Anthocyanin Biosynthetic Genes and Their Application to Flower Color Modification through Sense Suppression

zThe coding sequence is compared for each pair of genes. Comparisons were done using the gap program of the Wisconsin GCG sequence analysis package. yCHS = chalcone synthase; CHI = chalcone isomerase; DFR = dihydroflavonol reductase. xFirst row for each plant pair presents the percent amino acid similarity. wSecond row for each plant pair presents the percent amino acid identity. vThird row for each plant pair presents the percent nucleotide sequence identity. Flower color of important commercial cut flower crops is determined principally by two pigment types: anthocyanins and carotenoids. The former pigments give rise to orange, pink, red, purple, and blue, whereas the latter are principally responsible for a range of yellow and orange colors. The biosynthesis of anthocyanin pigments and the factors responsible for determining flower color from these pigments have been studied extensively (Forkmann, 1991). A good molecular genetic understanding of anthocyanin biosynthesis has been developed for snapdragon (Antirrhinum majus L.), petunia (Petunia ×hybrida Hort.), and corn (Zea mays L.). This understanding has made it possible to modify flower color of cut flower crops in a commercially meaningful way. There are two reasons to modify flower color commercially. First, the flower color of a variety with desirable agronomic or consumer characteristics can be modified to another flower color typical of that crop. For example, a white-flowering carnation (Dianthus caryophyllus L.) could be created from a red-flowering variety with highly desirable agronomic or consumer characteristics. Second, a flower color that does not occur naturally in a particular crop can be introduced into that crop. For example, a blue-flowering rose (Rosa hybrida L.) variety could be developed through the introduction of petunia genes whose products interact to produce blue pigmentation. To achieve these ends, either the expression of host plant genes must be suppressed or nonhost plant genes must be expressed. The introduced expression of nonhost plant genes can have unpredictable effects on flower color, and the final color depends on the precise biochemistry of anthocyanin biosynthesis in a particular variety. However, the range of flower colors resulting from suppression of an anthocyanin pathway gene is fairly predictable. I will focus here on the suppression of the first committed step in anthocyanin biosynthesis—chalcone synthase (see Fig. 1 for outline of the pathway). Completely white-flowering plants have been produced from redor purple-flowering plants through sense suppression of chalcone synthase expression in petunia (Napoli et al., 1990; van der Krol et al., 1990). This example will serve to illustrate some of the issues involved in modifying flower color through genetic engineering. It also will illustrate the practical application of flower color modification in chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura], carnation, and rose.