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

人为污染的有毒重金属土壤的定植是植物快速进化适应过程的一个有希望的模型。在富含炉甘石族金属（锌、镉、铅）的土壤上建立种群的大量平行事件只发生在拟南芥（拟南芥）的姊妹枝种中。有趣的是，在这些含金属的地点中，有一小部分不仅有a. halleri，而且还有密切相关的a. arenosa。在这些位点，两种植物的中间金属相关生理以及一些中间形态植物的出现表明了种间杂交的可能性。在这里，我们的目标是解决在这两个物种对炉甘石含金属土壤的适应中，halleri和a.a arensa之间的基因流动的作用，而不是每个物种内部的选择的作用。黑桫椤对含金属土壤的适应只需要进化出增强的耐金属性。即使在未受污染的土壤上，由于锌和镉的过量积累，即使在异常高浓度的> 3000和>100µg -1的干叶生物量下，a . halleri也已经表现出对炉甘石金属的全物种高耐受性。研究表明，在含金属土壤中，黑桫椤金属超耐受性的增强与金属超积累的衰减有关。相比之下，像几乎所有其他植物一样，a.a arenosa通常是金属排斥物种。我们在这里重点研究了炉甘石重金属污染和非污染地点的地理集群，这些地点今天在野外自然地同时生长着阿勒哈里和阿勒诺沙。这些都是用比较的方法来分析的，相对于非金属参考地点只容纳两种中的一种。我们评估了物种间全基因组的基因渗入，并定位了代表其他物种基因渗入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识别两个物种中选择的基因组区域，作为第一阶段的延续，我们将这种方法应用于A. halleri中罕见的铜超耐受性。为了测试适应的分子表型后果，我们比较了两种物种中选定的一组群体的基因表达。在这些地点收集的形态中间植物个体中，我们在田间对叶片和土壤组成进行了表征，以获得初始表型信息。我们通过与两个假设的亲本物种进行比较，确定了倍性水平，并在序列水平上分析了起源于halleri和a.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.