Arabidopsis root development is predicted to be regulated by yet unidentified carotenoid-derived metabolite(s). In this work, we screened known and putative carotenoid cleavage products and identified anchorene, a predicted carotenoid-derived dialdehyde (diapocarotenoid) that triggers anchor root development. Anchor roots are the least characterized type of root in Arabidopsis. They form at the root-shoot junction, particularly upon damage to the root apical meristem. Using Arabidopsis reporter lines, mutants and chemical inhibitors, we show that anchor roots originate from pericycle cells and that the development of this root type is auxin-dependent and requires carotenoid biosynthesis. Transcriptome analysis and treatment of auxin-reporter lines indicate that anchorene triggers anchor root development by modulating auxin homeostasis. Exogenous application of anchorene restored anchor root development in carotenoid-deficient plants, indicating that this compound is the carotenoid-derived signal required for anchor root development. Chemical modifications of anchorene led to a loss of anchor root promoting activity, suggesting that this compound is highly specific. Furthermore, we demonstrate by LC-MS analysis that anchorene is a natural, endogenous Arabidopsis metabolite. Taken together, our work reveals a new member of the family of carotenoid-derived regulatory metabolites and hormones.

Anchorene is an endogenous diapocarotenoid required for anchor root formation in Arabidopsis