Ancient events of polyploidy have been linked to huge evolutionary leaps in the tree of life, while increasing evidence shows that newly established polyploids have adaptive advantages in certain stress conditions compared to their relatives with a lower ploidy. The genus Saccharomyces is a good model for studying such events, as it contains an ancient whole-genome duplication event and many sequenced Saccharomyces cerevisiae are, evolutionary speaking, newly formed polyploids. Many polyploids have unstable genomes and go through large genome erosions; however, it is still unknown what mechanisms govern this reduction. Here, we sequenced and studied the natural S. cerevisiae × Saccharomyces kudriavzevii hybrid strain, VIN7, which was selected for its commercial use in the wine industry. The most singular observation is that its nuclear genome is highly unstable and drastic genomic alterations were observed in only a few generations, leading to a widening of its phenotypic landscape. To better understand what leads to the loss of certain chromosomes in the VIN7 cell population, we looked for genetic features of the genes, such as physical interactions, complex formation, epistatic interactions and stress responding genes, which could have beneficial or detrimental effects on the cell if their dosage is altered by a chromosomal copy number variation. The three chromosomes lost in our VIN7 population showed different patterns, indicating that multiple factors could explain the mechanisms behind the chromosomal loss. However, one common feature for two out of the three chromosomes is that they are among the smallest ones. We hypothesize that small chromosomes alter their copy numbers more frequently as a low number of genes is affected, meaning that it is a by-product of genome instability, which might be the chief driving force of the adaptability and genome architecture of this hybrid.

中文翻译：

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酵母属种间杂种的基因组不稳定性：适应性问题


古代的多倍体事件与生命树中巨大的进化飞跃有关，同时越来越多的证据表明，新建立的多倍体在某些胁迫条件下比其低倍性的亲戚具有适应性优势。酵母属是研究此类事件的一个很好的模型，因为它包含一个古老的全基因组重复事件，并且许多已测序的酿酒酵母从进化的角度来说是新形成的多倍体。许多多倍体的基因组不稳定，会经历大规模的基因组侵蚀；然而，目前尚不清楚是什么机制控制着这种减少。在这里，我们对天然酿酒酵母×库德里亚酵母杂交菌株 VIN7 进行了测序和研究，该菌株被选用于葡萄酒行业的商业用途。最奇异的观察结果是，其核基因组高度不稳定，仅在几代内就观察到剧烈的基因组改变，导致其表型景观扩大。为了更好地了解导致 VIN7 细胞群中某些染色体丢失的原因，我们寻找基因的遗传特征，例如物理相互作用、复杂形成、上位相互作用和应激反应基因，这些特征可能对 VIN7 细胞群产生有益或有害的影响。如果细胞的剂量因染色体拷贝数变异而改变。我们的 VIN7 群体中丢失的三条染色体表现出不同的模式，表明多种因素可以解释染色体丢失背后的机制。然而，三个染色体中的两个的一个共同特征是它们是最小的染色体之一。 我们假设，当受影响的基因数量较少时，小染色体会更频繁地改变其拷贝数，这意味着它是基因组不稳定性的副产品，这可能是这种杂交体的适应性和基因组结构的主要驱动力。