Theoretical Physics Seminar

How do the roots of plants know to grow down and to bend downward after reorientation? While many of the puzzle pieces of this age-old question are being unravelled, the role of physics in this process is poorly understood. We combined experiments and modelling to study the dynamics of plant roots under gravity (gravitropism). We collected a high-throughput, high-resolution experimental dataset of root bending dynamics, for a wide variety of root orientation conditions, and asked whether a single integrated model could link sensing (which occurs at the tip of the root) and bending/directed growth (some distance up the root). We derive a compact mathematical model that combines angle-sensing, signal transduction and a biomechanical response, and show, for the first time, how sensing-bending feedback loops predict experimentally observed transient dynamics upon sudden reorientation, as well as long-term bending dynamics across our entire dataset. We demonstrate our results in the mean-field to capture population dynamics as well as in a stochastic individual root setting. Combining our model with additional experimental data indicates important roles for sensing, signalling and biomechanical modulation, with overlapping timescales, which we begin to disentangle with additional experiments using both wild type and genetically perturbed strains.