title: Identification of a flavonol 7-O-rhamnosyltransferase gene determining flavonoid pattern in Arabidopsis by transcriptome coexpression analysis and reverse genetics.
abstract: Glycosylation plays a major role in the remarkable chemical diversity of flavonoids in plants including Arabidopsis thaliana. The wide diversity encoded by the large family-1 glycosyltransferase (UGT) gene family makes it difficult to determine the biochemical function of each gene solely from its primary sequence. Here we used transcriptome coexpression analysis combined with a reverse genetics approach to identify a gene that is prominent in determining the flavonoid composition of Arabidopsis. Using transcriptome coexpression analysis accessible on the ATTED-II public data base, the expression pattern of a UGT gene, UGT89C1, was found to be highly correlated with known flavonoid biosynthetic genes. No C-7 rhamnosylated flavonols were detected in either of two T-DNA ugt89c1 mutants. This specific metabolite deficiency in the mutants was complemented by stable transformation with the genomic fragment containing intact UGT89C1. Glutathione S-transferasefused recombinant UGT89C1 protein converted kaempferol 3-O-glucoside to kaempferol 3-O-glucoside-7-O-rhamnoside and recognized 3-O-glycosylated flavonols and UDP-rhamnose as substrates, but not flavonol aglycones, 3-O-glycosylated anthocyanins or other UDP-sugars. These results show that UGT89C1 is a flavonol 7-O-rhamnosyltransferase. The abundance of UGT89C1 transcripts in floral buds was consistent with the flavonoid accumulation of C-7 rhamnosylated flavonols in Arabidopsis organs. Our present study demonstrates that the integration of transcriptome coexpression analysis with a reverse genetic approach is a versatile tool for understanding a multigene family of a metabolic pathway in Arabidopsis.
authors.affiliation: RIKEN Plant Science Center, Yokohama 230-0045, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Yonekura-Sakakibara
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tohge
authors.forename: Rie
authors.initials: R
authors.lastname: Niida
authors.forename: Kazuki
authors.initials: K
authors.lastname: Saito
mesh_terms: D000872:Anthocyanins / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D044948:Flavonols / Q000378:metabolism; D015870:Gene Expression; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D006602:Hexosyltransferases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D044949:Kaempferols / Q000096:biosynthesis; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D000872:Anthocyanins; D029681:Arabidopsis Proteins; D044948:Flavonols; D044949:Kaempferols; C091955:kaempferol 3-rhamnosyldiglucoside; D006602:Hexosyltransferases; C521109:UGT89C1 protein, Arabidopsis