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

Saccharomyces

Mitochondrion

Vacuole

Nucleus

Endoplasmic reticulum

Secretory

Pathway

Golgi

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 Expression

DNA

mRNA

Protein

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

First Flight: Saccharomyces cerevisiae Strains

Glass 1: VL1Glass 2: Rhone 4600Glass 3: BCGlass 4: CKS-102Glass 5: M2Glass 6: Zymaflore X16