Methylation effect on chalcone synthase gene expression determines anthocyanin pigmentation in floral tissues of two Oncidium orchid cultivars
Resource
PLANTA, 236(2), 401-409
Journal
Orchid Biotechnology III
Pages
449-462
Date Issued
2012
Date
2012
Author(s)
Liu, Xiao-Jing
Chuang, Yao-Nung
Chiou, Chung-Yi
Chin, Dan-Chu
Shen, Fu-Quan
Yeh, Kai-Wun
Abstract
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 Angel, 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-O-glucoside, whereas Honey Angel was devoid of anthocyanin compounds. Among the five anthocyanin-biosynthetic genes, OgCHS was actively expressed in lip crests of Gower Ramsey flowers, but no transcripts of OgCHS were detected in Honey Angel 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 Angel flowers. Transcription factor genes regulating anthocyanin biosynthesis showed no distinctive differences in the expression levels of OgMYB1, 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 Angel. Overall, our results suggest that the failure of anthocyanin accumulation in Honey Angel floral tissues may be attributed to inactivation of the OgCHS gene resulting from the epigenetic methylation of the 5'-upstream promoter region.
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Type
journal article
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