One-sentence summary: TIR1/AFB signaling is required and sufficient for auxin-mediated PIN3 re-polarization and shoot gravitropic bending termination. Dear Editor, Gravitropism is a plant adaptive response that involves asymmetric auxin distribution (Friml et al., 2002; Rakusová et al., 2015; Su et al., 2017). The auxin asymmetry leading to the shoot and root bending is initiated by the gravity-induced subcellular relocalization of PIN auxin transporters (Friml et al., 2002; Kleine-Vehn et al., 2010; Rakusová et al., 2011). Bending termination is much less well characterized, although it depends on the re-establishment of the symmetrical auxin distribution due to auxin-mediated re-establishment of the symmetric PIN localization (Supplemental Fig. S1A; Rakusová et al., 2016, 2019). Which auxin signaling pathway mediates this auxin feedback on PIN repolarization and bending termination remains unknown. To evaluate which auxin signaling machinery mediates auxin feedback on PIN3 repolarization for bending termination, we examined two best characterized auxin perception pathways: (i) the nuclear auxin receptors TIR1/AFB, which mediate both transcriptional and non-transcriptional responses (Salehin et al., 2015; Fendrych et al., 2016, 2018); and (ii) the AUXIN BINDING PROTEIN1 (ABP1) pathway with an unclear function (Gao et al., 2015; Grones et al., 2015). While abp1 mutant showed a normal hypocotyl gravitropic response (Supplemental Fig. 1B), the tir1 afb2 afb3 triple hypocotyls were hyperbending (Fig. 1A), suggesting a defect in the