参与根尖干细胞维持的生长素相关关键基因RSD1的功能鉴定

The highly adapting abilities of plants to the changing environmental conditions mainly depend on the plasticity of root growth and development, which is largely attributed to the root stem cell maintenance and differentiation. There are many genes including AP2 transcription factor PLETHORAs (PLTs) , GRAS transcription factors SCARECROW (SCR) and SHORTROOT (SHR), and quiescent center ( QC）specific expressed WOX5 have been found to be involved in the root stem cell maintenance and differentiation. Auxin was also found to be crucial to maintain the root stem cell identity. However, we still don't have the clear regulation network about the root stem cell maintenance and differentiation. In order to identify more regulators in this process, we performed an EMS-induced mutagenesis screening, rsd1(root stem cell defective 1) was isolated and showed promoted root stem cell differentiation and QC division which is rarely happened in wild type. The DR5GUS staining signals were strongly reduced in rsd1 roots while they were increased in rsd1 leaves. In this project, we will further investigate the functional mechanism of RSD1 after mapping this gene. To the end, the genetic analysis, yeast screening, and transcriptome analysis will be carried out. Furthermore, auxin transport assays and free IAA measurement will be performed in order to figure out the differentiational DR5 signals between roots and leaves in rsd1. After systematically investigating the functional mechanisms of RSD1, we will enriched the regulator resources for creating a regulation network about the root stem cell maintenance and differentiation in the future.

植物高度适应周围环境的能力主要取决于以根干细胞为基础的可塑性调节。生长素和转录因子如PLTs、SCR、SHR、WOX5等已被发现是根干细胞活性调节的关键调控元件，但我们仍不清楚根干细胞维持和分化的调控网络。为了发掘更多该信号途径的调控因子，我们做了EMS诱导的突变体筛选，发现rsd1(root stem cell defective 1)能够促进根干细胞的分化和QC细胞的分裂。rsd1突变体根中DR5GUS信号的大大减弱而叶片中DR5GUS的信号大大增强。在图位克隆RSD1的基础上,我们将通过遗传分析，酵母双杂交，转录组分析等手段深入研究该基因的功能。同时，我们还将进行rsd1突变体生长素极性运输的测定及自由态生长素IAA的检测，以阐明导致rsd1突变体根和叶差异DR5GUS信号的机制。在系统研究RSD1功能的基础上，我们将为未来建立根干细胞维持和分化的调控网络大大丰富调控因子资源。

植物高度适应周围环境的能力主要取决于以根干细胞为基础的可塑性调节。为了发掘更多的参与根尖干细胞调控的关键调控元件，我们做了EMS 诱导的拟南芥突变体筛选，并鉴定了一批根干细胞龛维持缺陷的突变体。其中发现rsd1(root stem cell defective 1)突变体不仅有短根的表型，而且表现出明显的根干细胞的分化加快和静止中心（quiescent centre ，QC) 细胞分裂增强的表型。通过图位克隆分析发现，rsd1突变体根缺陷的表型是由于延伸因子复合体中的一个亚基ELP2突变引起的。研究发现，ELP2编码的蛋白在进化过程中具有保守的组蛋白乙酰转移酶活性，参与拟南芥叶片的发育，植物的免疫和非生物逆境胁迫响应。本课题主要研究ELP2调控根尖干细胞微环境的调控机理。我们的研究结果表明，根尖干细胞微环境维持的关键调控因子AP2转录因子PLT1 (PLETHORA1)和PLT2 (PLETHORA2), GRAS 转录因子比如SCR (SCARECROW) 和 SHR (SHORT ROOT) 及QC特异转录表达的基因WOX5在elp2突变体中都出现了明显的下调表达。另一方面，细胞周期G2/M 期转化的调控因子CYCB1在elp2突变体中的表达和野生型对照比较其表达水平显著提高。另外，参与生长素极性运输的转运载体PIN1和PIN2在elp2突变体表达明显降低，而且PIN1蛋白的极性也发生了改变，最终导致该突变体中根尖的生长素水平降低。另外，在elp2突变体中上述表达量降低的转录因子编码基因及表达量升高的细胞周期蛋白编码基因CYCB1其乙酰化水平或甲基化水平表型出明显的升高或降低，这与其表达量的变化是一致的，说明ELP2通过表观遗传调控的方式影响很多转录因子或其它调控元件的表达进而调控根尖干细胞为环境的维持。