Brassinosteroid coordinates cell layer interactions in plants via cell wall and tissue mechanics.

Growth coordination between cell layers is essential for development of most multicellular organisms. Coordination may be mediated by molecular signaling and/or mechanical connectivity between cells, but how genes modify mechanical interactions between layers is unknown. Here we show that genes driving brassinosteroid synthesis promote growth of internal tissue, at least in part, by reducing mechanical epidermal constraint. We identified a brassinosteroid-deficient dwarf mutant in the aquatic plant