A P-Loop NTPase Regulates Quiescent Center Cell Division and Distal Stem Cell Identity through the Regulation of ROS Homeostasis in <i>Arabidopsis</i> Root

Reactive oxygen species (ROS) are recognized as important regulators of cell division and differentiation. The Arabidopsis thaliana P-loop NTPase encoded by APP1 affects root stem cell niche identity through its control of local ROS homeostasis. The disruption of APP1 is accompanied by a reduction in ROS level, a rise in the rate of cell division in the quiescent center (QC) and the promotion of root distal stem cell (DSC) differentiation. Both the higher level of ROS induced in the app1 mutant by exposure to methyl viologen (MV), and treatment with hydrogen peroxide (H2O2) rescued the mutant phenotype, implying that both the increased rate of cell division in the QC and the enhancement in root DSC differentiation can be attributed to a low level of ROS. APP1 is expressed in the root apical meristem cell mitochondria, and its product is associated with ATP hydrolase activity. The key transcription factors, which are defining root distal stem niche, such as SCARECROW (SCR) and SHORT ROOT (SHR) are both significantly down-regulated at both the transcriptional and protein level in the app1 mutant, indicating that SHR and SCR are important downstream targets of APP1-regulated ROS signaling to control the identity of root QC and DSCs.活性氧（Reactive oxygen species, ROS）被公认为细胞分裂与分化的重要调控因子。由APP1编码的拟南芥（Arabidopsis thaliana）P环核苷三磷酸酶，通过调控局部ROS稳态，影响根干细胞龛的身份特征。APP1功能缺失会伴随ROS水平降低、静止中心（quiescent center, QC）细胞分裂速率升高，以及根远端干细胞（root distal stem cell, DSC）分化加速。在app1突变体中，经甲基紫精（methyl viologen, MV）处理诱导的ROS水平升高，与过氧化氢（hydrogen peroxide, H2O2）处理，均可挽救该突变体的表型，这表明QC细胞分裂速率升高与根远端干细胞分化增强，均可归因于低水平ROS。APP1在根顶端分生组织细胞的线粒体中表达，其编码产物具备ATP水解酶活性。调控根远端干细胞龛的关键转录因子，如SCARECROW（SCR）与SHORT ROOT（SHR），在app1突变体的转录与蛋白水平均显著下调，这说明SHR与SCR是APP1调控的ROS信号通路的重要下游靶标，共同控制根QC与DSC的身份特征。