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 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

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

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, 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

10. Septa
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.
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 Chytridiomycota—lack true hyphae
Zygomycota—coenocytic hyphae
Glomeromycota—coenocytic hyphae
Ascomycota—septate hyphae
Simple septa, Woronin bodies
Basidiomycota—septate 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 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. 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

17. “Unikont”—eukaryotic cell with one flagellum
Tree of eukaryotes, showing variation in genome size. From Keeling and Slamovits (2005). Current Opinion in Genetics and Development 15:
“Unikont”—eukaryotic 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

23. Other organelles
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

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 Teleomorph= sexual stage
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

29. Kingdom Fungi Phyla: Chytridiomycota Glomeromycota Zygomycota
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 fungus—including 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 (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:
Plasmogamy (cell fusion)
Karyogamy (nuclear fusion)
Meiosis (reduction division)

33. Fungal life cycles mitosis Life cycle is predominantly haploid (n)
Plasmogamy
n n+n
Karyogamy
n+n n
2n n
Meiosis

35. Fungal life cycles mitosis
Life cycle is predominantly dikaryotic (n + n)
Karyogamy
n + n n
Meiosis
2n n
n n + n
Plasmogamy

36. Fungal life cycles mitosis Life cycle is predominantly diploid (2n)
Meiosis
2n n
Plasmogamy
n n + n
n + n n
Karyogamy