Cell type boundaries organize plant development

In plants the dorsoventral boundary of leaves defines an axis of symmetry through thecentre of the organ separating the top (dorsal) and bottom (ventral) tissues. Although thepositioning of this boundary is critical for leaf morphogenesis, how the boundary is established andhow it influences development remains unclear. Using live-imaging and perturbation experimentswe show that leaf orientation, morphology and position are pre-patterned by HD-ZIPIII and KANgene expression in the shoot, leading to a model in which dorsoventral genes coordinate toregulate plant development by localizing auxin response between their expression domains.However we also find that auxin levels feedback on dorsoventral patterning by spatially organizingHD-ZIPIII and KAN expression in the shoot periphery. By demonstrating that the regulation ofthese genes by auxin also governs their response to wounds, our results also provide aparsimonious explanation for the influence of wounds on leaf dorsoventrality.