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

Saccharomyces Mitochondrion Vacuole Nucleus Endoplasmic reticulum Secretory Pathway Golgi

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 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 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 Chromosome Centromere Telomere

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

[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 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