Institute for Developmental Genetics, Heinrich Heine University, Düsseldorf, Germany.
Centro de Biologia Molecular Severo Ochoa, CSIC-UAM, Cantoblanco, Madrid, Spain.
Elife. 2023 Oct 20;12:e83334. doi: 10.7554/eLife.83334.
Plants produce new organs post-embryonically throughout their entire life cycle. This is due to stem cells present in the shoot and root apical meristems, the SAM and RAM, respectively. In the SAM, stem cells are located in the central zone where they divide slowly. Stem cell daughters are displaced laterally and enter the peripheral zone, where their mitotic activity increases and lateral organ primordia are formed. How the spatial arrangement of these different domains is initiated and controlled during SAM growth and development, and how sites of lateral organ primordia are determined in the peripheral zone is not yet completely understood. We found that the SHORTROOT (SHR) transcription factor together with its target transcription factors SCARECROW (SCR), SCARECROW-LIKE23 (SCL23) and JACKDAW (JKD), promotes formation of lateral organs and controls shoot meristem size. SHR, SCR, SCL23, and JKD are expressed in distinct, but partially overlapping patterns in the SAM. They can physically interact and activate expression of key cell cycle regulators such as () to promote the formation of new cell layers. In the peripheral zone, auxin accumulates at sites of lateral organ primordia initiation and activates SHR expression via the auxin response factor MONOPTEROS (MP) and auxin response elements in the promoter. In the central zone, the SHR-target SCL23 physically interacts with the key stem cell regulator WUSCHEL (WUS) to promote stem cell fate. Both SCL23 and WUS expression are subject to negative feedback regulation from stem cells through the CLAVATA signaling pathway. Together, our findings illustrate how SHR-dependent transcription factor complexes act in different domains of the shoot meristem to mediate cell division and auxin dependent organ initiation in the peripheral zone, and coordinate this activity with stem cell maintenance in the central zone of the SAM.
植物在整个生命周期中都会在后胚胎期产生新的器官。这是由于茎尖分生组织和根分生组织中的干细胞，分别是 SAM 和 RAM。在 SAM 中，干细胞位于中央区，在这里它们缓慢分裂。干细胞的后代被侧向移位并进入周围区，在这里它们的有丝分裂活性增加并形成侧生器官原基。在 SAM 生长和发育过程中，这些不同区域的空间排列是如何启动和控制的，以及侧生器官原基在周围区的位置是如何确定的，目前还不完全清楚。我们发现，SHORTROOT（SHR）转录因子与其靶转录因子 SCARECROW（SCR）、SCARECROW-LIKE23（SCL23）和 JACKDAW（JKD）一起，促进侧生器官的形成，并控制茎分生组织的大小。SHR、SCR、SCL23 和 JKD 在 SAM 中以不同但部分重叠的模式表达。它们可以物理相互作用并激活关键细胞周期调节剂的表达，如 ()，以促进新细胞层的形成。在周围区，生长素在侧生器官原基起始位点积累，并通过生长素响应因子 MONOPTEROS（MP）和 启动子中的生长素响应元件激活 SHR 的表达。在中央区，SHR 靶标 SCL23 与关键干细胞调节剂 WUSCHEL（WUS）物理相互作用，以促进干细胞命运。SCL23 和 WUS 的表达都受到来自干细胞的负反馈调节，通过 CLAVATA 信号通路。总之，我们的研究结果表明，SHR 依赖性转录因子复合物如何在茎分生组织的不同区域发挥作用，介导周围区的细胞分裂和生长素依赖的器官起始，并协调这一活性与 SAM 中央区的干细胞维持。
