Fig. 4

Plant meristem organization: (A-B) Shoot Apical Meristem (SAM). Schematic representation of Arabidopsis SAM. Tissues are depicted in false colors. Stem cell niche (SCN) function relies on the activity of WUS and STM to determine a cytokinin maximum in the Organizing Centre (OC) and on the induction of CLV3 by WUS that in turn represses WUS. Cell from SCN generate daughter cells composing the peripheral zone before differentiation and incorporation in lateral organs. (C-D) Root Apical Meristem (RAM): Schematic representation of Arabidopsis RAM. Tissues are depicted in false colors. All root tissues originate from stem cell niches (SCN, red line). SCN is patterned and maintained thanks to the formation of an auxin maximum in SCN (green gradient) and the activity of PLETHORA (PLTs) transcription factors. Along with SHR and SCR transcription factors, these mechanisms maintain stem cell function and counteract cytokinin activity, allowing for a predominance of cell division over cell differentiation in the meristematic zone