植物根系发育中SHR介导平周分裂的调控机制

Plants uptake water and nutrients through roots and therefore plant growth heavily depends on root development. One of the critical steps of root development is the regulation of cell division direction. Focusing on ground tissue patterning, researchers have identified a number of regulators, including an essential transcriptional factor, SHORT-ROOT(SHR). Evidence so far showed that SHR promotes the expression of another transcriptional factor, SCR in endodermal/cortex initials where both transcriptional factors activate the expression of CYCD6. As a result, division direction in endodermal/cortex initials switches from anticlinal to periclinal. However, it is still largely unknown what downstream factors of CYCD6 are and how SHR/CYCD6 pathways eventually affect division direction through regulating mitotic apparatus such as spindles and phragmoplasts. Our preliminary results revealed that SHR function is evolutionarily conserved and SHR can induce periclinal division in most root cells. This finding suggests there might exist a common downstream network that regulates periclinal division in different plant cells. In this proposal, we will examine the mechanism of SHR induction and explore the regulatory network downstream of CYCD6. On cellular level, we plan to identify factors that link SHR pathways and mitotic machinery. The experiments proposed here can provide new insights of cell division regulation during plant development and promote our understanding of plant organogenesis.

细胞分裂方向调控是植物器官发育的基础之一，本课题以根系为模型，以SHR介导的下游机制为研究对象，拟对植物平周分裂调控机制做深入研究。根系是植物吸收水分和养分的器官，其发育调控对于植物的生长至关重要。而细胞分裂方向的调控则是根系发育的关键一步。近些年以根系基本组织形成为模型，挖掘了一批促进细胞分裂由垂周到平周转变的基因，其中包括关键的SHORT-ROOT(SHR)转录因子。目前研究表明SHR通过促进SCR表达，进而激活CYCD6来诱导平周分裂。然而过去的研究仅集中在上游转录调控网络，下游如何通过影响有丝分裂元件来决定分裂方向尚不清楚。本研究拟综合多种手段来探索CYCD6下游调控网络，并在细胞层面上研究有丝分裂方向如何决定。并在此基础上探讨SHR介导的下游调控通路的普适性。因此本研究不但能促进我们对植物细胞分裂调控的深入认识，也为植物器官建成提供了理论基础。

本研究围绕植物根尖干细胞区域关键调控因子SHORT-ROOT（SHR），针对植物细胞命运决定机制和细胞分裂方向调控机制进行了深入研究。首先利用拟南芥为模式系统，通过不同启动子在植物根中不同细胞内表达SHR，发现SHR均能诱导细胞的平周分裂，从而改变根器官的几何结构。进一步发现SHR对于平周分裂的诱导机制非常保守，均是通过促进细胞周期蛋白CYCD6;1实现。在此基础上，丰富了植物发育领域长期的猜想，即细胞命运主要由位置信息决定，但是在细胞形成早期，谱系决定也参与细胞命运调控。更进一步，利用大豆为研究系统，发现SHR在大豆中的同源基因参与大豆根瘤器官的形成，对其调控机制的研究表明，SHR有可能通过不同同源基因收到根瘤菌诱导的不同，通过下游SCR转录因子和保守的CYCD6;1通路来调控根瘤器官发育。以上结果表明自然界中存在SHR介导的细胞分裂方向的保守调控，并且此调控不仅存在于根尖干细胞，也广泛参与了很多其他植物器官的形成。