TOWARD CONSTRUCTION OF SYNTENY MAPS AMONG CEREAL GENOMES .1. MOLECULAR CHARACTERIZATION OF CEREAL GENOMES AS PROBED BY RICE GENOMIC CLONES

Seventy five rice genomic clones were hybridized to eight cereal genom es, i.e., rice, maize, barley, rye, Einkorn wheat, Emmer Wheat, and tw o common wheats to characterize the genome features of cereals. The se quence of 75% (56 clones) of these clones were commonly detected in th e eight cereal DNAs, indicating that the cereal genomes contain those sequences homologous to probe DNAs. Sixteen percent (12 clones) reveal ed positive signals only in the rice DNA, harboring rice-specific sequ ences. Only 9 clones (12%) gave discrete bands in wheat DNAs, showing them to be possible candidates for probes for construction of a wheat RFLP map. Approximately, one-third of the clones (26/75) were transcri bed in the green leaves of cereals. Although these genomic clones were originally selected as low-copy clones, a quarter of them (18 clones) were multiplied in the rice geome, but not repetitively, and were thu s defined as multiple-copy clones. The remaining 76% of clones were cl assified as single-copy ones. The genome regions around multiple-copy clones had tendency to be more conservatively retained among the cerea l genomes, and showed more frequent transcription activity than single -copy regions. The distributions of these characterized clones were tr aced in the rice RFLP map. While rice-specific sequences were disperse d throughout the chromosomes, those commonly detected among the cereal genomes had a tendency to occur in clusters.