Acknowledgements: We thank the colleagues of the Laboratoire Reproduction et Développement des Plantes and the Institut de Biologie Moléculaire des Plantes for fruitful discussions on this work and for sharing material and advice. We thank Mathilde Sirlin-Josserand for her help with graphical representation and statistics in Figs. 1f, g, and 2c, and in Supplementary Fig. 2g. We also thank Miguel Perez-Amador, Jan Lohmann, Yvon Jaillais, Tai-ping Sun, Miguel Blazquez, David Alabadi, and the NASC for seeds and plasmids. We thank the personnel of SFR Biosciences (UMS3444/CNRS, US8/Inserm, ENS de Lyon, UCBL) facility PLATIM, and especially Jacques Brocard, for assistance with microscopy and image analysis. We also thank Claire Lionnet for her help with image analysis. This work was supported by the ANR-16-CE13-0014 (GrowthDynamics) grant to T.V. and P.A.; a European Research Council grant (GAtransport) to R.W.; a Guangdong Laboratory for Lingnan Modern Agriculture Grant NG2021001 to B.S.; a grant from the Israel Science Foundation (grant no. 1057/21) to R.W.Funder: Guangdong Laboratory for Lingnan Modern Agriculture Grant NG2021001Growth 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
