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

拟南芥（Arabidopsis halleri）是拟南芥（a.t aliana）的近亲之一，它表现出自然选择的极端特征，即必需金属锌（Zn）和有毒金属镉（Cd）的超积累水平比其他植物高出数百倍，并能够占领富含金属的栖息地。对欧洲黑桫椤的自然多样性进行了全面调查。叶片和土壤样品的多元素分析、植物发育阶段记录、生境和气候数据构成了同类数据中最大的野外数据集。例如，我们的分析揭示了锌在物种范围内的超积累和镉积累的巨大自然变化，这强烈依赖于生物地理区域。我们最近发现了一种环境污染最严重的污染物——铅的超积累。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，从而组装了最全面表征植物起源地点特征的植物集合。在统一条件下的表型分析揭示了叶片基因组谱的前所未有的自然变异。Zn和Cd的变异极大，金属的积累在金属污染地点的个体中明显受到部分抑制。金属的过度积累被认为对食草动物有保护作用。事实上，我们一直发现植物通过Cd和Zn进行元素防御对多种咀嚼食草动物有效，包括可能适应野外收集的昆虫。我们定义了一个28个个体的核心集合，对(i)金属超积累自然多样性的生理和分子机制进行深入的生理、分子和生态解剖，以及（ii）金属超积累元素防御的生态作用，其中包括Pb。在不同的土壤条件下，培育后的核心种质中，金属转运途径会比较有特点。研究金属积累和硫代葡萄糖苷含量作为十字花科植物主要的经典化学防御，以确定防御投入的变化及其与生境特征的关系。对极端个体的核心收集和基因组重测序进行全面的转录组分析，以及现有的分子洞察力，将指导选择直接测试的基因，以确定它们对金属积累自然变异的贡献。转基因株系将在本地黑草土壤上产生并进行表型分析。此外，利用适当的基因型和金属分配不同的转基因品系，将确定金属超积累作为一种抵御吸血昆虫的元素防御的贡献。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.