BMC Genomics 2006, 7:12 http://www.biomedcentral.com/1471-2164/7/12 Background Vacuolar accumulation of anthocyanins in berry skin is responsible for the pigmentation of red/blue grapevine (Vitis vinifera) cultivars. Anthocyanin biosynthesis is developmentally triggered at the onset of berry ripening (8–10 weeks after blooming) and lasts till harvest [1]. Expression profiling of structural genes and transcription factors has claimed a major role for the gene UFGT encod- ing a UDP-glucose:flavonoid 3-O-glucosyltransferase and its regulatory Myb-type gene VvMybA in conveying the flux of flavonoid intermediates towards the synthesis of anthocyanins [2,3]. The enzyme UFGT is synthesised since véraison under the control of VvMybA and catalyses the 3'-glycosidation of cyanidin- and delphinidin-based anthocyanidins [4]. The resulting stably coloured anthocyanins may undergo methylation upon the activity of methyl-transferases that convert cyanidin into peoni- din and delphinidin into petunidin or malvidin, similarly to how it occurs in other anthocyanin-producing species [5,6]. Cyanidin- and delphinidin-derived anthocyanins diverge from each other regarding the number of the substituted groups that are found on the B-ring of the flavonoid skel- eton (either two or three, respectively) and have their Table 1: List of the PCR primers used. chromatic properties affected accordingly. Cyanidin- based anthocyanins exhibit a reddish colour whereas del- phinidin-based anthocyanins are purple to blue. They jointly determine the tonality of red berry grape varieties and their corresponding wines. The relative proportion of the five anthocyanins is largely under genetic control and unique to each cultivar [7,8]. Sunlight exposition and water deficit have been shown to modulate to some extent the anthocyanin profile [9,10]. In plant species, the biosynthesis of cyanidin- and delphi- nidin-type precursors is driven, upstream of the enzyme UFGT, by the activity of two flavonoid 3'- and 3',5'- hydroxylases (F3'H and F3',5'H) that add either a single hydroxyl group at the 3' position or two hydroxyl groups at the 3' and 5' positions to dihydrokaempferol and/or dihydroquercetin. Once converted into 3'-dihydroquerce- tin or 3',5'-dihydromyricetin, these intermediates flow through common downstream enzymes to form di-sub- stituted and tri-substituted anthocyanins when the gene UFGT is expressed and to form other polyphenols (fla- vonols, leucoanthocyanins, catechins, proanthocyanins, tannins) at different developmental stages. F3'H and F3',5'H genes code for CYP75 cytochrome P450 hydroxy- lases that have been well characterised in the ornamental 5'→3' sequencea CCIGTIAANYTNGGNCARYTIBTIAA GCICKYTGIARIGTNARNCCRTA ATGCTGACNTAYGCIATGGCNAAYATG CGAARTCRTTICCYCKNGGNTCDATYTT ATTCGCCACCCTGAAATGAT CAACAAGAGCTGGACGCAGT AGCCGTTGATCTCACAGCTC GAAGTTCGACTGGTTATTAACAAAGAT AGGAGGAGTGCTTTAATGTTGGTA AAGAAGTTCGACAAGTTATTGACAAG AGCGCCTTAATGTTGGTAAGG CGTTGATCTCGCTGAAGGAT ATCATTTCAGGGTGGCGAAT GCTCACTATTACCAACATTAAAGCA AAGCTCACCCTTACCAACATTAAG GGCAAGTCAGACTCCACGAG TGGCCTTCATTTTGGTTAGC TCATCACTCAGGGCACAAAA TTACCGCCCTTGTCCTTGTA GCGTATTGATCATCCCTTGG CCAATATGTGGAGGAGGAACA CATCCAGGTTGTGAAGGACA AGGAGGCCTATGCATCAGAA GGAGCACCATTAAAGGCAAA CTAATGGGCATCAGGTTTCG CGTGCATATCATTTTCTTCCAA TTCAAGAAGTGGAGGCTGCT AGCACTGACTGCCTGATCCT Page 2 of 17 (page number not for citation purposes) Target DNA Plant F3'H Plant F3'H Plant F3'5'H Plant F3'5'H Grape F3'H Grape F3'H Grape F3'H Grape F3'5'H Grape F3'5'H Grape F3'5'H Grape F3'5'H Grape F3'H Grape F3'H Grape F3'5'H Grape F3'5'H Grape F3'5'H BES38C24-FM BES38C24-FM BES38C24-RM BES38C24-RM BES17K4-FM BES17K4-FM BES9C17-FM BES9C17-FM BES40A22-FM BES40A22-FM BES5A23-FM BES5A23-FM Name F3'H_S F3'H_AS F3'5'H_S F3'5'H_AS VvF3'H_S VvF3'H-indel_S VvF3'H_AS Vv3'5'H-1A_S VvF3'5'H-1A_AS Vv3'5'H-2A_S Vv3'5'H-2A_AS VvF3'H-intron_S VvF3'H-intron_AS Vv3'5'H-1A-intron_S Vv3'5'H-2A-intron_S Vv3'5'H-intron_AS 38C24-FM_S 38C24-FM_AS 38C24-RM_S 38C24-RM_AS 17K4-FM_S 17K4-FM_AS 9C17-FM_S 9C17-FM_AS 40A22-FM_S 40A22-FM_AS 5A23-FM_S 5A23-FM_AS a Degenerate IUB code: I = inosine; R = A or G; M = A or C; W = A or T; Y = C or T; S = C or G; D = A, G or T; N, A, C, G or T.