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 h1.3 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动物细胞中的染色质。这是否也与生物体内的组织生长有关还存在争议。在植物中，空中器官的出现是通过在茎尖分生组织的外围局部生长而发生的，而茎尖分生组织也含有干细胞小生境。有趣的是，已提出器官生长在鞍形器官-分生组织边界域中产生压缩。尚不清楚这种生长诱导的机械应力是否影响植物组织中的染色质。在这里，通过对体内随时间推移的核包膜进行成像并量化核变形，我们证明了该域中存在主动核压缩。我们开发了一种定量流水线，该流水线适合于识别边界深处非常变形的原子核的子集，其中随着细胞横向收缩，原子核逐渐变窄和变长。在该域中，我们发现，染色质染色和标记显示色中心数量减少，并且诱导了接头组蛋白H1.3的表达。作为力对染色质变化作用的进一步证据，用MicroVice进行人工压缩可在其余分生组织中诱导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，但这种相关性在染色体中丢失了。如染色质染色和标记所示，诱导了接头组蛋白H1.3的表达。作为力对染色质变化作用的进一步证据，用MicroVice进行人工压缩可在其余分生组织中诱导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，但这种相关性在染色体中丢失了。如染色质染色和标记所示，诱导了接头组蛋白H1.3的表达。作为力对染色质变化作用的进一步证据，用MicroVice进行人工压缩可在其余分生组织中诱导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，但这种相关性在染色体中丢失了。h1.3突变体。总而言之，我们揭示了植物中的器官发生会产生压缩作用，从而能够对单个细胞的染色质产生全局影响。