Toward construction of synteny maps among cereal genomes. I. Molecular characterization of cereal genomes as probed by rice genomic clones

Seventy five rice genomic clones were hybridized to eight cereal genomes, i.e., rice, maize, barley, rye, Einkorn wheat, Emmer Wheat, and two common wheats to characterize the genome features of cereals. The sequence of 75% (56 clones) of these clones were commonly detected in the eight cereal DNAs, indicating that the cereal genomes contain those sequences homologous to probe DNAs. Sixteen percent (12 clones) revealed positive signals only in the rice DNA, harboring rice-specific sequences. 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 transcribed 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 thus defined as multiplecopy clones. The remaining 76% of clones were classified as single-copy ones. The genome regions around multiple-copy clones had tendency to be more conservatively retained among the cereal genomes, and showed more frequent transcription activity than single-copy regions. The distributions of these characterized clones were traced in the rice RFLP map. While rice-specific sequences were dispersed throughout the chromosomes, those commonly detected among the cereal genomes had a tendency to occur in clusters.