The tailoring of root system architecture (RSA) for improved resource acquisition may help achieve a more sustainable intensification of crop productivity to meet future food demands1. The angle of root growth is a critical determinant of RSA and how plants access water and nutrients2,3, however, the gene pathways underpinning this trait are poorly understood. The peptide hormone receptor CEP RECEPTOR 1 (CEPR1) plays a crucial role in determining lateral root angles4–6. Arabidopsis and Medicago cepr1 knockout mutants display a steeper, more compact root system. The phytohormone auxin also promotes steeper lateral root angles7,8. RNA-seq revealed that Arabidopsis cepr1 roots are misregulated in several GRETCHEN HAGEN 3 (GH3) genes9. GH3s act semi-redundantly to inactivate auxin by conjugating it to amino acids10. We used a genetic approach combined with rhizobox and agar plate phenotyping to determine whether GH3 activity affects RSA, and if this occurs within the CEPR1 pathway. A gh3 octuple mutant had steeper lateral roots and a more compact root system akin to cepr1. In a panel of gh3 septuple mutants, the presence of a functional GH3.17, GH3.5 or GH3.6, but not GH3.9, all partially contributed to restoring a more wild type RSA phenotype compared to the octuple mutant. Interestingly, CRISPR-Cas9 knockout of CEPR1 in gh3 mutants resulted in additive root phenotypes, suggesting CEPR1 and GH3 genes operate independently to affect RSA. Hence, we propose the GH3 gene family as a target for modulating crop RSA and for further investigating the underlying mechanisms determining lateral root growth angles.