Selective advantages favour high genomic AT-contents in intracellular elements
Selective advantages favour high genomic AT-contents in intracellular elements
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DOI：
10.1371/journal.pgen.1007778
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发表时间：
2019-04-01
期刊：
影响因子：
4.5
通讯作者：
Kost, Christian
中科院分区：
文献类型：
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作者：
Dietel, Anne-Kathrin;Merker, Holger;Kost, Christian
染色体外遗传元件如细菌内共生体和质粒通常表现出相对于其宿主DNA增加的AT-含量。内共生基因组的AT-偏好通常被解释为中性进化过程，例如A+T增加的突变偏好。在这里，我们实验表明，主机依赖性元素的AT含量增加，可以选择性地青睐。通过引入富含A+ T或富含G+ C的质粒来操纵细菌细胞的核苷酸组成，我们证明了含有富含GC的质粒的细胞比含有富含AT的质粒的细胞更不适合。此外，富含GC的元素的成本可以通过提供G+C的前体而不是A+T的前体来补偿，从而将所观察到的适应性效应与核苷酸的细胞质可用性联系起来。因此，将富含AT和富含GC的质粒引入具有不同基因组GC含量的其他细菌物种揭示了富含G+ C的质粒的成本随着其宿主基因组DNA的GC含量的增加而降低。总之，我们的工作确定选择作为一个强大的进化力量，驱动细胞内遗传元件的基因组向更高的A+T contents.Author摘要内共生细菌的基因组通常比他们的自由生活的亲戚更AT-丰富。有趣的是，其他细胞内元件（如质粒或噬菌体）的基因组也往往比其宿主的基因组更富含AT。内共生体基因组的AT-偏好通常由中性进化过程来解释。然而，由于A+T核苷酸比G+C核苷酸更丰富且能量更便宜，另一种解释是选择性优势驱动细胞内元件的核苷酸组成。在这里，我们提供了强有力的实验证据表明，细胞内的元素，其基因组比宿主的基因组更AT-丰富，选择性地有利于主机水平。因此，我们的研究结果强调了选择对染色体外遗传因子的DNA碱基组成的重要性。
Extrachromosomal genetic elements such as bacterial endosymbionts and plasmids generally exhibit AT-contents that are increased relative to their hosts' DNA. The AT-bias of endosymbiotic genomes is commonly explained by neutral evolutionary processes such as a mutational bias towards increased A+T. Here we show experimentally that an increased AT-content of host-dependent elements can be selectively favoured. Manipulating the nucleotide composition of bacterial cells by introducing A+T-rich or G+C-rich plasmids, we demonstrate that cells containing GC-rich plasmids are less fit than cells containing AT-rich plasmids. Moreover, the cost of GC-rich elements could be compensated by providing precursors of G+C, but not of A+T, thus linking the observed fitness effects to the cytoplasmic availability of nucleotides. Accordingly, introducing AT-rich and GC-rich plasmids into other bacterial species with different genomic GC-contents revealed that the costs of G+C-rich plasmids decreased with an increasing GC-content of their host's genomic DNA. Taken together, our work identifies selection as a strong evolutionary force that drives the genomes of intracellular genetic elements toward higher A+T contents.Author summary Genomes of endosymbiotic bacteria are commonly more AT-rich than the ones of their free-living relatives. Interestingly, genomes of other intracellular elements like plasmids or bacteriophages also tend to be richer in AT than the genomes of their hosts. The AT-bias of endosymbiotic genomes is commonly explained by neutral evolutionary processes. However, since A+T nucleotides are both more abundant and energetically less expensive than G+C nucleotides, an alternative explanation is that selective advantages drive the nucleotide composition of intracellular elements. Here we provide strong experimental evidence that intracellular elements, whose genome is more AT-rich than the genome of the host, are selectively favoured on the host level. Thus, our results emphasize the importance of selection for shaping the DNA base composition of extrachromosomal genetic elements.