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Introductory Mycology

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Title: Introductory Mycology


1
Introductory Mycology Cell Structures
2
What are fungi?
  • Eukaryotic, spore-bearing, heterotrophic
    organisms that produce extracellular enzymes and
    absorb their nutrition.

3
Body Plan
  • unicellular (yeast), filamentous, or both
    (dimorphic)
  • Hypha (pl. hyphae) is the basic cellular unit
    in filamentous fungi they may be septate or
    coenocytic (aseptate) collectively a mycelium
  • limited tissue differentiation and division of
    labor
  • somatic reproductive structures
  • plectenchyma all organized fungal tissue,
    somatic reproductive

4
Fungal nuclei
  • 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)

5
Organism bp   genes
Escherichia coli  4,600,000 4288
Saccharomyces cerevisiae 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
humans 3,400,000,000 80,000
6
Fungi as model organisms
  • 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

7
Beadle and Tatum
Using the common bread mold Neurospora crassa, in
1941 developed the classic concept of one gene,
one enzyme Awarded Nobel Prize in 1945
8
Nuclear Status
  • Eukaryotic uni, bi- or multinucleate
  • Haploid, diploid (less frequent)
  • Monokaryon
  • (1 nucleus per hyphal compartment)
  • Dikaryon
  • (2 nuclei per hyphal compartment)
  • Homokaryotic
  • Heterokaryotic

9
  • Mitosis
  • intranuclear nuclear membrane doesn't breakdown
    during mitosis
  • centric in flagellated forms typical centrioles
    of eukaryotes
  • noncentric in nonflagellated forms possess
    spindle pole bodies (SPBs) differ from
    centrioles in lacking microtubular component

10
Organelles
  • typical eukaryote assemblage of organelles
  • fungal specific ones
  • mitochondria
  • endoplasmic reticulum
  • Golgi equivalents
  • single cisternal elements
  • vacuoles
  • microbodies
  • funx in fatty acid degradation,
  • N metabolism

11
Other organelles
  • Mitochondriaflattened or plate-like
    mitochondrial cristae in Fungi (similar to
    animals)
  • Golgi bodiesconsist 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

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14
Cell Wall
Chitin
  • well defined
  • chitin
  • ?1-4 n-acetyal glucosamine
  • ?-glucans
  • polymers of glucose
  • ?1-3 glucose
  • cellulose in some
  • ?1-4 glucose

Cellulose
? 1-3 glucan
chitin
?-glucans
15
Fungal cell wall composition
Structural components chitin microfibrils
ß(1-4)-linked polymer of N-acetylglucosamine chi
tosan in Zygomycota ß(1-4)-linked polymer of
glucosamine ß-linked glucans Gel-like
components Mannoproteins (form matrix throughout
wall
16
Other cell wall components
Antigenic glycoproteins, agglutinans,
adhesionson cell wall surface Melaninsdark
brown to black pigments (confer resistance to
enzyme lysis, confer mechanical strength and
protect cells from UV light, solar radiation and
desiccation) Plasma membranesemi-permeable
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  • fungal specific organelles involved in cell wall
    growth
  • Spitzenkorper or vacuole
  • associated with growing hyphal tips in septate
    fungi
  • chitosome
  • microvesicles transporting chitin synthases to
    growing cell wall

19
Nutrition
  • Heterotrophic
  • Secrete extracellular enzymes
  • Absorptive nutrition
  • Saprobes decay dead organic matter
  • pathogens biotroph, necrotroph
  • symbionts parasites - commensals - mutualists

20
Spores - a minute propagative unit functioning as
a seed, but differing from it in that a spore
does not contain a preformed embryo
Fruiting body - any complex fungal structure that
contains or bears spores a sporocarp
21
Reproduction
  • Sexual reproduction spores meiotically derived
    nuclei
  • Homothallic (selfing)
  • Heterothallic (outcrossing)
  • Genetic mating system
  • MAT loci
  • 1 to hundreds of sexes
  • Asexual reproduction
  • Spores with mitotically derived nuclei

22
Fungal Reproduction
  • Many fungi have the ability to reproduce by
    asexual and sexual means

23
Asexual Reproduction in Fungi
  • Fragmentation hyphae simply break off.
  • Budding small outgrowth of hyphae pinches off
  • Formation of spores
  • Sporangiospores produced in sporangia (sac-like
    structures) located on a sporangiophore.
  • Conidiospores produced at the tips of
    specialized hyphae

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Fungal reproduction
  • Anamorph asexual stage
  • Mitosporespore formed via asexual reproduction
    (mitosis), commonly called a conidium or
    sporangiospore
  • Teleomorph sexual stage
  • Meiosporespore formed via sexual reproduction
    (e.g., resulting from meiosis), type of spore
    varies by phylum

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Kingdom Fungi
  • Phyla
  • Zygomycota
  • Form asexual spores called sporangiospores
  • Meiosis occurs in zygospore
  • Ascomycota (including Deuteromycetes)
  • Form asexual spores called conidia
  • Meiosis occurs in ascus
  • Basidiomycota
  • Meiosis occurs in basidium

28
Fungal life cycles
  • The vegetative thallus predominates in the life
    cycle of a fungus
  • The thallus may be haploid (1n), dikaryotic (nn)
    or diploid (2n) in different groups of fungi
  • Ploidy of thallus is determined by the timing of
    these events in the life cycle
  • Plasmogamy (cell fusion)
  • Karyogamy (nuclear fusion)
  • Meiosis (reduction division)

29
Misc.
  • Life cycle simple to complex wide variety
  • Sporocarps microscopic or macroscopic, limited
    tissue differientiation
  • Habitat ubiquitous
  • Studied by mycologists!!!!!!

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31
Fungal life cycles
mitosis
Life cycle is predominantly haploid (n)
2n n
Meiosis
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33
Fungal life cycles
mitosis
Life cycle is predominantly dikaryotic (n n)
n n n
Plasmogamy
34
Fungal life cycles
mitosis
Life cycle is predominantly diploid (2n)
n n 2n
Karyogamy
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40
What are fungi?
  • Eukaryotic, spore-bearing, heterotrophic
    organisms that produce extracelluar enzymes and
    absorb their nutrition.

41
Fungi vs. "fungi"
  • Based on the phenotypic definitions or traits
    attributed to fungi, fungi do not comprise a
    single monophyletic group of organisms
  • more than one evolutionary origin
  • not all "fungi" are members of the Kingdom Fungi

42
Some characters that separate the the Kingdom
Fungi from protistan fungi
Kingdom Fungi Protistan
fungi mitochondria cristae flattened
cristae
tubular motile cells no motile cells or
motile cells with anterior posterior
flagellum or lateral heterokont flagella
cell wall carbohydrate ?glucans, chitin
?glucans, cellulose lysine
biosynthesis alpha-aminoadepic acid (AAA)
diaminopimelic (DAP) storage compound glycogen
mycolaminarins sterols ergosterol fucostero
l Phyla Chytridiomycota Oomycota (emphasize
d Zygomycota Myxomycota in class) Glomeromycota
Dictyosteliomycota
Basidiomycota Ascomycota
43
  • General characteristics of the Phyla of the
    Kingdom Fungi
  • basal lineages
  • Zygomycota (1000)
  • generally coenocytic mycelium
  • production of zygosporangia zygospores
  • no sporocarp production

44
  • Basidiomycota (22500)
  • septate mycelium
  • clamp connections
  • complex dolipore septa
  • dikaryotic, haploid mycelium
  • production of exospores (basidiospores) on a
    basidium
  • production of complex sporocarps
  • Ascomycota (35000)
  • septate mycelium
  • simple septa
  • monokaryotic, haploid mycelium
  • production of endospores (ascospores)
  • in an ascus
  • production of complex sporocarps
  • often dominant asexual reproduction

45
Nomenclature
Amanita muscaria
Kingdom - Fungi Phylum - Basidiomycota Class
- Hymenomycetes Order - Agaricales Family
- Amanitaceae Genus - Amanita Species
- A. muscaria
46
  • Medically important fungi are in four phyla
  • Ascomycota - Sexual reproduction in a sack called
    an ascus with the production of ascopspores.(
    Aspergillus, Blastomyces dermatidis, Histoplasma
    capsulatus)
  • Basidiomycota -Sexual reproduction in a sack
    called a basidium with the production of
    basidiospores.( Cryptococcus neoformans)
  • Zygomycota - sexual reproduction by gametes and
    asexual reproduction with the formation of
    zygospores.( Rhizopus, Mucor)
  • Deuteromycota(Fungi Imperfecti \Mitosporic Fungi)
    - no recognizable form of sexual reproduction.
    Includes most pathogenic fungi ( Sporothrix,
    Coccidioides immitis, Candida, Pneumocystis).

47
Introductory Mycology- Cell Structure
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