Department of Genetics and Applied Microbiology, University of Debrecen, Debrecen, Hungary.
FEMS Yeast Res. 2012 Sep;12(6):703-18. doi: 10.1111/j.1567-1364.2012.00820.x. Epub 2012 Jul 9.
The analysis of 57 synthetic interspecies hybrids revealed that Saccharomyces cerevisiae and Saccharomyces uvarum ( Saccharomyces bayanus var. uvarum) are isolated by a double sterility barrier: by hybrid sterility (hybrid cells cannot produce viable spores) operating in allodiploids and by F1 sterility (F1 cells cannot produce viable spores) operating in allopolyploids. F1-sterility is caused by mating-type heterozygosity. It can be overcome by eliminating chromosome 2 of the S. uvarum subgenome that carries a MAT locus. The loss of this MAT gene abolishes the repression of mating activity. In cultures of the resulting fertile alloaneuploid F1 segregants, the cells can conjugate with each other like haploids and form zygotes capable of performing meiotic divisions producing viable and fertile F2 spores. To the best of our knowledge, this is the first report on breaking down interspecies hybrid sterility by chromosome loss in eukaryotic organisms. The filial generations are genetically unstable and can undergo additional changes mainly in the S. uvarum subgenome (directional changes). It is proposed that regaining fertility and subsequent preferential reduction in one of the subgenomes may account for the formation of chimerical ('natural hybrid') genomes found among wine and brewery strains and may also play roles in speciation of hybrid taxa in the Saccharomyces genus.
对 57 个合成种间杂种的分析表明，酿酒酵母和葡萄汁有孢汉逊酵母（贝酵母变种）被双重不育性屏障所隔离：杂种不育性（杂种细胞不能产生有活力的孢子）作用于异源二倍体，以及 F1 不育性（F1 细胞不能产生有活力的孢子）作用于异源多倍体。F1 不育性是由交配型杂合性引起的。通过消除携带 MAT 基因座的 S. uvarum 亚基因组的第 2 条染色体可以克服 F1 不育性。失去这个 MAT 基因会消除对交配活性的抑制。在由此产生的可育异源单体 F1 分离子的培养物中，细胞可以像单倍体一样相互交配并形成能够进行减数分裂产生有活力和可育 F2 孢子的合子。据我们所知，这是首次在真核生物中通过染色体缺失打破种间杂种不育性的报告。后代在遗传上是不稳定的，可以主要在 S. uvarum 亚基因组中发生额外的变化（定向变化）。有人提出，恢复生育能力以及随后一个亚基因组的优先减少可能是在葡萄酒和啤酒厂菌株中发现的嵌合（“天然杂种”）基因组形成的原因，也可能在酿酒酵母属杂种分类群的物种形成中发挥作用。
