A transcriptomic hourglass in plant embryogenesis

摘要

Animal and plant development starts with a constituting phase called embryogenesis, which evolved independently in both lineages. Comparative anatomy of vertebrate development-based on the Meckel-Serres law and von Baer's laws of embryology from the early nineteenth century-shows that embryos from various taxa appear different in early stages, converge to a similar form during mid-embryogenesis, and again diverge in later stages. This morphogenetic series is known as the embryonic 'hourglass, and its bottleneck of high conservation in mid-embryogenesis is referred to as the phylotypic stage. Recent analyses in zebrafish and Drosophila embryos provided convincing molecular support for the hourglass model, because during the phylotypic stage the transcriptome was dominated by ancient genes and global gene expression profiles were reported to be most conserved. Although extensively explored in animals, an embryonic hourglass has not been reported in plants, which represent the second major kingdom in the tree of life that evolved embryogenesis. Here we provide phylotranscriptomic evidence for a molecular embryonic hourglass in Arabidopsis thaliana, using two complementary approaches. This is particularly significant because the possible absence of an hourglass based on morphological features in plants suggests that morphological and molecular patterns might be uncoupled. Together with the reported developmental hourglass patterns in animals, these findings indicate convergent evolution of the molecular hourglass and a conserved logic of embryogenesis across kingdoms.%当拟南芥从一个单细胞合子发育成一个成熟的植物胚胎时，它会经过一个阶段，在这个阶段，从系统发生学上来说非常古老的基因优先得到表达。这证实了最近对动物所做的研究，后者显示动物也有一个相似的胚胎发生时期，这个时期与十九世纪动物学家所认定的一个发育阶段是～致的(至少对脊椎动物来说是这样)：在这个阶段所有物种的胚胎都很像。 看来，在动物和植物从～个单细胞合子rn变为一个多细胞生物体的过程中，它们都独立地形成了一个相似的管理基因表达的方式，尽管它们的形态发育很不相同。