ISHS Acta Horticulturae 508: XIX International Symposium on Improvement of Ornamental Plants
TOWARDS NOVEL FLOWER COLORS IN FORSYTHIA BY GENETIC ENGINEERING |
| Authors: | C. Rosati, M. Duron, A. Cadic, C. Rosati, Ph. Simoneau |
| Abstract:
Molecular and biochemical studies were undertaken to characterise pigment composition and biosynthesis in Forsythia, a yellow-flowered ornamental shrub whose petals accumulate large amounts of carotenoids but lack anthocyanins. This work is part of a breeding program at INRA Angers Station, aimed at changing Forsythia flower color by genetic transformation. F. x intermedia cv. ‘Spring Glory’, a popular variety for which an Agrobacterium-mediated transformation system has already been developed, was taken as model genotype. Gene expression studies enabled to identify a late block in anthocyanin biosynthesis pathway in petals. In order to complement this block and induce de novo anthocyanin formation, several constructs were assembled and transformed plants have been recovered. More recently, transformation experiments with carotenoid gene constructs were also started, in order to modify the pathway toward the synthesis of red compounds. Transformants are expected to flower by spring 2000 and will undergo phenotypic, molecular and biochemical characterisation. Forsythia is a yellow-flowered shrub, widely grown for its great ornamental value and hardiness. Most species originated in the Far East and have been introduced to Europe since XIX century. Flowers bloom in early spring, before the leaves appear. All genotypes have yellow flowers, due to the presence of carotenoids and the absence of anthocyanins in petals. Anthocyanins do accumulate in other organs (e.g., senescing leaves, sepals and stems): this indicates an organ-specific regulation of the flavonoid pathway leading to the synthesis of such pigments. The lack of variability for flower color is a major limit to traditional breeding for this important ornamental trait. Against this background, a breeding program was started at INRA Station of Angers, aimed at changing Forsythia flower color by means of genetic transformation. F. x intermedia cv. ‘Spring Glory’ was chosen as the target genotype, since early studies demonstrated its amenability to in vitro culture (Duron, 1977). First efforts resulted in the establishment of an efficient Agrobacterium-mediated transformation system (Rosati et al., 1996). Meanwhile, biochemical and molecular studies were also carried out to understand in detail the flavonoid (and particularly anthocyanin) metabolism in Forsythia flower organs. The choice to study the flavonoid rather than the carotenoid pathway was due to higher amount of data available on this metabolism. The recent molecular and biochemical advances in the knowledge of the carotenoid pathway open the way to new strategies, as discussed at the end of this work. Flavonoids are secondary metabolites present in most plants, where they play important roles e.g. in UV-protection, response to a/biotic stresses, and, most notably, pigmentation. In fact, anthocyanins display the broadest palette of colors, determining red, orange and blue hues. The structural genes and enzymes from chalcone synthase (CHS) to | |
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