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Diversity of Saccharomyces cerevisiae

Diversity of Saccharomyces cerevisiae. Linda F. Bisson Department of Viticulture and Enology University of California, Davis. What Is a Yeast Strain?. Members of the same genus and species Differ in a measurable way Differences can be neutral or impact cell phenotypes.

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Diversity of Saccharomyces cerevisiae

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  1. Diversity of Saccharomycescerevisiae Linda F. Bisson Department of Viticulture and Enology University of California, Davis

  2. What Is a Yeast Strain? • Members of the same genus and species • Differ in a measurable way • Differences can be neutral or impact cell phenotypes

  3. What Is Strain Diversity? • Differences in information that is inherited • Differences in expression of inherited information

  4. What Causes Strain Diversity? • Differences in sequences of genes on nuclear chromosomes • Differences in position of gene sequences on chromosomes • Differences in organelle genomes or composition • Presence of extrachromosomal circular and linear nucleic acids • Inherited transcriptional states • Inherited protein conformational states

  5. Saccharomyces Nucleus Mitochondrion Secretory Pathway Golgi Vacuole Endoplasmic reticulum

  6. Daughter Cells Inherit • Full complement of mother cell’s chromosomes • Organelles: structure and DNA • Proteins, plasmids and expression patterns

  7. Sources of Inherited Information • Parental lineage • Lateral gene transfer: pick up of genetic information from environment • Hybrid formation with other related species or strains

  8. How Does Diversity Arise? • Change in DNA sequence • Change in position on chromosome • Development of prion state

  9. Gene Expression DNA mRNA Protein

  10. Gene Differences: Alleles • If gene sequence differs then protein sequence will differ • If protein sequence differs, activity may differ: • Amount of activity • Regulation of activity • Type of activity • Stability of activity

  11. How Are Gene Sequences Changed? • Oxidative damage of base pairs (reactive oxygen species derived from normal metabolism) • Misreading of base pairs (mistakes during DNA synthesis) • UV light damage to base pairs (failure of repair mechanisms) • Chemical agent damage (rare event)

  12. How Are Gene Sequences Changed? • Failure of mutation to be recognized and repaired • Makes cells more fit for their local environment • No selection against change

  13. How Does Diversity Arise? • Change in DNA sequence • Change in position on chromosome • Development of prion state

  14. What Are Chromosomes? • Linear pieces of DNA that carry genes, regulatory regions and spacer regions (Saccharomyces has 16) • Comprised of centromere (point of attachment to spindles during division) • Telomeres (ends) point of attachment to the nuclear membrane Centromere Chromosome Telomere

  15. Why Is Chromosome Position Important? • Position influences presence/absence of gene • Position influences level of expression • Position influences amplification of gene (number of copies)

  16. Impact of Position of Gene • In certain chromosomal areas basal level of expression is elevated (away from steric hindrance) • In certain chromosomal areas basal level of expression is decreased (near centromeres) • Gene adjacency can impact expression (interference from nearby genes)

  17. How Does Diversity Arise? • Change in DNA sequence • Change in position on chromosome • Development of prion state

  18. What Are Prions? • Protein-based inheritance • Proteins exist in different conformations • Conformation confers information • Most are stress-induced • Provide molecular memory of stress

  19. (Brown, Lindquist, 2009) [gar-] Presence of Glucose recognized and signal transduced by Rgt2/Snf3 to Yck1/2 which phosphorylate Std1 and Mth1, thus marking them for degradation. Rgt1 remains free in the cytosol, Hxt3 is still expressed. [GAR+] In absence of glucose or in [GAR+] Std1 interacts with Pma1, possibly altering Std1 affinity for Rgt1. They associate as a complex and enter the nucleus, inhibit HXT3 expression, leading to a 36 fold down-regulation of Hxt3! This alternate pathway is maintained as a dominant, heritable prion shift.

  20. Wine Yeast Strain Diversity Significant diversity exists among wine strains: • Presence/absence of genes • Allele differences (single nucleotide polymorphisms) • Chromosomal rearrangement is found • Differences in prion state are found

  21. What Does Wine Strain Diversity Mean? • Differences in fermentation parameters • Ability to dominate fermentation varies • Aroma compounds vary in type and concentration • Mouth feel factors differ • Sensitivity to stress varies

  22. First Flight: Saccharomyces cerevisiae Strains • Glass 1: VL1 • Glass 2: Rhone 4600 • Glass 3: BC • Glass 4: CKS-102 • Glass 5: M2 • Glass 6: Zymaflore X16

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