Fungal Life
Cycles
Prof. Khaled H. Abu-Elteen
Basic fungal life cycle
1. Zygotic - haploid phase is dominant
fig. 13.5b
Basic fungal life cycle
2. Fertilization doesn’t happen all at once
Plasmogamy - fusion
of cytoplasm
Karyogamy - fusion of
nuclei (gametes)
heterokaryotic
dikaryotic
fig. 31.2
3. Yeast for brewing and baking:
Saccharomyces cerevisiae
B. Zygomycota
1. No dikaryotic growth
2. Both sexual and asexual sporangia
C. Ascomycota - Life cycle
1. Dikaryotic growth
2. Fruiting body: ascocarp
3. Fertile layer with asci
4. Eight ascospores per
ascus (sac)
5. Asexual reproduction
via conidia
D. Basidiomycota - Life cycle
1. Dikaryotic growth
2. Fruiting body: basidiocarp
3. Fertile layer on gills
with basidia (“clubs”)
4. Four spores per
basidium
5. Asexual reproduction
is rare
D. Basidiomycota - structure
2. Fruiting body: basidiocarp
3. Fertile layer on gills
with basidia (“clubs”)
4. Four spores per
basidium
E. Deuteromycota - “fungi imperfecti”
1. Not a true phylum (not a natural group): polyphyletic
2. Fungi with no known sexual reproduction
3. Asexual reproduction by conidia
III. Fungal Mutualisms
Definitions:
Symbiosis - 2 organisms living together in
intimate physical contact
Mutualism - both organisms benefit from the
relationship
Parasitism - one benefits, one loses
Commensalism - one benefits, other not
affected
III. Fungal Mutualisms
Questions:
1. Definition of mutualism vs. symbiosis
2. What fungal and photosynthetic partners are
involved?
3. What is the “currency” of the mutualism? How do the
partners benefit?
4. What is the structure and/or morphology of the
organismal interaction?
5. What is the ecological importance?
FUNGAL LIFE CYCLES
ASEXUAL
HAPLOID
HAPLOID WITH
RESTRICTED DIPLOID
HAPLOID-DIKARYOTIC
DIKARYOTIC
HAPLOID-DIPLOID
DIPLOID
MITOSPORES
Result from mitosis and cell division
No change in nuclear ploidy
Usually produced in great quantities
Resistance to unfavorable
environmental conditions varies
Are important in dispersal
MITOSPORES
motile - zoospores
non-motile - produced from hyphae conidia
non-motile - produced from sporangia sporangiospores
MEIOSPORES
Result from meiosis
Are haploid
Are genetically different from
parent hyphae
May serve as a resistant stage
Are important in dispersal
CHLAMYDOSPORES
Nuclear ploidy same as parent cell
Formed from a vegetative cell or cells
Shape may reflect cell shape
Wall may become thickened and dark in color
Are resistant to unfavorable environmental
conditions
SPORE GERMINATION
DORMANCY
Constitutional (memnospores)
Exogenous (xenospores)
GERMINATION FACTORS
Water
Temperature
Nutrition
pH (4.5-6.5)
Oxygen
GERMINATION PROCESS
Water content increases; spore swells;
enzymes go into solution.
Vacuolation increases.
Endoplasmic reticulum & other organelles
increase
Respiration increases & mitochondria enlarge
and form more cristae.
GERMINATION PROCESS
Vesicles involved in wall synthesis appear.
Lipids disappear as they are used up as an energy
source.
An opening on the spore wall appears or the plug
in a germ pore is removed.
A hyphal tube, called the germ tube, emerges from
the opening or pore.
SPORE FORMATION
Metabolic state - sporulation competence
Initiation factors - 1. nutrition - concentration,
qualitative composition, relative
quantitative composition, sequence of
available nutrients. 2. water. 3. pH. 4.
O2/CO2 ratio. 5. light - quality/quantity. 6.
biological interactions. 7. temperature.
Method of formation.
SPORE CHARACTERISTICS
Low water content.
Large quantities of storage compounds.
Wall structure different from parent hyphae.
Wall differentiation (pitted, warted, spinulose,
gelatinous sheaths, appendages).
All cellular organelles are present except a
vacuole.
General Fungi Life Cycle
Note mostly haploid or
heterokaryotic
Dikaryotic if
“hetero” is 2
haploid
nuclei/cell
Diploid
only
transient
in most
fungal
species
Mitosis
products
Molds
Molds are asexually
reproducing (i.e., sporeforming), filamentous
fungi (i.e., not yeasts)
This is the mold Penicillium from
which the antibiotic penicillin is
isolated
Yeasts are
single-celled
fungi
Yeasts
Yeasts tend to inhabit very
moist habitats, which
includes plant and animal
tissues
Yeasts as a taxon
would be
polyphyletic
Yeasts tend to
grow
asexually (no
spores)
Zygomycete Life Cycle
Ascomycetes: Sac Fungi
Ascomycete form asci,
which are linear sacs
containing eight
ascospores
In many the
ascomycetes the
asci are arrayed into
fruiting bodies called
ascocarps
Asexually
produced
reproductive
cells are called
conidia
Have
extended
dikaryotic
stage
Many ascomycetes are
important plant
saprobes: they
decompose dead plant
material
Asci with Ascospores
Ascomycetes: Sac Fungi
These are not
mushrooms!!!
They are
ascocarps
Ascomycete Life Cycle
Basidiomycetes: Club Fungi
Both
mushrooms
and shelf fungi
are club fungi
Club fungi are not
limited to just
mushrooms and
shelf fungi, however
Best lignin
decomposers of
all fungi
Basidiocarps
produce
basidiospores
Like sac fungi,
have a longlived dikaryotic
stage
Basidiocarps
Mushrooms,
etc., are
basidiocarps
“By concentrating
growth in the
hyphae of
mushrooms, a
basidiomycete
mycelium can
quickly erect its
fruiting structures
in just a few
hours”
Basidicarps and Basidia
Basidia with basidiospores
Basidiomycete Life Cycle
The End