拟南芥根尖干细胞微环境建立与维持的激素调控分子机制

Arabidopsis root stem cell niche (RSCN) is localized in the root apical meristem, it contains the quiescent center (QC) and its surrounding stem cells.The QC appears to produce short-range signal maintaining the identity of root stem cells, thus, the QC is essential for the specification of the RSCN and maintenance of the undifferentiated state of stem cells.The RSCN established during embryogenesis provides the new cells for the growing root. The identity and activity of RSCN is important for root growth and development. Plant hormones and transcription factors are known to play a key role for the specification and maintenance of the RSCN. However, the upstream signaling components of transcription factors remain elusive. The PI’s previous work demonstrated that the RopGEF7, an activator of the small GTPase RAC/ROP acted in the specification and maintenance of the RSCN through the regulation of auxin mediated PLETHORA (PLT)- dependent pathway. The current work will isolate the signaling components in RopGEF7 network and define their functional roles in the regulation of the establishment and maintenance of the RSCN using a combination of Genetics, Cell biology, Molecular biology and Biochemistry approaches. The project will yield insights into the important processes “specification and maintenance of RSCN” that support the root normal growth and development. Understanding RopGEF7 network in the regulation of RSCN also have the implications for engineering crop plants with improved root architecture for enhanced tolerance to diverse environmental conditions.

拟南芥根尖干细胞微环境 (RSCN) 是根尖干细胞结构与功能的控制中心，也是根系正常生长发育的基础。生长素和转录因子在RSCN的特化与维持中起着至关重要的作用，但是对转录因子以外的信号元件的了解很少。申请人的实验室前期工作报道了小G蛋白ROP上游阳性调节蛋白RopGEF7在RSCN的特化与维持中的重要功能，揭示了RopGEF7通过生长素/PLETHORA (PLT)的信号机制影响RSCN的维持。我们拟开展的研究将综合采用分子遗传学、细胞生物学、生物化学等多学科技术手段， 利用前期工作获得的RSCN缺陷突变体和RopGEF7互作蛋白为切入点，深入研究这些RSCN调控因子的生物学功能，并且研究它们与植物激素信号的互作调控RSCN的特化与维持的分子机理。根系是植物吸收土壤水分和营养的重要器官，阐明根尖干细胞的形成和功能维持的分子调控体系，可为根系构型改良的作物育种提供理论依据。

根尖干细胞微环境位于根尖分生组织,它的结构与功能的稳定是胚后植物发育的基础。植物器官持续性发生需要一个稳定的分子调控网络维持植物干细胞与分化的子细胞之间的平衡。生长素是维持根尖干细胞微环境的主要位置信号。生长素在根尖形成的生长素高点(auxin maximum)对于维持根尖干细胞微环境的功能起着至关重要的作用。本项目以拟南芥为材料，从前期建立的RopGEF7pro-GUS的突变体库中筛选获得短根突变体，通过图位克隆方法分离基因。我们对其中的2个基因的功能进行了详细的研究。Xpl1突变体主根生长缓慢，在萌发后6天根分生组织即分化、QC报告基因表达受到明显抑制、生长素输出载体PIN1蛋白极性发生改变。XPL1敲除破坏根尖生长素高点的形成。该基因编码PEAMT,是磷脂酰胆碱生物合成途径的一个关键酶。Rpi1是另一个短根突变体，RPI1编码5-磷酸核糖异构酶。RPI突变抑制素高点形成。两个基因都通过生长素途径调控根尖干细胞微环境维持。这些研究结果揭示了根尖干细胞维持的新的调控机制，对于深入了解植物器官形成具有重要意义。