Root hairs are microscopic cells that allow plants to draw water and minerals from the soil. Their growth is highly distinctive: they elongate only from their tip, seemingly undisturbed by obstacles encountered along the way, as though an internal mechanism had already determined their final length. But how do these cells know when to stop growing?
In a study published in The Plant Cell, the team of Marie-Edith Chabouté and Alexandre Berr (Stress signaling to the nucleus, IBMP, CNRS/Unistra), in collaboration with partners in Lyon, Cambridge and Lund, sheds light on this question. By combining real-time microscopy, a microfluidic device and mathematical modelling, the researchers tracked the growth of Arabidopsis thaliana root hairs in vivo and identified three successive phases: fast growth, slowing growth, and early maturation. This transition coincides with an abrupt reorganization of the cytoskeleton (microtubules suddenly disappearing from the tip of the hair) together with a progressive movement of the nucleus toward the tip. By chemically or genetically disrupting these networks (fra2 and crwn1 mutant lines), the team showed that the cytoskeleton and the nucleoskeleton jointly drive the halt in growth, notably through a deformation that elongates the nucleus along the growth axis of the hair.
Building on these observations, the researchers developed a mathematical model that faithfully reproduces the growth dynamics observed experimentally. This work paves the way toward a more integrated understanding of polarized growth control in plants, a mechanism also at work in pollen tube growth.
