Affiliation:
1. Department of Cell and Systems Biology, University of Toronto, 3359 Mississauga Road North, Mississauga, Ontario, Canada L5L 1C6
Abstract
ABSTRACT
Epistatic interactions in which the phenotypic effect of an allele is conditional on its genetic background have been shown to play a central part in various evolutionary processes. In a previous study (J. B. Anderson et al., Curr. Biol. 20:1383-1388, 2010; J. R. Dettman, C. Sirjusingh, L. M. Kohn, and J. B. Anderson, Nature 447:585-588, 2007), beginning with a common ancestor, we identified three determinants of fitness as mutant alleles (each designated with the letter “
e
”) that arose in replicate
Saccharomyces cerevisiae
populations propagated in two different environments, a low-glucose and a high-salt environment. In a low-glucose environment,
MDS3e
and
MKT1e
interacted positively to confer a fitness advantage. Also,
PMA1e
from a high-salt environment interacted negatively with
MKT1e
in a low-glucose environment, an example of a Dobzhansky-Muller incompatibility that confers reproductive isolation. Here we showed that the negative interaction between
PMA1e
and
MKT1e
is mediated by alterations in intracellular pH, while the positive interaction between
MDS3e
and
MKT1e
is mediated by changes in gene expression affecting glucose transporter genes. We specifically addressed the evolutionary significance of the positive interaction by showing that the presence of the
MDS3
mutation is a necessary condition for the spread and fixation of the new mutations at the identical site in
MKT1
. The expected mutations in
MKT1
rose to high frequencies in two of three experimental populations carrying
MDS3e
but not in any of three populations carrying the ancestral allele. These data show how positive and negative epistasis can contribute to adaptation and reproductive isolation.
Publisher
American Society for Microbiology
Subject
Molecular Biology,General Medicine,Microbiology
Cited by
15 articles.
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