Natural variation, underlying molecular basis and ecological role of metal hyperaccumulation in Arabidopsis halleri

十字花科植物拟南芥是拟南芥的近缘种之一，具有天然选择的极端特征，即必需金属锌和有毒金属镉的超量积累，比其他植物高出几百倍，并具有在富含金属的生境中定居的能力。我们对欧洲沙棘的自然多样性进行了全面的调查。叶片和土壤样本的多元素分析、植物发育阶段的记录、生境和气候数据构成了这类数据中最大的野外数据集。例如，我们的分析揭示了物种范围内锌的过度积累和强烈依赖于生物地理区域的镉积累的巨大自然变异。我们最近在哈勒里发现了铅的过度积累，这是最具问题的环境污染物之一。我们将来自170多个自然地点的900多个基因型转移到温室中，从而汇集了关于植物起源地点的特征最全面的植物集合。在均匀的条件下对这个集合进行表型分析，发现了叶片离子轮廓的前所未有的自然变异。锌和镉的变异是极端的，金属污染场地的个体金属积累明显受到部分抑制。金属的过度堆积被认为是为了提供对食草动物的保护。事实上，我们一直发现，通过镉和锌的植物元素防御对广泛的咀嚼草食动物有效，包括可能适应野外采集的昆虫。我们定义了一个由28个个体组成的核心种质，对(I)自然多样性在金属超积累中潜在的生理和分子机制，以及(Ii)在金属超积累元素防御中的生态作用，新包括铅，进行了深入的生理、分子和生态剖析。在不同土壤条件下栽培后，核心种质中的金属转运途径将具有相对的特征。金属积累将与硫代葡萄糖苷作为十字花科植物主要的经典化学防御物质一起研究，以确定国防投资的变化及其与栖息地特征的关系。对核心样本的全面转录组分析和极端个体的基因组重新测序以及现有的分子洞察力将指导选择直接测试其对金属积累自然变异的贡献的基因。转基因品系将在原生黑曲霉土壤上产生并进行表型鉴定。此外，将使用适当的基因类型和不同的金属分配转基因品系来确定金属超积累作为抵御吸食昆虫的基本防御措施的贡献。我们的目标是揭示适应极端环境的关键步骤。

The Brassicaceae species Arabidopsis halleri, one of the closest relatives of A. thaliana, exhibits naturally selected extreme traits, namely hyperaccumulation of the essential metal zinc (Zn) as well as the toxic metal cadmium (Cd) to levels several hundred fold higher than other plants, and the ability to colonize metal-rich habitats. We conducted a comprehensive survey of natural diversity of European A. halleri. Multi-element analysis in leaf and soil samples, records of plant developmental stage, habitat and climatic data constitute the largest field dataset of its kind. Our analysis uncovered, for instance, species-wide hyperaccumulation of Zn and tremendous natural variation in Cd accumulation that is strongly dependent on the biogeographic region. We newly discovered in A. halleri the hyperaccumulation of lead (Pb), one of the most problematic environmental pollutants. We transferred more than 900 genotypes from over 170 natural sites into the greenhouse, thus assembling the plant collection that is most comprehensively characterized with respect to characteristics at the sites of plant origin. Phenotyping of this collection under uniform conditions revealed unprecedented natural variation in leaf ionomic profiles. Variation was extreme for Zn and Cd, and metal accumulation was apparently partially suppressed in individuals from metal-contaminated sites. Metal hyperaccumulation is hypothesized to afford protection against herbivory. Indeed, we consistently found that plant elemental defence through Cd and Zn is effective on a wide range of chewing herbivores including potentially adapted field-collected insects. We defined a core collection of 28 individuals for in-depth physiological, molecular, and ecological dissection of (i) the physiological and molecular mechanisms underlying natural diversity in metal hyperaccumulation, and (ii) the ecological role in elemental defence of metal hyperaccumulation, newly including Pb. Metal translocation pathways will be comparatively characterized in the core collection upon cultivation under a variety of edaphic conditions. Metal accumulation will be studied alongside glucosinolate contents as the major classical chemical defence in Brassicaceae to determine the variation in defence investment and its relation with habitat characteristics. Comprehensive transcriptome analysis of the core collection and genome re-sequencing of extreme individuals as well as existing molecular insight will guide the selection of genes to be tested directly for their contribution to natural variation in metal accumulation. Transgenic lines will be generated and phenotyped on native A. halleri soils. Furthermore, the contribution of metal hyperaccumulation as an elemental defence against sucking insects will be determined using appropriate genotypes and transgenic lines differing in metal partitioning. We aim to unravel key steps in the adaptation to an extreme environment.