Ornamental gentian plants have vivid-blue flowers. The main factor contributing to the flower colour
is
the accumulation of a polyacylated delphinidin ‘gentiodelphin’ in their petals. Although in vitro
studies proposed that acylation plays an important role in the stability and development of gentian
blue colour, the in vivo stability of the polyacylated anthocyanin was not clearly demonstrated.
Thus, to reveal the importance of anthocyanin modification, especially acylation, and to engineer
new colours of gentian flowers, we used chimeric RNAi technology to produce transgenic gentian
plants with downregulated anthocyanin 5,30 -aromatic acyltransferase (5/30 AT) and flavonoid 30 ,50
-hydroxylase (F30 50 H) activities, which are both essential enzymes for gentiodelphin
biosynthesis. Two lines of flower colour-modified plants were obtained from fifteen transgenic
gentian plants. Clone no. 1 exhibited a lilac flower colour and clone no. 15 exhibited pale-blue
flowers. RNA gel blot analysis confirmed that both transgenic lines had markedly suppressed 5/30 AT
transcripts, whereas clone no. 15 had fewer F30 50 H transcripts than clone no. 1 and
untransformed control plants. HPLC analysis of anthocyanin compositions showed that downregulation
of the 5/30 AT gene led to increased accumulation of non-acylated anthocyanins, as expected.
These results demonstrated that genetic engineering to reduce the accumulation of
polyacylated anthocyanins could cause modulations of flower colour.