Geometric-edge specification in cell growth mechanics and morphogenesis

生物学的一个基本挑战是解释复杂的有机体如何发展出自然界中观察到的错综复杂的解剖形式。农作物的生产力和效用严重依赖于特定解剖形式的发展，这些解剖形式通常与野生状态相比发生了巨大变化。生物形态的发展需要化学和机械信息在几个组织尺度上进行整合：分子组装成更大的组装体;分子组装组织内部细胞结构;细胞内结构决定细胞特性;细胞群组装成组织，组织组装成器官，器官组装成有机体。然而，这个高度复杂的过程非常稳健-例如，对称花朵上的花瓣每个都具有相似的大小和形状，或者现代小麦品种生长到非常均匀的高度。发展的一个奇怪的特点是，尽管在较低规模的组织（例如，细胞大小、形状和数量）生物形式在更高尺度下通常是稳健的。这很像一堵干石墙，尽管建造它的石头尺寸各不相同，但它具有固定的高度和厚度。最近的一个想法，支持我们最近的工作，是在组织的亚细胞尺度的变异性不只是“系统中的噪音”，但在更高的尺度上保持强大的可再现的形式的机制的重要组成部分。生物体的整体形状由其组成细胞的大小、形状和排列决定。植物细胞被坚硬的细胞壁所包围，细胞壁可以抵抗内部的高压并决定其形状。细胞壁还可以防止平面上的细胞相互滑动，就像它们在动物胚胎形成过程中所做的那样。因此，植物的最终形态主要是通过控制每个细胞生长的形状来决定的。这需要控制细胞生长的方向。生长是由细胞的内部压力驱动的，该压力在所有方向上都是平等的，因此生长的方向由细胞壁在该细胞的不同区域的机械特性决定。为了成功地产生最终的植物形态，细胞生长的控制必须在成百上千的细胞中协调。这需要生长器官中细胞之间的化学和机械信号。它还需要一种机制，使每个细胞都能对这些信号做出适当的反应，并采用适合其在最终结构中位置的形状。人们对这是如何发生的知之甚少。这项研究的主要目的是增加我们的理解-生长和形式是如何控制在单个植物细胞的水平-这是如何协调细胞之间，以实现适当的形式在多细胞水平-如何在较低尺度的变异性影响最终的形式我们将专注于一个重要的，新发现的，机制，有助于控制植物细胞生长。我们将研究这种机制在植物发育过程中所做出的分子和机械贡献。简而言之，我们最近在植物中发现了一种内部运输机制，可以将物质专门输送到细胞的几何边缘（即两个面相遇的地方）。我们已经证明，当这种运输机制被破坏时，细胞和组织变得混乱。我们认为这是一种机制的一部分，这种机制允许细胞调整自己的大小，形状和生长速度，以产生适当的最终形式。为了验证我们的假设，我们组建了一个由生物学家、物理学家和工程师组成的跨学科团队，通过结合计算模型、遗传和生化分析、4D光学显微镜和动态原子力显微镜的力学测量来解决这个问题。

A fundamental challenge in biology is to explain how complex organisms develop the intricate anatomical forms observed in nature. The productivity and utility of crop plants is critically dependent on the development of particular anatomical forms that are often grossly altered from the wild state. The development of biological form requires chemical and mechanical information to be integrated at several scales of organisation: molecules assemble into larger assemblies; molecular assemblies organise internal cell structures; intracellular structures determine cellular properties; groups of cells assemble into tissues, tissues into organs, and organs into organisms. This highly complex process is nevertheless remarkably robust - petals on a symmetrical flower each have similar size and shape for example, or modern wheat varieties which grow to a remarkably uniform height. A curious feature of development is that despite variability at lower scales of organisation (e.g., cell size, shape and number) biological form is typically robust at higher scales. This is rather like a dry-stone wall having a regular height and thickness despite variability in the sizes of the stones from which it is built. A recent idea, supported by our recent work, is that the variability at subcellular scales of organisation is not simply 'noise in the system' but is an essential part of the mechanism that maintains robust reproducible form at higher scales. The overall shape of an organism is determined by the size, shape and arrangement of its component cells. Plant cells are surrounded by a rigid cell wall that resists their high internal pressure and determines their shape. Cell walls also prevent cells in plan from slipping past each other as they do during the formation of animal embryos. Consequently, the final form of the plant is determined principally by controlling the shape into which each cell grows. This requires the direction of cell growth to be controlled. Growth is driven by the cells' internal pressure, which acts equally in all directions, so the direction of growth is determined by the mechanical properties of cells' wall at the different regions of that cell. To successfully generate the final plant form, the control of cell growth must be coordinated across hundreds and thousands of cells. This requires both chemical and mechanical signalling between cells in growing organs. It also requires mechanisms that allow each individual cell to respond appropriately to these signals, adopting a shape that is appropriate to its position in the final structure. Little is known about how this happens. This research aims primarily to increase our understanding of- how growth and form are controlled at the level of individual plant cells- how this is co-ordinated between cells to achieve proper form at the multicellular level- how variability at lower scales influences the final form We will focus on an important, newly discovered, mechanism that contributes to the control of plant cell growth. We will investigate the molecular and mechanical contribution that this mechanism makes during plant development. In short, we have recently discovered an internal transport mechanism in plants that delivers material specifically to the geometric edges of cells (i.e. where two faces meet). We have shown that when this transport mechanism is disrupted, cells and tissues become disorganised. We believe that this is part of a mechanism that allows cells to adjust their own size, shape and growth rate to produce an appropriate final form. We believe this is based on the detection of, and response to, mechanical stresses in the tissue.To test our hypotheses we have assembled an interdisciplinary team of biologists, physicists and engineers to tackle this problem with a combination of computational models, genetic and biochemical analysis, plus 4D-light microscopy and mechanical measurements by dynamic atomic-force microscopy.