Introduction to Kingdom Fungi
Pl P 421/521 General Mycology
LECTURE 2
What is a fungus?
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A eukaryotic, heterotrophic organism
devoid of chlorophyll that obtains its
nutrients by absorption, and reproduces
by spores.
Modes of nutrition
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Fungi=absorptive heterotrophs
Animals=phagotrophic heterotroph
Heterotroph (chemo-organotrophs):
an organism incapable of synthesizing
carbohydrates from inorganic sources;
requires preformed organic compounds
produced by other organisms

Plants=autotrophs
Hyphae (singular, hypha)
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Cylindrical, branching filaments composed
of a tubular cell wall filled with cytoplasm
and organelles
Most fungal hyphae are 2-10 m diameter
http://www.uoguelph.ca/~gbarron/MISCELLANEOUS/hairpen.htm
Fungal cell wall composition
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Structural components:
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chitin microfibrils [ß(1-4)-linked polymer of
N-acetylglucosamine]
chitosan in Zygomycota [ß(1-4)-linked
polymer of glucosamine]
ß-linked glucans
Gel-like components:
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Mannoproteins (form matrix throughout
wall)
Other cell wall components
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Antigenic glycoproteins, agglutinans,
adhesions—on cell wall surface
Melanins—dark brown to black
pigments (confer resistance to enzyme lysis,
confer mechanical strength and protect cells
from UV light, solar radiation and desiccation)

Plasma membrane—semi-permeable
Septa
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Septa—regular cross-walls formed in hyphae.
Hyphae with septa are septate, those lacking
septa except to delimit reproductive structures
and aging hyphae are called aseptate or
coenocytic.
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primary septa are formed as a process of hyphal
extension and generally have a septal pore, which
allows for cytoplasmic and organelle movement.
Secondary or adventitious septa are imperforate,
formed to wall off ageing parts of the mycelium.
Septal pores--Ascomycota

Woronin bodies
Septal pores--Basidiomycota
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Dolipore septa, septal pore caps or
parenthosomes
Septal pore cap
Fungal nuclei
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1--3 m diam
3--40 chromosomes
Up to 13--40 Mb (million base pairs) DNA
coding for 6,000 to 13,000 genes
Intranuclear division--nuclear envelope
remains intact during mitosis (unlike plants
and animals)
Organism
Escherichia coli
Saccharomyces cerevisiae
# bp
# genes
4,600,000
4288
13,000,000
5885
Caenorhabditis elegans
~100,000,000
~14,000
Arabidopsis thaliana
~120,000,000
~10,000
Drosophila melanogaster
~170,000,000
~12,000
~3,400,000,000
~80,000
humans
Tree of eukaryotes, showing
variation in genome size. From
Keeling and Slamovits (2005).
Current Opinion in Genetics and
Development 15: 601-608
“Unikont”—eukaryotic cell with
one flagellum
Fungi as model organisms
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Small genome relative to other eukaryotes
Many fungal genes are homologous to those in
other eukaryotes
Easy to grow, short life cycles
Haploid genomes amenable to mutation
Sexual stage for analysis of segregation and
recombination of genes; all products of meiosis
can be retrieved in haploid spores
Asexual (clonal) reproduction
Beadle and Tatum

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Using the common
bread mold
Neurospora crassa, in
1941 developed the
classic concept of
“one gene, one
enzyme”
Awarded Nobel Prize
in 1945
Fungal nuclei

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Usually haploid
Nuclear membrane persists during division
Nuclear associated organelles (NAOs):

Associated with the nuclear envelope; function
as microtubule-organizing centers during mitosis
and meiosis
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Spindle pole bodies
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In fungi that lack a flagellated stage in lifecycle
Centrioles
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In fungi and other organisms possessing flagellated stage
in lifecycle
Spindle Pole Body
Other organelles
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Mitochondria—flattened or plate-like
mitochondrial cristae in Fungi (similar to
animals)
Golgi bodies—consist of a single, tubular
cisternal element (stacked, plate-like
cisternae in animals and plants)
Other types:

ribosomes, endoplasmic reticulum, vacuoles, lipid
bodies, glycogen storage particles, microbodies,
microtubules, vesicles
Storage Compounds

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Glycogen, lipids and trehalose in fungi and
animals
Starch in plants
Animal Cell
Plant Cell
G. T. Cole. 1986. Microbiol. Rev. 50: 95-132
Fungal Reproduction

Many fungi have the
ability to reproduce by
asexual and sexual
means
Fungal reproduction

Anamorph= asexual stage
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Mitospore=spore formed via asexual
reproduction (mitosis), commonly called a
conidium or sporangiospore
Teleomorph= sexual stage

Meiospore=spore formed via sexual
reproduction (e.g., resulting from meiosis),
type of spore varies by phylum
Kingdom Fungi
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Phyla:
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Chytridiomycota
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Glomeromycota
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Form asexual spores called sporangiospores
Meiosis occurs in zygospore
Ascomycota (including Deuteromycetes)
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Form spores containing hundreds of nuclei; no known sexual reproduction
Zygomycota
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Form motile spores called zoospores
Meiosis occurs in resting sporangium
Form asexual spores called conidia
Meiosis occurs in ascus
Basidiomycota
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Meiosis occurs in basidium
Concept of fungal holomorph
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Asexual and sexual reproduction may be
separated in time and space
The holomorph is the entire fungus—
including asexual and sexual stages if
both are formed
Fungal life cycles
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The vegetative thallus predominates in the life
cycle of a fungus
The thallus may be haploid (1n), dikaryotic (n+n)
or diploid (2n) in different groups of fungi
Ploidy of thallus is determined by the timing of
these events in the life cycle:
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Plasmogamy (cell fusion)
Karyogamy (nuclear fusion)
Meiosis (reduction division)
Fungal life cycles
mitosis
Life cycle is
predominantly
haploid (n)
2n
Meiosis
n
n+n
Plasmogamy
n
n+n
2n
Karyogamy
Fungal life cycles
mitosis
Life cycle is
predominantly
dikaryotic (n + n)
n
n+n
Plasmogamy
n+n
2n
Karyogamy
2n
n
Meiosis
Fungal life cycles
mitosis
Life cycle is
predominantly
diploid (2n)
n+n
2n
n
Meiosis
2n
Karyogamy
n
n+n
Plasmogamy