Methylation effect on chalcone synthase gene expression determines anthocyanin pigmentation in floral tissues of two Oncidium orchid cultivars

• Published in: Planta 2012-08, Vol.236 (2), p.401-409
• Main Authors: Liu, Xiao-Jing, Chuang, Yao-Nung, Chiou, Chung-Yi, Chin, Dan-Chu, Shen, Fu-Quan, Yeh, Kai-Wun
• Format: Article
• Language: English
• Subjects: Acyltransferases - genetics; Acyltransferases - metabolism; Agriculture; Anthocyanins; Anthocyanins - analysis; Anthocyanins - biosynthesis; Biological and medical sciences; Biomedical and Life Sciences; Biosynthesis; Chalconoids; Color; Cultivars; DNA; DNA methylation; DNA, Complementary - genetics; Ecology; epigenetics; Flavonoids; Flowers; Flowers - genetics; Flowers - metabolism; Forestry; Fundamental and applied biological sciences. Psychology; Gene expression; Gene Expression Regulation, Enzymologic - genetics; Gene Expression Regulation, Plant - genetics; Genes; High-performance liquid chromatography; Honey; Inactivation; Life Sciences; Lip; Liquid chromatography; Methylation; Mosaics; Naringenin-chalcone synthase; Oncidium; Orchidaceae; Orchidaceae - cytology; Orchidaceae - enzymology; Orchidaceae - genetics; Organ Specificity; Original Article; petals; Pigmentation; Pigmentation - genetics; Plant Proteins - genetics; Plant Proteins - metabolism; Plant Sciences; Plants; Plants, Genetically Modified; Promoter regions; Promoter Regions, Genetic - genetics; Promoters; RNA, Plant - genetics; RNA, Plant - metabolism; sepals; Tissue culture; Tissues; Transcription factors
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-012-1616-z

The anthocyanin-biosynthetic pathway was studied in flowers of Oncidium Gower Ramsey with yellow floral color and mosaic red anthocyanin in lip crests, sepals and petals, and compared with the anthocyanin biosynthesis in flowers of Oncidium Honey Dollp, a natural somatoclone derived from tissue culture of Gower Ramsey, with a yellow perianth without red anthocyanins in floral tissues. HPLC analysis revealed that the red anthocyanin in lip crests of the Gower Ramsey cultivar comprised peonidin-3-O-glucoside, delphinidin-3-O-glucoside and cyanidin-3-Oglucoside, whereas Honey Dollp was devoid of anthocyanin compounds. Among the five anthocyaninbiosynthetic genes, OgCHS was actively expressed in lip crests of Gower Ramsey flowers, but no transcripts of OgCHS were detected in Honey Dollp floral tissues. Transient expression of OgCHS by bombardment confirmed that recovery of the OgCHS gene expression completed the anthocyanin pathway and produced anthocyanin compounds in lip crests of Honey Dollp flowers. Transcription factor genes regulating anthocyanin biosynthesis showed no distinctive differences in the expression level of OgMYBl, OgbHLH and OgWD40 between the two cultivars. A methylation assay revealed that the promoter of OgCHS was not methylated in Gower Ramsey, while a positive methylation effect was present in the upstream promoter region of OgCHS in Honey Dollp. Overall, our results suggest that the failure of anthocyanin accumulation in Honey Dollp floral tissues may be attributed to inactivation of the OgCHS gene resulting from the epigenetic methylation of 5'-upstream promoter region.