Single-Cell Transcriptomics Reveals that A Conserved GA-GASA1-ROS Module Promotes Lateral Root Founder Cell Specification.

The specification and commitment of lateral root founder cells (LRFCs) from postembryonic pericycle cells are critical steps in LR development, yet their earliest molecular determinants remain unclear. Using single-cell transcriptomics, we resolved transcriptional transitions guiding LRFC fate in Arabidopsis thaliana and identified five distinct phases of transcriptional progression during LRFC specification. Through differentially expressed gene analysis and phenotypic observation, we showed that application of exogenous GA (20 and 50 μM) promoted the nuclear migration and division in LRFCs independently of DELLA signaling, and revealed that Gibberellic acid-stimulated Arabidopsis 1 (GASA1) functions as a key mediator of gibberellin (GA) to accelerate the LRFC progression. Further histochemical staining and cytological observations demonstrated that GASA1 mediated the GA-triggered reactive oxygen species (ROS) accumulation to reinforce the LRFC commitment. The GA-GASA1-ROS module is evolutionarily conserved, with GA-ROS-driven LRFC commitment being fundamental across angiosperms. Notably, GASA1 emerged with root evolution in early land plants and diversified alongside lateral and shoot-borne root systems, revealing a conserved GA-ROS axis in plant organogenesis.