Authors: Yongzhen Pang Xiaofei Cheng David V Huhman Junying Ma Gregory J Peel Keiko YonekuraSakakibara Kazuki Saito Guoan Shen Lloyd W Sumner Yuhong Tang Jianqi Wen Jianfei Yun Richard A Dixon
Publish Date: 2013/04/17
Volume: 238, Issue: 1, Pages: 139-154
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′Oglucoside 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 laccaselike 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 cisacting elements and direct overlapping but partially distinct expression patterns UGT72L1 and MtANR are localized in the cytosol whereas TT10 is localized to the vacuole Overexpression of UGT72L1 in M truncatula hairy roots results in increased accumulation of PAlike 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
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