Colour genes (R and Rc) for grain and coleoptile upregulate flavonoid biosynthesis genes in wheat

Pigmentation of wheat grain and coleoptile is controlled by the R gene on chromosomes of the homoeologous group 3 and the Rc gene on chromosomes of the homoeologous group 7, respectively. Each of these genes is inherited monogenically. The pigment of grain has been suggested to be a derivative of catechin-tannin and that of coleoptile to be anthocyanin. These polyphenol compounds are known to be synthesized through the flavonoid biosynthesis pathway. We isolated 4 partial nucleotide sequences of the early flavonoid biosynthesis genes (CHS, CHI, F3H, and DFR) in wheat. The expression of these genes was examined in the developing grain of red-grained and white-grained wheat lines. CHS, CHI, F3H, and DFR were highly upregulated in the grain coat tissue of the red-grained lines, whereas there was no significant expression in the white-grained lines. These results indicate that the R gene is involved in the activation of the early flavonoid biosynthesis genes. As for coleoptile pigmentation, all 4 genes were expressed in the red coleoptile; however, DFR was not activated in the white coleoptile. The Rc gene appears to be involved in DFR expression. The possibility that wheat R and Rc genes might be transcription factors is discussed.