Genetic engineering of agronomic and ornamental traits in carnation

Genetic engineering of carnation (Dianthus caryophyllus L.), which ranks third in the world flower market, is a highly desirable goal for both researchers and commercial companies. Recently, we developed a unique and efficient transformation procedure for this cut flower. The main features of this carnation transformation procedure, which has been fully characterized, are its efficiency (ca. 2 transgenes per 10 explants) and suitability to numerous cultivars. The established transformation procedure was used to generate carnations with novel agronomic and ornamental traits. To obtain fungal resistance, transgenic carnation with osmotin, PR-1 and/or chitinase genes were generated. A high level of resistance in these transgenes to a major carnation pathogen (Fusarium oxysporum f. sp. dianthi, race 2) was demonstrated in greenhouse tests. The rolC gene from Agrobacterium rhizogenes, driven by a CaMV 35S promoter, was harnessed to generate carnation plants with improved performance: transgenic lines exibited dramatically improved rooting ability and production yield (in terms of both number of stem cuttings and number of flowering stalks per mother plant). Moreover, these traits were stable following 2 years of greenhouse testing. Interestingly, in carnation, rolC did not lead to the highly negative traits often ascribed to rol genes. An antisense approach was employed to block the anthocyanin biosynthetic pathway, using the flavanone 3-hydroxylase (fht) gene cloned from carnation; transgenic carnations were generated in an array of colors from a highly commercially successful monochromatic variety. Dramatic suppression of fht level/activity in transgenes that had lost their original color was confirmed by northern blot, RT-PCR and enzymatic assays. Sensory evaluation tests demonstrated that flowers of these carnation transgenes were also more fragrant than those of control plants. Furthermore, GC-MS analyses of volatiles revealed that the level of the benzoic acid derivative, methylbenzoate, was 10 to 100 times higher in these transgenes than in non-transgenic plants. The levels of analyzed fragrance compounds representing other metabolic pathways (terpenoids and fatty acid derivatives) were not affected in these transgenes. Two years of greenhouse testing have revealed that the transgenic lines are true-to-type and that the traits of interest (color, fragrance) are stable. These results, demonstrating the possibility of diverting metabolic flow from anthocyanins to the production of benzoic acid derivatives, reveal an alternative approach to olfactory enhancement of flower fragrance.