Polycomb蛋白动态调控早期花发育机制的研究

In multicellular organisms, epigenetic mechanisms provide stable gene expression patterns that enable the formation of diverse tissues and whole organs like flowers. Epigenetic processes cause heritable changes in gene activity that are not caused by changes in the DNA sequence that allows reversibility during development. Several major epigenetic regulators provide cells a developmental“memory” of on/off states of genes by histone residue modifications of their loci. The proposed project will focus on the role of Polycomb-group (PcG) proteins, which repress transcription by trimethylation of Histone H3 Lysine 27 (H3K27me3) at the loci of PcG target genes, in early flower development. A proper flower development is essential for regular fruit growth. Beside the fact that flowers are evolutionary compressed and transformed side shoots, floral primordia exhibit cryptic bracts in their early development. Recently, we published that PcG proteins are essential to suppress the outgrowth of that cryptic bracts as a full leaves under non-inductive conditions. We also co-authored a paper demonstrating that PcG proteins prevent indeterminacy of flowers by epigenetic silencing of the WUSCHEL gene encoding a key transcription factor that maintains stem cell fate. Furthermore, several other key regulators of flower development are encoded by PcG target genes. Nevertheless, the few studies regarding the role of PcG proteins and other epigenetic mechanisms in flower development focused mainly at single gene loci and it remains still unclear to what degree the spatiotemporal expression patterns of floral regulators are correlating with changes of the epigenetic marks. In our preliminary work, we used the AP1-GR ap1 cal system, which provide an enormous amount of either undifferentiated inflorescence meristem or synchronized differentiated flower tissue, and performed H3K27me3 ChIP seq. We found overall inverse relationship between the published gene expression data and changes of H3K27me3. Based on these findings, we want to dissect the temporal pattern changes more in depth and include ChIP seq of H3K4me3, a histone mark associated with transcription activation and RNA seq. Next, we want integrate a conditional PcG mutant in the AP1-GR ap1 cal system that will allow us to test the functional relevance of the PcG proteins by depleting PcG activity during induced flower development. In a third approach, we will generate state-of-the-art tools, affording cell-type specific analysis and allow us to dissect the spatiotemporal patterns of the chromatin marks and gene expression during early flower development. The data of the three approaches will be used to identify floral key regulators that are under the epigenetic control of H3K27me3 and/or H3K4me3 to investigate their relevance for flower development by mis-expression and mutant analyses. Furthermore, we will generate morphologic data to get an overall picture of the spatiotemporal pattern changes of transcription, epigenetic histone markers and morphology during early flower development, in order to provide useful reference data for crop breeding.

PcG蛋白在表观遗传水平抑制基因表达进而特异调控花发育。目前，成花调控因子研究多局限于单基因位点，整个基因组水平表观遗传变异与成花调控因子时空表达模式之间关系的研究仍欠缺。本研究前期使用一个成花诱导系统，能特异诱导大量未分化花序原基或相同发育阶段花组织。该系统表观组高通量测序结果表明PcG加载的组蛋白抑制标记变化与基因表达水平反向相关。本项目：一，进一步在组学水平解析组蛋白转录抑制、激活标记变化与转录组变化关系；二，在花发育过程中降低PcG活性，通过突变体表型研究PcG组分特异调控花发育的分子机制；三，使用INTACT技术分离花发育中特异细胞类型，在时空水平解析染色质修饰与基因表达的关系；四，表观组和转录组测序数据鉴定出的成花调控关键因子异位表达和突变体分析，以研究其对花发育的调控。本研究整合花发育形态、转录组及表观组变化模式探索早期花发育的分子调控机制，为提高作物产质及育种提供理论指导。

PcG蛋白在表观遗传水平抑制基因表达进而特异调控花发育。目前，成花调控因子研究多局限于单基因位点，本项目研究整个基因组水平表观遗传变异与成花调控因子时空表达模式之间的关系。本研究使用一个成花诱导系统，能特异诱导大量未分化花序原基或相同发育阶段花组织。该系统表观组高通量测序结果表明PcG加载的组蛋白抑制标记变化与花发育调控基因表达水平反向相关；揭示了PcG突变体花发育逆向进行和干细胞池无法中止的表型主要是由于PcG下游AGL24异位表达以及WUSCHEL和STM上调造成。在早期花发育过程中PcG在不同层次调控成花基因网络，进而促进花分生组织干细胞的命运中止。