Molecular Breeding of Flower Color

Molecular Breeding of Flower Color - 35 Molecular Breeding...

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Fig. 1 Natural occurrence of different flower colors in azalea ( Rhododendron spp.). ( A ) Two flowers with different colors were found in a same branch. ( B ) A small sector with red color was found in the white background of the petal. ( C ) A red flower was found in a cluster of white flowers. ( D ) A typical chimeric flower composed of two sectors of white and red colors. Fig. 2 Representative structures of pigments. Betacarotene ( β - carotene) belongs to carotenoids, and contributes reddish yellow color in some flowers. Betacyanin (red to red-violet color) and betaxanthin (yellow color) are two groups of betalains, which contribute flower pigmentation in several plants of a small group in the order Caryophyllales. Flavonoid is the major contributor in flower color in plant species. Flavonoid consists of two aromatic rings (A and B), and a heterocyclic C ring with oxygen. 35 Molecular Breeding of Flower Color Kin-Ying To * • Chen-Kuen Wang Institute of BioAgricultural Sciences, Academia Sinica, Taipei 115, Taiwan Corresponding author: * kyto@gate.sinica.edu.tw Keywords: anthocyanin, betalain, carotenoid, flavonoid, flower color, genetic engineering, pigmentation ABSTRACT Flower color contributes mainly to the market value of an ornamental plant, and coloration of flowers is determined by three classes of pigments: flavonoids, carotenoids and betalains. Flavonoids and carotenoids are widespread; however, betalains can be found only in plants of several genera in the order Caryophyllales, which belongs to one small group of angiosperms. Among these pigments, flavonoids (mainly anthocyanins) are the most common flower pigments contributing to a range of colors from yellow to orange to red to purple. During the past few decades, flavonoid biosynthetic pathway leading to anthocyanin production has been well established in various plant species, and genetic engineering of flavonoid/anthocyanin biosynthesis has been used to produce cultivars with novel pigmentation in flowers. Here we summarize the current status of molecular approaches in breeding flower coloration, and describe our study and prospective regarding flower color modification. 1. INTRODUCTION Flower color is one of the most attractive characteristics in ornamental plants, contributing to the major value in the floricultural market. In nature, various patterns regarding to the flower color can be easily observed ( Fig. 1 ); however, most of these phenotypic changes are not transmittable and thus novel varieties with commercial value cannot be obtained. Furthermore, alteration in flower pigmentation is a visible indicator to study expression and regulation of floral genes in plant molecular biology. Thus, examination and manipulation of flower color is not only important in basic research areas, it also has a great benefit in biotechnological applications. Generally speaking, flower color is predominantly determined by two classes of pigments: flavonoids and carotenoids. Flavonoids (mainly
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Molecular Breeding of Flower Color - 35 Molecular Breeding...

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