Laboratoire de Reproduction et Développement des Plantes, Université de Lyon, Université Claude Bernard Lyon 1, ENS de Lyon, Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAE), CNRS, 69364 Lyon Cedex 07, France;
Department of Astronomy and Theoretical Physics, Lund University, SE22362 Lund, Sweden.
Proc Natl Acad Sci U S A. 2021 Feb 23;118(8). doi: 10.1073/pnas.2017859118.
Artificial mechanical perturbations affect chromatin in animal cells in culture. Whether this is also relevant to growing tissues in living organisms remains debated. In plants, aerial organ emergence occurs through localized outgrowth at the periphery of the shoot apical meristem, which also contains a stem cell niche. Interestingly, organ outgrowth has been proposed to generate compression in the saddle-shaped organ-meristem boundary domain. Yet whether such growth-induced mechanical stress affects chromatin in plant tissues is unknown. Here, by imaging the nuclear envelope in vivo over time and quantifying nucleus deformation, we demonstrate the presence of active nuclear compression in that domain. We developed a quantitative pipeline amenable to identifying a subset of very deformed nuclei deep in the boundary and in which nuclei become gradually narrower and more elongated as the cell contracts transversely. In this domain, we find that the number of chromocenters is reduced, as shown by chromatin staining and labeling, and that the expression of linker histone H1.3 is induced. As further evidence of the role of forces on chromatin changes, artificial compression with a MicroVice could induce the ectopic expression of H1.3 in the rest of the meristem. Furthermore, while the methylation status of chromatin was correlated with nucleus deformation at the meristem boundary, such correlation was lost in the mutant. Altogether, we reveal that organogenesis in plants generates compression that is able to have global effects on chromatin in individual cells.
人工机械扰动会影响培养的动物细胞中的染色质。这是否与生物活体组织的生长也有关，目前仍存在争议。在植物中，气生器官的出现是通过分生组织顶端在芽的周围的局部生长而发生的，该顶端分生组织还包含一个干细胞小生境。有趣的是，有人提出器官生长会在马鞍形器官-分生组织边界域中产生压缩。然而，这种生长诱导的机械应力是否会影响植物组织中的染色质尚不清楚。在这里，通过在体内随时间对核被膜进行成像并定量测量核变形，我们证明了在该区域存在活跃的核压缩。我们开发了一种定量分析方法，能够识别边界深处和细胞横向收缩时逐渐变窄和变长的非常变形核的子集。在该区域，我们发现染色质染色和标记显示染色质浓缩中心的数量减少，并且连接组蛋白 H1.3 的表达被诱导。作为力对染色质变化作用的进一步证据，使用 MicroVice 进行人工压缩可以在分生组织的其余部分诱导 H1.3 的异位表达。此外，虽然染色质的甲基化状态与分生组织边界处的核变形相关，但在 突变体中这种相关性消失了。总之，我们揭示了植物器官发生产生的压缩能够对单个细胞中的染色质产生全局影响。
