Comparative genomic in situ hybridization analysis on the chromosomes of five grass species with rice genomic DNA probe
Comparative genomic in situ hybridization (cGISH) with biotin-labeled rice genomic DNA to the chromosomes of Zea mays, Hordeum vulgare, Sorghum bicolor, Setaria italic and Secale cereale were conducted to analyze genomic homology between rice and other grass (Gramineae) speices. At 75% stringency, the rice DNA probe generated large numbers of signals dispersedly distributed over all chromosomes in all target species. The nucleolar organizing regions (NORs), a few telomeres, most centromeric regions and numerous interstitial sites were detected. The signals in small genomes were relatively sparse and unevenly distributed along chromosomes, whereas those in large genomes were dense and basically evenly distributed. Chromosomal in situ suppression (CISS) experiments indicated that the signals represented the hybridization of repetitive DNAs is common between rice and the target genome. cGISH conducted at low and high stringency revealed that repetitive DNAs with ～65% homology are rich and those with ～90% homology are rare between rice and maize or barley. cGISH using maize genomic DNA probe to the rice chromosomes generated relatively sparse and unevenly distributed signals. Our results reveal that there exist besides rDNA and telomeric repeats, some other conserved repetitive DNAs among grass species of different subfamilies. Our results also suggest that ancient conserved repetitive DNAs had undergone considerable amplification in large grass genomes during evolution.
Key words: Comparative genomic in situ hybridization (cGISH), genomic homology, chromosome, grass genome, repetitive DNA.