Root development progression involves RALF peptide-mediated ROS signaling and pectin dynamics in rice

Root development involves the maintenance of longitudinal cell division, cell expansion, and maturation, which is coordinated by signaling networks composed of peptide ligand-receptor complexes and reactive oxygen species (ROS) homeostasis, and is coupled with dynamic cell-wall remodeling. However, these regulatory modules remain disconnected, and the systematic mechanisms that efficiently orchestrate root development remain elusive. Here, we uncover an intrinsic regulatory hub in rice that coordinates root development by integrating ROS transmembrane signaling with pectin structural organization. THESEUS3, a receptor-like kinase, interacts and phosphorylates RbohB to promote superoxide anion (O2−) generation, negatively regulating pectin demethylesterification in the meristem. Rice RAPID ALKALINIZATION FACTOR4 (OsRALF4), functioning as a ligand, balances O2− homeostasis through inhibiting THESEUS3-RbohB signaling in the meristem and modulates pectin demethylesterification. Demethylesterified pectin subsequently binds with OsRALF4 to mediate pectin bundling into a condensed structure, marking the onset of cell expansion. Our study establishes the integrated mechanistic framework underlying root development. An intrinsic hub that integrates the OsRALF4-THE3-RbohB pathway with the binding of OsRALF4-demethylesterified pectin modulates meristem homeostasis by balancing O2− and promotes cell expansion by pectin demethylesterification and condensation.