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Figure 1. 

Structural features of the half-size and full-size ABCG protein. Domain organization of (a) half-size, and (b) full-size ABCG members and their inverted topology. Light blue rounded rectangles represent TMD, while pink ones represent NBD. (c) Structural prediction of the two half-size ABCG proteins using AlphaFold3. The panel shows the predicted 3D structures. (d) Structural prediction of the full-size ABCG protein using AlphaFold3. The left panel shows the surface representations. Color-coding: light sea green/cornflower blue, TMD; pink/purple, NBD; red, coupling helices. Red and blue spheres along the outside of the domains represent dangling amino acid residues. The middle panel shows the full-size ABCG protein rotated 90° counterclockwise to expose the complete binding pocket in longitudinal section. The right panel shows a cross-sectional view of the predicted full-size ABCG structure, showing the hormone-binding and ATP-binding pockets. Red and blue spheres in the cross-section indicate positive and negative electrostatic states, respectively. NBD: Nucleotide-binding domain, TMD: Transmembrane domain.

Figure 2. 

Overview of ABCG transporters involved in ABA transport. A schematic representation of an Arabidopsis plant highlighting major tissues/organs involved in ABA synthesis and transport (middle), accompanied by subcellular localization of characterized ABCG transporters (left) and a simplified mechanism model (right). Blue arrows represent ABA or ABA-GE importers; red arrows indicate ABA exporters. Gray arrows indicate the direction of ABA movement. Numbers in colored circles correspond to tissue-specific expression sites shown in the plant diagram. Most transporters mediate the movement of bioactive ABA unless otherwise indicated (e.g., ABA-GE). All transporters shown were characterized in Arabidopsis thaliana unless a species prefix is provided. ABA, abscisic acid; ABA-GE, ABA-glucose ester; ER, endoplasmic reticulum; Mt, Medicago truncatula.

Figure 3. 

Overview of ABCG transporters involved in SL transport. Illustration of representative plant species with magnifications highlighting root tissues where ABCG transporters have been characterized. The central root schematic shows SL export sites, with red arrows representing SL export by ABCG transporters. Blue long arrows indicate the direction of ABCG long-distance transport. '×' indicates that ABCG protein transport is repressed. The numbers in circles indicate the names of ABCG transporters. SL, strigolactone; Pa, Petunia; Mt, Medicago truncatula; Sb, Sorghum bicolor; Sl, Solanum lycopersicum.

Figure 4. 

Overview of ABCG transporters involved in CK transport. Illustration of ABCG transporters in the plant shoot and root with magnifications highlighting tissues and cells where CK transporters are active. Characterized CK exporters (red arrows) are shown in relevant tissues. Yellow and green long arrows indicate the direction of tZ-type and iP-type CK, respectively. The numbers in circles indicate the names of ABCG transporters. PCC, phloem companion cells; R-PC, root pericycle; ?, unknown mechanism; CK, cytokinin; ER, endoplasmic reticulum; At, Arabidopsis thaliana; Os, Oryza sativa.

Figure 5. 

Overview of ABCG transporters involved in JA transport. (Left) Illustration of intracellular JA transport. (Right) Schematic of tissue expression of JA transporters. The numbers in circles indicate the names of ABCG transporters. Inset boxes are magnifications of the indicated tissues. Blue arrows represent importers; red arrows represent exporters. All transporters were characterized in Arabidopsis unless the transporter name begins with a species abbreviation. ?, unknown mechanism; JA, jasmonic acid; JA-Ile, jasmonoyl-isoleucine.

Figure 6. 

Overview of ABCG transporters involved in auxin precursor transport. (Left) Illustration of an Arabidopsis root highlighting the spatial context of IBA transport. (Right) Enlarged view of a root cell from the region marked in the left panel, illustrating the subcellular dynamics of IBA export. Red arrows represent exporters. The blue arrow indicates the direction of auxin precursor movement. The long red arrows indicate promotion, red T-shaped lines indicate inhibition, and the blue circle with 'P' represents phosphorylation. All transporters were characterized in Arabidopsis unless the transporter name begins with a species abbreviation. IBA, indole-3-butyric acid.

Figure 7. 

Collinearity analysis of ABCG genes across six representative monocot and eudicot species. Purple Bézier curves represent the collinear relationships of ABCG genes across species.