Rapid evolutionary adaptation to heavy metal-polluted soils in plant species of the genus Arabidopsis

重金属污染土壤的定殖是植物快速进化适应过程的一个有前途的模型。大量的平行事件的建立种群的土壤中富含炉甘石组的金属-锌（Zn），镉（Cd）和铅（Pb）-只发生在拟南芥的姐妹分支中的物种之间的阿哈勒里。thaliana. 有趣的是，这些含金属位点中的一小部分不仅存在A。halleri，但也有密切相关的物种A。arenosa。在这些网站上，中间金属相关的生理在这两个物种，以及一些植物的中间形态的发生表明经常性种间杂交的可能性。在这里，我们的目标是解决的作用，基因流之间的A。halleri和A. arenosa在这两个物种的适应炉甘石含金属的土壤，相比，每个物种单独的选择的作用。A. halleri对含金属土壤的作用仅仅需要进化出增强的金属超耐受性。A. halleri已经表现出物种范围内的超耐受炉甘石金属的结果，超积累的锌和镉的非常高的浓度>3,000和>100 μg g g-1干叶生物量，分别，即使在未污染的土壤。增强了A.已显示含金属土壤上的Halleri涉及金属超积累的衰减。相比之下，A.与几乎所有其他植物一样，arenosa通常是金属排斥物种。我们在这里集中在炉甘石重金属污染和非污染场地的地理集群的网站组，其中A。halleri和A. arenosa自然生长在一起的领域今天。这些进行了分析，在一个比较的方法，在非金属参考网站托管的两个物种之一。我们评估物种间基因组范围内的渐渗，并定位代表从其他物种渐渗的单倍型的基因组区域。与此同时，我们应用基因组扫描方法来确定基因组区域，已受到选择的两个物种中的任何一个，在延续的第一阶段，我们将这种方法应用于罕见的铜超耐受性在A。halleri。为了测试适应的分子表型后果，我们比较了两个物种的一组选定的人群之间的基因表达。在形态中间的植物个体收集在这些网站上，我们在该领域的特点叶和土壤成分，以获得初始的表型信息。我们通过与两个假设的亲本物种进行比较来确定倍性水平，并且我们在序列水平上分析了植物中起源于A的基因组成分。halleri和A. arenosa。

The colonization of soils anthropogenically polluted with toxic levels of heavy metals is a promising model for processes of rapid evolutionary adaptation in plants. A large number of parallel incidences of the establishment of populations on soils enriched in the calamine group of metals – zinc (Zn), cadmium (Cd) and lead (Pb) – have occurred only in Arabidopsis halleri among the species in the sister clade of A. thaliana. Interestingly, a small subset of such metalliferous sites host not only A. halleri but also the closely related species A. arenosa. At these sites, the intermediate metal-related physiology in both species as well as the occurrence of a few plants of intermediate morphology suggest the possibility of recurrent inter-species hybridization. Here we aim to address the role of gene flow between A. halleri and A. arenosa in the adaptation of both species to calamine metalliferous soils, as compared to the role of selection within each species individually. The adaptation of A. halleri to metalliferous soils merely required the evolution of enhanced metal hypertolerance. A. halleri already exhibits species-wide hypertolerance to calamine metals as a result of the hyperaccumulation of Zn and Cd to extraordinarily high concentrations of >3,000 and >100 µg g-1 dry leaf biomass, respectively, even on non-contaminated soils. Enhanced metal hypertolerance in A. halleri on metalliferous soils has been shown to involve an attenuation of metal hyperaccumulation. By contrast, A. arenosa is generally a metal excluder species, like almost all other plants. We focus here on geographically clustered site groups of calamine heavy metal-contaminated and non-contaminated sites where both A. halleri and A. arenosa naturally grow together in the field today. These are analysed in a comparative approach in relation to non-metalliferous reference sites hosting only one of the two species. We assess between-species introgression genome-wide and localize genomic regions representing haplotypes introgressed from the other species. In parallel, we apply genome scan approaches to identify genomic regions that have been subject to selection in either of the two species, in continuation of the first phase where we applied this approach to the rare incidences of copper hypertolerance in A. halleri. To test for molecular phenotypic consequences of adaptation, we compare gene expression among a chosen set of populations of both species. In morphologically intermediate plant individuals collected at these sites, we characterize leaf and soil composition in the field to obtain initial phenotypic information. We determine ploidy levels by comparison to the two hypothesized parental species, and we analyse plants at the sequence level with respect to the genomic components originating from A. halleri and A. arenosa.