FISH Analysis of Oryza latifolia and Oryza alta Genomes with 45S rDNA Probes

Using Fluorescence in Situ Hybridization with 45S rDNA probes, we analyzed two wild rice species, Oryza alta and Oryza latifolia, both having CCDD genomes. The results showed that the hybridization signals of 45S rDNA in O.latifolia chromosome preparations were distributed on different chromosomes with the number of 10~16. The same signals in O.alta chromosome preparations were 6 and distributed on three pairs of homologous chromosomes: with two pairs in short chromosome arms and the other one pair in long chromosome arms. The number and positions of 45S rDNA signals are stable in O.alta genome, but there are some dynamic changes of signals in O.latifolia genome. Our observations indicated that there are distinct differences between the two CCDD genomes. Comparative analysis of the karyotype of O.alta and O.latifolia chromosomes based on the Fluorescence in Situ Hybridization pictures showed vast differences. We propose that the genome of O.alta may be differentiated earlier in evolution and tend to be stable, while O.latifolia may still be in its evolutionary process. Based on the imbalance of evolution and differences of genomic structure, we propose that O.alta and O.latifolia can be divided into two wild rice species, which may be better conforming with their evolution characteristics. The mechanism and characteristics of 45s rDNA’s distribution in the chromosomes are discussed