Comparative karyotypic analysis of A and C genomes in the genus Oryza with C 0 t-1 DNA and RFLP

Abstract

Fluorescence in situ hybridization (FISH) was applied to somatic chromosomes preparations of Oryza sativa L. (AA), O. glaberrima (AA), and O. officinalis Wall. (CC) with a labeled probe of C 0 t-1 DNA. Genomic in situ hybridization to its own chromosomes (self-GISH) was conducted in a control experiment. The homologous chromosomes showed similar signal bands probed by C 0 t-1 DNA, while karyotypic analysis of chromosomes between A genome in the two cultivated species and C genome in O. officinalis were conducted based on the band patterns. The ideograms with C 0 t-1 DNA signal bands were also built. The nonuniform distribution of hybridization signals of C 0 t-1 DNA from O. sativa and that on its own chromosome of O. officinalis were observed. However, the similarity and correspondence between C 0 t-1 DNA signal patterns and genomic DNA signal patterns indicated that the self-GISH signals actually resulted from the hybridization of genomic repetitive sequences to the chromosomes. The restriction fragment length polymorphism (RFLP) marker, R2676, from the chromosome 8 of O. sativa and O. officinalis, was used as a probe to somatic hybrid on chromosomes for comparative karyotypic analysis between O. glaberrima and O. officinalis. The results showed that R2676 was located on the short arm of chromosome 7 in O. officinalis and chromosome 4 in O. glaberrima. The percentage distances from the centromere to hybridization sites were 91.56±5.62 and 86.20±3.17. Our results revealed that the relative length of O. officinalis chromosome 8 does not follow conventional chromosome length in descending order of number. C 0 t-1 DNA of A genome signals were detected in the end of the short arm of O. officinalis chromosome 8, indicating that the highly and moderately repetitive DNA sequences in this region were considerably similar between C and A genomes. However, the fluorescence intensity on the chromosomes of C 0 t-1 DNA of A genome was less than that of its own C genome from O. officinalis, which would be one of the causes for the fact that highly and moderately repetitive DNA sequences were amplified in O. officinalis. No homology signal of C 0 t-1 DNA from O. sativa was detected in the end of the long arm of O. glaberrima, indicating that repetitive DNA sequences of A genome in two cultivated rice were lost in the evolutional history. In this paper, using comparative karyotypic analysis of RFLP combined C 0 t-1 DNA signal bands, the evolutionary mechanism of genome in genus Oryza was also discussed.