Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA.
Proc Natl Acad Sci U S A. 2012 Dec 18;109(51):21152-7. doi: 10.1073/pnas.1210799110. Epub 2012 Dec 4.
Spatiotemporal control of the formation of organ primordia and organ boundaries from the stem cell niche in the shoot apical meristem (SAM) determines the patterning and architecture of plants, but the underlying signaling mechanisms remain poorly understood. Here we show that brassinosteroids (BRs) play a key role in organ boundary formation by repressing organ boundary identity genes. BR-hypersensitive mutants display organ-fusion phenotypes, whereas BR-insensitive mutants show enhanced organ boundaries. The BR-activated transcription factor BZR1 directly represses the cup-shaped cotyledon (CUC) family of organ boundary identity genes. In WT plants, BZR1 accumulates at high levels in the nuclei of central meristem and organ primordia but at a low level in organ boundary cells to allow CUC gene expression. Activation of BR signaling represses CUC gene expression and causes organ fusion phenotypes. This study uncovers a role for BR in the spatiotemporal control of organ boundary formation and morphogenesis in the SAM.
茎尖分生组织（SAM）中的干细胞巢决定了器官原基和器官边界的形成，从而控制器官的时空形成，决定了植物的模式和结构，但相关的信号机制仍知之甚少。本研究表明，油菜素内酯（BRs）通过抑制器官边界身份基因在器官边界形成中起关键作用。BR 超敏突变体表现出器官融合表型，而 BR 不敏感突变体显示出增强的器官边界。BR 激活转录因子 BZR1 直接抑制杯状子叶（CUC）家族的器官边界身份基因。在 WT 植物中，BZR1 在中央分生组织和器官原基的核中积累水平较高，但在器官边界细胞中积累水平较低，从而允许 CUC 基因表达。BR 信号的激活抑制 CUC 基因表达并导致器官融合表型。本研究揭示了 BR 在 SAM 中器官边界形成和形态发生的时空调控中的作用。
