Genetic analysis of the karyotype instability in natural wine yeast strains

Yeast strains isolated from the wild may show high rates of changes in their karyotypes during vegetative growth. We analysed over 500 karyotypes from mitotic and meiotic derivatives of strain DC5, which has a chromosome rearrangement rate of 8.2 x 10(-3) changes/generation. About 70% of the meiotic derivatives of DC5 had low rearrangement rates, with an average of 5.8 x 10(-4) changes/generation, suggesting that karyotype instability behaved as a dominant phenotype. Diploid derivatives with low karyotype variability in mitosis also had low rates of chromosomal rearrangement during meiosis, suggesting that the two phenotypes may be linked. DC5 and some of its meiotic derivatives (both with high and low karyotype variability) had chromosome XII hypervariable bands. Their distribution among the meiotic products indicates that they are not indicators for genetic instability. To our knowledge, data in this paper are the first to indicate that karyotypically unstable yeast strains may give stable progeny at high rates. Understanding of the relevant mechanism(s) may allow the design of genetic strategies to stabilize karyotypes from natural and/or industrial wine yeasts with unacceptable karyotype rearrangement rates.