Co-pigmentation and flavonoid glycosyltransferases in blue Veronica persica flowers

• Published in: Phytochemistry (Oxford) 2010-05, Vol.71 (7), p.726-735
• Main Authors: Ono, Eiichiro, Ruike, Miho, Iwashita, Takashi, Nomoto, Kyosuke, Fukui, Yuko
• Format: Article
• Language: English
• Subjects: Base Sequence; Biological and medical sciences; Chemical constitution; Cloning, Molecular; Co-pigment; DNA Primers; Flavonoid; Flavonoids - metabolism; Flowers - enzymology; Flowers - metabolism; Fundamental and applied biological sciences. Psychology; Glucosylation; Glucuronosylation; Glycosyltransferase; Glycosyltransferases - genetics; Glycosyltransferases - metabolism; Hydrogen-Ion Concentration; Lamiales; Magnetic Resonance Spectroscopy; Molecular Sequence Data; Phylogeny; Pigments, Biological; Plant physiology and development; Spectrometry, Mass, Electrospray Ionization; UGT; Veronica - enzymology; Veronica - metabolism; Veronica persica
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2010.02.008

cDNAs encoding flavone 7- O-glucuronosyltransferase and anthocyanin 3- O-glucoside-2″- O-glucosyltransferase involved in the biosynthesis of apigenin 7- O-(2- O-glucuronosyl)-glucuronide and delphinidin 3- O-(2- O-(6- O- p-coumaroyl-glucosyl)-6- O- p-coumaroyl-glucoside)-5- O-glucoside, respectively, were identified from Veronica persica. Given that the flavone showed bathochromic shift on the anthocyanin, preferential expression in the petals suggest an inevitable role of these enzymes in blue flower development. Glycosylation is one of the key modification steps for plants to produce a broad spectrum of flavonoids with various structures and colors. A survey of flavonoids in the blue flowers of Veronica persica Poiret (Lamiales, Scrophulariaceae), which is native of Eurasia and now widespread worldwide, led to the identification of highly glycosylated flavonoids, namely delphinidin 3- O-(2- O-(6- O- p-coumaroyl-glucosyl)-6- O- p-coumaroyl-glucoside)-5- O-glucoside (1) and apigenin 7- O-(2- O-glucuronosyl)-glucuronide (2), as two of its main flavonoids. Interestingly, the latter flavone glucuronide (2) caused a bathochromic shift on the anthocyanin (1) toward a blue hue in a dose-dependent manner, showing an intermolecular co-pigment effect. In order to understand the molecular basis for the biosynthesis of this glucuronide, we isolated a cDNA encoding a UDP-dependent glycosyltransferase (UGT88D8), based on the structural similarity to flavonoid 7- O-glucuronosyltransferases (F7GAT) from Lamiales plants. Enzyme assays showed that the recombinant UGT88D8 protein catalyzes the 7- O-glucuronosylation of apigenin and its related flavonoids with preference to UDP–glucuronic acid as a sugar donor. Furthermore, we identified and functionally characterized a cDNA encoding another UGT, UGT94F1, as the anthocyanin 3- O-glucoside-2″- O-glucosyltransferase (A3Glc2″GlcT), according to the structural similarity to sugar–sugar glycosyltransferases classified to the cluster IV of flavonoid UGTs. Preferential expression of UGT88D8 and UGT94F1 genes in the petals supports the idea that these UGTs play an important role in the biosynthesis of key flavonoids responsible for the development of the blue color of V. persica flowers.