title: A role for leucoanthocyanidin reductase in the extension of proanthocyanidins.
abstract: Proanthocyanidins (PAs) are the second most abundant plant polyphenolic compounds after lignin. PAs affect taste, mouth feel and astringency of many fruits, wines and beverages1,2, have been associated with reduced risks of cardiovascular disease, cancer and Alzheimer's disease3-5, can improve nutrition and prevent bloat in ruminant animals6and enhance soil nitrogen retention7. PAs are oligomers and polymers of flavan-3-ols, primarily (-)-epicatechin and (+)-catechin, but the mechanism by which the monomers polymerize and become insoluble is currently unknown. Leucoanthocyanidin reductase (LAR) has been shown to convert leucocyanidin to (+)-catechin8,9. Here, we report that loss of function of LAR in the model legume Medicago truncatula leads unexpectedly to loss of soluble epicatechin-derived PAs, increased levels of insoluble PAs, and accumulation of 4β-(S-cysteinyl)-epicatechin, which provides the 4→8 linked extension units during non-enzymatic PA polymerization. LAR converts 4β-(S-cysteinyl)-epicatechin back to epicatechin, the starter unit in PAs, thereby regulating the relative proportions of starter and extension units and consequently the degree of PA oligomerization.
authors.affiliation: BioDiscovery Institute, University of North Texas, Denton, Texas 76203-5017, USA.|Department of Biological Sciences, University of North Texas, Denton, Texas, USA.
authors.forename: Chenggang
authors.identifier: 0000-0002-0576-8567
authors.initials: C
authors.lastname: Liu
authors.affiliation: BioDiscovery Institute, University of North Texas, Denton, Texas 76203-5017, USA.|Department of Biological Sciences, University of North Texas, Denton, Texas, USA.
authors.forename: Xiaoqiang
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Biological Sciences, University of North Texas, Denton, Texas, USA.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Shulaev
authors.affiliation: BioDiscovery Institute, University of North Texas, Denton, Texas 76203-5017, USA.|Department of Biological Sciences, University of North Texas, Denton, Texas, USA.
authors.forename: Richard A
authors.identifier: 0000-0001-8393-9408
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D046913:Medicago truncatula / Q000235:genetics* / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D044945:Proanthocyanidins / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D044945:Proanthocyanidins; D010088:Oxidoreductases