Genetic control of UDP-glucose: anthocyanin 5-O-glucosyltransferase from flowers of Matthiola incana R.Br.

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Abstract
In flower extracts of defined genotypes of Matthiola incana, an enzyme was demonstrated which catalyzes the transfer of the glucosyl moiety of uridine 5′-diphosphoglucose (UDPGlc) to the 5-hydroxyl group of pelargonidin and cyanidin 3-glycosides and acylated derivatives. The best substrate for 5-glucosylation is the 3-xylosylglucoside acylated with p-coumarate, followed by the 3-xylosylglucoside and by the acylated (p-coumarate) 3-glucoside. The 3-glucoside itself is a very poor substrate. Besides UDPGlc, thymine 5′-diphosphoglucose is a suitable glucosyl-donor, but with a reduced reaction rate (42%). The anthocyanin 5-O-glucosyltransferase exhibits a pH optimum at 7.5 and is generally inhibited by divalent ions and by ethylenediaminetetraacetic acid and p-chloromercuribenzoate. Investigations on different genotypes showed that the 5-O-glucosyltransferase activity is clearly controlled by the gene l. In confirmation of earlier chemogenetic work, enzyme activity is only present in lines with the wild-type allele l+. The anthocyanin 5-O-glucosyltransferase activity is strictly correlated with the formation of 5-glucosylated anthocyanins during bud development.