MYB36 regulates the transition from proliferation to differentiation in the Arabidopsis root

Stem cells are defined by their ability to self-renew and produce daughter cells that proliferate and mature. These maturing cells transition from a proliferative state to a terminal state through the process of differentiation. In the Arabidopsis thaliana root the transcription factors SCARECROW and SHORTROOT regulate specification of the bi-potent stem cell that gives rise to the cortical and endodermal progenitors. Subsequent progenitor proliferation and differentiation generates mature endodermis, marked by the Casparian Strip: a cell wall modification that prevents ion diffusion into and out of the vasculature. We identified a transcription factor, MYB36 that regulates the transition from proliferation to differentiation in the endodermis. We show that SCARECROW directly activates MYB36 expression, which in turn directly regulates essential Casparian Strip formation genes. In addition, MYB36 represses extra divisions within the endodermis. Our results demonstrate that MYB36 is a critical positive regulator of differentiation and negative regulator of cell proliferation.