Seminars

In Arabidopsis roots, the phytohormone auxin and PLETHORA transcription factors control many aspects of developmental progression. Coordination of this progression defines zones of cell division, cell expansion and cell differentiation. We combined experiments and computational modelling to unravel a dynamic interplay between auxin and the PLT proteins. High and prolonged auxin concentrations generate a narrow PLT transcription domain, and a PLT protein gradient extends outward from this domain exploiting growth dilution and cell-to-cell movement.

What are the consequences of this transcription factor gradient with maximum expression values in the stem cell region? We show that different PLT levels define two distinct meristem zones and the expansion/differentiation boundary. We provide evidence that slow, auxin-dependent PLT thresholds stabilize developmental progression from stem cell to differentiated cell, while rapid PLT-independent auxin action allows fast tropic responses without disturbing the meristem boundary. I will discuss how this mechanism compares to a second noise-filtering mechanism that we found to be important for the control of asymmetric cell division.

How can a transcription factor gradient encode properties such as stemness and differentiation? We have approached this question by investigating the direct and indirect targets of PLT transcription factors using induced expression and ChIP-seq approaches. The results indicate that division and differentiation control through PLT transcription factors can be separated at the level of induced and repressed target genes.