title: Biosynthesis of proanthocyanidins in white clover flowers: cross talk within the flavonoid pathway.
abstract: Proanthocyanidins and anthocyanins are produced by closely related branches of the flavonoid pathway and utilize the same metabolic intermediates. Previous studies have shown a flexible mechanism of flux diversion at the branch-point between the anthocyanin and proanthocyanidin pathways, but the molecular basis for this mechanism is poorly understood. Floral tissues in white clover plants (Trifolium repens) produce both proanthocyanidins and anthocyanins. This makes white clover amenable to studies of proanthocyanidin and anthocyanin biosynthesis and possible interactions within the flavonoid pathway. Results of this study show that the anthocyanin and proanthocyanidin pathways are spatially colocalized within epidermal cells of petals and temporally overlap in partially open flowers. A correlation between spatiotemporal patterns of anthocyanin and proanthocyanidin biosynthesis with expression profiles of putative flavonoid-related genes indicates that these pathways may recruit different isoforms of flavonoid biosynthetic enzymes. Furthermore, in transgenic white clover plants with down-regulated expression of the anthocyanidin reductase gene, levels of flavan 3-ols, anthocyanins, and flavonol glycosides and the expression levels of a range of genes encoding putative flavonoid biosynthetic enzymes and transcription factors were altered. This is consistent with the hypothesis that flux through the flavonoid pathway may be at least partially regulated by the availability of intermediates.
authors.affiliation: Department of Primary Industries, Biosciences Research Division, Victorian AgriBiosciences Centre, Bundoora, Victoria 3083, Australia.
authors.forename: Shamila Weerakoon
authors.initials: SW
authors.lastname: Abeynayake
authors.forename: Stephen
authors.initials: S
authors.lastname: Panter
authors.forename: Ross
authors.initials: R
authors.lastname: Chapman
authors.forename: Tracie
authors.initials: T
authors.lastname: Webster
authors.forename: Simone
authors.initials: S
authors.lastname: Rochfort
authors.forename: Aidyn
authors.initials: A
authors.lastname: Mouradov
authors.forename: German
authors.initials: G
authors.lastname: Spangenberg
mesh_terms: D015536:Down-Regulation; D005419:Flavonoids / Q000378:metabolism*; D035264:Flowers; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D044945:Proanthocyanidins / Q000096:biosynthesis*; D029921:Trifolium / Q000235:genetics / Q000378:metabolism*
chemical_list: D005419:Flavonoids; D044945:Proanthocyanidins