Abstract

Gravitropism 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 was know known about the dynamics, regulation, and diversity of the entire bending and straightening process.

Recently, using vital kinematic imaging of the gravitropic movement of different organs from 11 angiosperms sampling the phylogenic tree of land angiosperms, we found that gravitropic straightening shares common traits across species, organs, and orders of magnitude. Surprisingly, 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, i.e. a proprioception. A minimal dynamical model of the movement of the plant during gravitropism and posture control , called the AC model has been designed , that can explain most of the diversity observed in experiments. Moreover the entire dynamics of the bending/straightening response is described by a single dimensionless “bending number” B that reflects the ratio between graviceptive and proprioceptive sensitivities, and defines both the final shape of the organ at equilibrium and the timing of curving and straightening. Proprioceptive sensing is thus as important as gravisensing in dynamical gravitropic control. In this seminar, I will discuss the possible mechanisms for plant proprioception, and their consequences for the involvement of the auxin signalling network in plant gravitropism, as well as the use of model-assisted phenotyping in genetic studies

R.BASTIEN, T. BOHR , B. MOULIA .† , S.DOUADY.† , 2013 . A unifying model of shoot gravitropism reveals proprioception as a central feature of posture control in plant. PNAS 110 (2 ): 755–760 († co-PI last authors, corresponding author ) J DUMAIS 2013 Beyond the sine law of plant gravitropism (commentary of the paper by Bastien et al 2013) PNAS 110 (2 ) 391–392.