title: TRANSPARENT TESTA10 encodes a laccase-like enzyme involved in oxidative polymerization of flavonoids in Arabidopsis seed coat.
abstract: The Arabidopsis thaliana transparent testa10 (tt10) mutant exhibits a delay in developmentally determined browning of the seed coat, also called the testa. Seed coat browning is caused by the oxidation of flavonoids, particularly proanthocyanidins, which are polymers of flavan-3-ol subunits such as epicatechin and catechin. The tt10 mutant seeds accumulate more epicatechin monomers and more soluble proanthocyanidins than wild-type seeds. Moreover, intact testa cells of tt10 cannot trigger H2O2-independent browning in the presence of epicatechin and catechin, in contrast with wild-type cells. UV-visible light detection and mass spectrometry revealed that the major oxidation products obtained with epicatechin alone are yellow dimers called dehydrodiepicatechin A. These products differ from proanthocyanidins in the nature and position of their interflavan linkages. Flavonol composition was also affected in tt10 seeds, which exhibited a higher ratio of quercetin rhamnoside monomers versus dimers than wild-type seeds. We identified the TT10 gene by a candidate gene approach. TT10 encodes a protein with strong similarity to laccase-like polyphenol oxidases. It is expressed essentially in developing testa, where it colocalizes with the flavonoid end products proanthocyanidins and flavonols. Together, these data establish that TT10 is involved in the oxidative polymerization of flavonoids and functions as a laccase-type flavonoid oxidase.
authors.affiliation: Laboratoire de Biologie des Semences, Unité Mixte de Recherche 204, Institut National de la Recherche Agronomique/Institut National Agronomique Paris-Grignon, Institut Jean-Pierre Bourgin, 78026 Versailles, France.
authors.forename: Lucille
authors.initials: L
authors.lastname: Pourcel
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Routaboul
authors.forename: Lucien
authors.initials: L
authors.lastname: Kerhoas
authors.forename: Michel
authors.initials: M
authors.lastname: Caboche
authors.forename: Loïc
authors.initials: L
authors.lastname: Lepiniec
authors.forename: Isabelle
authors.initials: I
authors.lastname: Debeaujon
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001483:Base Sequence; D004156:Catechol Oxidase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D005419:Flavonoids / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D042845:Laccase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011108:Polymers / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D012639:Seeds / Q000201:enzymology* / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D005419:Flavonoids; D011108:Polymers; D010088:Oxidoreductases; D004156:Catechol Oxidase; D042845:Laccase; C510496:TT10 protein, Arabidopsis