Flavonoid pigments are known to accumulate in red grains and coleoptiles of wheat and are synthesized through the flavonoid biosynthetic pathway. Flavanone 3-hydroxylase (F3H) is a key enzyme at a diverging point of the flavonoid pathway leading to production of different pigments: phlobaphene, proanthocyanidin, and anthocyanin. We isolated three F3H genes from wheat and examined a relationship between their expression and tissue pigmentation. Three F3Hs are located on the telomeric region of the long arm of chromosomes 2A, 2B, and 2D, respectively, designated as F3H-A1, F3H-B1, and F3H-D1. The telomeric regions of the long arms of the chromosomes of homoeologous group 2 of wheat showed a syntenic relationship to the telomeric region of the long arm of rice chromosome 4, on which rice F3H gene was also located. All three genes were highly activated in the red grains and coleoptiles and appeared to be controlled by flavonoid regulators in each tissue. 1. Introduction Flavonoid pigments are well known to play an important role in pigmentation of tissues such as flowers, fruits, and grains. These pigments not only render the tissues as more conspicuous but also add physiological function to tissues, such as protection against UV damage [1] and increased level of grain dormancy [2]. In wheat, red pigmentation was observed in many tissues including grain coats, coleoptiles, anthers, culms, and pericarps. Several genes affecting anthocyanin pigmentation (i.e., R-1 (R in former notation) for red grain, Rc for red coleoptile, Pan for purple anthers, Ra for red auricles, Pc for purple culms, and Pp for purple pericarp) have been reported [3]. Red-grained wheat has been reported to contain red flavonoid pigments, phlobaphene or proanthocyanidin (condensed tannin), in grain coat tissues [4]. In contrast, pigments of red coleoptiles were anthocyanin [5]. Phlobaphene, proanthocyanidin, and anthocyanin are synthesized through the common flavonoid biosynthetic pathway [6] (Figure 1). Phlobaphenes are compounds produced by polymerization of flavan-4-ols, which are synthesized by three enzymes: chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol 4-reductase (DFR) in the early steps of the flavonoid pathway. On the other hand, proanthocyanidin and anthocyanin are produced via 3,4-deoxy flavonoids, which are synthesized by four enzymes: CHS, CHI, F3H, and DFR. A step of F3H is a diverging point in the flavonoid pathway leading to the production of either phlobaphene or proanthocyanidin. Figure 1: Flavonoid biosynthetic pathway. The F3H gene is indicated
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