Control of seed and organ size by a ubiquitin-mediated signalling cascade

这项研究旨在了解植物器官，如花瓣、叶片和种子的特征大小是如何确定的。任何生物体最明显的特征之一就是它的大小，这是特定物种的高度特征，但在不同物种之间可能存在巨大差异。尽管这是一个如此明确和独特的特征，但人们对是什么决定了器官和整个生物体的最终大小知之甚少。我们知道，物种有一个非常狭窄的大小范围，他们增长到，然后停止增长。我们知道，器官的生长是通过分化的细胞在器官中执行不同的功能来实现的，当生长的器官达到最终尺寸时，细胞就会以严格协调的方式停止增殖。例如，一些器官，如肝脏，在手术缩小后表现出惊人的能力，可以长回原来的大小。生物学家认为，这可能是因为生长中的肝脏中的细胞(或另一个器官中的细胞，如植物花瓣)“知道”它们相对于邻近细胞的位置，并“记住”分裂了多少次，这样当它们在一个器官中分裂了设定的次数时，它们就会停止分裂。另一种观点认为，细胞在“场”或网格系统中生长，形成一个器官，该系统提供参考点，确定细胞停止分裂的时间。在老鼠、苍蝇和植物等不同的生物中，这两种观点都有实验证据，但在我们有望解释大小等基本生物学特征之前，还需要了解更多。这个项目的研究目的是更多地发现植物器官用来决定其最终大小的基本机制。与动物相比，植物提供了一些特殊的优势，因为每个细胞都被细胞壁包围，一旦分裂，细胞壁就会使它们无法移动。这意味着细胞的“命运”可以随着器官的生长而被绘制出来，这样我们就可以知道最终器官中的每个细胞起源于哪里。此外，叶子和花瓣是几个细胞层深的扁平细胞，因此在生长过程中很容易观察到它们。在植物中，现在可以追踪正在生长的叶子中的单个细胞，从而创造出许多新的理解水平。我们过去的工作已经确定了一种有趣的蛋白质，它在植物拟南芥的器官形成过程中限制细胞增殖。当它发生突变，不再正常工作时，花瓣和叶子等器官最多会增大25%。有趣的是，也会形成更大的种子，因为母株中的种子覆盖物要大得多。也有更多的种子形成，所以每株植物会产生更多、更大的种子。工业界对这一发现很感兴趣，他们现在正试图利用我们发现的基因让玉米和大豆植株获得更高的产量。在这个项目中，我们的目标是更多地了解这种蛋白质是如何工作的，我们已经积累了有助于计划下一阶段研究的证据。我们知道这种名为DA1的蛋白质(“DA”在中文中是“大”的意思，反映了JIC的一名中国研究人员的发现)，它能够切割其他蛋白质，我们已经确定了其中两种蛋白质。我们的目标是识别更多被切割的蛋白质，然后弄清楚它们如何影响叶片和花瓣的生长，以及DA1介导的切割如何协调这些蛋白质的活性，以获得合适的叶片和花瓣大小。我们还想更详细地了解DA1的切割活性是如何控制的，以及它在叶片生长过程中何时何地处于活跃状态。这项工作最终是有用的，因为作物的产量，例如小麦或稻谷，是由植物产生的种子的数量和大小决定的。在不对环境造成更大影响的情况下增加作物产量是我们在未来几年需要实现的一个关键目标，以养活世界人口，该项目产生的想法和资源可以为这些解决方案做出贡献。

This research aims to understand how the characteristic size of plant organs, such as petals, leaves and seeds is determined. One of the most obvious features of any organism is its size, which is highly characteristic for a given species but can vary hugely between species. Despite being such a clear and distinguishing feature, very little is known about what determines the final size of organs and whole organisms. We know that species have a very tight size range that they grow to, and then cease growing. We know organs grow through the multiplication of cells that differentiate to perform different functions in the organ, and that cells stop multiplying in a strictly coordinated manner when the growing organ reaches its final size. For example some organs, such as the liver, exhibit a remarkable ability to grow back to their exact original size after being surgically reduced. Biologists contend that this could be due to the cells in the growing liver (or those in another organ such as a plant petal) "know" where they are relative to neighboring cells and "remember" how many times that have divided, so that when they have divided a set number of times in an organ they stop dividing. Another view is that cells grow to form an organ within a "field" or grid system that provide points of reference that establish when cells stop dividing. There is experimental evidence for both points of view in diverse organisms such as mice, flies and plants, but much more needs to be understood before we can hope to explain such a basic biological characteristic as size. The aim of the research in this project is to discover more about the basic mechanisms that plant organs use to determine their final size. Plants offer some specific advantages compared to animals as each cell is surrounded by a cell wall that renders them immobile once they have divided. This means the "fate" of cells can be mapped as the organ grows so we can tell where each cell in the final organ originated. Also, leaves and petals are flat sheets of cells a few cell layers deep, so they can be easily observed during growth. In plants it is now possible to track the individual cells in a growing leaf, allowing many new levels of understanding to be created. Our past work has identified an interesting protein that limits cell proliferation during organ formation in the plant Arabidopsis. When mutated so it no longer functions correctly, organs such as petals and leaves grow up to 25% larger. Interestingly larger seeds also form, as the seed covering in the mother plant is much larger. There are also more seeds formed so each plant makes more, larger seeds. This discovery was interesting to industry, who are now trying to make maize and soybean plants yield more using the gene we discovered. In this project we aim to understand more about how this protein works, and we have amassed evidence that helps to plan the next stages of our research. We know the protein, called DA1 ("DA" is "big" in Chinese, reflecting its discovery by a Chinese researcher at JIC), is able to cleave other proteins, and we have identified two of these proteins. We aim to identify more proteins that are cleaved and then work out how they may influence leaf and petal growth, and how DA1-mediated cleavage may coordinate the activities of these proteins to achieve proper leaf and petal size. We also want to understand in more detail how the cleavage activity of DA1 is controlled, and where and when it is active during leaf growth. This work is ultimately useful because crop plant yield, for example wheat or rice grains, is determined by the number and size of seeds produced in plants. Increased crop production without making a larger environmental impact is a key goal we need to achieve in the coming years to feed the world population, and the ideas and resources produced in this project could contribute to these solutions.