The cost of copy number in a selfish genetic element: the 2-μM plasmid of Saccharomyces cerevisiae
The cost of copy number in a selfish genetic element: the 2-μM plasmid of Saccharomyces cerevisiae
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DOI：
10.1111/j.1420-9101.2012.02610.x
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发表时间：
2012-11-01
影响因子：
2.1
通讯作者：
Maclean，R. C.
中科院分区：
文献类型：
--
作者：
Harrison，E.;Koufopanou，V.;Maclean，R. C.
许多自主复制的遗传元件在细胞内以多个拷贝的形式存在。这些元素的拷贝数通常被认为对元素和宿主都有重要的适应性影响，但塑造其进化的力量还没有得到很好的理解。2 μm是一个多拷贝的酵母菌质粒，只编码四个基因，这些基因只参与质粒复制。酵母菌和2 μm之间适合度关系的一个简单模型是，质粒拷贝数在选择增加垂直传播（有利于高拷贝数）和选择降低毒力（有利于低拷贝数）之间进行权衡。为了测试这个模型，我们实验性地操纵质粒的拷贝数，并直接测量与高质粒拷贝数相关的生长速率降低方面的适应性成本。我们发现，2 μm的适应性负担随着质粒拷贝数的增加而增加，因此每个拷贝的适应性负担为0.17%（± 0.008%），大大超过了在酵母菌群中稳定维持的预期成本。我们的研究结果证明了拷贝数在酵母每2 μm关联进化中的至关重要性，并为未来研究选择如何塑造多拷贝元件的成本铺平了道路。
Many autonomously replicating genetic elements exist as multiple copies within the cell. The copy number of these elements is often assumed to have important fitness consequences for both element and host, yet the forces shaping its evolution are not well understood. The 2 μm is a multicopy plasmid ofSaccharomycesyeasts, encoding just four genes that are solely involved in plasmid replication. One simple model for the fitness relationship between yeasts and 2 μm is that plasmid copy number evolves as a trade‐off between selection for increased vertical transmission, favouring high copy number, and selection for decreased virulence, favouring low copy number. To test this model, we experimentally manipulated the copy number of the plasmid and directly measured the fitness cost, in terms of growth rate reduction, associated with high plasmid copy number. We find that the fitness burden imposed by the 2 μm increases with plasmid copy number, such that each copy imposes a fitness burden of 0.17% (± 0.008%), greatly exceeding the cost expected for it to be stably maintained in yeast populations. Our results demonstrate the crucial importance of copy number in the evolution of yeast per 2 μm associations and pave the way for future studies examining how selection can shape the cost of multicopy elements.