Genetic and hormonal feedbacks defining tissue polarity by broad brushes and fine PINs

动物和植物等多细胞生物体发育由不同类型的组织组成的特殊器官。器官的结构或模式由组织内的极性决定，例如径向或中侧对称。当细胞被赋予方向感时，极性就被确立了。尽管发育生物学家已经成功地确定了指定器官单个细胞类型所需的基因，甚至它们在遗传网络中如何相互作用，但我们对调节组织极性的机制知之甚少。开花植物大约在1.4亿年前进化，今天占植物界植物总数的90%以上。它们获得巨大成功的主要原因是果实作为包含发育中的种子的生殖器官的发育。受精后，果实滋养、保护和调节种子的有效传播，以确保后代的成功。果实有不同的形状和大小，但所有水果的共同之处是，它们从花中心的心皮结构发育而来，心皮融合形成雌蕊。有趣的是，200多年前，德国诗人和科学家约翰·沃尔夫冈·冯·歌德假设，所有的花器官实际上都是经过修饰的叶子。现代遗传学和分子生物学证实了歌德的预测，并揭示了心皮也是从叶子进化而来的。因此，雌蕊群是由一个更简单的基本计划形成的，并随着时间的推移进行修改，以优化其作为生殖器官的功能。例如，这些修饰允许在雌蕊群中心的子房中发育胚珠，这些胚珠将受精以发育种子。它们还负责在雌蕊顶端产生一种称为柱头的结构，以促进授粉，此外，修饰还导致在柱头下方形成花柱以支持花粉管的发育，这将引导花粉进入胚珠进行有效受精。子房具有中侧对称性，反映起源为两片融合的叶，而花柱和柱头为径向对称。因此，在从两片叶子形成雌蕊群的过程中，涉及到改变组织的极性。激素等移动信号可能会协调雌蕊中不同结构域和结构的生长。我们最近的工作表明，植物激素生长素具有如此突出的作用。在这个方案中，我们将以这些初步数据为基础，利用新开发的遗传和分子资源、数学模型以及DNA深度测序技术来：1)了解一组已知转录因子和生长素活性之间的相互作用如何调节特定组织的极性；2)识别受生长素/转录因子模块调控的途径和关键成分；3)研究生长素分布模式是如何建立的。通过这些研究，我们旨在提供对雌蕊群发育过程中组织极性建立的统一理解，并揭示生长素在允许营养叶向复杂生殖器官转变过程中的关键作用。

Multicellular organisms such as animals and plants develop specialised organs, which are composed of different types of tissues. The structure - or pattern - of organs is determined by the polarity within tissues such as for example radial or medio-lateral symmetry. Polarity is established when cells are provided with a sense of direction. Although developmental biologists have successfully identified genes required to specify individual cell types of an organ, and even how they interact in genetic networks, we know very little about the mechanisms that regulate tissue polarity. Flowering plants evolved about 140 million years ago and today comprise more than 90% of plants of the plant kingdom. The main reason for their enormous success is the development of fruits as the reproductive organ containing the developing seeds. After fertilisation, the fruit nurtures, protects and mediates the efficient dispersal of seeds to ensure success of future generations. Fruits occur in a range of shapes and sizes, but common to all fruits is that they develop from structures called carpels in the centre of the flower that fuse to form a gynoecium. Interestingly, the German poet and scientist Johann Wolfgang von Goethe hypothesised more than 200 years ago that all floral organs are in fact modified leaves. Modern genetics and molecular biology has confirmed Goethe's prediction, and revealed that also carpels are evolutionarily derived from leaves. The gynoecium is therefore formed from a simpler basic plan and modified over time to optimise its function as a reproductive organ. These modifications have for example allowed development of ovules in the ovary at the centre of the gynoecium that will be fertilised to develop seeds. They were also responsible for producing a structure at the tip of the gynoecium called stigma to facilitate pollination, and modifications furthermore resulted in the formation of a style just below the stigma to support the development of pollen tubes, which will guide the pollen to the ovules for efficient fertilisation. Whereas the ovary has medio-lateral symmetry reflecting the origin as two fused leaves, the style and stigma adopts radial symmetry. The modifications involved in creating the gynoecium from two leaves, therefore involved changing the polarity of tissues. Mobile signals such as hormones are likely to coordinate growth of the different domains and structures in the gynoecium. Our recent work suggests that the plant hormone auxin has such a prominent role. In this proposal we will build on these preliminary data and take advantage of newly developed genetic and molecular resources, mathematical modelling as well DNA-deep-sequencing technology to:1) understand how interaction between a known set of transcription factors and auxin activity regulate polarity of specific tissues.2) identify pathways and key components regulated by the auxin/transcription factor module.3) study how the auxin distribution pattern is established. Through these studies we aim to provide a unified understanding of tissue polarity establishment during gynoecium development and to reveal the key importance of auxin in allowing the transition from vegetative leaves to a complex reproductive organ.