Fig. 8. Proposed model illustrating ABCG17 and ABCG18 function in regulating ABA homeostasis under normal and abiotic stress conditions.

Under normal conditions, ABCG17 and ABCG18 promote ABA import into mesophyll cells. Under abiotic stress environments, ABCG17 and ABCG18 are transcriptionally repressed (similar to the double-knockdown lines), leading to free ABA availability to guard cells and long-distance translocation to the root. LR, lateral root.