解析CBL 在拟南芥根尖干细胞微环境维持中的调控作用

The continuous growth of root throughout their lifespan depends on the activity of root stem cells. Root stem cell niche (RSCN) is located within root apical meristem, which is organized structure and signaling center that is essential for root growth and development. Auxin plays a key role in maintaining the activity of RSCN. Recent studies have shown that plant endogenous metabolites such as amino acids are also important for promoting root development. But it is not clear how metabolism-related genes participate in the specific pathway to regulate root growth. 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. A forward genetic screen identified a quiescent center (QC) defective short root mutant named cbl with altered expression of RopGEF7pro:GUS. Map-based cloning technique was used to isolate the CBL gene, which encodes a key enzyme acting on the de novo biosynthesis of methionine (Met). The proposed work will screen the suppressors of cbl and isolate the genes to define the functional roles of them in the maintenance of RSCN using a combination of genetics, cell biology, molecular biology and biochemistry approaches. The expected results from this work are an integration of CBL and RopGEF7 into a genetic framework for RSCN function, molecular information on how Met links to auxin, and dynamic interactions between Met biosynthesis and hormone gradients within the root meristem. Dissecting the regulatory network that mediate the interaction of auxin and Met in the maintenance of RSCN also have the implications for engineering crop plants with improved root architecture for enhanced tolerance to diverse environmental conditions.

植物根尖干细胞微环境（简称RSCN）位于根尖生长点，是根系发育的组织和信号中心。生长素等激素信号在根尖干细胞的维持中起重要作用，但越来越多的证据表明植物内源的代谢物如氨基酸等也对根系的发育起重要的作用，目前尚不清楚代谢相关的基因如何参与特定的发育途径。申请人实验室前期工作用在RSCN表达的RopGEF7-GUS材料构建了EMS突变体库，筛选获得RSCN缺陷的短根突变体cbl。用图位克隆法分离了CBL基因，它编码甲硫氨酸合成途径的关键酶。我们拟开展的研究将综合采用分子遗传学、细胞生物学、生化等学科技术手段，以cbl突变体为切入点，筛选cbl的抑制子并克隆相关的基因；研究它们在根尖干细胞微环境维持中的功能。根系是植物吸收土壤水分和营养的重要器官，解析根尖干细胞的形成和功能维持的代谢与激素交叉的分子机制，可为根系构型改良的作物育种提供理论依据。

根系是植物吸收土壤水分和矿质营养以及植物与土壤环境互作的重要器官。植物根系来源于根尖干细胞微环境（简称RSCN）中的干细胞。植物根尖干细胞微环境位于根尖生长点，是根系发育的组织和信号中心。生长素等激素信号在根尖干细胞的维持中起重要作用，但越来越多的证据表明植物内源的代谢物如氨基酸等也对根系的发育起重要的作用，目前尚不清楚代谢相关的基因如何参与特定的发育途径。本项目以前期筛选获得RSCN缺陷的短根突变体cbl为切入点，CBL基因编码甲硫氨酸合成途径的第二个关键酶。CBL基因的突变导致胱硫醚β 裂解酶（CBL）活性下降，影响到甲硫氨酸从头合成，导致根尖干细胞不能正常维持。CBL基因在根尖静止中心强烈表达。该研究表明根尖干细胞微环境处缺乏甲硫氨酸局部合成，根细胞DNA甲基化和H3K4me3组蛋白甲基化水平降低，导致编码转录因子的根尖干细胞主调控基因PLETHORA1/2表达下调，进而影响到根尖干细胞维持。此外我们在作物水稻中研究了OsCBL的功能，OsCBL在花药与籽粒中表达很强。OsCBL的敲除突变体具有花粉囊发育和花粉发育的缺陷，种子结实率下降，籽粒减小。OsCBL的过表达植株，穗型增大，单株产量增加。本项目的研究揭示了甲硫氨酸的合成代谢途径与植物生长发育调控的互作机制，通过表观遗传的调控影响到生长素的极性运输，生长素调控的关键根尖干细胞的决定基因PLT1/2的表达，控制根尖干细胞微环境的稳定与维持。在单子叶植物水稻中， CBL主要影响植物的生殖发育，影响水稻的产量性状，这项工作加深了我们对植物代谢与植物发育互作机制的理解，为作物的遗传改良提供理论指导。