Investigation of the biosynthesis of 3‐deoxyanthocyanins in Sinningia cardinalis

Abstract

3‐Deoxyanthocyanins provide bright orange‐red colours to flowers of some members of the Gesneriaceae, including sinningia (Sinningia cardinalis). We examined 3‐deoxyanthocyanin biosynthesis in sinningia, in particular, the expression of key flavonoid biosynthetic genes and the activities of the encoded proteins. Two abundant 3‐deoxyanthocyanins, luteolinidin 5‐O‐glucoside and apigeninidin 5‐O‐glucoside, three flavone glycosides, luteolin 7‐O‐glucoside, luteolin 7‐O‐glucuronide and apigenin 7‐O‐glucuronide, and the cinnamic acid verbascoside were identified in sinningia petal tissue. Small amounts of a 3‐hydroxyanthocyanin were also detected in a limited region of the petal. cDNA clones for three flavonoid enzymes, flavanone 3‐hydroxylase (F3H), dihydroflavonol 4‐reductase/flavanone 4‐reductase (DFR/FNR) and anthocyanidin synthase (ANS), were isolated from a sinningia cDNA library made from petal RNA and used to measure transcript abundance during petal development. Only very low levels of F3H transcript were detected, while DFR/FNR transcript was highly abundant. ANS transcript levels were intermediate between these two. The F3H cDNA was shown to encode a functional F3H protein by complementation of the phenotype of an Antirrhinum majus F3H mutant. The recombinant DFR/FNR had activity against both flavanone and dihydroflavonol substrates to a comparable extent. The results suggest a mechanism of 3‐deoxyflavonoid biosynthesis in sinningia similar to that reported for Zea mays, in which lack of F3H activity allows action of the DFR/FNR on flavanone substrates and production of flavan‐4‐ols. These are then likely converted to 3‐deoxyanthocyanins through the action of the ANS and subsequent glucosylation.

Flavonoid Phytoalexin-Dependent Resistance to Anthracnose Leaf Blight Requires a Functional yellow seed1 in Sorghum bicolor

“…Furthermore, present evidence for the role of 3-deoxyanthocyanidins in disease resistance is not conclusive since these studies were carried out using non-isogenic lines. The structural similarities between 3-deoxyanthocyanidins and flavan-4-ols, the precursors of the red phlobaphene pigments found in sorghum and maize, suggest that these compounds might be synthesized via a common or overlapping pathway (Grotewold et al 1998;Chopra et al 2002;Winefield et al 2005). In a previous study, we showed that a mutable allele of an R2R3 MYB transcription factor encoded by Y1-cs is partially defective in the synthesis of 3-deoxyanthocyanidins (Chopra et al 2002).…”

Phenotypic Diversity of Anthocyanins in Sorghum Accessions with Various Pericarp Pigments

“…It appears that sorghum grain is the only known dietary source of 3-deoxyanthocyanidins except for the flowers of sinningia (Sinningia cardinalis), the silk tissues of maize (Zea mays), and the stalks of sugarcane (Saccharum sp.) [22][23][24]. The exceptional 3-deoxyanthocyanins in sorghum seems more stable than other anthocyanins, making them a desired natural food colorant [9,15].…”

(±)-Diinsininone: made nature's way

“…It is among the best studied of biosynthetic pathways in nature. [16][17][18] The optically active compounds 1 and 2 suggest a double union between two products emerging from the flavonoid pathway. It is reasonable to speculate that an organism would utilize an identical path for these structurally related natural products.…”