Biotechnology Laboratory

The UBC Biotechnology Laboratory presents Dr. Steven Oliver, of the University of Manchester, who will be giving a seminar "Old Wine In New Bottles: Genomic Approaches To Speciation And Fitness" on Thursday, June 3, 2004 in Wesbrook 201, from 10:00 - 11:00 am.

Abstract
The availability of complete genome sequences for Saccharomyces cerevisiae and a number of other yeasts, including members of the Saccharomyces ‘sensu stricto’, presents unparalleled opportunities to discover the molecular mechanisms involved in yeast evolution and elucidate genetic effects on the fitness of yeasts in their natural environments.

As with most classes of organisms, molecular phylogenies of yeasts are constructed using one or a few genes. This practice is fraught with similar dangers to the former practice of discriminating between species on the basis of one or a few phenotypic traits. In the genomic era, it should be possible to study phylogenetic relationships using all of the genes. Ideally, this would demand complete genome sequences for all species in a given taxon. This is impractical, but it is possible to gain useful phylogenetic information (including details of which genes are absent or over-represented) by carrying out hybridizations of genomic DNAs to gene arrays derived from the complete genome sequence of a paradigmatic species. I shall report on the experimental and bioinformatic methods that permit the exploitation of this approach.

The classical alternative to molecular phylogenetics is to define species biologically, in terms of their relative interfertility. The Saccharomyces ‘sensu stricto’ are a group of species that will mate with one another, but interspecific pairings produce sterile hybrids. Retrospective analysis of their genomes showed that translocations between these species’ chromosomes do not correlate with the group’s sequence-based phylogeny, but was unable to infer what contribution such rearrangements make to reproductive isolation between these yeasts. We have taken an interventionist, rather approach to the study of speciation by reconfiguring the S. cerevisiae genome so that it is collinear with that of S. mikatae. We found that this imposed genomic collinearity allows the generation of interspecific hybrids that produce a large proportion of spores that are viable, but extensively aneuploid. Similar results were obtained in crosses between wild-type S. cerevisiae and the naturally collinear species, S. paradoxus, but were not observed in non-collinear crosses. This is the first controlled comparison of the effect of chromosomal translocation on species barriers, and also suggests a mechanism for the generation of redundancy in the S. cerevisiae genome.

Competition experiments in chemostat culture demonstrated that the different translocation strains of S. cerevisiae show small, but significant, differences in selective fitness. I shall discuss genomic approaches to the measurement of the impact of individual genes on the fitness of S. cerevisiae in a variety of environmental conditions, and assess the prospects for molecular studies on yeast ecology.

Hosted by Drs. Phil Hieter and Jim Kronstad of the UBC Biotechnology Laboratory

Posted by at 11:46 AM on May 31, 2004