title: Carotene Hydroxylase Activity Determines the Levels of Both α-Carotene and Total Carotenoids in Orange Carrots.
abstract: The typically intense carotenoid accumulation in cultivated orange-rooted carrots (Daucus carota) is determined by a high protein abundance of the rate-limiting enzyme for carotenoid biosynthesis, phytoene synthase (PSY), as compared with white-rooted cultivars. However, in contrast to other carotenoid accumulating systems, orange carrots are characterized by unusually high levels of α-carotene in addition to β-carotene. We found similarly increased α-carotene levels in leaves of orange carrots compared with white-rooted cultivars. This has also been observed in the Arabidopsis thaliana lut5 mutant carrying a defective carotene hydroxylase CYP97A3 gene. In fact, overexpression of CYP97A3 in orange carrots restored leaf carotenoid patterns almost to those found in white-rooted cultivars and strongly reduced α-carotene levels in the roots. Unexpectedly, this was accompanied by a 30 to 50% reduction in total root carotenoids and correlated with reduced PSY protein levels while PSY expression was unchanged. This suggests a negative feedback emerging from carotenoid metabolites determining PSY protein levels and, thus, total carotenoid flux. Furthermore, we identified a deficient CYP97A3 allele containing a frame-shift insertion in orange carrots. Association mapping analysis using a large carrot population revealed a significant association of this polymorphism with both α-carotene content and the α-/β-carotene ratio and explained a large proportion of the observed variation in carrots.
authors.affiliation: University of Freiburg, Faculty of Biology II, Freiburg, Germany.
authors.forename: Jacobo
authors.initials: J
authors.lastname: Arango
authors.affiliation: Agrocampus Ouest, Unité Mixte de Recherche 1345 Institut de Recherche en Horticulture et Semences, Angers, France.
authors.forename: Matthieu
authors.identifier: http://orcid.org/0000-0003-3039-818X
authors.initials: M
authors.lastname: Jourdan
authors.affiliation: Agrocampus Ouest, Unité Mixte de Recherche 1345 Institut de Recherche en Horticulture et Semences, Angers, France.
authors.forename: Emmanuel
authors.identifier: http://orcid.org/0000-0003-4384-3107
authors.initials: E
authors.lastname: Geoffriau
authors.affiliation: University of Freiburg, Faculty of Biology II, Freiburg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Beyer
authors.affiliation: University of Freiburg, Faculty of Biology II, Freiburg, Germany ralf.welsch@biologie.uni-freiburg.de.
authors.forename: Ralf
authors.identifier: http://orcid.org/0000-0002-2865-2743
authors.initials: R
authors.lastname: Welsch