The role of cell geometry, growth and mechanics in plant cell division.

由于植物生长是共质体，植物必须通过精确调节细胞生长和分裂来创造它们的形式。有人提出，植物有对称细胞分裂的默认规则，定义为子细胞具有相同命运的分裂。提出的规则是基于细胞的几何形状，生长方向或机械应力，尽管这些似乎都不能捕捉植物范围内的细胞行为。由于这些因素是相互关联的，似乎所有细胞都有一个潜在的默认规则，观察到的差异是由于不同的生长速率，细胞感知的机械环境或其他参数。也有报道称，非对称或形成性分裂通常不遵循默认规则，并且几何不对称和子细胞命运不对称之间存在关联。 在这个项目中，我们将使用计算形态动力学方法来量化3D中的生长和细胞分裂，以确定细胞使用哪些参数来定向分裂。我们将建立一个三维力学模型的组织研究，以确定细胞感知的应力，以及如何将这些可能被整合到分裂平面方向的确定。然后，我们将扩展该模型，以了解如何修改规则的形成分裂。我们将主要使用两个生物系统开发的其他合作伙伴在RU。拟南芥侧根的发生是Maizel实验室的研究重点，拟南芥胚珠和珠被的发育是Schneitz实验室的研究重点。两者都是研究初级形态发生的良好系统，因为它们开始具有相对较少的细胞，具有可变的并且通常高度各向异性的生长，并且导致具有几种不同细胞类型的非平凡形状的规格。该系统显示出全3D成像的前景，在侧根出现的情况下，全3D时间推移。我们将使用这些系统来确定拟南芥侧根和胚珠细胞分裂的默认规则，目标是统一以前提出的许多不同但似乎相关的分裂规则。我们将研究如何将形成性划分整合到模型中，以及它们是否只是潜在机制的简单变体。我们也将探讨这些系统中几何不对称与命运不对称之间的关系。

Since plant growth is symplastic, plants must create their form by precisely regulating cell growth and division. It has been proposed that plants have default rules for symmetric cell division, defined as divisions where the daughter cells have the same fate. Proposed rules have been based on the geometry of the cell, growth directions, or mechanical stresses, although none of these seems able to capture plant-wide cell behaviour. Since these factors are interrelated, it seems likely that there is an underlying default rule for all cells, and the differences observed are due to different growth rates, the mechanical environment perceived by the cell or other parameters. It has also been reported that non-symmetric or formative divisions often do not follow the default rule, and that there is an association between geometric asymmetry and daughter cell fate asymmetry.  In this project we will use a computational morphodynamics approach to quantify growth and cell division in 3D, to determine which parameters the cell is using to orient division. We will build a 3D mechanical model of the tissue under study, in order to determine the stresses that cell perceives, and how these may be integrated into the determination of division plane orientation. We will then extend the model to understand how rules might be modified for formative divisions.We will primarily use two biological systems developed by other partners in the RU. The emergence of Arabidopsis lateral root is the focus of the Maizel lab, and the development of the Arabidopsis ovule and integuments is the focus of the Schneitz lab. Both are good systems to study primary morphogenesis, as they begin with relatively few cells, have variable and often highly anisotropic growth, and result in the specification of non-trivial shapes with several different cell types. The systems show promise for full 3D imaging, and in the case of lateral root emergence, full 3D time-lapse. We will use these systems to determine the default rules for cell division in the Arabidopsis lateral root and the ovule, with the goal to unify the many different but seemingly related division rules proposed previously. We will investigate how formative divisions can be integrated into the model, and whether they are just a straightforward variation of the underlying mechanism. We will also investigate the relationship between geometry asymmetry and fate asymmetry in these systems.