Abstract
Purple carrots (Daucus carota ssp. sativus var. atrorubens Alef.) accumulate large amounts of cyanidin-based anthocyanins in their taproots. Cyanidin can be glycosylated with galactose, xylose, and glucose in sequence by glycosyltransferases resulting in cyanidin 3-xylosyl (glucosyl) galactosides in purple carrots. The first step in the glycosylation of cyanidin is catalysis by UDP-galactose: cyanidin galactosyltransferase (UCGalT) transferring the galactosyl moiety from UDP-galactose to cyanidin. In the present study, a gene from ‘Deep purple’ carrot, DcUCGalT1, was cloned and heterologously expressed in E. coli BL21 (DE3). The recombinant DcUCGalT1 galactosylated cyanidin to produce cyanidin-3-O-galactoside and showed optimal activity for cyanidin at 30 °C and pH 8.6. It showed lower galactosylation activity for peonidin, pelargonidin, kaempferol and quercetin. It accepted only UDP-galactose as a glycosyl donor when cyanidin was used as an aglycone. The expression level of DcUCGalT1 was positively correlated with anthocyanin biosynthesis in carrots. The enzyme extractions from ‘Deep purple’ exhibited galactosylation activity for cyanidin, peonidin and pelargonidin, while those from ‘Kuroda’ (a non-purple cultivar) did not.
Highlights
Numerous publications have proposed that anthocyanins are protective compounds in human health[1,2,3,4,5]
We investigated the relationship between the DcUCGalT1 expression levels and anthocyanin accumulation to understand the importance of the role of DcUCGalT1 in the biosynthesis of anthocyanins in purple carrot taproots
DcUCGalT1 was identified by amino acid sequence similarity to A. cordata anthocyanin 3-O-glactosytransferase (Accession No AB103471) with the BLAST tool in the CarrotDB
Summary
Numerous publications have proposed that anthocyanins are protective compounds in human health[1,2,3,4,5] These health-promoting effects have made anthocyanin-rich foods increasingly popular. Many glycosyltransferases from various species have shown glycosylation activity for anthocyanins in previous investigations, only those from carrots[20], peach (Prunus persica)[21], udo (Aralia cordata Thunb.)[22,23] and kiwifruit (Actinidia chinensis)[24] have been confirmed to be UDP-galactose:cyanidin galactosyltransferase (UCGalT). We cloned a gene of UCGalT from purple carrot (DcUCGalT1) and determined its ability to galactosylate cyanidin, peonidin, pelargonidin, kaempferol and quercetin. We investigated the relationship between the DcUCGalT1 expression levels and anthocyanin accumulation to understand the importance of the role of DcUCGalT1 in the biosynthesis of anthocyanins in purple carrot taproots
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