Lecture 2 Intro to Kingdom Fungi

8/4/2019 Lecture 2 Intro to Kingdom Fungi

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Introduction to Kingdom Fungi

Pl P 421/521 General Mycology

LECTURE 2


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What is a fungus?

A eukaryotic, heterotrophic organism

devoid of chlorophyll that obtains itsnutrients by absorption, and reproducesby spores.


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Modes of nutrition

Fungi=absorptive heterotrophs

Animals=phagotrophic heterotroph

Heterotroph (chemo-organotrophs):an organism incapable of synthesizingcarbohydrates from inorganic sources;requires preformed organic compoundsproduced by other organisms

Plants=autotrophs


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Hyphae (singular, hypha)

Cylindrical, branching filaments composedof a tubular cell wall filled with cytoplasm

and organelles Most fungal hyphae are 2-10 m diameter


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http://www.uoguelph.ca/~gbarron/MISCELLANEOUS/hairpen.htm


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Fungal cell wall composition

Structural components: chitin microfibrils [(1-4)-linked polymer of

N-acetylglucosamine] chitosan in Zygomycota [(1-4)-linked

polymer of glucosamine]

-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 blackpigments (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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Septa

Septaregular cross-walls formed in hyphae.Hyphae with septa are septate, those lackingsepta except to delimit reproductive structures

and aging hyphae are called aseptate orcoenocytic. 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.


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Septal pores--Ascomycota

Woronin bodies


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Septal pores--Basidiomycota

Dolipore septa, septal pore caps orparenthosomes

Septal pore cap


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Fungal nuclei

1--3 m diam

3--40 chromosomes

Up to 13--40 Mb (million base pairs) DNAcoding for 6,000 to 13,000 genes

Intranuclear division--nuclear enveloperemains intact during mitosis (unlike plantsand 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
http://www.genetics.wisc.edu/index.htmlhttp://genome-www.stanford.edu/Saccharomyces/http://helios.bto.ed.ac.uk/mbx/C_elegans/Ce_intro.htmlhttp://sequence-www.stanford.edu/ara/ArabidopsisSeqStanford.htmlhttp://fruitfly.berkeley.edu/http://www.ornl.gov/hgmis/http://www.ornl.gov/hgmis/http://fruitfly.berkeley.edu/http://sequence-www.stanford.edu/ara/ArabidopsisSeqStanford.htmlhttp://helios.bto.ed.ac.uk/mbx/C_elegans/Ce_intro.htmlhttp://genome-www.stanford.edu/Saccharomyces/http://www.genetics.wisc.edu/index.html


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Tree of eukaryotes, showing

variation in genome size. FromKeeling and Slamovits (2005).Current Opinion in Genetics andDevelopment 15: 601-608

Unikonteukaryotic cell withone flagellum


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Fungi as model organisms

Small genome relative to other eukaryotes

Many fungal genes are homologous to those inother 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 meiosiscan be retrieved in haploid spores

Asexual (clonal) reproduction


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Beadle and Tatum

Using the commonbread mold

Neurospora crassa, in1941 developed theclassic concept ofone gene, one

enzyme Awarded Nobel Prize

in 1945


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Fungal nuclei

Usually haploid

Nuclear membrane persists during division

Nuclear associated organelles (NAOs): Associated with the nuclear envelope; function

as microtubule-organizing centers during mitosisand meiosis Spindle pole bodies

In fungi that lack a flagellated stage in lifecycle Centrioles

In fungi and other organisms possessing flagellated stagein lifecycle


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Spindle Pole Body


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Other organelles

Mitochondriaflattened or plate-likemitochondrial cristae in Fungi (similar toanimals)

Golgi bodiesconsist of a single, tubularcisternal element (stacked, plate-likecisternae in animals and plants)

Other types: ribosomes, endoplasmic reticulum, vacuoles, lipid

bodies, glycogen storage particles, microbodies,microtubules, vesicles


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Storage Compounds

Glycogen, lipids and trehalose in fungi andanimals

Starch in plants


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Animal Cell Plant Cell


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G. T. Cole. 1986. Microbiol. Rev. 50: 95-132


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Fungal Reproduction

Many fungi have theability to reproduce by

asexual and sexualmeans


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Fungal reproduction

Anamorph= asexual stage

Mitospore=spore formed via asexual

reproduction (mitosis), commonly called aconidium or sporangiospore

Teleomorph= sexualstage

Meiospore=spore formed via sexualreproduction (e.g., resulting from meiosis),type of spore varies by phylum


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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


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Concept of fungal holomorph

Asexual and sexual reproduction may beseparated in time and space

The holomorph is the entire fungusincluding asexual and sexual stages ifboth are formed


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Fungal life cycles

The vegetative thallus predominates in the lifecycle 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 ofthese events in the life cycle: Plasmogamy (cell fusion)

Karyogamy (nuclear fusion)

Meiosis (reduction division)


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2n n

Fungal life cycles

Plasmogamy

n n+n

Karyogamy

n+n 2n

Life cycle is

predominantly

haploid (n)

mitosis

Meiosis


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n n + n

Fungal life cycles

Karyogamy

n + n 2n

Meiosis

2n n

Life cycle is

predominantly

dikaryotic (n + n)

mitosis

Plasmogamy


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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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Lecture 2 Intro to Kingdom Fungi