Introduction to Ascomycota (continued); Archiascomycetes and Saccharomycetales

1
Introduction to Ascomycota (continued)
Archiascomycetes and Saccharomycetales

• Pl P 421/521
• Lecture 5

2
Nuclear condition

• Monokaryon
• A single type of nucleus in a cell or mycelium
• Dikaryon
• A pair of closely associated, sexually compatible
  nuclei in a cell or mycelium (n n)
• Heterokaryon (heterokaryosis)
• a condition in which genetically different nuclei
  are associated with the same protoplast or the
  same mycelium

3
Parasexual Cycle(Pontecorvo, 1956)

• Establishment of heterokaryon
• Mutation
• Hyphal fusion
• Fusion of two different nuclei to form diploid
• Haploidization by aneuploidy

4
From Gary Cole http//gsbs.utmb.edu/microbook/c
h073.htm
5
Sexual Reproduction

• Sexual spores (meiosporesascospores) formed in
  sac-like structure called ascus (pl. asci)
• Site of meiosis
• Three main types of asci in Ascomycota
• Prototunicate ascus
• Unitunicate ascus
• Bitunicate ascus

6
Ascus types Prototunicate

• Thin-walled ascus
• Ascospores released by breakdown of wall

7
Ascus types Unitunicate

• Inner and outer ascus walls do not separate
  during ascospore release
• Ascospores released through specialized
  adaptation at ascus tip

8
Unitunicate Asci
9
Ascus tip
Refractive ring, Neurospora
Amyloid ring, Xylaria
10
Ascus tip

• Operculum
• Cap that detaches along preformed line

11
Ascus types Bitunicate

• Also called Jack-in-the Box ascus
• Inner and outer wall layers separate during
  ascospore discharge
• Inner (endotunica)thin and extensible
• Outer (exotunica)thick, inextensible
• Inner wall balloons out beyond outer wall

12
(No Transcript)
13
Bitunicate Ascus
14
Bitunicate ascus
Endotunica
Exotunica
Protoventuria barriae
15
Ascomatal types

• Cleistothecium
• Completely enclosed, no preformed opening
• Perithecium
• Apical pore (ostiole) through with ascospores are
  released
• Pseudothecium
• Ascocarp with asci formed in cavity (locule)
  within stromatic tissue
• Apothecium
• Ascocarp with asci exposed at maturity

16
Ascocarp types
stroma
Perithecium
Pseudothecium
17
Ascocarp types
Cleistothecium
Apothecium
18
Whats inside?

• Asci-scattered or in hymenium
• Hamatheciumsterile elements
• Paraphyses
• Apical paraphyses
• Epithecium
• Periphyses
• Pseudoparaphyses

19
Ascocarps ascogenous hyphae specialized ascus
tip conidia Woronin bodies
Absence of ascogenous hyphae and ascocarps most
asci without specialized tips
Classification from Alexopoulos et al. 1996
20
Phylogeny of basal AscomycotanSSU and nLSU rDNA
Sugiyama et al. 2006. Mycologia 98 1002
21
Archiascomycetes--taxa

• Neolecta
• Taphrinales
• TaphrinaT. deformans, peach leaf curl
• Protomyces
• Schizosaccharomycetales
• Schizosaccharomycesfission yeast
• Saitoellasoil yeast
• Pneumocystiscausal agent of virulent pneumonia
  (P. carinii)

22
Pneumocystis

• Considered to be a protozoan until 1980s
• Lacks ergosterol in cell walls
• Major cause of pneumonia in immunocompromised
  patients
• Life cycle and morphology poorly understood

23
ae Taphrina spp.
Sugiyama et al. 2006. Mycologia 98 1001
f, g Protomyces
i, j Saitoella
Schizosaccaromyces
Pneumocystis
Neolecta
24
Schizosaccharomyces
25
Archiascomycetes/Taphrinomycotina

• Diverse group, includes saprotrophs and parasites
  (animal and plant)
• Grouped together primarily by rDNA sequence data

26
Saccharomycetales/Saccharomycotina(Hemiascomycete
s)

• Ascomycetous yeasts
• Characterized by absence of ascogenous hyphae and
  ascocarps
• Asci mostly prototunicate
• Occur in slime fluxes, nectar, fresh or decaying
  fruitable to grow in high osmotic conditions
  (high sugar content)
• Others occur in soil, dung, water, digestive
  tracts of animals
• Many species are symbiotic with insects

27
Importance

• Brewing
• Baking
• Distilling
• Food production
• Industrial applications
• Model systems (S. cerevisiae)
• Animal pathogens

28
Somatic structures

• Yeast
• A single-celled fungus that reproduces by budding
  (or fission)
• Pseudomycelium
• Series of cells adhering after budding
• True mycelium
• Produced through apical tip growth

29
Budding
Multilateral
Bipolar
30
Asexual reproduction

• Conidia
• Arthrospores

31
karyogamy
plasmogamy
budding
copulation
2n somatic cells
1n somatic cells
meiosis
Mature ascus
32
Identification

• Microscopic appearance
• Unicellular or budding
• Size shape of yeast cells
• Multilateral or bipolar budding
• Form, structure and mode of ascus formation
• Ascospore shape

33
Identification

• Physiological tests91 different tests
• Ferment different sugars
• Assimilation tests (carbon and nitrogen source)
• Vitamin requirements
• Growth at 37C
• Growth in cyclohexamide
• Hydrolyse urea
• Form acid

34
Classification

• Saccharomycetaceae
• Unicellular, multilateral budding
• Nadsoniaceae, Saccharomycodaceae
• Unicellular, lemon-shaped, bipolar budding
• Eremotheciaceae, Metschnikowiaceae
• Mycelial, elongate ascus, needle-like ascospores
• Cephaloascaceae,Dipodascaceae, Lipomycetaceae
• Mycelial, hat-shaped ascospores, ascophores,
  insect association