Mutational hotspots can determine evolutionary outcomes and make evolution repeatable. Hotspots are products of multiple evolutionary forces including mutation rate heterogeneity, but this variable is often hard to identify. In this work we reveal that a powerfully deterministic genetic hotspot can be built and broken by a handful of silent mutations. We observed this when studying homologous immotile variants of the bacteria Pseudomonas fluorescens, AR2 and Pf0-2x. AR2 resurrects motility through highly repeatable de novo mutation of the same nucleotide in >95% lines in minimal media (ntrB A289C). Pf0-2x, however, evolves via a number of mutations meaning the two strains diverge significantly during adaptation. We determined that this evolutionary disparity was owed to just 6 synonymous variations within the ntrB locus, which we demonstrated by swapping the sites and observing that we were able to both break (>95% to 0% in AR2) and build (0% to 80% in Pf0-2x) a powerfully deterministic mutational hotspot. Our work reveals a fundamental role for silent genetic variation in determining adaptive outcomes.

中文翻译：

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可以通过沉默的遗传变化建立和破坏决定高度可重复进化的突变热点

突变热点可以确定进化结果，并使进化可重复。热点是包括突变率异质性在内的多种进化力的产物，但是这个变量通常很难识别。在这项工作中，我们揭示了可以通过少数沉默突变来建立和破坏强大的确定性遗传热点。我们在研究荧光假单胞菌，AR2和Pf0-2x的同源运动变体时观察到了这一点。AR2通过在最小培养基（ntrB）中> 95％的品系中相同核苷酸的高度可重复的从头突变来恢复运动A289C）。然而，Pf0-2x是通过许多突变进化而来的，这意味着这两种菌株在适应过程中会发生很大的差异。我们确定这种进化差异是由于ntrB基因座内只有6个同义变异所致，我们通过交换位点并观察到我们能够断裂（AR2中> 95％至0％）和构建（0％至Pf0-2x中有80％）是确定性强的突变热点。我们的工作揭示了沉默遗传变异在确定适应性结果中的基本作用。