DWARF14 and KARRIKIN INSENSITIVE2 mediate signaling of the apocarotenoid zaxinone in Arabidopsis

The natural growth regulator zaxinone increases the levels of the phytohormones strigolactone (SL) and abscisic acid in Arabidopsis ( Arabidopsis thaliana ) via unknown mechanisms. We demonstrate that parts of the effects of zaxinone in Arabidopsis depend on the SL receptor DWARF14 ( At D14), the karrikin receptor KARRIKIN INSENSITIVE2 ( At KAI2), and the F-Box protein MORE AXILLARY BRANCHING2 ( At MAX2) that mediates the signaling of SLs and karrikins. Binding assays and co-crystallization revealed zaxinone as an additional ligand of At D14 and an SL antagonist that interrupts the interaction of At D14 with At MAX2. Zaxinone also bound to At KAI2. These findings unveil a perception mechanism for zaxinone in Arabidopsis and demonstrate the capability of At D14 and At KAI2 to bind signaling molecules, other than strigolactones or karrikins, and mediate their transduction.