Department of Algal Development and Evolution, Max Planck Institute for Developmental Biology, Tübingen, Germany.
Plant Reprod. 2021 Dec;34(4):267-285. doi: 10.1007/s00497-021-00422-3. Epub 2021 Jul 8.
Plants and algae have a complex life history that transitions between distinct life forms called the sporophyte and the gametophyte. This phenomenon-called the alternation of generations-has fascinated botanists and phycologists for over 170 years. Despite the mesmerizing array of life histories described in plants and algae, we are only now beginning to learn about the molecular mechanisms controlling them and how they evolved. Epigenetic silencing plays an essential role in regulating gene expression during multicellular development in eukaryotes, raising questions about its impact on the life history strategy of plants and algae. Here, we trace the origin and function of epigenetic mechanisms across the plant kingdom, from unicellular green algae through to angiosperms, and attempt to reconstruct the evolutionary steps that influenced life history transitions during plant evolution. Central to this evolutionary scenario is the adaption of epigenetic silencing from a mechanism of genome defense to the repression and control of alternating generations. We extend our discussion beyond the green lineage and highlight the peculiar case of the brown algae. Unlike their unicellular diatom relatives, brown algae lack epigenetic silencing pathways common to animals and plants yet display complex life histories, hinting at the emergence of novel life history controls during stramenopile evolution.
植物和藻类具有复杂的生活史，它们在孢子体和配子体这两种截然不同的生命形式之间转换。这种被称为世代交替的现象已经吸引了植物学家和藻类学家 170 多年。尽管植物和藻类的生活史描述令人着迷，但我们才刚刚开始了解控制它们的分子机制以及它们是如何进化的。表观遗传沉默在真核生物的多细胞发育过程中对基因表达的调控起着至关重要的作用，这引发了人们对其对植物和藻类生活史策略影响的疑问。在这里，我们追溯了表观遗传机制在植物界的起源和功能，从单细胞绿藻到被子植物，并试图重建影响植物进化过程中生活史转变的进化步骤。这个进化场景的核心是将表观遗传沉默从一种基因组防御机制适应为交替世代的抑制和控制。我们将讨论范围扩大到绿藻之外，并强调褐藻这一特殊情况。与它们的单细胞硅藻亲缘关系不同，褐藻缺乏动物和植物共有的表观遗传沉默途径，但却表现出复杂的生活史，这暗示了在不等鞭毛类植物的进化过程中出现了新的生活史控制机制。
