Soil stresses affect crop yields and present global agricultural challenges1. Soil compaction triggers reduction in root length and radial expansion driven by the plant hormone ethylene2. Here we report how ethylene controls cell wall biosynthesis to promote root radial expansion. We demonstrate how soil compaction stress, via ethylene, upregulates Auxin Response Factor1 in the root cortex, which represses cellulose synthase (CESA) genes. CESA repression drives radial expansion of root cortical cells by modifying the thickness of their cell walls, which results in a thicker epidermis and thinner cortex. Our research links ethylene signalling with root cell wall remodelling, and reveals how dynamic regulation of cellulose synthesis controls root growth in compacted soil.
