A Genetic Framework for the Control of Cell Division and Differentiation in the Root Meristem

TLDR

Plant growth and development are sustained by meristems whose activity is regulated by auxin and cytokinin, whose interaction in specifying developmental outcomes remains poorly understood. Using comprehensive genetic and molecular analysis in Arabidopsis, the authors show that the cytokinin‑responsive transcription factor ARR1 activates SHY2/IAA3, a repressor of auxin signaling that down‑regulates PIN auxin transporters, thereby inducing auxin redistribution and promoting cell differentiation. Conversely, auxin triggers SHY2 degradation, maintaining PIN activity and cell division, and the resulting balance of differentiation and division that controls root meristem size and growth emerges from the cytokinin‑auxin regulatory circuit centered on SHY2.

Abstract

Plant growth and development are sustained by meristems. Meristem activity is controlled by auxin and cytokinin, two hormones whose interactions in determining a specific developmental output are still poorly understood. By means of a comprehensive genetic and molecular analysis in Arabidopsis, we show that a primary cytokinin-response transcription factor, ARR1, activates the gene SHY2/IAA3 (SHY2), a repressor of auxin signaling that negatively regulates the PIN auxin transport facilitator genes: thereby, cytokinin causes auxin redistribution, prompting cell differentiation. Conversely, auxin mediates degradation of the SHY2 protein, sustaining PIN activities and cell division. Thus, the cell differentiation and division balance necessary for controlling root meristem size and root growth is the result of the interaction between cytokinin and auxin through a simple regulatory circuit converging on the SHY2 gene.