Abstract
To control morphogenesis, molecular regulatory networks have to interfere with the mechanical properties of the indi-vidual cells of developing organs and tissues, but how this is achieved is not well known. We study this issue here in the shoot meristem of higher plants, a group of undifferenti-ated cells where complex changes in growth rates and direc-tions lead to the continuous formation of new organs [1, 2]. Here, we show that the plant hormone auxin plays an impor-tant role in this process via a dual, local effect on the extracellular matrix, the cell wall, which determines cell shape. Our study reveals that auxin not only causes a limited reduction in wall stiffness but also directly interferes with wall anisotropy via the regulation of cortical microtubule dy-namics. We further show that to induce growth isotropy and organ outgrowth, auxin somehow interferes with the cortical microtubule-ordering activity of a network of proteins, in-cluding AUXIN BINDING PROTEIN 1 and KATANIN 1. Numer-ical simulations further indicate that the induced isotropy is sufficient to amplify the effects of the relatively minor changes in wall stiffness to promote organogenesis and the establishment of new growth axes in a robust manner.