BACKGROUND Rockweeds are among the most important foundation species of temperate rocky littoral shores. In the Baltic Sea, the rockweed Fucus vesiculosus is distributed along a decreasing salinity gradient from the North Atlantic entrance to the low-salinity regions in the north-eastern margins, thus, demonstrating a remarkable tolerance to hyposalinity. The underlying mechanisms for this tolerance are still poorly understood. Here, we exposed F. vesiculosus from two range-margin populations to the hyposaline (2.5 PSU - practical salinity unit) conditions that are projected to occur in the region by the end of this century as a result of climate change. We used transcriptome analysis (RNA-seq) to determine the gene expression patterns associated with hyposalinity acclimation, and examined the variation in these patterns between the sampled populations. RESULTS Hyposalinity induced different responses in the two populations: in one, only 26 genes were differentially expressed between salinity treatments, while the other population demonstrated up- or downregulation in 3072 genes. In the latter population, the projected future hyposalinity induced an acute response in terms of antioxidant production. Genes associated with membrane composition and structure were also heavily involved, with the upregulation of fatty acid and actin production, and the downregulation of ion channels and alginate pathways. Changes in gene expression patterns clearly indicated an inhibition of the photosynthetic machinery, with a consequent downregulation of carbohydrate production. Simultaneously, energy consumption increased, as revealed by the upregulation of genes associated with respiration and ATP synthesis. Overall, the genes that demonstrated the largest increase in expression were ribosomal proteins involved in translation pathways. The fixation rate of SNP:s was higher within genes responding to hyposalinity than elsewhere in the transcriptome. CONCLUSIONS The high fixation rate in the genes coding for salinity acclimation mechanisms implies strong selection for them. The among-population differentiation that we observed in the transcriptomic response to hyposalinity stress suggests that populations of F. vesiculosus may differ in their tolerance to future desalination, possibly as a result of local adaptation to salinity conditions within the Baltic Sea. These results emphasise the importance of considering interspecific genetic variation when evaluating the consequences of environmental change.

中文翻译：

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褐藻墨角藻对低盐度的基因调控反应。


背景岩藻是温带岩石沿岸最重要的基础物种之一。在波罗的海，岩藻墨角藻从北大西洋入口到东北边缘的低盐度区域沿着递减的盐度梯度分布，因此表现出对低盐度的显着耐受性。这种耐受性的潜在机制仍然知之甚少。在这里，我们将两个分布范围边缘种群的 F. vesiculosus 暴露于低盐度（2.5 PSU - 实际盐度单位）条件下，预计到本世纪末，由于气候变化，该地区将出现这种情况。我们使用转录组分析 (RNA-seq) 来确定与低盐度适应相关的基因表达模式，并检查了采样群体之间这些模式的变化。结果 低盐度在两个群体中引起不同的反应：其中一个群体中，只有 26 个基因在盐度处理之间存在差异表达，而另一个群体中 3072 个基因表现出上调或下调。在后一人群中，预计未来的低盐度会引起抗氧化剂产生的急性反应。与膜组成和结构相关的基因也密切相关，脂肪酸和肌动蛋白产生上调，离子通道和藻酸盐途径下调。基因表达模式的变化清楚地表明光合作用机制受到抑制，从而导致碳水化合物产生的下调。同时，与呼吸和 ATP 合成相关的基因上调表明，能量消耗增加。 总体而言，表现出表达增加最大的基因是参与翻译途径的核糖体蛋白。 SNP:s 的固定率在响应低盐度的基因中比在转录组中的其他地方更高。结论 编码盐度驯化机制的基因的高固定率意味着对它们的强烈选择。我们在对低盐度胁迫的转录组反应中观察到的种群间差异表明，F. vesiculosus 种群对未来海水淡化的耐受性可能有所不同，这可能是由于波罗的海内局部适应盐度条件的结果。这些结果强调了在评估环境变化的后果时考虑种间遗传变异的重要性。