Abstract
Anthocyanins are major constituents of flower color and their biosynthesis pathway leading to anthocyanidin 3-glucosides is well conserved among higher plants. The glucosylation was catalyzed by anthocyanidin 3-glucosyltransferase (A3GT). Anthocyanidin 3-glucosides are usually further glucosylated with other glucosyltransferases. However, in rose, a single enzyme (anthocyanin 5, 3-glucosyltransferase) glucosylates 5-position of an anthocyanidin followed by 3-position (Ogata et al., 2005). We isolated a rose genomic clone encoding a protein (RhA3GT) belonging to the A3GT family (46-57% identity). RhA3GT showed A3GT activity in vitro. The expression level of this gene in rose petals is below detection level in northern analysis. A rose cDNA, encoding a protein with 42-44% identity to A3GTs, was also isolated. The protein (RhF3GT) showed glucolyltransferase activity to flavonols but not to anthocyanidins in vitro. Transgenic rose plants habouring an RNAi construct of RhF3GT gene exhibited white or paler flower color due to decrease of anthocyanins.
