Carotenoid metabolism negatively regulates auxin-mediated root growth

Abstract

AbstractCarotenoids support plant developmental activities as photosynthesis and photoprotective pigments, they also provide precursors for production of phytohormone abscisic acid and strigolactones, or bioactive apocarotenoids. Herein, the role of carotenoids as sources of apocarotenoids, which control endogenous auxin levels and plant root architecture was examined. Inhibition of β-carotene biosynthesis with the phytoene desaturase (PDS) inhibitor fluridone suppresses root growth, consequently inducing lateral root growth. PDS was confirmed to be the target of fluridone via the expression of the fluridone-insensitive trait35S::mHvPDSin anArabidopsisplant. Inhibiting β-carotene biosynthesis elevated endogenous auxin levels and activated auxin signaling, thereby suppressing root growth. In addition, the root growth of the auxin-deficient mutantyucQwas partially restored via fluridone treatment. Consequently, suppressing PDS activity increases endogenous auxin levels and suppresses root growth. Conversely, the carotenoid pool indirectly suppresses endogenous auxin levels. Exogenous application of retinal, an apocarotenoid derived from β-carotene, complemented fluridone-mediated root growth inhibition and partially recovered auxin-mediated growth inhibition. Moreover, retinal inhibited the induction of the auxin-inducible reporterpIAA19::ElucPEST, indicating an antagonistic effect of retinal on endogenous auxin levels. Interestingly, the auxin-deficient mutantswei2 wei7andyucQaccumulated more β-carotene compared with the wild type. The expression ofCCDs, which converts β-carotene into apocarotenoids, is auxin-inducible and increases following fluridone treatment. These results indicate feedback regulation during apocarotenoid biosynthesis in plant tissue. Thus, we conclude carotenoid regulates auxin levels and response, and this regulation is mediated by apocarotenoid retinal.One-sentence summaryThe β-carotene-derived apocarotenoid retinal negatively regulates auxin levels and signaling and controls root growth.