Positive regulator of plant growth which acts as an efflux pump involved in the major root-to-shoot (acropetal) long-distance cytokinin (CK) transport via the xylem sap (PubMed:24513716, PubMed:24778257, PubMed:26517905, PubMed:28398838). Together with ABCG9 and ABCG11, required for vascular development by regulating lipid/sterol homeostasis (PubMed:24112720). Involved in CK-dependent responses to oxidative stress such as hydrogen peroxide H(2)O(2) (PubMed:27550996). (Microbial infection) Required for SNC1-mediated defense response against the virulent pathogen Pseudomonas syringae pv. tomato DC3000 by promoting the accumulation of trans-zeatin (tZ)-type cytokinins (CK) in the shoot. Forms heterodimers with ABCG11. Accumulates primarily in the pericycle and stelar cells of roots (PubMed:24513716, PubMed:24778257). Expressed in leaves, stems, flowers and siliques, and, at low levels, in roots (PubMed:24112720, PubMed:24513716, PubMed:24778257). Accumulates in the phloem (PubMed:24112720). In roots, observed in the central cylinder (vascular tissues), but absent from division zones (PubMed:24112720, PubMed:24513716, PubMed:24778257). Present in the vascular system of the cotyledons and rosette leaves (PubMed:24112720, PubMed:24513716). Also observed in phloem cells of the flower stem (PubMed:24112720). Accumulates also in the mature anthers of open flowers and in siliques (PubMed:24513716). Repressed by hydrogen peroxide H(2)O(2) in a CRF6-dependent manner. Weak growth, small inflorescences and rosettes, slender stems, and short and retarded primary root growth leading to dwarf plants (PubMed:24513716, PubMed:24778257, PubMed:28398838). Impaired translocation of trans-zeatin (tZ)-type cytokinins (CK) from roots to shoots (acropetal), thereby affecting the plant growth and development and leading to a reduced cytokinin content in xylem sap (PubMed:24513716, PubMed:24778257). Defective in sterol (e.g. 24-methylene cholesterol and sitosterol) composition (PubMed:24112720). Vascular patterning defects in cotyledons and the floral stem, with a stronger phenotype in plant missing also ABCG9 and ABCG11 (PubMed:24112720). Altered responses to oxidative stress (e.g. hydrogen peroxide H(2)O(2)) (PubMed:27550996). Suppression of the SNC1-mediated defense response due to a deficiency of tZ-type CK in the shoot (PubMed:28398838). Belongs to the ABC transporter superfamily. ABCG family. Eye pigment precursor importer (TC 3.A.1.204) subfamily.