Introductory Mycology

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Introductory Mycology Cell Structures
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What are fungi?

• Eukaryotic, spore-bearing, heterotrophic
  organisms that produce extracellular enzymes and
  absorb their nutrition.

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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

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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)

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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
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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

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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
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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

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• 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

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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

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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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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
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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
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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

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Nutrition

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

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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
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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

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Fungal Reproduction

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

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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

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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)

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Misc.

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

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Fungal life cycles
mitosis
Life cycle is predominantly haploid (n)
2n n
Meiosis
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Fungal life cycles
mitosis
Life cycle is predominantly dikaryotic (n n)
n n n
Plasmogamy
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Fungal life cycles
mitosis
Life cycle is predominantly diploid (2n)
n n 2n
Karyogamy
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What are fungi?

• Eukaryotic, spore-bearing, heterotrophic
  organisms that produce extracelluar enzymes and
  absorb their nutrition.

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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

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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
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• General characteristics of the Phyla of the
  Kingdom Fungi
• basal lineages
• Zygomycota (1000)
• generally coenocytic mycelium
• production of zygosporangia zygospores
• no sporocarp production

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• 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

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Nomenclature
Amanita muscaria
Kingdom - Fungi Phylum - Basidiomycota Class
- Hymenomycetes Order - Agaricales Family
- Amanitaceae Genus - Amanita Species
- A. muscaria
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• 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).

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Introductory Mycology- Cell Structure