Abstract
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.
Highlights
Flavonoid pigments are well known to play an important role in pigmentation of tissues such as flowers, fruits, and grains
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
We studied a relationship between Flavanone 3-hydroxylase (F3H) expression and tissue pigmentation of lines with red grain and red coleoptile (R/Rc), red grain and white coleoptile (R/rc), white grain and red coleoptile (r/Rc), and white grain and white coleoptile (r/rc)
Summary
Flavonoid pigments are well known to play an important role in pigmentation of tissues such as flowers, fruits, and grains. In wheat, red pigmentation was observed in many tissues including grain coats, coleoptiles, anthers, culms, and pericarps. Red-grained wheat has been reported to contain red flavonoid pigments, phlobaphene or proanthocyanidin (condensed tannin), in grain coat tissues [4]. Proanthocyanidin and anthocyanin are produced via 3,4-deoxy flavonoids, which are synthesized by four enzymes: CHS, CHI, F3H, and DFR. Activation of flavonoid biosynthetic genes is required for pigmentation of plant tissue. Transcription factors involved in expression of flavonoid genes have been studied extensively and identified in several plant species, including Arabidopsis and maize. The TT2 (MYB-type) factor of Arabidopsis is required for proanthocyanidin production in the seed coat [8]. Our group showed that R-1 gene which regulates grain color in wheat was considered to be an MYB-type transcription factor [9]. Expressions of F3HA1, F3H-B,1 and F3H-D1 were associated with pigmentation and appeared to be enzymes that are required for pigment synthesis
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