Data from: Evolution of nickel hyperaccumulation and serpentine adaptation in the Alyssum serpyllifolium species complex

Metal hyperaccumulation is an uncommon but highly distinctive adaptation found in certain plants that can grow on metalliferous soils. Here we review what is known about evolution of metal hyperaccumulation in plants and describe a population-genetic analysis of the Alyssum serpyllifolium (Brassicaceae) species complex that includes populations of nickel-hyperaccumulating as well as non-accumulating plants growing on serpentine (S) and non-serpentine (NS) soils, respectively. To test whether the S and NS populations belong to the same or separate closely related species, we analysed genetic variation within and between four S and four NS populations from across the Iberian peninsula. Based on microsatellites, genetic variation was similar in S and NS populations (average Ho=0.48). The populations were significantly differentiated from each other (overall FST=0.23), and the degree of differentiation between S and NS populations was similar to that within these two groups. However, high S versus NS differentiation was observed in DNA polymorphism of two genes putatively involved in adaptation to serpentine environments, IREG1 and NRAMP4, whereas no such differentiation was found in a gene (ASIL1) not expected to play a specific role in ecological adaptation in A. serpyllifolium. These results indicate that S and NS populations belong to the same species and that nickel hyperaccumulation in A. serpyllifolium appears to represent a case of adaptation to growth on serpentine soils. Further functional and evolutionary genetic work in this system has the potential to significantly advance our understanding of the evolution of metal hyperaccumulation in plants.金属超富集现象（Metal hyperaccumulation）是一类罕见却极具特征的适应性性状，见于部分可在含金属土壤中生长的植物。本研究综述了当前学界关于植物金属超富集演化的已知认知，并针对细叶庭荠（Alyssum serpyllifolium，十字花科Brassicaceae）物种复合体开展种群遗传学分析——该复合体包含分别生长于蛇纹石（S）与非蛇纹石（NS）土壤的镍超富集植物种群与非富集植物种群。为验证蛇纹石种群与非蛇纹石种群是否属于同一或近缘的不同物种，本研究对采自伊比利亚半岛全境的4个蛇纹石种群与4个非蛇纹石种群的种群内及种群间遗传变异进行了分析。基于微卫星标记（microsatellites）的分析结果显示，蛇纹石种群与非蛇纹石种群的遗传变异水平相近（平均观测杂合度Ho=0.48）。各该种群间均存在显著遗传分化（整体固定指数FST=0.23），且蛇纹石种群与非蛇纹石种群间的遗传分化程度，与两类种群内部的分化程度相近。然而，在2个推定参与蛇纹石环境适应的基因IREG1与NRAMP4的DNA多态性中，观测到蛇纹石种群与非蛇纹石种群间存在显著分化；而在细叶庭荠中未被认为具有生态适应特异性功能的基因ASIL1中，则未观测到此类分化。上述结果表明，蛇纹石种群与非蛇纹石种群隶属于同一物种，且细叶庭荠中的镍超富集现象，似乎代表了对蛇纹石土壤生长环境的适应性演化案例。针对该体系开展的后续功能遗传学与演化遗传学研究，有望极大推动学界对植物金属超富集演化机制的认知。