Saccharomyces cerevisiae x Saccharomyces kudriavzevii VIN7 genome analysis. Saccharomyces cerevisiae x Saccharomyces kudriavzevii strain:VIN7

Ancient events of polyploidy have been linked to huge evolutionary leaps in the tree of life, while increasing evidence show that newly established polyploids have adaptive advantages in certain stress condition compared to relatives with 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 governance this reduction. Here we sequenced and studied the commercial S. cerevisiae x S. kudriavzevii hybrid strain: VIN7. The most singular observation is that the genome is highly unstable and drastic genomic alterations were observed in only a few generations, leading to a widening of the phenotypic landscape. To better understand what leads to the loss of certain chromosomes in the population, we look for genetic features of the genes, such as physical interactions, complexes, 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 mechanism behind chromosomal loss. However, one common feature for two out of the three chromosomes is that they are among the smallest. We hypothesis that small chromosomes alter more frequently their copy number as a low number of genes are affected, meaning it is a by-product of genome instability, which might be the chief driving force of the adaptability and genome architecture of this hybrid.

多倍化（polyploidy）的远古事件曾与生命之树中的重大进化跃迁紧密关联，而越来越多的证据显示，相较于倍性更低的近缘类群，新形成的多倍体在特定胁迫条件下具备适应性优势。酿酒酵母属（Saccharomyces）是研究此类事件的优良模式类群：该属既存在远古全基因组复制事件，且诸多已完成测序的酿酒酵母（Saccharomyces cerevisiae）从进化视角来看属于新形成的多倍体。多数多倍体基因组具有不稳定性，会经历大规模的基因组侵蚀过程，但目前仍不清楚调控这一基因组缩减机制的具体分子通路。本研究对商业杂交菌株VIN7（酿酒酵母Saccharomyces cerevisiae × 库德里阿兹威酵母Saccharomyces kudriavzevii）进行了测序与分析。最具特殊性的观测结果为该菌株基因组具有高度不稳定性：仅经过数代培养便出现了剧烈的基因组变异，进而拓宽了其表型谱。为进一步明确群体中部分染色体丢失的驱动机制，我们对相关基因的遗传特征展开了探究，包括物理相互作用、蛋白复合物、上位相互作用（epistatic interactions）以及胁迫响应基因——若染色体拷贝数变异（copy number variation）导致这些基因的剂量发生改变，可能会对细胞产生有益或有害的影响。本研究中VIN7群体所丢失的三条染色体呈现出不同的丢失模式，提示存在多种因素共同参与调控染色体丢失的分子机制。不过，三条染色体中有两条具备一个共同特征：二者均属于基因组中较小的染色体之列。我们提出假说：小型染色体的拷贝数变异发生频率更高，这是因为其涉及的基因数量较少，该过程或为基因组不稳定性的副产物；而基因组不稳定性或许正是该杂交菌株适应性演化与基因组架构形成的核心驱动力。