Acts as a component of the auxin efflux carrier. Seems to be involved in the basipetal auxin transport. Mediates the formation of auxin gradient which is required to ensure correct organogenesis. Coordinated polar localization of PIN1 is directly regulated by the vesicle trafficking process and apical-basal PIN1 polarity also depends on the phosphorylation of conserved serine residues by PID kinase. The ARF-GEF protein GNOM is required for the correct recycling of PIN1 between the plasma membrane and endosomal compartments. Interacts with TOPP4 (PubMed:11574889). Interacts with FYPP1 AND FYPP3 (PubMed:22715043). Expressed at the basal side of elongated parenchymatous xylem cells. Expressed during embryogenesis. Already detected in the 8-cell stage at the inner cell boundaries. Later, polarity is gradually established at the basal side of provascular cells then in epidermis cells. Down-regulated by endoplasmic reticulum stress treatment. Plants exhibit developed naked, pin-shaped inflorescences and abnormalities in the number, size, shape, and position of lateral organs. Belongs to the auxin efflux carrier (TC 2.A.69.1) family.