MYB36 regulates the transition from proliferation to differentiation in the Arabidopsis root (Liberman et al, Biology, Duke). Arabidopsis thaliana strain:Columbia-0

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, and that MYB36 likely acts in a feed-forward loop to regulate essential Casparian Strip formation genes. We show that myb36 mutants have delayed and defective barrier formation as well as extra divisions in the meristem. Our results demonstrate that MYB36 is a critical positive regulator of differentiation and negative regulator of cell proliferation.

干细胞的核心特征为具备自我更新能力，并可产生具备增殖与成熟潜能的子细胞。这些正在成熟的细胞会通过分化过程，从增殖状态转变为终末状态。在拟南芥根部，转录因子SCARECROW与SHORTROOT可调控可分化为皮层和内皮层祖细胞的双潜能干细胞的特化过程。后续祖细胞的增殖与分化可形成成熟内皮层，其标志性特征为凯氏带（Casparian Strip）——一种可阻断离子向维管组织内外扩散的细胞壁修饰结构。本研究鉴定出一个可调控内皮层中增殖向分化转变的转录因子MYB36。研究证实，SCARECROW可直接激活MYB36的表达，且MYB36大概率通过前馈环路调控参与凯氏带形成的关键功能基因。实验结果表明，myb36突变体存在屏障形成延迟与缺陷，且分生组织中出现额外细胞分裂。本研究结果证实，MYB36是细胞分化的关键正向调控因子，同时也是细胞增殖的负向调控因子。