Introduction to Kingdom Fungi

1
Introduction to Kingdom Fungi
Pl P 421/521 General Mycology LECTURE 2
2
What is a fungus?

• A eukaryotic, heterotrophic organism devoid of
  chlorophyll that obtains its nutrients by
  absorption, and reproduces by spores.

3
Modes of nutrition

• Fungiabsorptive heterotrophs
• Animalsphagotrophic heterotroph
• Heterotroph (chemo-organotrophs)
• an organism incapable of synthesizing
  carbohydrates from inorganic sources requires
  preformed organic compounds produced by other
  organisms
• Plantsautotrophs

4
Hyphae (singular, hypha)

• Cylindrical, branching filaments composed of a
  tubular cell wall filled with cytoplasm and
  organelles
• Most fungal hyphae are 2-10 ?m diameter

5
http//www.uoguelph.ca/gbarron/MISCELLANEOUS/hair
pen.htm
6
(No Transcript)
7
Fungal cell wall composition

• Structural components
• 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
• Mannoproteins (form matrix throughout wall)

8
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

9
(No Transcript)
10
Septa

• Septaregular 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.
• 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.

11
Kingdom Fungi

• Chytridiomycotalack true hyphae
• Zygomycotacoenocytic hyphae
• Glomeromycotacoenocytic hyphae
• Ascomycotaseptate hyphae
• Simple septa, Woronin bodies
• Basidiomycotaseptate hyphae
• Dolipore septa, parenthesomes

12
Septal pores--Ascomycota

• Woronin bodies

13
Septal pores--Basidiomycota

• Dolipore septa, septal pore caps or parenthosomes

Septal pore cap
14
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)

15
(No Transcript)
16
(No Transcript)
17
Tree of eukaryotes, showing variation in genome
size. From Keeling and Slamovits (2005). Current
Opinion in Genetics and Development 15 601-608
Unikonteukaryotic cell with one flagellum
18
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

19
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

20
Fungal nuclei

• 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
• Spindle pole bodies
• In fungi that lack a flagellated stage in
  lifecycle
• Centrioles
• In fungi and other organisms possessing
  flagellated stage in lifecycle

21
Spindle Pole Body
22
(No Transcript)
23
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

24
Storage Compounds

• Glycogen, lipids and trehalose in fungi and
  animals
• Starch in plants

25
Animal Cell
Plant Cell
26
G. T. Cole. 1986. Microbiol. Rev. 50 95-132
27
Fungal Reproduction

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

28
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

29
Kingdom Fungi

• Phyla
• Chytridiomycota
• Form motile spores called zoospores
• Meiosis occurs in resting sporangium
• Glomeromycota
• Form spores containing hundreds of nuclei no
  known sexual reproduction
• 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

30
Concept of fungal holomorph

• Asexual and sexual reproduction may be separated
  in time and space
• The holomorph is the entire fungusincluding
  asexual and sexual stages if both are formed

31
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)

32
(No Transcript)
33
Fungal life cycles
mitosis
Life cycle is predominantly haploid (n)
2n n
Meiosis
34
(No Transcript)
35
Fungal life cycles
mitosis
Life cycle is predominantly dikaryotic (n n)
n n n
Plasmogamy
36
Fungal life cycles
mitosis
Life cycle is predominantly diploid (2n)
n n 2n
Karyogamy
37
(No Transcript)