Plant Genome IV Conference Plant Genome IV Conference
Several rice DNAs have been visualized on the identified rice chromosomes by in situ hybridization methods. Rice chromosomes were identified by imaging methods and a quantitative chromosome map was constructed (Fukui and Iijima 1991). 45S ribosomal RNA genes (45SrDNA) were visualized by the three different labelling methods of radioactive, coloration, and fluorescent probes for the first time. Variability in the number of the 45SrDNA loci and also geographical inclination were revealed (Fukui et al. 1994). The locus of another ribosomal RNA genes, 5SrDNA was determined in conjunction with in situ hybridization (ISH) and imaging methods. Different from the 45SrDNA loci, 5SrDNA occupies only one locus regardless of Oryza spp. so far examined (Kamisugi et al. 1994). Four different rice repeated sequences (TrsA, TrsB, TrsC and RIRE1) were visualized by fluorescence in situ hybridization (FISH). Each repeated sequence occupies its unique position on rice chromosomes, although most of them were found at subtelomeric regions of rice chromosomes. The subtelomeric positioning of TrsA was unequivocally revealed by multicolor FISH (McFISH) using two different probes of telomeric sequences and TrsA simultaneously. RIRE1 was found all over the genome of O. australiensis. YAC, BAC and cosmid clones were also successfully mapped on the identified rice chromosomes by FISH. Typical examples of mapping these clones will be presented at the workshop in detail.