Biochemical characterization of a cinnamoyl-CoA reductase from wheat

Cinnamoyl-CoA reductase (CCR) is responsible for the CoA ester -> aldehycle conversion in monolignol biosynthesis, which can divert phenylpropanoid-derived metabolites into the biosynthesis of lignin. To gain a better understanding of lignin biosynthesis in wheat (Triticum aestivum L.), a cDNA encoding CCR was isolated and named Ta-CCR2. DNA hybridization analyses demonstrated that the Ta-CCR2 gene exists in three copies in the wheat genome. RNA blot hybridization indicated that Ta-CCR2 was expressed most abundantly in root and stem tissues that were in the process of lignification. The secondary and three-dimensional structures of Ta-CCR2 were analyzed by molecular modeling. Recombinant Ta-CCR2 protein purified from E coli converted feruloyl CoA, 5-OH-feruloyl CoA, sinapoyl CoA and caffeoyl CoA with almost similar efficiency, suggesting that it is involved in both G and S lignin synthesis. Ta-CCR2 had a very low V-max value for 4-coumaroyl CoA, which may serve as a mechanism to control metabolic flux to H lignin in vivo. Furthermore, the reaction mechanism of Ta-CCR2 was analyzed in relation to its possible three-dimensional structure. The activity of Ta-CCR2 in relation to lignin biosynthesis is discussed.