Together with ABCG36, regulates auxin homeostasis and responses by playing a dual role in coumarine (and derivatives) and in the auxin precursor indole 3-butyric acid (IBA) efflux transport, thus influencing roots and root hairs development (PubMed:24015802, PubMed:20498067). Mediates coumarin exudation in the rhizosphere, especially in iron (Fe) deficient conditions, with a strong specificity for highly oxygenated compounds such as scopoletin and derivatives, dihydroxyscopoletin, esculetin, fraxin, fraxetin and esculin; these molecules improve plant Fe nutrition (PubMed:28623273, PubMed:26517905, PubMed:24015802). Involved in the cellular detoxification of xenobiotics by promoting the excretion of some auxinic herbicides including 2,4-dichlorophenoxyacetic acid (2,4-D), 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) and other members of the phenoxyalkanoic acid family as well as the polar auxin transport inhibitor, napthylphthalamic acid (NPA) (PubMed:24015802, PubMed:16877699, PubMed:20498067). May be a general defense protein (By similarity). Polarized localization at the outermost side of root epidermal and cap cells. Expressed in roots and, to a lower extent, in seedlings. In roots, mostly expressed in the cells of the lateral root cap and epidermal cells at the root tip (PubMed:16877699, PubMed:20498067). In shoots, confined to the stipules (PubMed:16877699). Induced by cycloheximide (CHX) and cold/dark treatment (PubMed:12430018). Up-regulated in response to iron (Fe) deficiency (PubMed:24015802). Defects in efflux of the auxin precursor indole-3-butyric acid (IBA) associated with developmental defects such as abnormally long root hairs and increased lateral root production (PubMed:20498067). Strongly reduced coumarin (e.g. highly oxygenated compounds scopoletin, dihydroxyscopoletin, esculetin, fraxin, fraxetin and esculin) exudation in the rhizosphere, especially in iron (Fe) deficient conditions (PubMed:28623273, PubMed:24015802). Hypersensitivity to iron (Fe) deficiency (PubMed:24015802). Increased sensitivity to the auxinic herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) and 2-naphthoxyacetic acid (2-NOA), but normal responses to the endogenous auxins indole-3-acetic acid (IAA), phenylacetic acid (PAA) and indole-butyric acid (IBA) (PubMed:16877699, PubMed:20498067). Hypersensitivity to polar auxin transport inhibitors including napthylphthalamic acid (NPA), 1-naphthoxyacetic acid (1-NOA), 2-(1-pyrenoyl)benzoic acid (PBA) and 2,3,5-triiodobenzoic acid (TIBA) (PubMed:16877699, PubMed:20498067). Belongs to the ABC transporter superfamily. ABCG family. PDR (TC 3.A.1.205) subfamily.