Table_1_Integrated Metabolome and Transcriptome Analyses Reveal Dissimilarities in the Anthocyanin Synthesis Pathway Between Different Developmental Leaf Color Transitions in Hopea hainanensis (Dipterocarpaceae).XLSX

Changes in plant leaf color during development are directly related to the accumulation or degradation of certain phytochemicals such as anthocyanins. Since some anthocyanins can be beneficial to human health and provide insights into the biology of leaves, the underlying processes and timing by which plants produce these molecules has been the focus of numerous studies. The tree species Hopea hainanensis generally produces green leaves at all growth stages; however, a few explored individuals have been identified possessing red leaves on the top of the seedlings at a young stage. While the phenomenon of leaf color varying with age has been studied in several species, the underlying mechanisms are largely unknown in H. hainanensis. Using a metabolomics approach, the young red leaves in H. hainanensis were found to contain higher levels of anthocyanins and flavonoids than the young green-leaved individuals. Among anthocyanins, pelargonidin and cyanidin were the most likely candidates contributing to the red color of the young leaves. Transcriptome results indicated the genes related to the production of these anthocyanins were significantly upregulated, leading to greater accumulation of red pigments. Specifically, the expression of several MYB and bHLH genes in young red leaf lines was significantly higher than that in the young green leaf lines, especially HhMYB66, HhMYB91, HhMYB6, and HhbHLH70. As such these four transcription factors are probably the main regulatory genes resulting in young red leaves in H. hainanensis. From these results, comparative analyses with other species can be made to better understand the evolution of pigment biosynthesis and how anthocyanins function in plant metabolism and evolution/adaptation.

植物叶片发育过程中色彩的变化与特定植物化学物质，如花青素的积累或降解密切相关。鉴于某些花青素对人体健康有益，并能揭示叶片的生物学特性，因此，植物产生这些分子的潜在过程及其时间节点一直是众多研究的热点。海南望天树（Hopea hainanensis）这一树种在所有生长阶段通常产生绿色叶片；然而，已有少数个体被发现，在幼苗早期阶段顶部叶片呈现红色。尽管叶片颜色随年龄变化的现象在多个物种中已有研究，但在海南望天树中，其背后的机制尚不清楚。采用代谢组学方法研究发现，海南望天树幼苗的红色叶片含有比绿色叶片个体更高的花青素和黄酮类化合物。在花青素中，天竺葵定和锦葵定可能是导致幼苗叶片呈现红色的最有可能的候选物质。转录组分析结果显示，与这些花青素产生相关的基因表达显著上调，导致红色色素的积累增加。具体而言，在幼苗红色叶片系中，MYB和bHLH基因家族的几个基因的表达水平显著高于绿色叶片系，尤其是HhMYB66、HhMYB91、HhMYB6和HhbHLH70。因此，这四个转录因子可能是导致海南望天树幼苗产生红色叶片的主要调控基因。基于这些结果，可以与其他物种进行对比分析，以更好地理解色素生物合成的进化以及花青素在植物代谢和进化/适应中的作用。