Genetic control of cell layer interactions in plants via tissue mechanics

Plant development depends on coordination of growth between different cell layers. Coordination may be mediated by molecular signalling or mechanical connectivity between cells, but evidence for genetic control via direct mechanics has been lacking. We show that a brassinosteroid-deficient dwarf mutant of the aquatic plant Utricularia gibba has twisted internal tissue, likely caused by a mechanical constraint from a slow-growing epidermis creating tissue stresses. This conclusion is supported by showing that inhibition of brassinosteroid action in an Arabidopsis mutant compromised for cell adhesion, enhances epidermal crack formation, an indicator of increased tissue tension. Thus, genes driving brassinosteroid synthesis can promote growth of internal tissue by reducing mechanical epidermal constraint, showing that tissue mechanics plays a key role in coordinating growth between cell layers. One-Sentence Summary Internal twists in a mutant carnivorous plant reveal how genes control growth via tissue mechanics.