Biology of Fungi Sexual Developmentpeople.ysu.edu/~crcooper01/Fungal Biology Lecture 4b (F09).pdf · Lecture: Growth and Development, Part B BIOL 4848/6948 - Fall 2009 3 BIOL 4848/6948

Lecture: Growth and Development, Part B

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BIOL 4848/6948 (v. F09) Copyright © 2009 Chester R. Cooper, Jr.

Fungal Growth and Development

Biology of Fungi


Sexual Development  Sexual reproduction involves three

fundamental processes:  Plasmogamy - fusion of haploid cells  Karyogamy - fusion of haploid nuclei  Meiosis - reduction division

 Two fundamental points of sexual reproduction  Nature of sexuality  Serves as a survival mechanism


Sexual Development (cont.)  Nature of sexuality

 Homothallic vs. heterothallic  Governed by mating type genes (compatibility)  Arrangement of mating types

  Bipolar compatibility - governed by a single gene locus where one of a non-allelic pair of genes (idiomorph) exists

  Tetrpolar compatibility - two mating type gene pairs of multiple idiomorphs


Sexual Development (cont.)  Mating type and

hormonal control  Chytridiomycota

  Allomyces is a homothallic fungus that produces separate male and female gametangia that release motile gametes Gametangia of Allomyces. Source: www.palaeos.com/

Fungi/Lists/Glossary/GlossaryG.html


Sexual Development (cont.)


Sexual Development (cont.)  Mating type and hormonal control

 Chytridiomycota (cont.)   Females release a pheromone, serinin, that attracts

the male gametes   Male gametes move along a concentration gradient   Sirenin and carotenoid color produced in male

gametangia are produced from the same precursor, indicating mating type gene controls development of the sex organs


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Sexual Development (cont.)  Oomycota

  Homothallic or heterothallic, but in most cases produces a colony with both male and female sex organs (antheridia and oogonia)

  Mating type genes control capatibility

  Hormonal control in Achlya  Female produces antheridiol

causing the male to increase production of cellulase which induces hyphal branching to increase


Sexual Development (cont.)   Hormonal control in Achlya

(cont.)  Once triggered by

antheridiol, males release oogoniols that induce oogonia development

 Eventually, male branches (antherida) fuse with oogonia


Sexual Development (cont.)

Oogonium and antheridium of Achlya. Source: www.palaeos.com/Fungi/Lists/Glossary/GlossaryG.html


Sexual Development (cont.)  Zygomycota

  Homothallic or heterothallic   Two mating type genes that govern conversion of β-

carotene to a prohormone   Prohormone is eventually converted by mating-type

specific gene to trisporic acid   Trisporic acid volatilizes and causes hyphae of

opposite mating type to grow towards one another and fuse to form a zygospore


Trisporic acid hormonal system in mating within the Zygomycota. Sources: www.palaeos.com/Fungi/Lists/Glossary/GlossaryG.html

and Deacon, 2006



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Sexual Development (cont.)  Ascomycota

  Typically two mating types a cells and α cells   Best characterized system is that of Saccharomyces   Mating is controlled by the MAT gene locus of

flanked by two other loci, MATa and MATα   A copy of one loci is made and inserted into MAT

gene locus - this is now the mating type of the cell   This copy can switch out after each new bud cell is

produced


Mating type loci of Saccharomyces. Source: nitro.biosci.arizona.edu/courses/EEB320-2005/Lecture13/lecture13.html


Diagram of life cycle of Saccharomyces. Source: nitro.biosci.arizona.edu/courses/EEB320-2005/Lecture13/lecture13.html


Sexual Development (cont.)  Ascomycota (cont.)

  MATα are responsible for producing:  Peptide hormones a-factor and α-factor  Hormone receptors  Cell surface agglutinins

  α cells constitutively release α-factor that is recognized by a receptor on a cells

  a cells cease growth and arrest at G1 phase of the cell cycle, then release a-factor


Sexual Development (cont.)  Ascomycota (cont.)

  Different mating types then form outgrowths (“schmoo” cells) with strain specific agglutinins on their surfaces

  Agglutinins cause cells to bind to one another, which then leads to fusion (plasmogamy), followed by karyogamy (diploid formation)

  Subsequent induction of meiosis produces four ascospores


“Schmoo cell”, formation of zygotes via fusion of yeast cells, and ascospores of Schizosaccharomyces. Sources:

www.biomade.nl/AmphipathicProteins.htm, www.jbc.org,

www.visualsunlimited.com/browse/vu227/vu227486.html and,


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BIOL 4848/6948 (v. F09) Copyright © 2009 Chester R. Cooper, Jr. BIOL 4848/6948 (v. F09) Copyright © 2009 Chester R. Cooper, Jr.

Diagram of life cycle of Saccharomyces. Source: www.brooklyn.cuny.edu/bc/ahp/LAD/C9/C9_tetrads.html


Sexual Development (cont.)  Basidiomycota

  Most are heterothallic having one or two mating type loci (typically termed A and B) with mulitiple idiomorphs at each locus (e.g., A1, A2, A3, etc.)

  Successful matings occur with different idiomorphs at each locus (e.g., A1, B1 x A2, B2)

  Different pairings of idiomorphs have allowed a dissection of the functions of the mating-type genes  A locus - controls pairing and synchronous

division of nuclei and initiation of clamp formation  B locus - controls septal dissolution, fusion of

clamp branches, and increased glucanase activity



Mating reactions between haploid isolates of Armillaria ostoyae (with bifactorial mating system): 1. Incompatible mating (incompatibility factors A1B1 x A1B1). 2. hemicompatible I (incomp. factors A1B1 x A1B2). 3. hemicompatible II (incomp. factors A1B1 x A2B1). 4. compatible mating, resulting in diploid

mycelium (incomp. factors A1B1 x A2B2).Source: www.padil.gov.au/viewPest.aspx?id=518 BIOL 4848/6948 (v. F09) Copyright © 2009 Chester R. Cooper, Jr.

Species identification with the aid of mating test. 1. A. ostoyae haploid (lower) x A. borealis haploid (intersterile – no reaction). 2. A. ostoyae diploid (lower) x A. borealis haploid (intersterile – no reaction). 3. A. ostoyae haploid x A. ostoyae haploid (compatible – rapid diploidisation). 4. A.

ostoyae diploid (lower) x A. ostoyae haploid (intersterile – slow diploidisation of the haploid tester) .Source: www.padil.gov.au/viewPest.aspx?id=518

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Biology of Fungi Sexual Developmentpeople.ysu.edu/~crcooper01/Fungal Biology Lecture 4b (F09).pdf · Lecture: Growth and Development, Part B BIOL 4848/6948 - Fall 2009 3 BIOL 4848/6948