introduction to kingdom fungi pl p 421/521 general mycology lecture 2
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Introduction to Kingdom Fungi
Pl P 421/521 General Mycology LECTURE 2
What is a fungus?
A eukaryotic, heterotrophic organism devoid of chlorophyll that obtains its nutrients by absorption, and reproduces by spores.
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
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
http://www.uoguelph.ca/~gbarron/MISCELLANEOUS/hairpen.htm
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)
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
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.
Septal pores--Ascomycota
Woronin bodies
Septal pores--Basidiomycota
Dolipore septa, septal pore caps or parenthosomes
Septal pore cap
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)
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
Tree of eukaryotes, showing variation in genome size. From Keeling and Slamovits (2005). Current Opinion in Genetics and Development 15: 601-608
“Unikont”—eukaryotic cell with one flagellum
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
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
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
Spindle Pole Body
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
Storage Compounds
Glycogen, lipids and trehalose in fungi and animals
Starch in plants
Animal Cell Plant Cell
G. T. Cole. 1986. Microbiol. Rev. 50: 95-132
Fungal Reproduction
Many fungi have the ability to reproduce by asexual and sexual means
Fungal reproduction
Anamorph= asexual 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
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
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
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)
2n n
Fungal life cycles
Plasmogamy
n n+n
Karyogamy
n+n 2n
Life cycle is predominantly haploid (n)
mitosis
Meiosis
n n + n
Fungal life cycles
Karyogamy
n + n 2n
Meiosis
2n n
Life cycle is predominantly dikaryotic (n + n)
mitosis
Plasmogamy
n + n 2n
Fungal life cycles
Meiosis
2n n
Plasmogamy
n n + n
Life cycle is predominantly diploid (2n)
mitosis
Karyogamy
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