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
What Is Strain Diversity?
Differences in information that is inherited
Differences in expression of inherited information
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
Daughter Cells Inherit
Full complement of mother cell’s chromosomes
Organelles: structure and DNA
Proteins, plasmids and expression patterns
Sources of Inherited Information
Parental lineage
Lateral gene transfer: pick up of genetic information from environment
Hybrid formation with other related species or strains
How Does Diversity Arise?
Change in DNA sequence
Change in position on chromosome
Development of prion state
Gene Expression
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 sequence
Change in position on chromosome
Development 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
Why Is Chromosome Position Important?
Position influences presence/absence of gene
Position influences level of expression
Position 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 sequence
Change in position on chromosome
Development of prion state
What Are Prions?
Protein-based inheritance
Proteins exist in different conformations
Conformation confers information
Most are stress-induced
Provide molecular memory of stress
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 parameters
Ability to dominate fermentation varies
Aroma compounds vary in type and concentration
Mouth feel factors differ
Sensitivity to stress varies
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
…