The mutual inhibition between PLETHORAs and ARABIDOPSIS RESPONSE REGULATORs controls root zonation.

During organogenesis a key step towards the development of a functional organ is the separation of cells in specific domains with different activities. Mutual inhibition of gene expression has been shown to be sufficient to establish and maintain these domains during organogenesis of several multicellular organisms. Here we show that the mutual inhibition between the PLTs and the ARRs transcription factors is sufficient to separate cell division and cell differentiation during root organogenesis. In particular, we show that ARR1 suppresses PLTs activities and that PLTs suppress ARR1 and ARR12 by targeting their protein for degradation via the KMD2 F-box protein. These findings reveal new important aspects of the complex process of root zonation and development.