ABA importers ABCG17 and ABCG18 redundantly regulate seed size in Arabidopsis.

The stress hormone abscisic acid (ABA) plays a crucial role in mediating plant responses to the environment and regulating plant development. In this study, we demonstrate that two ABA importers, ABCG17 and ABCG18, control seed size by regulating the ABA levels transported into the embryo. Double knockdown of ABCG17 and ABCG18 resulted in lower ABA accumulation in the embryo, wider siliques, and increased overall seed size. Leaf phloem-specific ABA induction in the aba2-1 background showed that ABA could move from the vasculature to control seed size. ABCG17 and ABCG18 are expressed in leaves, and the reproductive organs septum, and valves but not in the developing seeds, suggesting that ABCG17 and ABCG18 affect seed size maternally. Together, the results shed light on the molecular mechanisms by which ABA is transported to the embryo to determine seed size.