Himi Eiko, Nisar Ahmed, Noda Kazuhiko
Research Institute for Bioresources, Okayama University, Japan.
Genome. 2005 Aug;48(4):747-54. doi: 10.1139/g05-026.
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.
小麦籽粒和胚芽鞘的色素沉着分别由同源群3染色体上的R基因和同源群7染色体上的Rc基因控制。这些基因均按单基因方式遗传。籽粒色素被认为是儿茶素-单宁的衍生物，而胚芽鞘色素则为花青素。已知这些多酚化合物是通过类黄酮生物合成途径合成的。我们分离出了小麦中类黄酮生物合成早期基因（CHS、CHI、F3H和DFR）的4个部分核苷酸序列。检测了这些基因在红粒和白粒小麦品系发育籽粒中的表达情况。CHS、CHI、F3H和DFR在红粒品系的种皮组织中高度上调，而在白粒品系中无明显表达。这些结果表明，R基因参与类黄酮生物合成早期基因的激活。至于胚芽鞘色素沉着，所有4个基因均在红色胚芽鞘中表达；然而，DFR在白色胚芽鞘中未被激活。Rc基因似乎参与DFR的表达。文中还讨论了小麦R基因和Rc基因可能是转录因子的可能性。
