Chromosomal location of 45S rDNA and dfr gene in Citrus sinensis

Dihydroflavonol 4-reductase (DFR) is a key enzyme in the anthocyanin biosynthesis. In this study, the localization of 45S rDNA and dfr gene (named as CsDFR-bo) of the blood orange (Citrus sinensis Osbeck cv. Ruby) on chromosomes was investigated by fluorescence in situ hybridization (FISH). A karyotype of C. sinensis was reconstructed based on the length of mitotic metaphase chromosomes. The 45S rDNAs were localized on chromosomes 2p and 7q. The detection ratios of 45S rDNA in the two chromosomes were 69.5 and 77.3 %, respectively. The CsDFR-bo was proved to be a single-copy gene and localized on chromosome 3p. The detection ratio of CsDFR-bo was 8.2 %.