Tissue folding at the organ-meristem boundary results in nuclear compression and chromatin compaction.

Abstract

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.

Plant phenotyping relevance

植物組織内の核変形を経時イメージングで定量化する解析パイプラインを開発し、核の形態状態を抽出しているため、表現型取得法が研究上実質的に中心である。

Code and data availability

The paper's Data Availability statement deposits original confocal phenotyping data (meristem/nucleus imaging) in the Cambridge repository and provides the authors' segmentation/quantification analysis pipeline scripts on the Sainsbury Laboratory GitLab. Both are paper-specific, public, and actionable.