G3 (Bethesda). 2012 Feb;2(2):299-311. doi: 10.1534/g3.111.000745. Epub 2012 Feb 1.
Polyploidization is an important process in the evolution of eukaryotic genomes, but ensuing molecular mechanisms remain to be clarified. Autopolyploidization or whole-genome duplication events frequently are resolved in resulting lineages by the loss of single genes from most duplicated pairs, causing transient gene dosage imbalance and accelerating speciation through meiotic infertility. Allopolyploidization or formation of interspecies hybrids raises the problem of genetic incompatibility (Bateson-Dobzhansky-Muller effect) and may be resolved by the accumulation of mutational changes in resulting lineages. In this article, we show that an osmotolerant yeast species, Pichia sorbitophila, recently isolated in a concentrated sorbitol solution in industry, illustrates this last situation. Its genome is a mosaic of homologous and homeologous chromosomes, or parts thereof, that corresponds to a recently formed hybrid in the process of evolution. The respective parental contributions to this genome were characterized using existing variations in GC content. The genomic changes that occurred during the short period since hybrid formation were identified (e.g., loss of heterozygosity, unilateral loss of rDNA, reciprocal exchange) and distinguished from those undergone by the two parental genomes after separation from their common ancestor (i.e., NUMT (NUclear sequences of MiTochondrial origin) insertions, gene acquisitions, gene location movements, reciprocal translocation). We found that the physiological characteristics of this new yeast species are determined by specific but unequal contributions of its two parents, one of which could be identified as very closely related to an extant Pichia farinosa strain.
多倍化是真核生物基因组进化的一个重要过程，但随之而来的分子机制仍有待阐明。同源多倍化或全基因组复制事件经常通过大多数复制对中单个基因的丢失而在后续的谱系中得到解决，导致暂时的基因剂量失衡，并通过减数分裂不育加速物种形成。异源多倍化或种间杂种的形成引发了遗传不相容性的问题（贝特森-多布赞斯基-穆勒效应），并可能通过在后续的谱系中积累突变变化来解决。在本文中，我们表明，一种耐渗酵母物种，Pichia sorbitophila，最近在工业中浓缩山梨醇溶液中分离出来，说明了最后一种情况。它的基因组是同源和同系染色体或其部分的嵌合体，对应于进化过程中最近形成的杂种。利用现有 GC 含量的变化，对该基因组的各自亲本贡献进行了特征描述。鉴定了在杂种形成后的短时间内发生的基因组变化（例如，杂合性丢失、rDNA 的单侧丢失、相互交换），并将其与分离自共同祖先后的两个亲本基因组所经历的变化区分开来（即 NUMT（线粒体来源的核序列）插入、基因获得、基因位置移动、相互易位）。我们发现，这个新酵母物种的生理特征是由其两个亲本的特定但不等的贡献决定的，其中一个亲本可以被鉴定为与现存的 Pichia farinosa 菌株非常密切相关。
