structure.
http://tolweb.org/tree?group=Basidiomycota&contgroup=Fungi
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