Protein complex stoichiometry and expression dynamics of transcription factors modulate stem cell division (PNAS)

Stem cells are a group of undifferentiated cells that can divide and differentiate to form new organs. In Arabidopsis roots, the quiescent center (QC: the mitotically inactive group of cells) helps regulate the division of surrounding initials and maintain the stem cell fate. What makes the QC different from surrounding stem cells, and how does it regulate the division of its surrounding initials? To address this, Clark et al. studied two transcription factors that form a complex, SCR (SCARECROW) and SHR (SHORTROOT), and determined their roles in the division of QC and Cortex Endodermis Initials (CEI). Using an ordinary differential equation model, the authors were able to predict a higher percentage of the oligomeric state, 1SHR:2SCR and 2SHR:2SCR stoichiometry, in QC compared to CEI. The authors also identified WUSCHEL-RELATED HOMEOBOX5 (WOX5) and SEUSS (SEU) as putative transcriptional regulators of SHR expression. Additionally, the authors also showed how SHR: SCR temporal dynamics can modulate the division of CEI and QC and how SHR homodimer is required for QC division. Overall, the authors in this paper were able to use both mathematical models and experimental data to highlight the role of protein complex stoichiometry in modulating the division of two different cell types in the Arabidopsis root stem cell niche. (Summary by Sunita Pathak @psunita980) Proc. Natl. Acad. Sci. USA 10.1073/pnas.2002166117