title: Tissue-Specific Apocarotenoid Glycosylation Contributes to Carotenoid Homeostasis in Arabidopsis Leaves.
abstract: Attaining defined steady-state carotenoid levels requires balancing of the rates governing their synthesis and metabolism. Phytoene formation mediated by phytoene synthase (PSY) is rate limiting in the biosynthesis of carotenoids, whereas carotenoid catabolism involves a multitude of nonenzymatic and enzymatic processes. We investigated carotenoid and apocarotenoid formation in Arabidopsis (Arabidopsis thaliana) in response to enhanced pathway flux upon PSY overexpression. This resulted in a dramatic accumulation of mainly β-carotene in roots and nongreen calli, whereas carotenoids remained unchanged in leaves. We show that, in chloroplasts, surplus PSY was partially soluble, localized in the stroma and, therefore, inactive, whereas the membrane-bound portion mediated a doubling of phytoene synthesis rates. Increased pathway flux was not compensated by enhanced generation of long-chain apocarotenals but resulted in higher levels of C13 apocarotenoid glycosides (AGs). Using mutant lines deficient in carotenoid cleavage dioxygenases (CCDs), we identified CCD4 as being mainly responsible for the majority of AGs formed. Moreover, changed AG patterns in the carotene hydroxylase mutants lutein deficient1 (lut1) and lut5 exhibiting altered leaf carotenoids allowed us to define specific xanthophyll species as precursors for the apocarotenoid aglycons detected. In contrast to leaves, carotenoid hyperaccumulating roots contained higher levels of β-carotene-derived apocarotenals, whereas AGs were absent. These contrasting responses are associated with tissue-specific capacities to synthesize xanthophylls, which thus determine the modes of carotenoid accumulation and apocarotenoid formation.
authors.affiliation: Faculty of Biology II, University of Freiburg, D-79104 Freiburg, Germany (K.L., F.W., M.H., P.S., P.B., R.W.); andInstitute of Bio- and Geosciences,: Pflanzenwissenschaften, Forschungszentrum Jülich, D-52425 Juelich, Germany (K.G.B., S.M.).
authors.forename: Kira
authors.identifier: http://orcid.org/0000-0003-0973-891X
authors.initials: K
authors.lastname: Lätari
authors.affiliation: Faculty of Biology II, University of Freiburg, D-79104 Freiburg, Germany (K.L., F.W., M.H., P.S., P.B., R.W.); andInstitute of Bio- and Geosciences,: Pflanzenwissenschaften, Forschungszentrum Jülich, D-52425 Juelich, Germany (K.G.B., S.M.).
authors.forename: Florian
authors.identifier: http://orcid.org/0000-0002-9941-5550
authors.initials: F
authors.lastname: Wüst
authors.affiliation: Faculty of Biology II, University of Freiburg, D-79104 Freiburg, Germany (K.L., F.W., M.H., P.S., P.B., R.W.); andInstitute of Bio- and Geosciences,: Pflanzenwissenschaften, Forschungszentrum Jülich, D-52425 Juelich, Germany (K.G.B., S.M.).
authors.forename: Michaela
authors.initials: M
authors.lastname: Hübner
authors.affiliation: Faculty of Biology II, University of Freiburg, D-79104 Freiburg, Germany (K.L., F.W., M.H., P.S., P.B., R.W.); andInstitute of Bio- and Geosciences,: Pflanzenwissenschaften, Forschungszentrum Jülich, D-52425 Juelich, Germany (K.G.B., S.M.).
authors.forename: Patrick
authors.identifier: http://orcid.org/0000-0002-8529-4161
authors.initials: P
authors.lastname: Schaub
authors.affiliation: Faculty of Biology II, University of Freiburg, D-79104 Freiburg, Germany (K.L., F.W., M.H., P.S., P.B., R.W.); andInstitute of Bio- and Geosciences,: Pflanzenwissenschaften, Forschungszentrum Jülich, D-52425 Juelich, Germany (K.G.B., S.M.).
authors.forename: Kim Gabriele
authors.identifier: http://orcid.org/0000-0003-4961-652X
authors.initials: KG
authors.lastname: Beisel
authors.affiliation: Faculty of Biology II, University of Freiburg, D-79104 Freiburg, Germany (K.L., F.W., M.H., P.S., P.B., R.W.); andInstitute of Bio- and Geosciences,: Pflanzenwissenschaften, Forschungszentrum Jülich, D-52425 Juelich, Germany (K.G.B., S.M.).
authors.forename: Shizue
authors.initials: S
authors.lastname: Matsubara
authors.affiliation: Faculty of Biology II, University of Freiburg, D-79104 Freiburg, Germany (K.L., F.W., M.H., P.S., P.B., R.W.); andInstitute of Bio- and Geosciences,: Pflanzenwissenschaften, Forschungszentrum Jülich, D-52425 Juelich, Germany (K.G.B., S.M.).
authors.forename: Peter
authors.initials: P
authors.lastname: Beyer
authors.affiliation: Faculty of Biology II, University of Freiburg, D-79104 Freiburg, Germany (K.L., F.W., M.H., P.S., P.B., R.W.); andInstitute of Bio- and Geosciences,: Pflanzenwissenschaften, Forschungszentrum Jülich, D-52425 Juelich, Germany (K.G.B., S.M.) ralf.welsch@biologie.uni-freiburg.de.
authors.forename: Ralf
authors.identifier: http://orcid.org/0000-0002-2865-2743
authors.initials: R
authors.lastname: Welsch
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002338:Carotenoids / Q000096:biosynthesis / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D002853:Chromatography, Liquid; D049308:Dioxygenases / Q000235:genetics / Q000378:metabolism; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase / Q000235:genetics / Q000378:metabolism; D006027:Glycosides / Q000378:metabolism; D006031:Glycosylation; D006706:Homeostasis; D015151:Immunoblotting; D013058:Mass Spectrometry; D009154:Mutation; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D024341:Xanthophylls / Q000378:metabolism; D019207:beta Carotene / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D006027:Glycosides; D024341:Xanthophylls; D019207:beta Carotene; D002338:Carotenoids; C100185:(all-E) phytoene; C000592331:CCD4 protein, Arabidopsis; D049308:Dioxygenases; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; C004984:apocarotenal