Arabidopsis response to the apocarotenoid zaxinone involves interference with strigolactone signaling via binding to DWARF14

The natural growth regulator zaxinone increases the levels of the phytohormones strigolactone (SL) and abscisic acid in Arabidopsis (Arabidopsis thaliana) via unknown mechanisms. Here we demonstrate that part of the effect of zaxinone in Arabidopsis depend on the SL receptor DWARF14 (AtD14) and the F-Box protein MORE AXILLARY BRANCHING2 (AtMAX2) that mediate the signaling of SLs and karrikins. Binding assays and co-crystallization reveal zaxinone as an additional ligand of AtD14 and an SL antagonist that interrupts the interaction of AtD14 with AtMAX2. Zaxinone also binds to the karrikin receptor KARRIKIN INSENSITIVE2 (AtKAI2). These findings unveil a perception mechanism for zaxinone in Arabidopsis and demonstrate the capability of AtD14 to bind signaling molecules, other than strigolactones and mediate their transduction.