Growth angles of distinct root classes in wheat are determined by a gradient of anti-gravitropic activity

Abstract The spatial arrangement of plant roots in soil is shaped by different root classes with distinct gravitropic setpoint angles (GSAs) 1,2,3 . GSA is thought to arise from a balance between gravitropism and an opposing anti-gravitropic offset (AGO) 2–5 , but how this balance is established across root classes remains unclear. Here we show, using hexaploid wheat ( Triticum aestivum ), that root class-specific GSAs emerge from a gradient of AGO activity acting on a conserved gravitropic response. Primary and seminal roots differ quantitatively in AGO strength, with successive seminal root classes exhibiting progressively stronger AGO and correspondingly shallower GSAs. We demonstrate that this AGO gradient requires parallel pathways controlled by EGT1 6 and EGT2 7 . Disruption of AGO abolishes root-class differences in gravitropic behaviour, producing uniformly steep root systems and altering root-class-specific transcriptional programmes associated with cell wall organisation and redox processes. These architectural changes are accompanied by reduced agronomic performance under both irrigated and non-irrigated field conditions. Our findings establish antigravitropic regulation as a quantitative mechanism underlying root system architecture and demonstrate its importance for crop performance.