Differential growth dynamics control aerial organ geometry.

How gene activities and biomechanics together direct organ shapes is poorly understood. Plant leaf and floral organs develop from highly similar initial structures and share similar gene expression patterns, yet they gain drastically different shapes later—flat and bilateral leaf primordia and radially symmetric floral primordia, respectively. We analyzed cellular growth patterns and gene expression in young leaves and flowers of Arabidopsis thaliana and found significant differences in cell growth rates, which correlate with convergence sites of phytohormone auxin that require polar auxin transport. In leaf primordia, the PRESSED - FLOWER -expressing middle domain grows faster than adjacent adaxial domain and coincides with auxin convergence. In contrast, in floral primordia, the LEAFY -expressing domain shows accelerated growth rates and pronounced auxin convergence. This distinct cell growth dynamics between leaf and flower requires changes in levels of cell-wall pectin de-methyl-esterification and mechanical properties of the cell wall. Data-driven computer model simulations at organ and cellular levels demonstrate that growth differences are central to obtaining distinct organ shape, corroborating in planta observations. Together, our study provides a mechanistic basis for the establishment of early aerial organ symmetries through local modulation of differential growth patterns with auxin and biomechanics. [Display omitted] • Leaf and floral primordia share similar gene expression and initial domain partition • Local growth-rate differences across domains explain primordia shape differences • Two primordia have different patterns of cell-wall rigidity and auxin convergence • When incorporating growth dynamics, models explain different organ shapes Peng et al. show that different growth dynamics determine the shape of plant aerial organs, leaf and floral primordia, which share similar initial geometry. Experiments and simulations are combined to link growth dynamics with biomechanics and polar auxin transport. [ABSTRACT FROM AUTHOR]