title: The identification of a vacuolar iron transporter involved in the blue coloration of cornflower petals.
abstract: The blue petal color of the cornflower (Centaurea cyanus) is caused by protocyanin, a kind of metalloanthocyanin, which is a self-assembled supramolecular metal complex pigment. Protocyanin is composed of six molecules of anthocyanin, six molecules of flavone, one ferric ion, and one magnesium ion. The ferric ion is essential for blue color development. Here, we identify the vacuolar iron transporter gene (CcVIT) from the blue petals of C. cyanus and its function is identified and characterized. The CcVIT transcript was observed only in the petals. Its amino acid sequence is highly homologous to the Arabidopsis thaliana (AtVIT1) and Tulipa gesneriana (TgVit1) vacuolar iron transporters. Heterologous expression of the CcVIT gene in yeast indicated that the corresponding gene product transports ferrous ion into vacuoles. Analysis of purple mutant-line petals clarified that the anthocyanin and flavone components were the same as those found in plants with blue petals, but the amount of iron ions in the colored cells decreased, and consequently the amount of blue protocyanin was reduced. The CcVIT gene was expressed even in purple mutant petals, however, an amino acid substitution (A236E) occurred in that case. This change in the CcVIT gene sequence also resulted in loss of iron transport activity. The CcVIT protein thus plays a critical role in the blue coloration of cornflower petals.
authors.affiliation: Graduate School of Information Science, Nagoya University, Japan. yoshidak@is.nagoya-u.ac.jp
authors.forename: Kumi
authors.initials: K
authors.lastname: Yoshida
authors.forename: Takashi
authors.initials: T
authors.lastname: Negishi
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport / Q000235:genetics; D027682:Cation Transport Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D035264:Flowers / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D006027:Glycosides / Q000096:biosynthesis / Q000737:chemistry; D007501:Iron / Q000378:metabolism*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D010802:Phylogeny; D010858:Pigmentation / Q000235:genetics; D010860:Pigments, Biological / Q000096:biosynthesis / Q000737:chemistry; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014617:Vacuoles / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D006027:Glycosides; D010860:Pigments, Biological; D010940:Plant Proteins; C504639:protocyanin; D007501:Iron
keywords: Amino acid substitution; Asteraceae; Blue flower coloration; Centaurea cyanus; Iron distribution; Metalloanthocyanin; Protocyanin; Vacuolar iron transporter