Selective accumulation of delphinidin derivatives in tobacco using a putative flavonoid 3′,5′-hydroxylase cDNA from Campanula medium

Blue flowers generally contain 3',5'-hydroxylated anthocyanins (delphinidin derivatives) as pigments, which are formed only in the presence of flavonoid 3',5'hydroxylases (F3'5'H). Heterologous expression of a F3'5'H gene therefore provides an opportunity to produce novel blue flowers for a number of ornamental plants missing blue flowering varieties. However, our previous study indicated difficulties in obtaining good accumulation of delphinidin derivatives in plants expressing F3'5'H. Here we report the isolation of a putative F3'5'H cDNA (Ka1) from canterbury bells (Campanula medium) and its expression in tobacco. Surprisingly, compared with other F3'5'H cDNAs, Kal encoded a protein with a unique primary structure that conferred high competence in the accumulation of delphinidin derivatives (up to 99% of total anthocyanins) and produced novel purple flowers. These results suggest that, among F3'5'H cDNAs, Ka1 is the best genetic resource for the creation of fine blue flowers by genetic engineering.