Control of leaf shape through non-cell autonomous TCP4 regulation

Leaf development requires coordinated growth across distinct tissue layers, integrating genetic regulation with mechanical coupling to achieve proper organ shaping. However, the mechanisms coordinating differentiation and growth across layers to ensure coherent leaf morphogenesis remain poorly understood. Therefore, we investigated the role of TCP4 as a potential central regulator of interlayer communication coupling genetic and mechanical signals during Arabidopsis leaf development. Three-dimensional analyses revealed pronounced asymmetry in the expression of TCP4 and its negative regulator, MIR319C, across developing primordia, establishing spatially patterned differentiation cues. Tissue-specific perturbations demonstrated that TCP4 activity in either epidermis or subepidermis modulates cell proliferation and expansion across layers through both protein mobility and mobility-independent signalling mechanisms. Strong epidermal TCP4 induction arrested leaf development by prematurely suppressing proliferation and preventing symmetry breaking, thereby locking primordia in cylindrical states. Live imaging revealed fundamental reprogramming of growth anisotropy, with TCP4 driving cortical microtubule alignment, increasing cell wall stiffness, and establishing layer-specific pectin patterns. Together, these findings establish TCP4 as an integrator of genetic and mechanical signals across leaf tissue layers, coupling transcriptional programmes to cytoskeletal organisation, cell wall remodelling, and cross-layer mechanical feedback.