Together with ABCG37, regulates auxin homeostasis and responses by playing a dual role in coumarine (e.g. esculin) and in the auxin precursor indole 3-butyric acid (IBA) efflux transport, thus influencing cotyledons, roots and root hairs development (PubMed:26517905, PubMed:19648296, PubMed:28623273, PubMed:20498067). Mediates the transport (export into the apoplast) of distinct indole-type metabolites in distinct biological processes; a precursor of 4-O-beta-D-glucosyl-indol-3-yl formamide (4OGlcI3F), a pathogen-inducible tryptophan-derived compound (e.g. upon Blumeria graminis conidiospore inoculation), being a probable substrate in extracellular pathogen defense (PubMed:26023163). Involved in the cellular detoxification of xenobiotics by promoting the excretion of some auxinic herbicides including 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) and other members of the phenoxyalkanoic acid family but not 2,4-dichlorophenoxyacetic acid (2,4-D) (PubMed:20498067). Mediates thymidine exudation in the rhizosphere (PubMed:28623273). May be a transporter of lignin precursors during tracheary element differentiation (PubMed:28921082). Key factor that controls the extent of cell death in the defense response (PubMed:24889055). Necessary for both callose deposition and glucosinolate activation in response to pathogens (PubMed:23815470, PubMed:26023163). As a central component of nonhost resistance (NHR), required for limiting invasion by nonadapted pathogens including powdery mildews (e.g. Blumeria graminis and Erysiphe pisi), root-penetrating pathogenic fungi (e.g. Fusarium oxysporum), Phakopsora pachyrhizi and Colletotrichum gloeosporioides (anthracnose fungi), probably by sensing Ca(2+) via interactions with calmodulins (e.g. CaM7) (PubMed:20605856, PubMed:24889055, PubMed:26023163, PubMed:26315018, PubMed:29085068). Confers resistance to cadmium (Cd) and lead (Pb), probably as an efflux pump of Cd2+ or Cd conjugates, and possibly, of chemicals that mediate pathogen resistance. Promotes resistance to abiotic stresses (e.g. drought and salt stress) and favors general growth by preventing sodium accumulation in plants (PubMed:20088904). Required for microbe-associated molecular patterns (MAMPs)- and salicylic acid (SA)-dependent hypersensitive cell death (HR), involving indole glucosinolate breakdown products (e.g. indole-3-acetonitrile), probably in a PEN2 myrosinase-dependent metabolic pathway, triggered by the recognition of effectors from incompatible pathogens including oomycetes and bacteria (e.g. AvrRpm1 and AvrRps4) and benzothiadiazole- (BTH), and leading to an induced protection against pathogens (e.g. Pseudomonas syringae pv. tomato DC3000, Golovinomyces orontii and Hyaloperonospora arabidopsidis) (PubMed:23815470, PubMed:24889055, PubMed:26023163, PubMed:28434950). Interacts, in a Ca(2+)-dependent manner, with calmodulins CaM3, CaM7 and several CaM-like proteins (CML8, CML9, CML12/CAL4, CML37 and CML38), as well as with calcium regulated proteins CBL4/SOS3 and KIC. Constitutively present and uniformly distributed throughout the plasma membrane in both leaves epidermal and mesophyll cells of plants in normal conditions (PubMed:23836668, PubMed:28910579). Polarized localization at the outermost side of root epidermal and cap cells, in the outer lateral membrane domain facing the environment; the trafficking and endocytic recycling between the endoplasmic reticulum, the trans-Golgi network and the plasma membrane is ACT7-, EAP3- and ALA3-dependent, but the polar localization to the outer lateral membrane domain requires EXO84B (PubMed:20451385, PubMed:27803190, PubMed:28434950, PubMed:29085068, PubMed:20498067). Incorporated transiently at the host-pathogen interface or into pathogen-induced papillae and haustorial encasement structures outside of the plasma membrane upon infection with a pathogen, in an actin-dependent manner; this translocation seems not regulated by phosphorylation (PubMed:23836668, PubMed:28434950, PubMed:29085068, PubMed:28910579). Ubiquitous (at protein level). Higher levels in root hairs, stomata, epidermal cells, and hydathodes. Concentrated at the infection site of infected plants, including papillae and haustoria (PubMed:23836668). Accumulates at the periphery of lateral root cap and root epidermal cells, especially in the outer lateral membrane domain facing the environment (PubMed:19648296, PubMed:27803190). Accumulates during tracheary element differentiation. Induced by cycloheximide (CHX), cold/dark treatment, cadmium, lead, sclareol and sclareolide. Repressed by abscisic acid (ABA). Induced by infection of avirulent and virulent bacterial pathogens (Pseudomonas syringae pv. tomato with or without avrRpt2, avrRpm1 or avrRps4, respectively) and fungal pathogens (e.g. Colletotrichum gloeosporioides) (PubMed:20605856, PubMed:23815470, PubMed:23836668, PubMed:24889055). Strong focal but transient accumulation outside of the plasma membrane within papillae or at the host-pathogen interface, in response to pathogens and in the presence of pathogen-associated molecular patterns (PAMPs) such as flagellin-derived peptides (e.g. flg22 and elf18), and cell walls of fungal pathogens and insect pests derived molecules (e.g. hydrolyzed chitin); this focal accumulation requires actin and is suppressed by the bacterial effector AvrPto (PubMed:23815470, PubMed:23836668). Phosphorylated upon perception of pathogen-associated molecular patterns (PAMPs); phosphorylations at Ser-40 and Ser-45, which likely regulate transport activity, are required for plant defense against pathogens (e.g. Blumeria graminis), but dispensable for recruitment to the host-pathogen interface and penetration sites (PubMed:26315018, PubMed:28910579). Phosphorylation at Ser-841 seems to be required for protein stability (PubMed:28910579). Defects in efflux of the auxin precursor indole-3-butyric acid (IBA) associated with developmental defects such as abnormally long root hairs, increased lateral root production and larger cotyledon expansion (PubMed:19648296, PubMed:20498067). Reduced thymidine and coumarin (e.g. scopolin) exudation in the rhizosphere (PubMed:28623273). Overaccumulation in leaves of 4-O-beta-D-glucosyl-indol-3-yl formamide (4OGlcI3F) upon Blumeria graminis conidiospore inoculation, a pathogen-inducible tryptophan-derived compound, which biosynthesis is dependent on the PEN2 metabolic pathway (PubMed:26023163). Reduced shoot fresh weight (PubMed:20088904). Less sensitive to compatible pathogens (Pseudomonas syringae pv tomato) due to accelerated cell death and lesion formation (PubMed:16415066, PubMed:16473969). Decreased hypersensitive cell death (HR) triggered by the recognition of effectors from oomycete and bacterial pathogens, thus leading to a compromised resistance to incompatible pathogen (e.g. P.syringae pv. tomato DC3000 and Hyaloperonospora arabidopsidis) (PubMed:23815470, PubMed:24889055). Increased susceptibility to the necrotrophic pathogen Plectosphaerella cucumerina (PubMed:26023163). Increased sensitivity to the root-penetrating pathogenic fungus Fusarium oxysporum (PubMed:29085068). Extensive leaf chlorosis and reduced fungal growth upon infection by the host-adapted pathogen Golovinomyces orontii associated with an hyperaccumulation of both free and total salicylic acid (SA) as well as pathogen-inducible hydrogen peroxides in leaves (PubMed:26023163). Impaired microbe-associated molecular patterns (MAMPs)-induced (e.g. flg22) callose deposition (PubMed:26023163). Hypersensitivity to root growth inhibition by IBA and 2,4-dichlorophenoxybutyric acid (2,4-DB), an analog of IBA (PubMed:19648296, PubMed:26023163, PubMed:20498067). Higher sensitivity to drought stress (PubMed:20088904). Increased sensitivity to the non adapted fungal pathogen Colletotrichum gloeosporioides and to powdery mildews (e.g. Blumeria graminis and Erysiphe pisi) probably due to the reduction of preinvasion plant defenses upon appressoria formation and leading to lesions at infection sites (PubMed:20605856, PubMed:26023163). Belongs to the ABC transporter superfamily. ABCG family. PDR (TC 3.A.1.205) subfamily.