Biogeography, population genetics and rapid centromere evolution in Saccharomyces cerevisiae

酿酒酵母是一种酵母，可以将酒精加入清酒、葡萄酒和啤酒中，并用于制作面包。一些酿酒酵母菌株也独立于人类生活在橡树的树皮和周围的土壤中。部分是因为清酒、葡萄酒、啤酒和面包非常有趣，部分是因为这种单细胞真菌如此简单，但与动植物细胞有许多共同之处，研究人员在实验室对其进行了数十年的研究。现在，在细胞和分子水平上对酿酒酵母的了解可能比任何动物、植物或其他真菌都要好，但人们对其生态学知之甚少。这项研究将有助于更好地了解欧洲的酿酒酵母，以及它们在不同栖息地和地理位置的迁徙和与亲缘关系的距离。在北美、东南亚和世界各地的橡树树皮中已经发现了酿酒酵母，在荷兰和芬兰的土壤中也发现了酿酒酵母，但在欧洲的橡树中还没有发现。在最近的一项研究中，北美的科学家发现，用酒精和糖对树皮和土壤进行预处理会导致酿酒酵母的分离，尽管它们在树皮和土壤中的出现很少被注意到。这项技术的使用很可能导致在欧洲橡树上发现酿酒酵母。在这项研究中，少量的土壤、树皮或葡萄将被带回实验室并分析酵母菌的存在。以这种方式发现的酵母的DNA序列被研究以寻找遗传细分的迹象。如果有迹象表明，来自不同栖息地或不同地理区域的酵母中盛行着不同类型的DNA序列，那么这表明现在或甚至在过去的几千年里，这些地点之间几乎没有混合。来自不同地点的DNA序列之间的差异可以导致对不同栖息地或地区的酵母菌之间合理混合的时间的估计。这项研究将使用酵母中可能进化最快的DNA序列类型-着丝粒-变化迅速的东西最有可能发现即使是非常相似的酵母之间的差异，因此将最大限度地减少发现差异所需的DNA序列的数量。着丝粒的快速进化虽然对这项研究很有用，但也非常令人好奇。着丝粒在任何类型的细胞分裂中都起着至关重要的作用。它们形成了细胞的机械附着在细胞的所有遗传物质上的点，并将DNA平等地分裂成下一代细胞。20世纪80年代的实验室实验表明，着丝粒DNA序列的某些类型的变化会导致各种类型的失败，从最具破坏性的生长和繁殖失败到酵母后代的生育力下降。为什么如此重要的东西会发展得如此之快？这种快速进化是否会对生长、生育或物种间的生殖隔离产生影响？我还将使用酵母生态调查的数据来解决这个问题。这些来自自然种群的数据，加上几个简单的实验室实验，应该可以揭示着丝粒快速进化的原因和后果。

Saccharomyces cerevisiae is the species of yeast that puts the alcohol into sake, wine and beer and is used to make bread. Some S. cerevisiae strains also live independently of humans in the bark of oak trees and the soil around them. Partly because sake, wine, beer and bread are so interesting and partly because this single-celled fungus is so simple yet has much in common with animal and plant cells, researchers have studied it in the laboratory for decades. Now S. cerevisiae is probably better understood at the cellular and molecular level than any animal, plant or other fungus, yet little is known about its ecology. This study will lead to a better understanding of S. cerevisiae in Europe and how far they migrate and mix with their relatives in different habitats and geographic locations. S. cerevisiae has been discovered in the bark of oak trees in North America, South East Asia and various other parts of the world, they have also been found in soils from Holland and Finland, but they have not yet been discovered in the oaks of Europe. In a recent study, scientists in North America discovered that pretreating bark and soil with alcohol and sugar led to the isolation of S. cerevisiae, even though their occurrence in bark and soil would otherwise rarely be noticed. The use of this technique is likely to lead to the discovery of S. cerevisiae in European oaks. In this study, small amounts of soil, bark or grapes will be taken back to the lab and analysed for the presence of yeasts. The DNA sequences of the yeasts that are discovered in this way are studied for signs of genetic subdivision. If there are signs that different types of DNA sequence prevail among the yeasts from different habitats or different geographic regions, then that suggests that there has been little or no admixture between these sites now or even in the last few thousand years. The level of difference among the DNA sequences from different sites can lead to an estimate of approximately how long it has been since there was reasonable mixture between the yeasts of different habitats or regions. This study will use what is probably the most rapidly evolving type of DNA sequence in yeasts - the centromere - something that changes fast is most likely to pick up the differences among even very similar yeasts, and so will minimise the amount of DNA sequence necessary to spot differences. Though useful for the purposes of this study, the rapid evolution of centromeres is also very curious. Centromeres play a crucial role in any kind of cell division. They form the points at which the cell's machinery attaches to all the genetic material of a cell and organises the equal division of DNA into the next generation of cells. Laboratory experiments in the 1980s showed that certain types of change to the DNA sequence of a centromere resulted in various types of failure, from the most devastating failures in growth and reproduction to reduced fertility among a yeast's offspring. Why would something so important be evolving so fast? Might this rapid evolution have consequences for growth, fertility or the reproductive isolation between species? I will also use the data from the investigation into yeast ecology to address this question. These data from natural populations together with a couple of simple laboratory experiments should reveal the causes and consequences of rapid centromere evolution.