Laboratoire de Reproduction et Développement des Plantes, Université de Lyon, ENS de Lyon, UCBL, INRAE, CNRS, 69364 Lyon Cedex 07, France.
Mechanobiology Institute, National University of Singapore, 117411 Singapore, Singapore.
Proc Natl Acad Sci U S A. 2020 Dec 22;117(51):32731-32738. doi: 10.1073/pnas.2008895117. Epub 2020 Dec 7.
In plant cells, cortical microtubules (CMTs) generally control morphogenesis by guiding cellulose synthesis. CMT alignment has been proposed to depend on geometrical cues, with microtubules aligning with the cell long axis in silico and in vitro. Yet, CMTs are usually transverse in vivo, i.e., along predicted maximal tension, which is transverse for cylindrical pressurized vessels. Here, we adapted a microwell setup to test these predictions in a single-cell system. We confined protoplasts laterally to impose a curvature ratio and modulated pressurization through osmotic changes. We find that CMTs can be longitudinal or transverse in wallless protoplasts and that the switch in CMT orientation depends on pressurization. In particular, longitudinal CMTs become transverse when cortical tension increases. This explains the dual behavior of CMTs in planta: CMTs become longitudinal when stress levels become low, while stable transverse CMT alignments in tissues result from their autonomous response to tensile stress fluctuations.
在植物细胞中，皮层微管（CMTs）通常通过指导纤维素合成来控制形态发生。CMT 的排列被认为取决于几何线索，即微管在计算机模拟和体外与细胞长轴对齐。然而，CMTs 在体内通常是横向的，即沿着预测的最大张力排列，对于圆柱形加压容器来说，最大张力是横向的。在这里，我们在单细胞系统中采用微井装置来测试这些预测。我们将原生质体横向限制以施加曲率比，并通过渗透压变化来调节加压。我们发现，无壁原生质体中的 CMT 可以是纵向的或横向的，CMT 取向的转换取决于加压。具体来说，当皮层张力增加时，纵向 CMT 变为横向。这解释了 CMT 在植物体内的双重行为：当应力水平降低时，CMTs 变为纵向，而组织中稳定的横向 CMT 排列则是由于它们对拉伸应力波动的自主响应。
