Mechanism of dynamic reorientation of cortical microtubules due to mechanical stress

TL;DR

This paper proposes a theoretical model explaining how mechanical stress and gravity perception lead to the reorientation of cortical microtubules, affecting plant cell growth and shape, with implications for gravitropism, phototropism, and mechanical responses.

Contribution

It introduces a novel theoretical framework linking gravity perception, auxin flux, and microtubule reorientation in plant cells, highlighting a universal mechanism for cellular response to environmental stimuli.

Findings

Microtubules reorient perpendicular to gravity and light stimuli.

Reorientation influences cellulose microfibril growth and cell shape.

The model suggests a universal mechanism for microtubule response to mechanical cues.

Abstract

Directional growth caused by gravitropism and corresponding bending of plant cells has been explored since 19th century, however, many aspects of mechanisms underlying the perception of gravity at the molecular level are still not well known. Perception of gravity in root and shoot gravitropisms is usually attributed to gravisensitive cells, called statocytes, which exploit sedimentation of macroscopic and heavy organelles, amyloplasts, to sense the direction of gravity. Gravity stimulus is then transduced into distal elongation zone, which is several mm far from statocytes, where it causes stretching. It is suggested that gravity stimulus is conveyed by gradients in auxin flux. We propose a theoretical model that may explain how concentration gradients and/or stretching may indirectly affect the global orientation of cortical microtubules, attached to the cell membrane and induce their dynamic reorientation perpendicular to the gradients. In turn, oriented microtubules arrays direct the growth and orientation of cellulose microfibrils, forming part of the cell external skeleton and determine the shape of the cell. Reorientation of microtubules is also observed in reaction to light in phototropism and mechanical bending, thus suggesting universality of the proposed mechanism.