Unifying model of shoot gravitropism reveals proprioception as a central feature of posture control in plants

摘要

Gravitropism, the slow reorientation of plant growth in response to gravity, is a key determinant of the form and posture of land plants. Shoot gravitropism is triggered when statocysts sense the local angle of the growing organ relative to the gravitational field. Lateral transport of the hormone auxin to the lower side is then enhanced, resulting in differential gene expression and cell elongation causing the organ to bend. However, little is known about the dynamics, regulation, and diversity of the entire bending and straightening process. Here, we modeled the bending and straightening of a rod-like organ and compared it with the gravitropism kinematics of different organs from 11 angiosperms. We show that gravitropic straightening shares common traits across species, organs, and orders of magnitude. The minimal dynamic model accounting for these traits is not the widely cited gravisensing law but one that also takes into account the sensing of local curvature, what we describe here as a graviproprioceptive law. In our model, the entire dynamics of the bending/straightening response is described by a single dimensionless "bending number" B that reflects the ratio between graviceptive and pro-prioceptive sensitivities. The parameter B defines both the final shape of the organ at equilibrium and the timing of curving and straightening. B can be estimated from simple experiments, and the model can then explain most of the diversity observed in experiments. Proprioceptive sensing is thus as important as gravisensing in gravitropic control, and the B ratio can be measured as phenotype in genetic studies.%INRA (Institut National de la Recherche Agronomique), UMR0547 (Unite Mixte de Recherche PIAF Physique et Physiologie Integratives de I'Arbre Fruitier et Forestier), F-63100 Clermont-Ferrand, France,Clermont Universite, Universite Blaise Pascal, UMR0547 (Unite Mixte de Recherche PIAF Physique et Physiologie Integratives de I'Arbre Fruitier et Forestier), BP 10448, F-63000 Clermont-Ferrand, France,Matiere et Systemes Complexes, Universite Paris-Diderot, 75025 Paris Cedex 13, France;Department of Physics and Center for Fluid Dynamics, Technical University of Denmark, DK-2800 Lyngby, Denmark;INRA (Institut National de la Recherche Agronomique), UMR0547 (Unite Mixte de Recherche PIAF Physique et Physiologie Integratives de I'Arbre Fruitier et Forestier), F-63100 Clermont-Ferrand, France,Clermont Universite, Universite Blaise Pascal, UMR0547 (Unite Mixte de Recherche PIAF Physique et Physiologie Integratives de I'Arbre Fruitier et Forestier), BP 10448, F-63000 Clermont-Ferrand, France;Matiere et Systemes Complexes, Universite Paris-Diderot, 75025 Paris Cedex 13, France;