Pattering and growth are coordinated early in the cell cycle

During development, cells in multicellular organisms undergo a series of heavily regulated steps that lead to their differentiation into specific cell types. When this process goes wrong – it can lead to diseases like cancer and developmental malformations. Unlike animals, where differentiation stops primarily after embryogenesis, plants grow continuously and have differentiating cells throughout their lifespan. One major differentiation process occurs when a specific stem cell divides formatively into the endodermis and cortex. In the model system - Arabidopsis thaliana, SHORTROOT (SHR) and SCARECROW (SCR) are transcription factors (TFs) that regulate the decision-making process of whether to divide formatively or proliferatively. Using an inducible SHR system, we followed the dynamics of these TFs and observed the cell outcome in long timelapses with high temporal resolution of more than 1000 cells. We linked the trajectories of SCR to SHR and showed that monostable models explain better the SCR dynamics than the previously suggested bistable switch [1]. Furthermore, we propose and validate an alternative model, where a low threshold of SHR and SCR levels in the early stages of the cell cycle can lead to asymmetric divisions. This model suggests that the decision to divide formatively must occur early in the cell cycle.

[1] Cruz-Ramírez, et al. https://doi.org/10.1016/j.cell.2012.07.017.