ISHS Acta Horticulturae 651: XXI International Eucarpia Symposium on Classical versus Molecular Breeding of Ornamentals - Part II
CLONING AND HETEROLOGOUS EXPRESSION OF FLAVONOID GENES OF OSTEOSPERMUM HYBRIDS |
| Authors: | C. Seitz, A. Hauser, G. Forkmann, S. Martens |
| Keywords: | Osteospermum, carotenoids, flavonoid biosynthesis, chalcone synthase, flavonoid 3¿,5¿-hydroxylase |
| Abstract:
Petals of Osteospermum exhibit white, yellow and rose to lilac colours. Chemical and biochemical investigations elucidated the basis of flower colour in Osteospermum. Besides carotenoids, which were shown to be responsible for the yellow colour, flavonoids were identified to be the main colour-giving compounds. Different amounts of derivatives of the anthocyanidin delphinidin cause the rose to lilac colour range. In addition to delphinidin, derivatives of flavonols were found to be present in the petals. Enzyme assays elucidated the biosynthetic path leading to the formation of the 3’-, 4’-, and 5’-hydroxylated delphinidin. Because of distinct substrate specifities of the early enzymes of the flavonoid pathway, chalcone synthase, chalcone isomerase, and flavanone 3-hydroxylase, dihydrokaempferol is supposed to be the main branch point. This compound was shown to be hydroxylated in 3’- and 5’-position by flavonoid 3’, 5’-hydroxylase to dihydromyricetin which is subsequently reduced by dihydroflavonol 4-reductase to leucodelphinidin, the precursor of delphinidin. Molecular biological investigations of two key steps allowed a confirmation of the enzymological findings. The protein of a heterologously expressed full length chalcone synthase cDNA-clone was shown to preferentially use 4-coumaroyl-CoA as a substrate leading to the formation of naringenin after isomerisation by chalcone isomerase. In contrast to this, caffeoyl-CoA as a substrate resulted in the formation of only low amounts of eriodictyol. 3’, 5’-hydroxylation, which is indispensable for the formation of delphinidin, was demonstrated with the protein of a heterologously expressed F3’5’H full-length cDNA-clone. Fragments of the other main structural flavonoid genes of Osteospermum are now available and further molecular biological investigation will be performed. | |
Download Adobe Acrobat Reader (free software to read PDF files) | |
