Brassinosteroids positively regulate growth through asymmetrical division

Brassinosteroids are plant hormones that play important roles in cell proliferation and expansion, but it is still unclear exactly what those roles are. Vukasinovic and colleagues show, in Arabidopsis thaliana root cells, that instrinsic brassinosteroid gradients signal anticlinal division. Single-cell RNA sequencing and vertical microscopy with automatic root tracking were used to observe brassinosteroid activity via both fluorescence and transcription in individual cells as the root progressed through the cell cycle. During the G1 phase, brassinosteroid activity increases, and the uneven distribution of the brassinosteroid signaling components leads to assymetric cell division, resulting in one brassinosteroid-active cell and one supporting cell. Using this information, a computational modeling simulation of growth in the root meristem was created to understand the importance of this asymmetrical division. By having the one daughter cell highly express brassinosteroids and the other express them on a delay, the process avoids negative feedback between signaling and biosynthesis and allows increased cell proliferation in the meristem. This work represents a major step forward in understanding brassinosteroid-regulated growth. Additionally, the root cell cycle reference and markers developed from the scRNA-seq data could inform many future experiments, even beyond brassinosteroids. (Summary by Elise Krespan) Cell 10.1016/j.cell.2025.02.011