Generation of reiterative growth patterns in plants

每一种开花植物都是由重复的单元组成的：叶、茎、枝、花和根轴。重复也可能发生在器官内，就像橡树叶的多个裂片一样。这种分化依赖于生长区域，分生组织，产生微观生长模块，具有刻板的基因活性模式。了解生长模块的启动和间距是如何控制的，对于我们预测植物器官的数量、排列和形状的能力是至关重要的，这些都是重要的农艺性状。两个因素在生长模块控制中起作用。一个是生长模块生产的限制，植物的定义区域，称为感受态区。其次，生长模块相互作用，使得新模块远离先前的模块产生，从而产生间隔模式。人们已经提出了关于模块-模块相互作用的假设，但我们对能力区是如何控制的知之甚少。这个跨学科的项目建立在拟南芥基因CUC 2的初步结果之上。通常，CUC 2在叶缘基部是活跃的，在那里产生锯齿状生长模块。然而，如果CUC 2在整个叶片中被激活，锯齿就会沿着叶缘沿着，形成分形图案（锯齿上的锯齿）。这些研究结果表明，本地化的CUC 2活动通常限制了模块形成的能力区，并提供了一个机会来研究能力控制的原则，以及它如何与模块模块限制相互作用。我们假设CUC 2的调控将模块限制在叶的基部区域，而另一个基因KANADI将它们限制在叶缘。如果CUC 2在KANADI活性降低的植物中过度活跃，我们预计生长模块将在整个叶表面和边缘产生。我们的第一个目标是在两个物种中测试这一预测：拟南芥和大麦。通过比较这两个系统，我们的目标是建立一般原则如何适用于不同的分类群体，以及它们与作物的相关性。第二个目标是利用分形行为表现出过度活跃的CUC 2叶片测试假设模块模块之间的相互作用在一个简化的上下文中。通过跟踪这些植物叶片发育过程中的细胞，我们将能够建立模块间距的规则，区分细胞不同末端的标记（极性标记）如何随时间变化，生长如何影响锯齿形状，细胞分裂如何调节，以及这些特性如何在锯齿程度不同的叶片之间变化。第三个目标是在不同的时间和地点诱导过度活跃的CUC 2，以测试哪些基因被CUC 2激活，以及它们是直接激活还是通过细胞之间的信号传导激活。我们还将确定叶缘中的CUC 2活性是否对生长的影响至关重要，并测试候选信号分子。第四个目标是确定CUC 2如何与植物生长激素生长素相互作用，生长素已知会影响生长模块的形成。这将通过确定过度活跃的CUC 2在植物中的作用来实现，其中生长素运输受到药物或基因突变的影响。第五个目标是根据我们的实验观察开发计算模型，以澄清不同假设的预测，从而区分它们。满足这些目标将提供一个更深层次的机械理解能力是如何控制和相互作用与模块模块的限制，以产生迭代的增长模式，支撑我们的能力，预测和修改植物生长和架构。

Every flowering plant is made up of repeating units: leaves, stems, branches, flowers and root axes. Repetition may also occur within organs, as with the multiple lobes of an oak leaf. Such reiterations depend on growing regions, meristems, producing microscopic growth modules, which have stereotypic patterns of gene activity. Understanding how the initiation and spacing of growth modules is controlled is fundamental for our ability to predict the number, arrangement and shape of organs on a plant, key traits of agronomic importance. Two elements are at play in growth module control. One is restriction of growth module production to defined regions of the plant, termed competence zones. Secondly, growth modules interact with each other such that new modules are produced far away from previous ones, creating a spacing pattern. Hypotheses have been proposed for module-module interaction but we know much less about how the competence zone is controlled. This interdisciplinary project builds on preliminary results with a gene in Arabidopsis, CUC2. Normally CUC2 is active at the base of the leaf margin, where serration growth modules are produced. However, if CUC2 is activated throughout the leaf, serrations are produced all along the leaf margin, creating a fractal pattern (serrations upon serrations). These findings indicate that localised CUC2 activity normally restricts the zone of competence for module formation, and provide an opportunity to study the principles of competence control and how it interacts with module-module restriction. We hypothesise that regulation of CUC2 restricts modules to basal regions of the leaf, and that another gene, KANADI, restricts them to the leaf margin. If CUC2 is overactive in a plant with reduced KANADI activity, we expect growth modules to be produced throughout the leaf surface and margin. Our first objective is to test this prediction in two species: Arabidopsis and barley. By comparing these two systems we aim to establish how generally principles apply across different taxonomic groups, and their relevance to crops. The second objective is to exploit the fractal behaviour exhibited by leaves with overactive CUC2 to test hypotheses for module-module interactions in a simplified context. By following the cells of these plants as the leaf develops, we will be able to establish rules for module-module spacing, how markers that distinguish different ends of the cell (polarity markers) change over time, how growth influences serration shape, how cell divisions are modulated, and how these properties vary between leaves with different extents of serration. The third objective is to induce over-active CUC2 at different times and places, to test ideas for which genes are activated by CUC2 and whether they are activated directly or via signalling between cells. We will also determine whether CUC2 activity in the leaf margin is critical for effects on growth, and test candidate signalling molecules. The fourth objective is to determine how CUC2 interacts with the plant growth hormone, auxin, which is known to influence growth module formation. This will be achieved by determining the effect of overactive CUC2 in plants where auxin transport is compromised by drugs or genetic mutations. The fifth objective is to develop computational models based on our experimental observations to clarify predictions of different hypotheses and thus discriminate between them. Meeting these objectives will provide a deeper mechanistic understanding of how competence is controlled and interacts with module-module restrictions to generate reiterative growth patterns, underpinning our ability to predict and modify plant growth and architecture.