Department of Biology, Duke University, Durham, NC 27708, United States.
Department of Biology, Duke University, Durham, NC 27708, United States.
Mol Phylogenet Evol. 2020 Oct;151:106904. doi: 10.1016/j.ympev.2020.106904. Epub 2020 Jul 6.
The flavonoids, one of the largest classes of plant secondary metabolites, are found in lineages that span the land plant phylogeny and play important roles in stress responses and as pigments. Perhaps the most well-studied flavonoids are the anthocyanins that have human health benefits and help plants attract pollinators, regulate hormone production, and confer resistance to abiotic and biotic stresses. The canonical biochemical pathway responsible for the production of these pigments is well-characterized for flowering plants yet its conservation across deep divergences in land plants remains debated and poorly understood. Many early land plants such as mosses, liverworts, and ferns produce flavonoid pigments, but their biosynthetic origins and homologies to the anthocyanin pathway remain uncertain. We conducted phylogenetic analyses using full genome sequences representing nearly all major green plant lineages to reconstruct the evolutionary history of the anthocyanin biosynthetic pathway then test the hypothesis that genes in this pathway are present in early land plants. We found that the entire pathway was not intact until the most recent common ancestor of seed plants and that orthologs of many downstream enzymes are absent from seedless plants including mosses, liverworts, and ferns. Our results also highlight the utility of phylogenetic inference, as compared to pairwise sequence similarity, in orthology assessment within large gene families that have complex duplication-loss histories. We suggest that the production of red-violet flavonoid pigments widespread in seedless plants, including the 3-deoxyanthocyanins, requires the activity of novel, as-yet discovered enzymes, and represents convergent evolution of red-violet coloration across land plants.
类黄酮是植物次生代谢产物中最大的一类，存在于跨越陆地植物系统发育的谱系中，在应激反应和作为色素中发挥重要作用。也许研究得最多的类黄酮是花色苷，它们对人体健康有益，有助于植物吸引传粉者、调节激素产生，并赋予植物对非生物和生物胁迫的抗性。负责生产这些色素的典型生化途径在开花植物中得到了很好的描述，但它在陆地植物的深度分化中是否保守仍然存在争议，并且了解甚少。许多早期的陆地植物，如苔藓、地钱和蕨类植物，都会产生类黄酮色素，但它们的生物合成起源和与花色苷途径的同源性仍然不确定。我们使用代表几乎所有主要绿色植物谱系的全基因组序列进行系统发育分析，以重建花色苷生物合成途径的进化历史，然后检验该途径的基因存在于早期陆地植物中的假设。我们发现，直到种子植物的最近共同祖先，整个途径才完整，并且许多下游酶的同源物在无籽植物中缺失，包括苔藓、地钱和蕨类植物。我们的结果还强调了在具有复杂重复缺失历史的大基因家族中进行同源性评估时，与成对序列相似性相比，系统发育推断的效用。我们认为，在无籽植物中广泛存在的红色-紫色类黄酮色素的产生，包括 3-去氧花色苷，需要新的、尚未发现的酶的活性，并且代表了陆地植物中红色-紫色颜色的趋同进化。
