Proanthocyanidins (PAs) are primarily composed of the flavan-3-ol subunits (-)-epicatechin and/or (+)-catechin, but the basis for their different starter and extension unit compositions remains unclear. Genetic and biochemical analyses show that, in the model legume Medicago truncatula, two 2-oxoglutarate-dependent dioxygenases, anthocyanidin synthase (ANS) and its homologue leucoanthocyanidin dioxygenase (LDOX), are involved in parallel pathways to generate, respectively, the (-)-epicatechin extension and starter units of PAs, with (+) catechin being an intermediate in the formation of the (-)-epicatechin starter unit. The presence/absence of the LDOX pathway accounts for natural differences in PA compositions across species, and engineering loss of function of ANS or LDOX provides a means to obtain PAs with different compositions and degrees of polymerization for use in food and feed.
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We thank S. Temple for critical reading of the manuscript and V. Shulaev for assistance with high mass accuracy LCMS. This work was supported by Forage Genetics International Inc. and the University of North Texas.
R.A.D. and J.H.J. are inventors on a United States provisional patent application filed by the University of North Texas that describes methods for engineering PA composition.
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Jun, J.H., Xiao, X., Rao, X. et al. Proanthocyanidin subunit composition determined by functionally diverged dioxygenases. Nature Plants 4, 1034–1043 (2018). https://doi.org/10.1038/s41477-018-0292-9
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