title: Polygenic evolution of a sugar specialization trade-off in yeast.
abstract: The evolution of novel traits can involve many mutations scattered throughout the genome. Detecting and validating such a suite of alleles, particularly if they arose long ago, remains a key challenge in evolutionary genetics. Here we dissect an evolutionary trade-off of unprecedented genetic complexity between long-diverged species. When cultured in 1% glucose medium supplemented with galactose, Saccharomyces cerevisiae, but not S. bayanus or other Saccharomyces species, delayed commitment to galactose metabolism until glucose was exhausted. Promoters of seven galactose (GAL) metabolic genes from S. cerevisiae, when introduced together into S. bayanus, largely recapitulated the delay phenotype in 1% glucose-galactose medium, and most had partial effects when tested in isolation. Variation in GAL coding regions also contributed to the delay when tested individually in 1% glucose-galactose medium. When combined, S. cerevisiae GAL coding regions gave rise to profound growth defects in the S. bayanus background. In medium containing 2.5% glucose supplemented with galactose, wild-type S. cerevisiae repressed GAL gene expression and had a robust growth advantage relative to S. bayanus; transgenesis of S. cerevisiae GAL promoter alleles or GAL coding regions was sufficient for partial reconstruction of these phenotypes. S. cerevisiae GAL genes thus encode a regulatory program of slow induction and avid repression, and a fitness detriment during the glucose-galactose transition but a benefit when glucose is in excess. Together, these results make clear that genetic mapping of complex phenotypes is within reach, even in deeply diverged species.
authors: Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, California 94720, USA.
authors: Jeremy I
authors: JI
authors: Roop
authors: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA.|Buck Institute for Research on Aging, Novato, California 94945, USA.
authors: Kyu Chul
authors: KC
authors: Chang
authors: Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, California 94720, USA.|Buck Institute for Research on Aging, Novato, California 94945, USA.
authors: Rachel B
authors: RB
authors: Brem
mesh_terms: D000483:Alleles; D050260:Carbohydrate Metabolism / Q000187:drug effects / Q000235:genetics*; D017124:Conserved Sequence / Q000235:genetics; D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology; D019143:Evolution, Molecular; D005690:Galactose / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal / Q000235:genetics*; D056084:Genetic Fitness / Q000235:genetics; D056426:Genetic Loci / Q000235:genetics*; D005947:Glucose / Q000378:metabolism; D020412:Multifactorial Inheritance / Q000235:genetics*; D010641:Phenotype; D010802:Phylogeny; D011401:Promoter Regions, Genetic / Q000235:genetics; D012440:Saccharomyces / Q000145:classification / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism
chemical_list: D003470:Culture Media; D005947:Glucose; D005690:Galactose