Cytogenetic comparisons between A and G genomes in Oryza using genomic in situ hybridization

The genomic structures ofOryza sativa (A genome) and O.meyeriana (G genome) were comparatively studied using bieolor genomic in situ hybridization (GISH).GISH was clearly able to discriminate between the chromosomes of O. sotiva and O.meyeriana in the interspecific F_1 hybrids without blocking DNA,and co-hybridization was hardly detected. The average mitotic chromosome length of O.meyeriana was found to be 1.69 times that of O.sativa.A comparison of 4,6-diamidino-2-phenylindole staining showed that the chromosomes of O.meyeriana were more extensively labelled, suggesting that the G genome is amplified with more repetitive sequences than the A genome.In interphase nuclei,9-12 chromocenters were normally detected and nearly all the chromocenters constituted the G genome-specific DNA.More and larger chromocenters formed by chromatin compaction corresponding to the G genome were detected in the hybrid compared with its parents.During pachytene of the F_1 hybrid,most chromosomes of A and G did not synapse each other except tot 1-2 chromosomes paired at the end of their arms.At meiotic metaphase I,three types of chromosomal associations,i.e.O,sativa-O,sotiva(A-A),O.sativa-O,meyeriana (A-G) and O.meyeriana-O,meyeriana (G-G),were observed in the F_1 hybrid.The A-G chromosome pairing configurations included bivalcnts and trivalents.The results provided a foundation toward studying genome organization and evolution of O.meyeriana.