Wang Jun-Ting Johnson, Priscilla Ng Ping Ling, Powers Maceo E, Brem Rachel B
Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA, 94720.
Graduate Group in Comparative Biochemistry, University of California, Berkeley, Berkeley, CA, 94720.
bioRxiv. 2025 May 13:2025.05.07.652752. doi: 10.1101/2025.05.07.652752.
Many traits of interest in biology evolved long ago and are fixed in a particular species, distinguishing it from other sister taxa. Elucidating the mechanisms underlying such ancient traits has been a central goal for evolutionary biologists. The yeast is unique among its relatives for its ability to thrive at high temperature, via a genetic architecture that remains incompletely understood. We sought to understand the contribution of species variation in mitochondrial DNA to yeast thermotolerance. We used mitochondrial transgenesis to show that mitotypes were sufficient for a partial boost to thermotolerance and respiration in the background. These mitochondrial alleles worked best when the background also harbored a pro-thermotolerance nuclear genotype, attesting to positive epistasis between the two genomes. The benefits of alleles in terms of respiration and growth at high temperature came at the cost of worse performance in cooler conditions. Together, our results establish this system as a case in which mitoalleles have fitness benefits and work well in multiple backgrounds; given the high mutation rate of the mitochondrial compartment, they were also likely extra easy for the ancestral population to acquire. We thus propose a broader model in which mitochondrial variants may prove to be especially good candidates in the search for genetic mechanisms of the adaptive process.
生物学中许多令人感兴趣的性状早在很久以前就已进化形成，并在特定物种中固定下来，使其有别于其他姐妹分类群。阐明这些古老性状背后的机制一直是进化生物学家的核心目标。酵母在其亲属中独一无二，因为它能够通过一种尚未完全了解的遗传结构在高温下茁壮成长。我们试图了解线粒体DNA中的物种变异对酵母耐热性的贡献。我们利用线粒体转基因技术表明，线粒体基因型足以在特定背景下部分提高耐热性和呼吸作用。当背景中还存在有利于耐热性的核基因型时，这些线粒体等位基因的效果最佳，证明了两个基因组之间存在正向上位性。线粒体等位基因在高温下对呼吸作用和生长的益处是以在较凉爽条件下表现较差为代价的。总之，我们的研究结果表明，这个系统是一个线粒体等位基因具有适应性优势且在多种背景下都能良好发挥作用的例子；鉴于线粒体区室的高突变率，它们对于祖先种群来说可能也特别容易获得。因此，我们提出了一个更广泛的模型，其中线粒体变异可能被证明是寻找适应性过程遗传机制的特别好的候选者。
