Proprioception as a key contro of gravitropic mouvements and plant posture in the aerial organs of plants
Résumé
Gravitropism, the turning movement of plants aligning to the direction of gravity is a salient trait of land plants. If its motors and early signaling have been thoroughly investigated, the control of the overall movement and its capacity to effectively align to the gravity direction has only started to be elucidated recently. This has been achieved by combining i) quantitative records of the kinematics of tropism in 11 plant species sampling angiosperms phylogeny and ii) a heuristic modelling of the dynamics and diversity of the bending and straightening process. It was shown that the sensing of the local inclination angle by statocytes is not sufficient to bring the organ back to the gravity direction after tilting. Alignment to the direction of gravity and proper control of the plant posture can only be achieved through a balanced cross-talk between gravisensing and a proprioceptive control, tending to straighten the organ. This balance is captured by a single imensionless number B that fully controls the diversity of the movement and of the final posture of the plant. Moreover, our results suggest that the proprioceptive sensitivity has been selectively tuned to avoid the two pitfalls of tropism through differential growth: curvature fixing where growth stops and passive orientation drift.