背景回顾：Growth extent and direction determine cell and whole-organ architecture. 

提出问题：How they are spatio-temporally modulated to control size and shape is not well known.

主要研究：Here we tackled this question by studying the effect of brassinosteroid (BR) signalling on the structure of the root meristem. 

结果1-BR信号对于细胞生长速率和各向异性的影响：Quantification of the three-dimensional geometry of thousands of individual meristematic cells across different tissue types showed that the modulation of BR signalling yields distinct changes in growth rate and anisotropy, which affects the time that cells spend in the meristem and has a strong impact on the final root form. 

结果2-BR信号对于细胞体积没有影响：By contrast, the hormone effect on cell volume was minor, establishing cell volume as invariant to the effect of BR. 

小结论1：Thus, BR has the highest effect on cell shape and growth anisotropy, regulating the overall longitudinal and radial growth of the meristem, while maintaining a coherent distribution of cell sizes. 

结果4-模型模拟揭示inner和outer组织对于BR的差异响应：Moving from single-cell quantification to the whole organ, we developed a computational model of radial growth. The simulation demonstrates how differential BR-regulated growth between the inner and outer tissues shapes the meristem and thus explains the non-intuitive outcomes of tissue-specific perturbation of BR signalling. 

小结论2：The combined experimental data and simulation suggest that the inner and outer tissues have distinct but coordinated roles in growth regulation.

 摘 要 

生长程度和方向决定了细胞和整个器官的结构。它们的大小和形状是如何在时空水平上被调控还不清楚。本文中，作者通过研究油菜素类内酯BR信号转导对根分生组织结构的影响来解析这个问题。作者通过对不同组织类型的数千个单个分生组织细胞的三维几何进行量化，结果表明对BR信号转导的调控会导致不同的生长速率和各向异性的改变，影响了细胞处于分生状态的时间，并且对于最终的根的形态产生了比较强烈的影响。相反，激素对于细胞体积的影响甚微，因此对于BR效应来说，细胞体积是一个不变量。因此，BR对于细胞形态和生长的各向异性具有最大的影响，调控了分生组织在纵向和径向上的整体生长，同时又保持了细胞大小的相干分布。从单个细胞的量化到整个器官，作者开发了一个径向生长的计算模型。模拟数据显示了内层和外层的组织受到BR的差异调控塑造了分生组织，因此也解释了为何通过组织特异性的BR信号扰动会得到非直观的结果。结合实验数据和模拟结果，结果表明内层和外层组织在生长调控方面具有不同的，但却相互协调的作用。