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

重金属污染土壤的定植是植物快速进化适应过程的一种很有前途的模式。在富含炉甘石金属锌(锌)、镉(镉)和铅(铅)的土壤上建立种群的大量平行事件仅发生在拟南芥中，而拟南芥是拟南芥的姐妹支系。有趣的是，这类含金属地点的一小部分不仅是哈勒氏原虫的宿主，还包括与之密切相关的物种。在这些地点，两个物种与金属相关的中间生理以及少数中间形态的植物的出现表明了反复发生物种间杂交的可能性。在这里，我们的目的是研究哈勒氏针茅和斑潜蝇之间的基因流在这两个物种适应炉甘石金属土壤中的作用，并比较每个物种内选择的作用。哈勒氏菌对金属土壤的适应只需要增强的金属超耐性的进化。即使在未受污染的土壤上，由于锌和镉对超高浓度的&gt；3000和&gt；100微克g-1干叶生物量的过度积累，哈勒里已经表现出对炉甘石金属的物种范围的高度耐受性。在含金属的土壤上，哈勒氏木霉对金属的超耐受性的增强涉及到金属超积累的减弱。相比之下，白木香和几乎所有其他植物一样，通常是一种排除金属的物种。我们在这里关注的是炉甘石重金属污染和非污染场地的地理聚集性站点组，今天在这些场地上，哈勒氏木霉和金边木兰自然生长在一起。对这两个物种中只有一个物种所在的非金属参照点进行了比较分析。我们在全基因组范围内评估物种间的导入，并定位代表从其他物种导入的单倍型的基因组区域。同时，我们应用基因组扫描方法来识别在这两个物种中的任何一个物种中受到选择的基因组区域，这是第一阶段的继续，在第一阶段中，我们将这种方法应用于罕见的铜质耐受在哈勒氏菌中的发生。为了测试适应的分子表型结果，我们比较了两个物种选定的一组种群中的基因表达。在这些地点收集的形态中等的植物个体中，我们对田间的叶片和土壤成分进行表征，以获得初步的表型信息。我们通过与两个假想的亲本物种进行比较来确定倍性水平，并在序列水平上分析植物起源于A.halli和A.arenosa的基因组成分。

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.