Strigolactones promote the localisation of the ABA exporter ABCG25 at the plasma membrane in root epidermal cells of Arabidopsis thaliana

The phytohormones strigolactones crosstalk with abscisic acid (ABA) in acclimation to osmotic stress, as ascertained in leaves. However, our knowledge about underground tissues is limited, and null in Arabidopsis. Namely, if strigolactones affect ABA transport across plasma membranes has never been addressed. We evaluated the effect of strigolactones on the localisation of ATP BINDING CASSETTE G25 (ABCG25), an ABA exporter in Arabidopsis thaliana. Wild-type, strigolactone-insensitive and -depleted seedlings expressing a GFP:ABCG25 construct were treated with ABA or strigolactones, and GFP was quantified by confocal microscopy in different subcellular compartments of epidermal root cells. We show that strigolactones promote the localisation of an ABA transporter at the plasma membrane by enhancing its endosomal recycling. Genotypes altered in strigolactone synthesis or perception are not impaired in ABCG25 recycling promotion by ABA, which acts downstream or independent of strigolactones in this respect. Additionally, we confirm that osmotic stress decreases strigolactone synthesis in A. thaliana root cells; and that such decrease may support local ABA retention under low water availability, by allowing ABCG25 internalisation. Thus, a new mechanism for ABA homeostasis regulation is proposed in the context of osmotic stress acclimation: the fine tuning by strigolactones of ABCG25 localisation in root cells.