Bilateral BBSRC-SFI: Characterization of a novel Polycomb group protein complex and its effects on the plant epigenome

我们细胞中的DNA被包装在称为组蛋白的蛋白质上。最近已经清楚的是，组蛋白蛋白可以通过许多不同的方式进行修饰，例如通过添加甲基，这可以影响附近的基因的活性。组蛋白的这些变化通常被称为表观遗传标记，这些变化之所以重要，不仅是因为它们影响了基因活性，还因为在某些情况下，它们是通过细胞分裂而遗传的。对组蛋白蛋白的密集研究表明，细胞包含复杂的机制，不仅可以“写”表观遗传标记，还可以读取它们，即识别和解释它们以产生输出，如关闭基因。此外，还有可以去除特定痕迹并逆转其效果的“橡皮”。最重要的组蛋白编写者之一是Polycomb group(PcG)蛋白，它控制着动植物发育的许多方面，被认为为细胞提供对重要事件的稳定记忆。例如，在植物中，PcG蛋白通过让细胞记住是否发生了冬天来帮助植物在一年中的正确时间开花。在冬季，寒冷的温度会导致与开花有关的某些基因被关闭，而PcG蛋白对于确保细胞在春季和夏季气温上升时“记住”关闭这些基因非常重要。在很长一段时间里，PcG蛋白是如何导致这些稳定的记忆的，这完全是一个谜。在过去的十年里，取得了重大进展。特别是，人们发现一组PcG蛋白质，称为PRC2，共同作用于一种酶，使包装DNA的四种组蛋白之一上的特定氨基酸甲基化。此外，测序技术的发展意味着我们现在可以识别生物体中哪些基因以这种方式被修饰，以及这与它们的活动有何关系。由于PcG蛋白控制着许多重要经济性状(例如开花、种子大小和杂交后代的生存能力)所涉及的基因，因此了解PRC2的活性是如何调节的是很重要的。目前这一提议的起点是我们发现了几种称为ALP的蛋白质，我们从遗传证据中发现了这些蛋白质，这些蛋白质与PcG相反，并参与了基因的开关。后来我们发现，有些令我们惊讶的是，ALP蛋白和PRC2 PcG蛋白在一个大型的多蛋白复合体中共同作用。我们认为，当ALP蛋白与PRC2蛋白结合时，它们会抑制它们的活性，从而克服了PcG抑制基因活性的正常作用。更令人惊讶的是，ALP1蛋白被证明与被称为转座酶的蛋白质有关，转座酶帮助被称为转座子的寄生元素在植物和动物基因组中增殖。由于ALP蛋白在包括谷物在内的植物中广泛保守，我们认为它们可以提供一个有用的工具来改变植物的表观遗传标记，并最终改变有用的农业性状。为了做到这一点，我们需要知道ALP蛋白对PRC2蛋白有什么影响，它们针对的是哪些基因，以及它们对基因组上表观遗传标记的分布有什么影响。在我们早期的工作中，我们已经开发了许多完成这项工作所需的遗传资源。我们还发现了ALP蛋白对植物感知冬季的能力(春化反应)的一种不寻常的影响，并希望调查这是否是ALP蛋白改变了春化重要基因的表观遗传标记的结果。我们建议分别与爱丁堡大学和都柏林三一学院的实验室合作进行本申请中概述的研究。我们两个小组拥有互补的研究优势和专业知识，我们相信，作为一个团队，我们可以成功地解决仅靠一个小组无法回答的问题。

The DNA in our cells is packaged on proteins called histones. Recently it has become clear that the histone proteins can be modified in many different ways, for example by addition of methyl groups, and that this can affect the activity of genes nearby. These changes in the histone proteins - often termed epigenetic marks - are important not only because they affect gene activity, but also because in some cases they are inherited through cell division. Intense research focus on the histone proteins has revealed that cells contain sophisticated machinery not only to "write" epigenetic marks, but also to read them, i.e. recognise and interpret them to produce an output such as turning a gene off. In addition, there are "erasers" that can remove specific marks and reverse their effects. One of the most important histone writers are the Polycomb group (PcG) proteins, which control many aspects of development in animals and plants and are thought to provide cells with a stable memory of important events. For example, in plants the PcG proteins help plant flower at the right time of year by giving cells a memory of whether or not winter has occurred. During winter the cold temperatures result in certain genes involved in flowering being switched off and the PcG proteins are important in making sure that cells "remember" to keep these genes off when temperatures increase during spring and summer. For a long time it was a complete mystery how PcG proteins caused these stable memories. In the last ten years there have been major advances. In particular, it has been found that a group of PcG proteins, called PRC2, act together as an enzyme which methylates a specific amino acid on one of the four histone proteins that package DNA. Furthermore, technical developments in sequencing mean that we can now identify which genes in an organism are modified in this way, and how this relates to their activity. Because PcG proteins control genes involved in many economically important traits (flowering, seed size, and the viability of hybrids for example) it is important to know how the activity of the PRC2 is regulated.The starting point for the present proposal was our discovery of several proteins, called ALP, which we found from genetic evidence which suggested that they act oppositely to the PcG and are involved in switching genes on. We later found, somewhat to our surprise, that the ALP proteins and the PRC2 PcG proteins act together in a large multiprotein complex. We think that when the ALP proteins associate with the PRC2 proteins they inhibit their activity so that the normal role of PcG in repressing gene activity is overcome. A further surprise was that the ALP1 protein turns out to be related to proteins called transposases which help parasitic elements called transposons to proliferate in plant and animal genomes. Because the ALP proteins are widely conserved in plants, including cereals, we think they could provide a useful tool to alter the epigenetic marks in plants and ultimately to modify useful agricultural traits. In order to do this, we need to know what effect ALP proteins have on PRC2 proteins, which genes they target, and what effects they have on the distribution of epigenetic marks over the genome. We have developed many of the genetic resources necessary to do this in our earlier work. We have also uncovered an unusual effect of ALP proteins on plants ability to perceive winter (the vernalization response) and wish to investigate whether this is a result of ALP proteins altering epigenetic marks at genes important for vernalization.We propose to conduct the research outlined in this application as a partnership between our laboratories at the University of Edinburgh and Trinity College Dublin, respectively. Our two groups have complementary research strengths and expertise and we believe that, as a team, we can successfully address questions that could not be answered by one group alone.