Growth at the shoot apical meristem (SAM) is essential for shoot architecture construction. The phytohormones gibberellins (GA) play a pivotal role in coordinating plant growth, but their role in the SAM remains mostly unknown. Here, we developed a ratiometric GA signaling biosensor by engineering one of the DELLA proteins, to suppress its master regulatory function in GA transcriptional responses while preserving its degradation upon GA sensing. We demonstrate that this degradation-based biosensor accurately reports on cellular changes in GA levels and perception during development. We used this biosensor to map GA signaling activity in the SAM. We show that high GA signaling is found primarily in cells located between organ primordia that are the precursors of internodes. By gain- and loss-of-function approaches, we further demonstrate that GAs regulate cell division plane orientation to establish the typical cellular organization of internodes, thus contributing to internode specification in the SAM.

茎尖分生组织（SAM）的生长对于茎结构的构建至关重要。植物激素赤霉素 (GA) 在协调植物生长中发挥着关键作用，但它们在 SAM 中的作用仍然知之甚少。在这里，我们通过设计一种 DELLA 蛋白开发了一种比例式 GA 信号生物传感器，以抑制其在 GA 转录反应中的主要调节功能，同时保留其在 GA 传感时的降解。我们证明，这种基于降解的生物传感器可以准确报告发育过程中 GA 水平和感知的细胞变化。我们使用该生物传感器来绘制 SAM 中的 GA 信号传导活动图。我们发现，高 GA 信号传导主要存在于位于器官原基之间的细胞中，这些细胞是节间的前身。通过功能获得和功能丧失的方法，我们进一步证明 GA 调节细胞分裂平面方向以建立节间的典型细胞组织，从而有助于 SAM 中的节间规范。