A role for ascorbate conjugates of (+)-catechin in proanthocyanidin polymerization

• Published in: Nature communications Vol. 13; no. 1; p. 3425
• Main Authors: Yu, Keji, Dixon, Richard A., Duan, Changqing
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 14.06.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 140/58; 45/77; 631/449/1736; 631/449/2667; 631/92; Ascorbic acid; Biosynthesis; Catechin; Catechin - metabolism; Conjugates; Epicatechin; Flavonoids; Flowers; Grapes; Humanities and Social Sciences; Metabolites; Monomers; multidisciplinary; Natural polymers; Oligomerization; Plant Proteins - metabolism; Polymerization; Polymers; Proanthocyanidins; Proanthocyanidins - metabolism; Science; Science (multidisciplinary); Seeds; Vitis - genetics
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-31153-2

Proanthocyanidins (PAs) are natural polymers of flavan-3-ols, commonly (+)-catechin and (−)-epicatechin. However, exactly how PA oligomerization proceeds is poorly understood. Here we show, both biochemically and genetically, that ascorbate (AsA) is an alternative “starter unit” to flavan-3-ol monomers for leucocyanidin-derived (+)-catechin subunit extension in the Arabidopsis thaliana anthocyanidin synthase ( ans ) mutant. These (catechin) n :ascorbate conjugates (AsA-[C] n ) also accumulate throughout the phase of active PA biosynthesis in wild-type grape flowers, berry skins and seeds. In the presence of (−)-epicatechin, AsA-[C] n can further provide monomeric or oligomeric PA extension units for non-enzymatic polymerization in vitro, and their role in vivo is inferred from analysis of relative metabolite levels in both Arabidopsis and grape. Our findings advance the knowledge of (+)-catechin-type PA extension and indicate that PA oligomerization does not necessarily proceed by sequential addition of a single extension unit. AsA-[C] n defines a new type of PA intermediate which we term “sub-PAs”. Proanthocyanidins are natural polymers of flavan-3-ols produced by plants. Here the authors provide genetic and biochemical evidence for the involvement of ascorbate linked flavan-3-ol oligomers in the extension of the proanthocyanidin chain.