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，组蛋白可以以许多不同的方式进行修饰，例如通过添加甲基，这可以影响附近基因的活性。组蛋白的这些变化-通常称为表观遗传标记-很重要，不仅因为它们影响基因活性，而且因为在某些情况下，它们是通过细胞分裂遗传的。对组蛋白质的深入研究表明，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，例如关闭基因。此外，还有“橡皮擦”，可以删除特定的标记和扭转其影响。最重要的组蛋白作家之一是Polycomb组（PcG）蛋白，它控制着动物和植物发育的许多方面，并被认为为细胞提供重要事件的稳定记忆。例如，在植物中，PcG蛋白帮助植物在一年中的正确时间开花，让细胞记住冬天是否已经发生。在冬季，寒冷的温度导致某些与开花有关的基因被关闭，PcG蛋白在确保细胞“记住”在春季和夏季温度升高时保持这些基因关闭方面非常重要。很长一段时间以来，PcG蛋白如何引起这些稳定的记忆一直是一个谜。在过去的十年里，取得了重大进展。特别是，已经发现一组PcG蛋白，称为PRC 2，作为一种酶一起作用，甲基化包装DNA的四种组蛋白蛋白之一上的特定氨基酸。此外，测序技术的发展意味着我们现在可以确定生物体中哪些基因以这种方式被修饰，以及这与它们的活性如何相关。因为PcG蛋白控制着许多重要经济性状的基因（例如开花、种子大小和杂种的生存力），重要的是知道PRC 2的活性是如何调节的。本发明的出发点是我们发现了几种蛋白质，称为ALP，我们从遗传学证据中发现，它们的作用与PcG相反，并参与了基因的启动。我们后来发现，令我们惊讶的是，ALP蛋白和PRC 2 PcG蛋白在一个大的多蛋白复合物中一起起作用。我们认为，当ALP蛋白与PRC 2蛋白结合时，它们抑制它们的活性，从而克服了PcG抑制基因活性的正常作用。另一个令人惊讶的是，ALP 1蛋白与称为转座酶的蛋白质相关，这种蛋白质有助于称为转座子的寄生元件在植物和动物基因组中增殖。由于ALP蛋白在包括谷类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中的表观遗传标记，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PRC 2蛋白有什么影响，它们靶向哪些基因，以及它们对表观遗传标记在基因组中的分布有什么影响。我们已经开发了许多必要的遗传资源，以便在我们早期的工作中做到这一点。我们还发现了ALP蛋白对植物感知冬季能力（春化反应）的不寻常的影响，并希望调查这是否是ALP蛋白改变春化重要基因的表观遗传标记的结果。我们建议在爱丁堡大学和Trinity College都柏林的实验室之间分别进行本申请中概述的研究。我们的两个小组具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无法单独回答的问题。

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.