title: Functional characterization of proanthocyanidin pathway enzymes from tea and their application for metabolic engineering.
abstract: Tea (Camellia sinensis) is rich in specialized metabolites, especially polyphenolic proanthocyanidins (PAs) and their precursors. To better understand the PA pathway in tea, we generated a complementary DNA library from leaf tissue of the blister blight-resistant tea cultivar TRI2043 and functionally characterized key enzymes responsible for the biosynthesis of PA precursors. Structural genes encoding enzymes involved in the general phenylpropanoid/flavonoid pathway and the PA-specific branch pathway were well represented in the library. Recombinant tea leucoanthocyanidin reductase (CsLAR) expressed in Escherichia coli was active with leucocyanidin as substrate to produce the 2R,3S-trans-flavan-ol (+)-catechin in vitro. Two genes encoding anthocyanidin reductase, CsANR1 and CsANR2, were also expressed in E. coli, and the recombinant proteins exhibited similar kinetic properties. Both converted cyanidin to a mixture of (+)-epicatechin and (-)-catechin, although in different proportions, indicating that both enzymes possess epimerase activity. These epimers were unexpected based on the belief that tea PAs are made from (-)-epicatechin and (+)-catechin. Ectopic expression of CsANR2 or CsLAR led to the accumulation of low levels of PA precursors and their conjugates in Medicago truncatula hairy roots and anthocyanin-overproducing tobacco (Nicotiana tabacum), but levels of oligomeric PAs were very low. Surprisingly, the expression of CsLAR in tobacco overproducing anthocyanin led to the accumulation of higher levels of epicatechin and its glucoside than of catechin, again highlighting the potential importance of epimerization in flavan-3-ol biosynthesis. These data provide a resource for understanding tea PA biosynthesis and tools for the bioengineering of flavanols.
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
authors.forename: Yongzhen
authors.initials: Y
authors.lastname: Pang
authors.forename: I Sarath B
authors.initials: IS
authors.lastname: Abeysinghe
authors.forename: Ji
authors.initials: J
authors.lastname: He
authors.forename: Xianzhi
authors.initials: X
authors.lastname: He
authors.forename: David
authors.initials: D
authors.lastname: Huhman
authors.forename: K Mudith
authors.initials: KM
authors.lastname: Mewan
authors.forename: Lloyd W
authors.initials: LW
authors.lastname: Sumner
authors.forename: Jianfei
authors.initials: J
authors.lastname: Yun
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D053898:Biosynthetic Pathways / Q000235:genetics; D002851:Chromatography, High Pressure Liquid; D005419:Flavonoids / Q000737:chemistry / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D015723:Gene Library; D017343:Genes, Plant / Q000235:genetics; D007700:Kinetics; D046913:Medicago truncatula / Q000235:genetics; D060847:Metabolic Engineering; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics; D030821:Plants, Genetically Modified; D044945:Proanthocyanidins / Q000096:biosynthesis*; D011994:Recombinant Proteins / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013662:Tea / Q000201:enzymology* / Q000235:genetics; D014026:Nicotiana / Q000378:metabolism
chemical_list: D005419:Flavonoids; D010940:Plant Proteins; D044945:Proanthocyanidins; D011994:Recombinant Proteins; D013662:Tea; C013221:proanthocyanidin; C404987:flavan-3-ol