diversity of saccharomyces cerevisiae linda f. bisson department of viticulture and enology...
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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 speciesDiffer in a measurable wayDifferences can be neutral or impact cell
phenotypes
What Is Strain Diversity?
Differences in information that is inheritedDifferences in expression of inherited
information
What Causes Strain Diversity?Differences in sequences of genes on nuclear
chromosomesDifferences in position of gene sequences on
chromosomesDifferences in organelle genomes or compositionPresence of extrachromosomal circular and linear
nucleic acids Inherited transcriptional states Inherited protein conformational states
Daughter Cells Inherit
Full complement of mother cell’s chromosomes
Organelles: structure and DNAProteins, plasmids and expression
patterns
Sources of Inherited Information
Parental lineageLateral gene transfer: pick up of genetic
information from environmentHybrid formation with other related species
or strains
How Does Diversity Arise?
Change in DNA sequenceChange in position on chromosomeDevelopment of prion state
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
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)
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
How Does Diversity Arise?
Change in DNA sequenceChange in position on chromosomeDevelopment of prion state
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
ChromosomeCentromere
Telomere
Why Is Chromosome Position Important?
Position influences presence/absence of gene
Position influences level of expressionPosition influences amplification of gene
(number of copies)
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)
How Does Diversity Arise?
Change in DNA sequenceChange in position on chromosomeDevelopment of prion state
What Are Prions?
Protein-based inheritanceProteins exist in different conformationsConformation confers information Most are stress-inducedProvide molecular memory of stress
[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.
(Brown, Lindquist, 2009)
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
What Does Wine Strain Diversity Mean?
Differences in fermentation parametersAbility to dominate fermentation variesAroma compounds vary in type and
concentrationMouth feel factors differSensitivity to stress varies