A Family of Transcriptional Co-repressors Controlling Multiple Processes in Plants

活着的有机体需要打开和关闭他们的基因的表达，以响应他们的环境。转录因子与特定的DNA序列结合，控制基因的激活或抑制。关闭基因表达并不是简单的没有激活：主动关闭目标基因的表达至关重要。例如，在这项提案中，我们将研究两种情况，其中抑制目标基因是植物必不可少的过程所必需的。在一个例子中，我们将研究抑制在激素信号传递中的作用，在另一个例子中，我们将研究抑制在保持生长顶端(分生组织)的未分化细胞池中的作用，这对植物调节其发育以响应年龄和环境是必不可少的。转录因子通过一类称为转录共抑制因子的蛋白质来抑制基因表达。这些蛋白质不能与DNA结合，必须与转录因子相互作用，才能被招募到基因的调节区。靶基因的特异性由转录因子提供，抑制能力由共抑制因子提供。我们鉴定了植物共抑制因子家族的第一批成员，在这里我们称之为TTW家族。模式植物拟南芥中有5种TTW蛋白。其他研究表明，该家族是植物激素生长素信号传递机制的核心部分。每个细胞感知其生长素环境并调节其基因表达以响应环境的能力，在塑造植物并使其发挥功能方面发挥了巨大作用。了解生长素水平如何转化为开启和关闭基因的指令是过去5年的主要科学成就之一。我们现在知道，这个信号传递过程中的一个关键角色能够通过招募TTW家族的成员来关闭基因表达。因此，TTW家族已经与两个不同的过程直接相关，这两个过程对植物生命至关重要：分生组织维持和生长素信号传递。我们有新的数据表明，TTW家族的影响比这要广泛得多。我们的证据表明，仅TTW家族中的一个成员就帮助至少110种不同的转录因子抑制目标基因。这也表明TTW家族参与了另一个植物激素信号通路；这表明茉莉酸和生长素信号通路之间在组织上的显著相似性延伸到这类共抑制物的共同使用。鉴于基因调控的许多方面似乎都集中在这一小类蛋白质上，我们理解它们是如何工作的是很重要的。为此，我们提出了三个目标来解决以下问题：1.像生长素信号通路一样，在茉莉酸信号通路中是否需要TTW共抑制物家族来实现抑制功能？2.我们能否利用TTW共抑制子与分生组织维持之间的联系来了解TTW共抑制子的作用模式？3.我们能否定义TTW蛋白与植物转录因子之间相互作用的全部范围，以便我们能够准确地定义是什么允许任何转录因子招募TTW共抑制子？第一个问题让我们更多地了解重要的荷尔蒙信号通路，并揭示了不同蛋白质以相似方式组织的方式之间惊人的进化相似性。第二个问题解释了分生组织维持和TTW蛋白之间的联系，并展示了TTW蛋白是如何主动关闭基因表达的。最后一个问题将产生一个社区资源来对TTW-转录因子的相互作用进行分类，并应该有助于我们定义确定哪些转录因子与哪些共抑制物相互作用的规则。

Living organisms need to turn expression of their genes on and off in response to their environment. Transcription factors bind to specific DNA sequences and control whether genes are activated or repressed. Turning off gene expression is not simply the absence of activation: actively shutting down expression of target genes is of vital importance. For example, in this proposal we will look at two cases where repressing target genes is required for essential plant processes. In one example, we will investigate the role of repression in hormone signalling and in the other we will look at the role of repression in maintaining the pool of undifferentiated cells at the growing tip of the shoot (the meristem) that is essential for plants to modulate their development in response to age and environment. Transcription factors repress gene expression using a class of proteins called transcriptional co-repressors. These proteins cannot bind DNA and must interact with transcription factors to be recruited to the regulatory regions of genes. Target gene specificity is contributed by the transcription factor and the repressive capacity is provided by the co-repressor. We identified the first members of a small family of plant co-repressors that here we call the TTW family. There are five TTW proteins in the model plant Arabidopsis. Others have shown that this family is required as a central part of the signalling mechanism for the plant hormone auxin. The ability of each cell to perceive its auxin environment and to regulate expression of its genes in response to that environment plays a huge part in shaping the plant and allowing it to function. Understanding how auxin levels are translated into instructions to turn genes on and off has been one of the major scientific achievements of the last 5 years. We now know that one of the key players in this signalling process is able to shut down gene expression by recruiting members of the TTW family. The TTW family is therefore already linked directly to two distinct processes that are central to plant life: meristem maintenance and auxin signalling. We have new data that indicate that the influence of the TTW family is much wider than this. Our evidence shows that just one member of the TTW family helps a minimum of 110 different transcription factors to repress target genes. It also implicates the TTW family in another phytohormone signalling pathway; suggesting that the remarkable organisational similarities between the jasmonic acid and auxin signalling pathways extend to a common use of this class of co-repressors. Given that many aspects of gene regulation appear to converge on this small family of proteins it is important that we understand how they work. To this end we propose three objectives that address the following questions: 1. Is the TTW family of co-repressors required to enact the repressive function in the jasmonic acid signalling pathway, as it is in the auxin signalling pathway? 2. Can we use the connection between the TTW corepressors and meristem maintenance to understand the mode of action of the TTW co-repressors? 3. Can we define the full extent of the interactions between the TTW proteins and plant transcription factors so that we can define exactly what allows any transcription factor to recruit a TTW co-repressor? The first question allows us to understand more about a vital hormone signalling pathway and reveals a remarkable evolutionary similarity between the way in which different proteins become organised in a similar way. The second question, explains the link between meristem maintenance and the TTW proteins, and shows how the TTW proteins actively shut down gene expression. The final question will produce a community resource to catalogue TTW - transcription factor interactions and should also help us to define the rules that determine which transcription factors interact with which co-repressors.