Clowers Katie J, Will Jessica L, Gasch Audrey P
Laboratory of Genetics, University of Wisconsin-Madison, 425-G Henry Mall, Madison, WI, 53706, USA.
Great Lakes Bioenergy Research Center, 1552 University Ave., Madison, WI, 53704, USA.
Mol Ecol. 2015 Dec;24(23):5886-98. doi: 10.1111/mec.13439. Epub 2015 Nov 20.
Differential adaptation to distinct niches can restrict gene flow and promote population differentiation within a species. However, in some cases the distinction between niches can collapse, forming a hybrid niche with features of both environments. We previously reported that distinctions between vineyards and oak soil present an ecological barrier that restricts gene flow between lineages of Saccharomyces cerevisiae. Vineyard isolates are tolerant to stresses associated with grapes while North American oak strains are particularly tolerant to freeze-thaw cycles. Here, we report the isolation of S. cerevisiae strains from Wisconsin cherry trees, which display features common to vineyards (e.g. high sugar concentrations) and frequent freeze-thaw cycles. Genome sequencing revealed that the isolated strains are highly heterozygous and represent recent hybrids of the oak × vineyard lineages. We found that the hybrid strains are phenotypically similar to vineyard strains for some traits, but are more similar to oak strains for other traits. The cherry strains were exceptionally good at growing in cherry juice, raising the possibility that they have adapted to this niche. We performed transcriptome profiling in cherry, oak and vineyard strains and show that the cherry-tree hybrids display vineyard-like or oak-like expression, depending on the gene sets, and in some cases, the expression patterns linked back to shared stress tolerances. Allele-specific expression in these natural hybrids suggested concerted cis-regulatory evolution at sets of functionally regulated genes. Our results raise the possibility that hybridization of the two lineages provides a genetic solution to the thriving in this unique niche.
对不同生态位的差异适应可限制基因流动并促进物种内种群分化。然而，在某些情况下，生态位之间的差异可能会消失，形成兼具两种环境特征的混合生态位。我们之前报道过，葡萄园和橡树土壤之间的差异构成了一种生态屏障，限制了酿酒酵母谱系间的基因流动。葡萄园分离株能耐受与葡萄相关的胁迫，而北美橡树菌株则对冻融循环具有特别的耐受性。在此，我们报告了从威斯康星州樱桃树中分离出的酿酒酵母菌株，这些菌株表现出葡萄园常见的特征（如高糖浓度）以及频繁的冻融循环。基因组测序显示，分离出的菌株高度杂合，代表了橡树×葡萄园谱系的近期杂交种。我们发现，杂交菌株在某些性状上与葡萄园菌株表型相似，但在其他性状上更类似于橡树菌株。樱桃菌株在樱桃汁中生长得格外好，这增加了它们已适应这一生态位的可能性。我们对樱桃、橡树和葡萄园菌株进行了转录组分析，结果表明，取决于基因集，樱桃树杂交种呈现出类似葡萄园或类似橡树的表达模式，在某些情况下，表达模式与共同的胁迫耐受性相关。这些天然杂交种中的等位基因特异性表达表明，在一组功能调控基因处存在协同的顺式调控进化。我们的结果提出了一种可能性，即两个谱系的杂交为在这个独特生态位中蓬勃发展提供了一种遗传解决方案。
