Root growth responses to mechanical impedance are regulated by a network of ROS, ethylene and auxin signalling in Arabidopsis.

O_LIThe growth and development of root systems, essential for plant performance, is influenced by mechanical properties of the substrate in which the plants grow. Mechanical impedance, such as by compacted soil, can reduce root elongation and limit crop productivity. C_LIO_LITo understand better the mechanisms involved in plant root responses to mechanical impedance stress, we investigated changes in the root transcriptome and hormone signalling responses of Arabidopsis to artificial root barrier systems in vitro. C_LIO_LIWe demonstrate that upon encountering a barrier, reduced Arabidopsis root growth and the characteristic step-like growth pattern is due to a reduction in cell elongation associated with changes in signalling gene expression. Data from RNA-sequencing combined with reporter line and mutant studies identified essential roles for reactive oxygen species, ethylene and auxin signalling during the barrier response. C_LIO_LIWe propose a model in which early responses to mechanical impedance include reactive oxygen signalling that is followed by integrated auxin and ethylene responses to mediate root growth changes. Inhibition of ethylene responses allows improved growth in response to root impedance, a result that may inform future crop breeding programmes. C_LI