Outer epidermal edges mediate cell-cell adhesion for tissue integrity in plants

Cell-cell adhesion in plants is generally thought to be primarily mediated by the middle lamella, a supposedly thin adhesive layer of the cell wall. Here, we challenge this view. Through computational simulation we found that outer edges of cellular interfaces of the epidermis are hotspot for cell separating tensile stress. Characterization of the ultrastructure of those edges in planta revealed that they are locally thickened regions that harbor cellulose lamellae and pectin-based structural continuity across adjacent cells. We confirmed their dominant role for adhesion by studying mutants where those edges are defective and through direct mechanical testing. This reveals the key role of outer epidermal cell edges, rather than the middle lamella, in mediating cell-cell adhesion for tissue integrity in plants.