拟南芥光形态建成的染色质重塑机制研究

In the critical window of photomorphogenic developmental process, plants transcriptionally respond to light is controlled in two layers, genetics and epigenetics. However, less is known regarding chromatin-based regulatory mechanism. ENHANCED PHOTOMORPHOGENIC1 [EPP1, which is in accordance with SHAL1, temporarily named in the project (31000530) of the National Science Foundation of China], an ATP-dependent chromatin remodeling factor, was identified as a repressor of photomorphogenesis. EPP1 is repressed by light, especially in the hypocotyls in a photoreceptor-dependent manner. EPP1 is recruited to the promoters of cell elongation related genes by both HY5 and HYH through physical interaction. EPP1 in turn negatively regulates HY5 by repressing trimethylation of histone H3 Lys 27 at the target loci, thereby regulating hypocotyl elongation. In this continued project, we further found that HD1, a histone deacetylase, interacts with EPP1 in plant cells, and represses the acetylation marked photosynthetic genes in common with EPP1. Based on the results above and the relative reports in the fields of animal and plant, this project aimed to elucidate the mechanism that how EPP1 exerts its chromatin remodeling activities to repress photomorphogenesis in concert with histone deacetylase. Furthermore, it is interesting to pick out the upstream transcription factor(s), which directly regulate(s) EPP1 to relay the light signal, to fill the gaps of EPP1 signaling pathway. Our deepgoing study put special emphasis on the underlying mechanism of the regulation and activities of EPP1, and will help to probe the mechanism of chromatin remodeling activity in plant adaptation to the ambient light condition, and provide new insight into the fine tuning of the regulation of the photomorphogenic process.

光形态建成的转录调控涉及遗传和表观遗传两方面，表观遗传在该过程中的研究相当有限。我们的研究表明EPP1作为ATP酶依赖的染色质重塑因子，是抑制光形态建成的重要因子。EPP1的表达，尤其在下胚轴中的表达受光抑制，且依赖光受体。EPP1与HY5/HYH互作，被后二者共同招募到细胞伸长因子的启动子，并抑制这些启动子的H3K27me3水平来负调控HY5的功能。本延续项目以上述研究为基础，结合动、植物中的相关报道，发现组蛋白去乙酰化酶HD1和EPP1在植物细胞中互作，且被二者共同抑制的光合基因受组蛋白乙酰化修饰。我们将研究EPP1如何发挥其染色质重塑因子的作用，与组蛋白去乙酰化酶协同抑制光形态建成。此外，上游转录因子如何直接调控EPP1的表达作为新的研究点，使EPP1的研究更趋完整。该项目的继续深入实施有助于揭示植物适应光环境变化的染色质重塑机制，为光形态建成的精细调控提供新见解。

植物的生长和发育，包括细胞伸长和幼苗形态建成受到内源激素如油菜素内酯和赤霉素以及外源环境因子如光和温度的调控。然而如何将这些信号因子整合，从而调控细胞伸长的分子机制在很大程度上仍是未知。. 研究发现PKL可以分别和光信号通路的PIF3转录因子以及油菜素内酯信号通路的BZR1转录因子直接相互作用。这种互作通过将PKL招募至靶基因，从而改变区域染色质的状态，抑制H3K27组蛋白三甲基化，从而促进基因表达及实现细胞伸长。赤霉素信号通路的重要蛋白因子DELLA起相反的功能，它们通过与PKL互作削弱后者结合靶基因的能力。此外还发现外源施加赤霉素GA3和油菜素内酯BL能抑制细胞伸长相关基因上H3K27me3的富集。. 研究还发现拟南芥PKL突变导致其对28℃相对高温的敏感性显著降低。植物生物钟中心振荡器成员CCA1可以直接结合PKL启动子，在cca1突变体中PKL基因的表达减弱。同时，cca1突变体也呈现出对高温敏感性降低的现象。进一步研究还发现PKL调控了下游两个细胞伸长相关因子IAA19和IAA29的H3K27me3水平，进而改变了二者的基因表达。. 由上可见，染色质重塑因子PKL是将内外源信号因子整合，进而调控植物生长发育的重要交汇点。