Mechanical Stress Acts via Katanin to Amplify Differences in Growth Rate between Adjacent Cells in Arabidopsis

The presence of diffuse morphogen gradients in tissues supports a view in which growth is locally homogenous. Here we challenge this view: we used a high-resolution quantitative approach to reveal significant growth variability among neighboring cells in the shoot apical meristem, the plant stem cell niche. This variability was strongly decreased in a mutant impaired in the microtubule-severing protein katanin. Major shape defects in the mutant could be related to a local decrease in growth heterogeneity. We show that katanin is required for the cell's competence to respond to the mechanical forces generated by growth. This provides the basis for a model in which microtubule dynamics allow the cell to respond efficiently to mechanical forces. This in turn can amplify local growth-rate gradients, yielding more heterogeneous growth and supporting morphogenesis. [Display omitted] ► Growth is locally heterogeneous in the plant shoot apical meristem by default ► Mechanical stress can amplify differential growth between neighboring cells ► Katanin provides the cell with competence to respond to local force fields ► Katanin is required to maintain growth heterogeneity and meristem shape Cells in the shoot apical meristem use the microtubule-severing protein katanin to detect mechanical stresses imposed by the growth of their neighbors. Surprisingly, this sensing mechanism amplifies rather than minimizes differences in growth rate, and the resulting growth heterogeneity is crucial for morphogenesis.