Untargeted metabolic profiling reveals geography as the strongest predictor of metabolic phenotypes of a cosmopolitan weed

Plants produce a multitude of metabolites that contribute to their fitness and survival, and play a role in local adaptation to environmental conditions. The effects of environmental variation is particularly well studied within the genus Plantago, however, previous studies have largely focused on targeting specific metabolites. Studies exploring metabolome wide changes are lacking, and the effects of natural environmental variation and herbivory on the metabolomes of plants growing in situ remain unknown. An untargeted metabolomic approach using ultra-high performance liquid chromatography-mass spectrometry, coupled with variation partitioning, general linear mixed modelling, and network analysis was used to detect differences in metabolic phenotypes of Plantago major in fifteen natural populations across Denmark. Geographic region, distance, habitat type, phenological stage, soil parameters, light levels, and leaf area, were investigated for their relative contributions to explaining differences in foliar metabolomes. Herbivory effects were further investigated by comparing metabolomes from damaged and undamaged leaves from each plant. Geographic region explained the greatest number of significant metabolic differences. Soil pH had the second largest effect, followed by habitat and leaf area, whilst phenological stage had no effect. No evidence of the induction of metabolic features was found between leaves damaged by herbivores compared to undamaged leaves on the same plant. Differences in metabolic phenotypes explained by geographic factors are attributed to genotypic variation and/or unmeasured environmental factors that differ at the regional level in Denmark. A small number of specialised features in the metabolome may be involved in facilitating the success of a widespread species such as Plantago major into such wide range of environmental conditions, though overall resilience in the metabolome was found in response to environmental parameters tested. Untargeted metabolomic approaches have great potential to improve our understanding of how specialised plant metabolites respond to environmental change and assist in adaptation to local conditions.

植物会合成大量代谢物，这些代谢物有助于其生存与适合度提升，并在物种对环境的局部适应过程中发挥关键作用。环境变异对植物的影响在车前属（Plantago）植物中已有较为充分的研究，但既往研究多聚焦于特定代谢物的分析。目前尚缺乏针对代谢组（metabolome）全域变化的系统性研究，且自然环境变异与植食作用对原位生长植物代谢组的影响仍不明确。本研究针对丹麦境内15个自然种群的大车前草（Plantago major），采用超高效液相色谱-质谱联用（ultra-high performance liquid chromatography-mass spectrometry）非靶向代谢组学方法，结合变异分区分析、广义线性混合模型与网络分析，探究其代谢表型的差异。研究考察了地理区域、空间距离、生境类型、物候期、土壤参数、光照水平与叶面积等因素对叶片代谢组差异的相对解释贡献度。此外，通过对比单株植物上受植食损伤与未受损伤叶片的代谢组，进一步探究了植食作用的影响效应。结果显示，地理区域对代谢差异的解释度最高；土壤pH次之，随后依次为生境类型与叶面积，而物候期未产生显著影响。未发现同一植株上受植食损伤叶片与未损伤叶片间存在代谢特征诱导的证据。地理因素所解释的代谢表型差异，可归因于丹麦区域层面存在差异的基因型变异与/或未被测定的环境因素。尽管在所测试的环境参数下，代谢组整体表现出一定的弹性，但其内少量特化代谢特征或许有助于大车前草这类广布物种在多样环境条件下成功定植。非靶向代谢组学方法具有巨大潜力，可加深我们对植物特化代谢物如何响应环境变化、并协助物种适应局部环境的认知。