Diversity of Saccharomyces Cerevisiae ( Linda F. Bisson )

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

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