title: Medicago glucosyltransferase UGT72L1: potential roles in proanthocyanidin biosynthesis.
abstract: In the first reaction specific for proanthocyanidin (PA) biosynthesis in Arabidopsis thaliana and Medicago truncatula, anthocyanidin reductase (ANR) converts cyanidin to (-)-epicatechin. The glucosyltransferase UGT72L1 catalyzes formation of epicatechin 3'-O-glucoside (E3'OG), the preferred substrate for MATE transporters implicated in PA biosynthesis in both species. The mechanism of PA polymerization is still unclear, but may involve the laccase-like polyphenol oxidase TRANSPARENT TESTA 10 (TT10). We have employed a combination of cell biological, biochemical and genetic approaches to evaluate this PA pathway model. The promoter regions of UGT72L1 and MtANR share common cis-acting elements and direct overlapping, but partially distinct, expression patterns. UGT72L1 and MtANR are localized in the cytosol, whereas TT10 is localized to the vacuole. Over-expression of UGT72L1 in M. truncatula hairy roots results in increased accumulation of PA-like compounds, and loss of function of UGT72L1 partially reduces epicatechin, E3'OG and extractable PA levels in M. truncatula seeds. Expression of UGT72L1 in A. thaliana leads to a massive increase in E3'OG in immature seed, but reduced levels of extractable PAs. However, when UGT72L1 was expressed in the Arabidopsis tt10 mutant, extractable PA levels increased and seed coat browning was delayed. Our results suggest that glycosylation of epicatechin is important for both PA precursor transport and assembly, but that additional redundant pathways may exist.
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA.
authors.forename: Yongzhen
authors.initials: Y
authors.lastname: Pang
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Cheng
authors.forename: David V
authors.initials: DV
authors.lastname: Huhman
authors.forename: Junying
authors.initials: J
authors.lastname: Ma
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Peel
authors.forename: Keiko
authors.initials: K
authors.lastname: Yonekura-Sakakibara
authors.forename: Kazuki
authors.initials: K
authors.lastname: Saito
authors.forename: Guoan
authors.initials: G
authors.lastname: Shen
authors.forename: Lloyd W
authors.initials: LW
authors.lastname: Sumner
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Tang
authors.forename: Jianqi
authors.initials: J
authors.lastname: Wen
authors.forename: Jianfei
authors.initials: J
authors.lastname: Yun
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002392:Catechin / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D042845:Laccase / Q000235:genetics / Q000378:metabolism; D046913:Medicago truncatula / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009247:NADH, NADPH Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D044945:Proanthocyanidins / Q000096:biosynthesis* / Q000235:genetics; D011401:Promoter Regions, Genetic; D012639:Seeds / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; D044945:Proanthocyanidins; C013221:proanthocyanidin; D002392:Catechin; D042845:Laccase; C510496:TT10 protein, Arabidopsis; D009247:NADH, NADPH Oxidoreductases; D005964:Glucosyltransferases