Extended Data Fig. 1: Anatomical organization of the Arabidopsis root apex.

Nuclei are identified by the constitutive expression of a histone H3.3-GFP protein (green) and the cell walls were stained with propidium iodide. On the radial axis, concentrical cell layers can be identified from the outermost epidermal layer to the cortex, endodermis, pericycle and vascular tissues. On the longitudinal axis, the root apical meristem (RAM), the focus of our study, occupies the more distal (or rootward) zone and contains all proliferating cells⁵². The RAM is followed by an elongation zone, where cells stop proliferation, enter the endocycle and initiate elongation, and finally a differentiation zone where cells acquire their final differentiated state. Within the RAM, a group of rarely dividing cells, the quiescent center (QC) cells, is located distally and is surrounded by stem cells^53,54 that give rise to all different root cells types (see inset). Asymmetric division of these stem cells renders the first derivatives that undergo several divisions within the transit amplifying compartment before arresting the cell cycle and initiating an elongation process, coinciding with the RAM boundary⁹, which is defined by a complex hormonal balance^55,56.