Self-confined expression in the Arabidopsis root stem cell niche

Abstract: Stem cell niches are local microenvironments that preserve their unique identity while communicating with adjacent tissues. In the primary root of Arabidopsis thaliana, the stem cell niche comprises the expression of two transcription factors, BRAVO and WOX5, among others. Intriguingly, these proteins confine their own gene expression to the niche, as evidenced in each mutant background. Here we propose through mathematical modeling that BRAVO confines its own expression domain to the stem cell niche by attenuating its WOX5-dependent diffusible activator. This negative feedback drives WOX5 action to be spatially restricted as well. The results show that WOX5 diffusion and sequestration by binding to BRAVO is sufficient to drive realistic confined BRAVO expression at the stem cell niche. We propose that attenuation of a diffusible activator can be a general mechanism to confine genetic activity to a small region while at the same time maintain signaling within it and with the surrounding cells.