Genomic Exploration of the Hemiascomycetous Yeasts: 20. Evolution of gene redundancy compared to Saccharomyces cerevisiae

Abstract

We have evaluated the degree of gene redundancy in the nuclear genomes of 13 hemiascomycetous yeast species. Saccharomyces cerevisiae singletons and gene families appear generally conserved in these species as singletons and families of similar size, respectively. Variations of the number of homologues with respect to that expected affect from 7 to less than 24% of each genome. Since S. cerevisiae homologues represent the majority of the genes identified in the genomes studied, the overall degree of gene redundancy seems conserved across all species. This is best explained by a dynamic equilibrium resulting from numerous events of gene duplication and deletion rather than by a massive duplication event occurring in some lineages and not in others. ß 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

Genomic Exploration of the Hemiascomycetous Yeasts: 18. Comparative analysis of chromosome maps and synteny withSaccharomyces cerevisiae

“…It is su¤cient to account for the partially duplicated structure of the S. cerevisiae genome [7^9], although additional mechanisms such as entire chromosome duplication (aneuploidy) are not excluded. In this view, genomic redundancy is a dynamic equilibrium between merodiploid formation and gene deletion, consistent with the distribution of gene families observed in the 13 yeast species studied [29]. Loss of synteny between neighboring genes results from the above mechanism as well as from reciprocal translocations which preserve gene orientation.…”

Genomic Exploration of the Hemiascomycetous Yeasts: 10.Kluyveromyces thermotolerans

“…Among 682 couples of genes [29], we observed 56.5% conserved synteny between the two yeasts. This value is close to S. kluyveri (53.5%) [30], K. lactis (47.3%) [31], and K. marxianus var.…”

“…We analyzed the 297 remaining pairs and we identi¢ed 173 pairs corresponding to an ancestral gene organization as described in [29]. Further, we have identi¢ed 44 trans-chromosomal series (see [29] for a global analysis).…”

“…A recent article shows that speciation in sensu stricto yeasts of the genus Saccharomyces is not related to reciprocal translocation [38]. To explore the importance of reciprocal translocation, we performed a systematic analysis of local gene orientation [29]. A reciprocal translocation must conserve relative gene orientation with respect to the centromere.…”

“…This high value is not compatible with reciprocal translocation which conserves relative orientation. Therefore, the reciprocal translocation cannot be considered the major event of chromosome rearrangement due to the high proportion of inverted pairs [29].…”