result in PIN1 relocalization in hypocotyl cells in this process. In gain-of-function PID mutants, which exhibit a collapsed root phenotype, PIN1 is relocated to the apical plasma membrane and the auxin gradient is disrupted in the roots. Notably, several different PP2A mutants have a similar phenotype as the PID gain-of-function mutants, indicating the antagonistic regulation of PIN1 polarization by PID and PP2A. Recently, several PID-dependent Ser/Thr phosphorylation sites in PIN1 were identified that are involved in the basal-to-apical PIN1 polarity shift. The shift in PIN1 localization also requires a BFA-sensitive trafficking pathway. BFA, a fungal toxin that Blue-Light-Induced PIN1 Distribution inhibits GNOM, causes PIN1 to accumulate in endosomes called BFA compartments. GNOM, a member of the ARF-GEF family, is needed for PIN1 recycling from endosomes to the plasma membrane. In this study, we investigate the role of PIN1-regulated auxin 10082199 distribution during root negative phototropic response. Our results show that blue light illumination can shift the PIN1 localization from intracellular compartments to the basal plasma membrane in root stele cells, which result in asymmetric auxin distribution and root negative phototropism. Moreover, the BFA-sensitive vesicle trafficking pathway and the MedChemExpress TG-02 activity of PID/PP2A are also needed for blue-light-induced PIN1 distribution and root negative phototropic response. Results PIN1 is Needed for Root Negative Phototropism and Asymmetric Auxin Distribution Recently, it has been reported that auxin efflux carriers are involved in plant tropic response, such as hypocotyl phototropism, hypocotyl gravitropism, root gravitropism and root negative phototropism. The reduced root negative phototropic response in pin3-4 mutant implies the redundant function of auxin transporters in this process. PIN1 as a key factor in hypocotyl phototropism may also participate in root negative phototropism. In order to test the contribution of PIN1 to the root negative phototropism, we used the loss-of-function pin1 in the following experiments. Because pin1 null mutants are completely sterile, PIN1/pin1 heterozygous seedlings were used for the physiological experiments and pin1 homozygous plants were identified by genotyping after the experiments. As expected, the detailed kinetics of root negative phototropic bending in pin1 homozygous mutants confirmed that PIN1 is involved in root negative phototropic response. Furthermore, the effects of polar auxin transport inhibitor N-1naphthylphthalamic acid in wild-type seedlings indicated that polar auxin transport is needed for root negative phototropic response. Next, we investigated 10092645 whether PIN1 is needed for generating the asymmetric auxin distribution in root negative phototropic response. We used the auxin responsive DR5REV::GFP line, which reliably reveals the pattern of auxin distribution in roots. Consistent with previous report, an asymmetric DR5 activity is detected in unilateral blue light illuminated roots of wild-type seedlings. In contrast, reduced asymmetry in DR5 activity is observed in pin1 homozygous mutants as compared with the wild-type plants. These results reveal a role of PIN1 in root negative phototropism, and indicate that PIN1 activity is needed for the generation of asymmetric auxin distribution during root negative phototropic response. and 3B), in addition to the vacuole in the dark. However, upon unilateral blue light illumination, PIN1-GFP reloresult in PIN1 relocalization in hypocotyl cells in this process. In gain-of-function PID mutants, which exhibit a collapsed root phenotype, PIN1 is relocated to the apical 
plasma membrane and the auxin gradient is disrupted in the roots. Notably, several different PP2A mutants have a similar phenotype as the PID gain-of-function mutants, indicating the antagonistic regulation of PIN1 polarization by PID and PP2A. Recently, several PID-dependent Ser/Thr phosphorylation sites in PIN1 were identified that are involved in the basal-to-apical PIN1 polarity shift. The shift in PIN1 localization also requires a BFA-sensitive trafficking pathway. BFA, a fungal toxin that Blue-Light-Induced PIN1 Distribution inhibits GNOM, causes PIN1 to accumulate in endosomes called BFA compartments. GNOM, a member of the ARF-GEF family, is needed for PIN1 recycling from endosomes to the plasma membrane. In this study, we investigate the role of PIN1-regulated auxin distribution during root negative phototropic response. Our results show that blue light illumination can shift the PIN1 localization from intracellular compartments to the basal plasma membrane in root stele cells, which result in asymmetric auxin distribution and root negative phototropism. Moreover, the BFA-sensitive vesicle trafficking pathway and the activity of PID/PP2A are also needed for blue-light-induced PIN1 distribution and root negative phototropic response. Results PIN1 is Needed for Root Negative Phototropism and Asymmetric Auxin Distribution Recently, it has been reported that auxin efflux carriers are involved in plant tropic response, such as hypocotyl phototropism, hypocotyl gravitropism, root gravitropism and root negative phototropism. The reduced root negative phototropic response in pin3-4 mutant implies the redundant function of auxin transporters in this process. PIN1 as a key factor in hypocotyl phototropism may also participate in root negative phototropism. In order to test the contribution of PIN1 to the root negative phototropism, we used the loss-of-function pin1 in the following experiments. Because pin1 null mutants are completely sterile, PIN1/pin1 heterozygous seedlings were used for the physiological experiments and pin1 homozygous plants were identified by genotyping after the experiments. As expected, the detailed kinetics of root negative phototropic bending in pin1 homozygous mutants confirmed that PIN1 is involved in root negative phototropic response. Furthermore, the effects of polar auxin transport inhibitor N-1naphthylphthalamic acid in wild-type seedlings indicated that polar auxin transport is needed for root negative phototropic response. Next, we investigated whether PIN1 is needed for generating the asymmetric auxin distribution in root negative 15130089 phototropic response. We used the auxin responsive DR5REV::GFP line, which reliably reveals the pattern of auxin distribution in roots. Consistent with previous report, an asymmetric DR5 activity is detected in unilateral blue light illuminated roots of wild-type seedlings. In contrast, reduced asymmetry in DR5 activity is observed in pin1 homozygous mutants as compared with the wild-type plants. These results reveal a role of PIN1 in 1417961 root negative phototropism, and indicate that PIN1 activity is needed for the generation of asymmetric auxin distribution during root negative phototropic response. and 3B), in addition to the vacuole in the dark. However, upon unilateral blue light illumination, PIN1-GFP relo
