amplification of a zygosaccharomyces bailii dna segment in wine yeast genomes by extrachromosomal circular dna formation放大的zygosaccharomyces bailii葡萄酒酵母基因组dna片段的染色体外的环状dna形成.pdfVIP

Amplification of a Zygosaccharomyces bailii DNA Segment in Wine Yeast Genomes by Extrachromosomal Circular DNA Formation 1 ´ ´ 1 1 1 1 Virginie Galeote , Frederic Bigey , Emmanuelle Beyne , Maite Novo , Jean-Luc Legras , Serge 2 1 Casaregola , Sylvie Dequin * 1 INRA, UMR1083 Sciences Pour l’Œnologie, Montpellier, France, 2 CIRM-Levures, INRA, UMR1319 Micalis, AgroParisTech, Thiverval-Grignon, France Abstract We recently described the presence of large chromosomal segments resulting from independent horizontal gene transfer (HGT) events in the genome of Saccharomyces cerevisiae strains, mostly of wine origin. We report here evidence for the amplification of one of these segments, a 17 kb DNA segment from Zygosaccharomyces bailii, in the genome of S. cerevisiae strains. The copy number, organization and location of this region differ considerably between strains, indicating that the insertions are independent and that they are post-HGT events. We identified eight different forms in 28 S. cerevisiae strains, mostly of wine origin, with up to four different copies in a single strain. The organization of these forms and the identification of an autonomously replicating sequence functional in S. cerevisiae, strongly suggest that an extrachromosomal circular DNA (eccDNA) molecule serves as an intermediate in the amplification of the Z. bailii region in yeast genomes. We found little or no sequence similarity at the breakpoint regions, suggesting that the insertions may be mediated by nonhomologous recombination. The diversity between these regions in S. cerevisiae represents roughly one third the divergence among the genomes of wine strains