83.植物におけるクマリン類生合成の鍵酵素である桂皮酸類オルト位水酸化酵素の解析(口頭発表)

抄録

Coumarins are ubiquitously found as the plant secondary metabolites in plants and are biosynthesized via ortho-hydroxylation of cinnamates by cinnamates 2'-hydroxylase (C2'H), which is a key enzyme in coumarins biosynthesis. We investigated C2'Hs from Arabidopsis and sweet potato (Ipomoea batatas), which accumulate the glucosides of scopoletin and umbelliferone, respectively. Previous studies showed that C2'H is a 2-oxoglutarate-dependent dioxygenase and catalyzes ortho-hydroxylation of the CoA-ester of cinnamates to yield coumarins. The results suggest that the chemical composition of coumarins in plant species is determined by the substrate specificity of C2'H in each of the plants. To understand coumarins biosynthesis in various plants, we have isolated a C2'H (LjC2'H) cDNA from Lotus japonicus, in which coumarins have not yet been found so far. We found that LjC2'H catalyzes ortho-hydroxylation of feruloyl-CoA and cafeoyl-CoA to form scopoletin and esculetin, respectively. We have also isolated a C2'H cDNA from grapefruit (Citrus x paradisi). Grapefruit accumulates furanocoumarins, which is derived from umbelliferone, and characterization of grapefruit C2'H is in progress. In addition, we have established bacterial biosynthesis of coumarins. Plant C2'Hs were co-expressed with 4-coumaroyl CoA:ligase in E. coli, and the feeding of cinnamates resulted in the accumulation of coumarins in the culture medium.