Karyotype analysis of three Solanum plants using combined PI-DAPI staining and double fluorescence in situ hybridization with 45S and 5S rDNA probes
In this study, mitotic metaphase chromosomes of Solanum surattense Burm., Solanum lyratum Thunb. and Solanum photeinocarpum Nakam. were well prepared using an advanced chromosome preparation method. The chromosomes were distinguished by combined PI-DAPI (CPD) staining and double fluorescence in situ hybridization (FISH) with 45S and 5S rDNA probes and their molecular cytogenetic karyotypes were established. Although, the karyotype of S. surattense Burm. and S. photeinocarpum Nakam was first established, the karyotype formulas of the three Solanum plants (S. surattense Burm., S. lyratum Thunb. and S. photeinocarpum Nakam) can be described as follows: 2n=24=18m +4sm+2st (2SAT), 2n=24=18m +4sm+2st (2SAT) and 2n=24=18m +6sm (2SAT). Moreover, the karyotype asymmetry of the three species belongs to 2A type. After CPD staining, the centromeres of all chromosomes in the three species were shown as red CPD bands, indicating the presence of GC-rich DNA sequences in the chromosomes. Subsequential double FISH shows that S. surattense Burm., S. lyratum Thunb. and S. photeinocarpum Nakam, all have a pair of 45S rDNA sites located on chromosomes, and all of these 45S rDNA sites correspond to the respective prominent CPD banded regions. S. surattense Burm., S. lyratum Thunb. and S. photeinocarpum Nakam correspond to the CPD banded regions at the ends of chromosomes 8, 10 and 12, respectively. The three Solanum plants all have a pair of 5S rDNA sites. In S. surattense Burm., the 5S rDNA sites are located on the long arm of the 6th chromosome pair, while the 5S rDNA sites of S. lyratum Thunb. and S. photeinocarpum Nakam are all located on the short arms of the 4th chromosome pair. Our study shows that the CPD bands and rDNA FISH signals provide effective chromosome markers allowing us to establish accurate molecular cytogenetic karyotypes of the three species tested.
Key words: Solanum surattense Burm. Solanum lyratum Thunb., Solanum photeinocarpum Nakam, karyotype, CPD staining, fluorescence in situ hybridization (FISH).