PIN proteins and architectural change in plants.

生物学中的一个关键挑战是了解复杂形状和特殊功能的身体部位是如何在发育过程中产生的。在植物中，整体形状反映了分枝模式、叶片起始模式和叶片从顶端开始的相对生长。这些特征对植物生产力的影响很大，因为它们影响光合作用中的光拦截。因为许多作物是几乎没有分枝的草，所以叶子的形状和它们在茎周围的排列特别重要。出于这些原因，了解调控叶片排列和生长的基本机制对科学家来说是相当有兴趣的。为了研究这个问题，我们正在研究一种苔藓(Physcomitrella Patens)，和许多植物一样，它的叶子在茎周围呈螺旋状排列。作为叶片发育的模型，Physcomitrella具有许多优势。苔藓是一个进化的古老群体，在这个群体中，大多数在其他植物中发挥作用的基因家族由较少的家族成员代表，这使得精确定位基因功能变得更容易。植株非常小，顶端由单个细胞组成。叶片以单细胞的形式发生，是单细胞层的厚度。这意味着我们已经能够开发出一种在显微镜下拍摄芽起始、叶片起始和叶片发育的技术，并可以产生关于细胞分裂和生长如何影响整体植物形状的定量信息。如果没有计算输入，对这些数据的分析和解释是困难的，所以我们正在与计算机科学家合作，以确定影响形状的关键因素。到目前为止，这样的计算分析已经将叶子的发育抽象为组织规模，或者专注于发育的特定方面，以最大限度地减少计算机处理的限制。由于苔藓叶片的细胞很少，我们已经能够生成一个叶片发育的细胞模型，该模型对细胞分裂和生长对最终叶片形状的贡献做出了具体的预测。一种植物激素，生长素，在调节番茄和拟南芥等植物的叶片起始模式和叶片形状方面发挥了主要作用，因为它调节细胞身份和生长的决定。生长素的调节分布是其活性的一个关键方面，而生长素的运输是由属于一个小基因家族的载体蛋白影响的。目前评估载体蛋白如何影响生长素分布和对整体形状的影响的方法受到多个基因家族成员对运输的贡献的限制。监测开花植物叶片中生长素的分布也是具有挑战性的，因为这只能通过监测生长素反应基因活性的变化来间接实现，而且开花植物叶片具有复杂的组织成分，限制了组织在显微镜下的渗透。苔藓枝条在解剖和遗传上的简单性再次带来了优势。利用苔藓植物了解植物形状的另一个优势是，苔藓枝条对大多数枝条系统具有独立的进化起源。这意味着，如果调控形状的机制与其他研究较好的类群共享，如开花植物，它们很可能是植物形状的通用调控者。因此，我们所产生的知识将非常广泛地适用。

A key challenge in biology is to understand how body parts with complex shapes and specialized functions arise during development. In plants, the overall shape reflects the pattern of branching, the pattern of leaf initiation and the relative growth of leaves initiated from the tip. These traits impact strongly on plant productivity because they affect light interception in photosynthesis. Because many crop species are grasses that have little branching, the shape of leaves and their arrangement around the stem are particularly important. For these reasons, understanding the basic mechanisms that regulate leaf arrangements and growth is of considerable interest to scientists. To study this problem, we are working on a moss (Physcomitrella patens), which like many plants, has leaves that are arranged in a spiral pattern around the stem. Physcomitrella has many advantages as a model for leaf development. Mosses are an evolutionary ancient group in which most gene families functioning in other plants are represented by fewer family members, making it simpler to pinpoint gene function. The plants are very small and the shoot apex is made up of a single cell. Leaves initiate as a single cell and are a single cell layer thick. This means that we have been able to develop a technique for filming shoot initiation, leaf initiation and leaf development microscopically, and can generate quantitative information about how cell division and growth contribute to overall plant shape. Analysis and interpretation of this data is difficult without computational input, so we are working with computer scientists to identify key contributors to shape. Such computational analyses have so far abstracted leaf development to the tissue scale, or focussed on a specific aspect of development to minimise computer processing constraints. Because moss leaves have few cells, we have been able to generate a cellular model of leaf development that has made specific predictions about the contribution of cell division and growth to final leaf shape.A plant hormone, auxin, plays a primary role in modulating leaf initiation patterns and leaf shape in plants like tomato and Arabidopsis as it regulates decisions about cell identity and growth. The regulated distribution of auxin is a key aspect of its activity, and transport is effected by carrier proteins belonging to a small gene family. Current approaches for evaluating how the carrier proteins effect the auxin distribution and impact on overall shape are limited by the contribution of multiple gene family members to transport. Monitoring the auxin distribution in flowering plant leaves has also been challenging as it can only be achieved indirectly by monitoring changes in the activity of auxin responsive genes, and flowering plant leaves have a complex tissue composition that limits tissue penetration in microscopy. The anatomical and genetic simplicity of the moss shoot again brings an advantage.A further advantage in using moss to understand how plant shape is attained is that moss shoots have an independent evolutionary origin to most shoot systems. This means that if the mechanisms regulating shape are shared with other better studied groups like flowering plants, they are likely to be universal regulators of plant shape. The knowledge that we genenerate will therefore be very broadly applicable.