Brassinosteroid gene regulatory networks at cellular resolution

Brassinosteroids (BRs) are plant steroid hormones that regulate diverse processes such as cell division and cell elongation. BRs control thousands of genes through gene regulatory networks (GRNs) that vary in space and time. We used time series single-cell RNA-sequencing to identify BR-responsive gene expression specific to different cell types and developmental stages of the Arabidopsis root, uncovering the elongating cortex as a site where BRs trigger a shift from proliferation to elongation associated with increased expression of cell wall-related genes. Our analysis revealed HAT7 and GTL1 as BR-responsive transcription factors that regulate cell elongation in the cortex. These results establish the cortex as an important site for BR-mediated gene expression and unveil a BR signaling network regulating the transition from proliferation to elongation, illuminating new aspects of spatiotemporal hormone response. ### Competing Interest Statement P.N.B. is the co-founder and Chair of the Scientific Advisory Board of Hi Fidelity Genetics, a company that works on crop root growth.