CONTROL OF CELL DIVISION AND DIFFERENTIATION IN THE ARABIDOPSIS ROOT - STUDIES ON THE AUXIN RESISTAN 3 (AXR3) GENE

Abstract

Tight and balanced control of cell division and cell differentiation is crucial for plant development. In Arabidopsis, auxin signaling mediated by its repressors AUX/IAA proteins, plays a key role in mediating root development and growth. However, it is still not well understood how AUX/IAA proteins coordinates cell division and cell differentiation in the Arabidopsis root. Here, we show that gain-of-function mutations in the AXR3 gene, encoding the AUX/IAA protein IAA17, result in defective stem cell specification and formative cell divisions in the root ground tissue layer. Genetics interaction studies suggest that AXR3 acts in parallel with SCR, SHR and PLT genes, mediating patterning of the Arabidopsis root stem cell niche. Intriguingly, AXR3 expresses only in differentiated root cap cells and differentiating or differentiated cells proximal to the root meristem, indicating a non-cell-autonomous mode of regulation. Indeed we found that AXR3 could regulate auxin distribution and accumulation in the stem cell niche by repressing the activities of several PIN auxin efflux facilitators in the AXR3-expressing cells. Together, our results reveal, for the first time, that auxin signaling in the differentiating or differentiated cells could direct cell specification and division in the stem cell niche.