Consequently, ethylene signaling mutants ( I ein2 i , I ein3 i , and I ctr1 i ) or insensitive mutants ( I aux1 i and I pin2 i ) either grow longer or are less inhibited when encountering the physical barrier, corroborating the model that ethylene-induced auxin biosynthesis and redistribution is a driving force for root growth inhibition under mechanical stress ([16], [15]; [18]). Root growth responses to mechanical impedance are regulated by a network of ROS, ethylene and auxin signalling in Arabidopsis. Auxin steers roots to penetrate hard barriers Auxin is one of the major phytohormones that regulates root development and plastic responses to environmental cues ([7]). Keywords: Auxin; calcium signaling; ethylene; mechanical impedance; natural variation; reactive oxygen species; root penetrability EN Auxin calcium signaling ethylene mechanical impedance natural variation reactive oxygen species root penetrability 4612 4614 3 08/16/22 20220811 NES 220811 Soil drying and compaction increase mechanical impedance, a common problem in agricultural soils that adversely impacts crop productivity. [Extracted from the article]