Functional characterization and evolutionary history of plant PRC1 RING finger protein homologs

聚梳组(PcG)编码一组在进化过程中保守的染色质修饰蛋白，维持对靶基因的稳定遗传抑制。在果蝇和脊椎动物中，靶基因的抑制是由两个PcG复合体共同控制的：多梳抑制复合体(PRC)2，它通过添加组蛋白甲基标记标记靶标；以及Prc1，它作为转录抑制的“效应器”工作。在拟南芥中，根据亚基组成和蛋白质功能已经假设了三个PRC2等价物；然而，在植物中还没有确定PRC1组分的同源物，这开启了植物采用与动物不同的机制来维持转录抑制的可能性。令人惊讶的是，我们最近的数据库搜索显示，在拟南芥和水稻基因组中存在一些假定的PRC1组分的同源基因。这些蛋白质之间保守的结构域结构有利于PRC1在高等植物中的功能保守。由于PcG介导的沉默机制在真核基因调控中起着至关重要的作用，因此基因调控机制的改变对种间分化可能是至关重要的。因此，更好地理解控制基因调控的机制是发育和进化生物学的核心。在这个提案中，我们将使用生化和遗传学的方法来研究这些植物PRC1蛋白同源物是否在功能上与它们的动物同源物保守，或者它们是否在这些生物体中扮演不同的角色。此外，利用比较基因组学方法，我们将研究这些重要发育基因在植物中的进化史。这两种方法的融合将为理解PcG沉默机制的演变提供一把钥匙。

The Polycomb group (PcG) encodes a set of chromatin-modifying proteins conserved during evolution that maintains stably inherited repression of target genes. In Drosophila and vertebrates, the repression of the target genes is controlled by the cooperation of two PcG complexes: Polycomb repressive complex (PRC)2 that labels the targets by adding histone methyl marks, and PRC1 that works as an “effector” of transcriptional repression. In Arabidopsis, three PRC2 equivalents have been hypothesized based on subunit composition and protein function; however, homologs of PRC1 components have not been identified in plants, opening the possibility that plants employ alternative mechanisms from that of animals to maintain the transcriptional repression. Surprisingly, our recent database search revealed the presence of putative homologs of some of the PRC1 components in Arabidopsis and rice genomes. The conserved domain architecture among these proteins favours the functional conservation of PRC1 in higher plant. Since PcG-mediated silencing mechanism plays an essential role in eukaryotic gene regulation, changes in the mechanism that control gene regulation may be fundamentally important for interspecific differentiation. Therefore, a better understanding of the mechanism that control gene regulation is central for developmental and evolutionary biology. In this proposal, using biochemical and genetic approaches we will investigate whether these plant PRC1 protein homologs are functionally conserved to their animal counterparts or if they play a different role in these organisms. In addition, using a comparative genomics approach we will study the evolutionary history of these important developmental genes in plants. The fusion of the two approaches will provide a key to understand the evolution of the PcG silencing mechanism.