Laboratory of Biochemistry, Wageningen University and Research, Wageningen 6708 WE, The Netherlands.
Physical Chemistry and Soft Matter, Wageningen University and Research, Wageningen 6708 WE, The Netherlands.
Development. 2023 Nov 15;150(22). doi: 10.1242/dev.201943. Epub 2023 Nov 9.
Plant external surfaces are often covered by barriers that control the exchange of molecules, protect from pathogens and offer mechanical integrity. A key question is when and how such surface barriers are generated. Post-embryonic surfaces have well-studied barriers, including the cuticle, and it has been previously shown that the late Arabidopsis thaliana embryo is protected by an endosperm-derived sheath deposited onto a primordial cuticle. Here, we show that both cuticle and sheath are preceded by another structure during the earliest stages of embryogenesis. This structure, which we named the embryonic envelope, is tightly wrapped around the embryonic surface but can be physically detached by cell wall digestion. We show that this structure is composed primarily of extensin and arabinogalactan O-glycoproteins and lipids, which appear to form a dense and elastic crosslinked embryonic envelope. The envelope forms in cuticle-deficient mutants and in a mutant that lacks endosperm. This embryo-derived envelope is therefore distinct from previously described cuticle and sheath structures. We propose that it acts as an expandable diffusion barrier, as well as a means to mechanically confine the embryo to maintain its tensegrity during early embryogenesis.
植物的外部表面通常被屏障覆盖，这些屏障控制着分子的交换，防止病原体入侵，并提供机械完整性。一个关键问题是这些表面屏障何时以及如何产生。胚胎后期的表面有研究得很好的屏障，包括角质层，先前的研究表明，拟南芥晚期胚胎被一层由胚乳衍生的鞘包裹，沉积在原始角质层上。在这里，我们发现在胚胎发生的最早阶段，在角质层和鞘之前还有另一种结构。我们将这个结构命名为胚胎包膜，它紧紧地包裹在胚胎表面，但可以通过细胞壁消化将其物理分离。我们表明，这个结构主要由伸展蛋白和阿拉伯半乳聚糖 O-糖蛋白和脂质组成，它们似乎形成了一个密集而有弹性的交联的胚胎包膜。该包膜在缺乏角质层的突变体和缺乏胚乳的突变体中形成。因此，这种由胚胎产生的包膜与先前描述的角质层和鞘结构不同。我们提出，它作为一种可扩展的扩散屏障，以及一种机械限制胚胎的手段，以在早期胚胎发生过程中保持其整体性。
