Cellular and regulatory basis of the early stages of stem development.

实际上，植物的所有地上部分都起源于被称为茎顶端分生组织的特殊结构，在那里保持着活跃分裂细胞的储备。几十年的研究揭示了许多关于分生组织外围如何启动新叶或花的问题。相比之下，鲜为人知的是，被称为肋分生组织的SAM基底区是如何产生新的茎组织的。这在一定程度上是由于肋骨分生组织无法使用成像方法，而成像方法在揭示分生组织功能的其他方面发挥了关键作用。茎的起源不仅是一个相对被忽视的主要植物发育过程，而且在作物改良中也非常重要：茎的高度和粗壮影响植物在恶劣天气中倒下的可能性，植物有多少资源可以用于结果实和种子，以及收获它们的容易程度。在包括小麦在内的一些植物中，茎还储存淀粉，为籽粒灌浆提供能量储备。在这里，我们建议利用成像技术的最新发展来揭示支撑干细胞发育的细胞分裂和生长模式，以及这种细胞行为如何受到肋骨分生组织中起作用的调控基因的影响。以拟南芥为模型，我们将专注于控制茎发育的基因，即使是在水稻等远缘关系的作物中也是如此。具体地说，我们的目标是回答以下问题：1.什么细胞分裂和生长模式支撑着干细胞形成的早期阶段？我们将使用高分辨率成像和基于计算机的3D重建来获得关于发育中的干细胞生长和分裂的定量数据。我们还将使用对细胞进行遗传标记的方法，并允许我们跟踪它们的后代如何对新组织的形成做出贡献。2.调控基因如何影响1中研究的细胞行为？我们将使用相同的方法来比较正常植物和茎发育因调控基因突变而改变的植物。3.发育茎上的生长和组织形成是如何协调的？这个问题将通过植物来解决，在这些植物中，调控基因只在发育中的干细胞的一部分细胞中被激活；这将使我们能够确定特定的细胞和组织是否产生控制邻近细胞和组织行为的信号。4.在干细胞发育过程中，调节基因对细胞行为和信号的影响，是什么基因表达的变化？调控基因通常激活或抑制一整套其他基因，从而导致细胞行为的变化。我们将比较不同干细胞调节剂激活引起的基因活性变化，以揭示哪些基因介导了它们对细胞分裂、生长和信号的影响。除了让我们深入了解植物如何生长的一个主要但鲜为人知的方面，所产生的知识和方法预计将有助于未来的作物育种。通过了解早期茎发育的细胞学基础，将有可能设计出更精确的方法来操纵作物育种中的茎结构。

Virtually all of the aerial parts of the plant originate from specialised structures called shoot apical meristems, where reserves of actively dividing cells are maintained. Decades of study have revealed much about how new leaves or flowers are initiated in the periphery of the meristems. In contrast, little is known about how new stem tissues are produced by the basal region of the SAM, called the rib meristem. This has been in part due to the inaccessibility of the rib meristem to imaging methods that had a key role in revealing other aspects of meristem function. The origin of the stem is not only a major plant developmental process that has been relatively neglected, but is also of great importance in crop improvement: the height and sturdiness of the stem affect the likelihood that plants fall over in bad weather, how much of the plant's resources can be directed to making fruits and seeds, and how easy it is to harvest them. In some plants, including wheat, the stem also stores starch that provides energy reserves for grain filling. Here, we propose to take advantage of recent developments in imaging techniques to reveal the cell division and growth patterns that underpin stem development and how this cell behaviour is influenced by regulatory genes that function in the rib meristem. Using Arabidopsis as the model, we will focus on genes that also control stem development even in distantly related crop plants, such as rice. Specifically, we aim to answer the following questions: 1. What patterns of cell division and growth underpin the early stages of stem formation? We will use high-resolution imaging and computer-based 3D reconstruction to obtain quantitative data on cell growth and division in the developing stem. We will also use methods that genetically mark cells and allow us to follow how their descendants contribute to the formation of new tissues. 2. How do regulatory genes influence the cell behaviour studied in 1? We will use the same methods to compare normal plants and plants in which stem development is altered by mutation of regulatory genes. 3. How is growth and tissue formation co-ordinated across the developing stem? This question will be addressed using plants in which regulatory genes are activated in only a subset of the cells of the developing stem; this will allow us to determine whether specific cells and tissues produce signals that control the behaviour of adjacent cells and tissues. 4. What changes in gene expression underlie the effects of regulatory genes on cell behaviour and signalling during stem development? Regulatory genes typically activate or repress whole sets of other genes to cause changes in cell behaviour. We will compare changes in gene activity caused by activation of different stem regulatory to reveal what genes mediate their effects on cell division, growth and signalling. In addition to giving us insight into a major but poorly understood aspect of how plants grow, the knowledge and methods produced are expected to aid future crop breeding. By knowing the cellular basis for early stem development, it will be possible to design more precise ways to manipulate stem architecture during crop breeding.