Abstract text: Soil stresses affect crop yields and present global agricultural challenges. 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 and stiffness of their cell walls, which results in a thicker epidermis and thinner cortex. These results link ethylene signaling with root cell wall remodeling, and reveal how dynamic regulation of cellulose synthesis and cell wall mechanics to control root growth in compacted soil. We will further showcase how we use custom-built confocal microscopy to directly image root growth in real-life soil to understand root behavior in compacted soil under near-physiological conditions.