Extreme environments offer powerful opportunities to study how different organisms have adapted to similar selection pressures at the molecular level. Arctic plants have adapted to some of the coldest and driest biomes on Earth and typically possess suites of similar morphological and physiological adaptations to extremes in light and temperature. Here, we compare patterns of molecular evolution in three Brassicaceae species that have independently colonized the Arctic and present some of the first genetic evidence for plant adaptations to the Arctic environment. By testing for positive selection and identifying convergent substitutions in orthologous gene alignments for a total of 15 Brassicaceae species, we find that positive selection has been acting on different genes, but similar functional pathways in the three Arctic lineages. The positively selected gene sets identified in the three Arctic species showed convergent functional profiles associated with extreme abiotic stress characteristic of the Arctic. However, there was little evidence for independently fixed mutations at the same sites and for positive selection acting on the same genes. The three species appear to have evolved similar suites of adaptations by modifying different components in similar stress response pathways, implying that there could be many genetic trajectories for adaptation to the Arctic environment. By identifying candidate genes and functional pathways potentially involved in Arctic adaptation, our results provide a framework for future studies aimed at testing for the existence of a functional syndrome of Arctic adaptation in the Brassicaceae and perhaps flowering plants in general.

中文翻译：

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北极十字花科极端非生物胁迫适应的多种遗传轨迹。

极端环境为研究不同生物如何在分子水平上适应相似的选择压力提供了强大的机会。北极植物已经适应了地球上一些最冷和最干燥的生物群落，并且通常拥有一系列相似的形态和生理适应性，可以适应极端的光照和温度。在这里，我们比较了三个独立于北极殖民地的十字花科物种的分子进化模式，并提出了一些植物适应北极环境的第一个遗传证据。通过测试阳性选择并在总共15个十字花科物种的直系同源基因比对中鉴定趋同替换，我们发现阳性选择已作用于不同的基因，但在三个北极谱系中具有相似的功能途径。在三个北极物种中鉴定出的积极选择的基因集显示出与北极极度非生物胁迫特征相关的趋同功能分布。但是，几乎没有证据表明在相同位点有独立固定的突变以及作用于相同基因的阳性选择。这三个物种似乎通过改变相似的应激反应途径中的不同成分而进化出了相似的适应套装，这暗示着可能有许多遗传轨迹可以适应北极环境。通过确定可能与北极适应有关的候选基因和功能途径，我们的结果为今后的研究提供了一个框架，旨在测试在十字花科和一般开花植物中是否存在北极适应功能综合征。