Stem cells divide and differentiate to form all of the specialized cell types in a multicellular organism. In the Arabidopsis root, stem cells are maintained in an undifferentiated state by a less mitotically active population of cells called the quiescent center (QC). Determining how the QC regulates the surrounding stem cell initials, or what makes the QC fundamentally different from the actively dividing initials, is important for understanding how stem cell divisions are maintained. Here we gained insight into the differences between the QC and the cortex endodermis initials (CEI) by studying the mobile transcription factor SHORTROOT (SHR) and its binding partner SCARECROW (SCR). We constructed an ordinary differential equation model of SHR and SCR in the QC and CEI which incorporated the stoichiometry of the SHR-SCR complex as well as upstream transcriptional regulation of SHR and SCR. Our model prediction, coupled with experimental validation, showed that high levels of the SHR-SCR complex are associated with more CEI division but less QC division. Furthermore, our model prediction allowed us to propose the putative upstream SHR regulators SEUSS and WUSCHEL-RELATED HOMEOBOX 5 and to experimentally validate their roles in QC and CEI division. In addition, our model established the timing of QC and CEI division and suggests that SHR repression of QC division depends on formation of the SHR homodimer. Thus, our results support that SHR-SCR protein complex stoichiometry and regulation of SHR transcription modulate the division timing of two different specialized cell types in the root stem cell niche.

干细胞分裂并分化以形成多细胞生物中的所有特殊细胞类型。在拟南芥中根，干细胞通过称为休眠中心（QC）的有丝分裂活跃程度较低的细胞群维持在未分化状态。确定QC如何调节周围干细胞的初始字母，或使QC与主动分裂的初始字母根本不同的原因，对于理解如何维持干细胞的分裂非常重要。在这里，我们通过研究移动转录因子SHORTROOT（SHR）及其结合伴侣SCARECROW（SCR），深入了解了QC与皮质内胚层缩写（CEI）之间的差异。我们在QC和CEI中构建了SHR和SCR的微分方程模型，该模型结合了SHR-SCR配合物的化学计量以及SHR和SCR的上游转录调控。我们的模型预测以及实验验证，结果表明，高水平的SHR-SCR复合物与更多的CEI部门有关，而与QC部门较少有关。此外，我们的模型预测使我们能够提出推定的上游SHR调节器SEUSS和WUSCHEL相关的HOMEOBOX 5，并通过实验验证其在QC和CEI部门中的作用。此外，我们的模型确定了QC和CEI划分的时机，并建议SHR对QC划分的抑制取决于SHR同型二聚体的形成。因此，我们的结果支持SHR-SCR蛋白复合物的化学计量和SHR转录的调控可调节根干细胞生态位中两种不同专门细胞类型的分裂时间。我们的模型预测使我们能够提出推定的上游SHR调节器SEUSS和WUSCHEL相关的HOMEOBOX 5，并通过实验验证其在QC和CEI部门中的作用。此外，我们的模型确定了QC和CEI划分的时间，并建议SHR对QC划分的抑制取决于SHR同型二聚体的形成。因此，我们的结果支持SHR-SCR蛋白复合物的化学计量和SHR转录的调控可调节根干细胞生态位中两种不同专门细胞类型的分裂时间。我们的模型预测使我们能够提出推定的上游SHR调节器SEUSS和WUSCHEL相关的HOMEOBOX 5，并通过实验验证其在QC和CEI部门中的作用。此外，我们的模型确定了QC和CEI划分的时机，并建议SHR对QC划分的抑制取决于SHR同型二聚体的形成。因此，我们的结果支持SHR-SCR蛋白复合物的化学计量和SHR转录的调控可调节根干细胞生态位中两种不同专门细胞类型的分裂时间。