Molecular Characterization of the Heterochromatin of Poncirus trifoliata Raf. Using a Satellite DNA Sequence

摘要

In order to get a molecular characterization of each chromosome of Poncirus trifoliata, we firstly stained the chromosomes with the fluorochromes CMA and DAPI, which allow the identification of heterochromatin as CMA+/DAPI- bands, differentiating the nine chromosome pairs into three groups with different banding patterns. Using fluorescent in situ hybridization (FISH) we have demonstrated that the 5S and 45 S rRNA gene families were always adjacent to each other and located in three chromosome pairs. Further, we described a set of BACs from a genomic library of P. trifoliata which differentially labeled seven out of nine chromosome pairs. In the present work, we hybridized ire situ a satellite DNA sequence isolated from Citrus sinensis, using primers based on the 181 pb satellite sequence described by Beridze et al. (1992). This satellite DNA, which is the main repetitive fraction of Citrus and Poncirus genomes, hybridized on all CMA+ bands of trifoliate orange, except on the rDNA sites. These data suggest that the CMA+ heterochromatic blocks of Citrus and Poncirus are homologous to each other and further support the close phylogenetic relationship between these two genera.