Seminars

The Arabidopsis root serves as a powerful model to dissect how cellular context influences hormone signaling. To enable investigations of these dynamics with single-cell resolution, we constructed a comprehensive single-cell RNA-seq atlas of Arabidopsis roots, highlighting continuous developmental trajectories and providing novel insights into cell identity transitions. Leveraging this atlas as a reference, we have explored how different cellular contexts influence brassinosteroid signaling across cell types, developmental gradients, and phases of the cell cycle. Using time-series single-cell RNA-seq, we identified the elongating cortex as a crucial site where brassinosteroids activate cell wall-related genes, promoting a shift from proliferation to elongation (Nolan et al., 2023, Science). Our analysis revealed HAT7 and GTL1 as brassinosteroid-responsive transcription factors central to this context-dependent transition. Tissue-specific CRISPR experiments confirmed that brassinosteroid signaling within the cortex facilitates cell expansion to promote root growth. In addition, we uncovered additional temporal complexity whereby brassinosteroid signaling fluctuates according to cell-cycle context, decreasing during mitosis and increasing in the G1 phase. Remarkably, polarity-guided uneven mitotic divisions generate daughter cells with distinct brassinosteroid signaling and biosynthesis states, bypassing traditional negative feedback loops and optimizing meristem activity (Vukasinovic and Hsu, et al., 2025, Cell). Our ongoing research combines single-cell RNA-seq, spatial transcriptomics, and large-scale CRISPR screening to define molecular mechanisms underlying the switch from proliferation to differentiation and the cell-cell communication essential for coordinated organ growth. Collectively, our findings underscore the fundamental influence of cellular context on hormone signaling, providing key insights for the precise engineering of root architecture to enhance plant resilience and productivity.