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C ‐Glycosyltransferases catalyzing the formation of di‐ C ‐glucosyl flavonoids in citrus plants
Author(s) -
Ito Takamitsu,
Fujimoto Shunsuke,
Suito Fumiaki,
Shimosaka Makoto,
Taguchi Goro
Publication year - 2017
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.13555
Subject(s) - glycosyltransferase , phloretin , biosynthesis , flavonoid biosynthesis , flavonoid , chemistry , enzyme , biochemistry , escherichia coli , gene , stereochemistry , antioxidant , gene expression , transcriptome
Summary Citrus plants accumulate many kinds of flavonoids, including di‐ C ‐glucosyl flavonoids, which have attracted considerable attention due to their health benefits. However, the biosynthesis of di‐ C ‐glucosyl flavonoids has not been elucidated at the molecular level. Here, we identified the C ‐glycosyltransferases ( CGT s) Fc CGT ( UGT 708G1) and Cu CGT ( UGT 708G2) as the primary enzymes involved in the biosynthesis of di‐ C ‐glucosyl flavonoids in the citrus plants kumquat ( Fortunella crassifolia ) and satsuma mandarin ( Citrus unshiu ), respectively. The amino acid sequences of these CGT s were 98% identical, indicating that CGT genes are highly conserved in the citrus family. The recombinant enzymes Fc CGT and Cu CGT utilized 2‐hydroxyflavanones, dihydrochalcone, and their mono‐ C ‐glucosides as sugar acceptors and produced corresponding di‐ C ‐glucosides. The K m and k cat values of Fc CGT toward phloretin were <0.5 μ m and 12.0 sec −1 , and those toward nothofagin (3ʹ‐ C ‐glucosylphloretin) were 14.4 μ m and 5.3 sec −1 , respectively; these values are comparable with those of other glycosyltransferases reported to date. Transcripts of both CGT genes were found to concentrate in various plant organs, and particularly in leaves. Our results suggest that di‐ C ‐glucosyl flavonoid biosynthesis proceeds via a single enzyme using either 2‐hydroxyflavanones or phloretin as a substrate in citrus plants. In addition, Escherichia coli cells expressing CGT genes were found to be capable of producing di‐ C ‐glucosyl flavonoids, which is promising for commercial production of these valuable compounds.