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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Evolutionary erosion of yeast sex chromosomes by mating-type switching accidents
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Evolutionary erosion of yeast sex chromosomes by mating-type switching accidents

机译：交配型转换事故对酵母性染色体的进化侵蚀

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摘要

We investigate yeast sex chromosome evolution by comparing genome sequences from 16 species in the family Saccharomyceta-ceae, including data from genera Tetrapisispora, Kazachstania, Naumovozyma, and Torulaspora. We show that although most yeast species contain a mating-type (MAT) locus and silent HML and HMR loci structurally analogous to those of Saccharomyces cerevisiae, their detailed organization is highly variable and indicates that the MAT locus is a deletion hotspot. Over evolutionary time, chromosomal genes located immediately beside MAT have continually been deleted, truncated, or transposed to other places in the genome in a process that is gradually shortening the distance between MAT and HML. Each time a gene beside MAT is removed by deletion or transposition, the next gene on the chromosome is brought into proximity with MAT and is in turn put at risk for removal. This process has also continually replaced the triplicated sequence regions, called Z and X, that allow HML and HMR to be used as templates for DNA repair at MAT during mating-type switching. We propose that the deletion and transposition events are caused by evolutionary accidents during mating-type switching, combined with natural selection to keep MAT and HML on the same chromosome. The rate of deletion accelerated greatly after whole-genome duplication, probably because genes were redundant and could be deleted without requiring transposition. We suggest that, despite its mutational cost, switching confers an evolutionary benefit by providing a way for an isolated germinating spore to reform spores if the environment is too poor.
机译：我们通过比较来自酵母菌科的16种物种的基因组序列来研究酵母性染色体进化，包括Tetrapisispora，Kazachstania，Naumovozyma和Torulaspora属的数据。我们显示，虽然大多数酵母菌种都包含一个交配型（MAT）基因座和沉默的HML和HMR基因座，其结构与酿酒酵母相似，但它们的详细组织却高度可变，表明MAT基因座是一个删除热点。在进化过程中，位于MAT旁边的染色体基因在不断缩短MAT与HML之间距离的过程中不断被删除，截断或转位到基因组中的其他位置。每次通过删除或转座去除MA​​T旁的一个基因时，染色体上的下一个基因就会与MAT靠近，从而面临被删除的风险。此过程还连续替换了称为Z和X的三重复序列区域，该区域允许HML和HMR用作交配类型转换期间MAT进行DNA修复的模板。我们建议删除和易位事件是由交配类型转换期间的进化事故引起的，结合自然选择以使MAT和HML保持在同一条染色体上。全基因组复制后，删除速度大大加快，可能是因为基因是多余的，可以在不需要转座的情况下删除。我们建议，尽管代价高昂，但转换却可以提供进化优势，如果环境太差，转换可以提供一种隔离的发芽孢子改造孢子的方法。

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