A Comparative Analysis of Multi-Probe Fluorescence In Situ Hybridisation (FISH) Karyotypes in 26 Pinus Species (Pinaceae)

Every species has a unique karyotype, but certain genera have common karyptypes among species. The markers (chromosome length and centromere position) used in traditional karyotyping do not distinguish all chromosome pairs in the genus Pinus. However, the application of multi-probe fluorescence in situ hybridisation (FISH) procedures allowed exact karyotyping of 26 Pinus congeners. We used these new data to examine species relationships. The 35S rDNA and 5S rDNA, Arabidopsis-type telomere repeat sequences, and the proximal CMA band-specific repeat (PCSR) of P. densiflora were used as FISH probes for our analysis of chromosomes in 26 Pinus species. Each species had a unique FISH karyotype and most homologous chromosome pairs were identified. The FISH karyotypes were used to compare corresponding or homologous chromosomes among the species. Common or similar FISH signal patterns appeared in closely related species. Species that had inherited common FISH signal patterns were classified into four karyotype groups. We used cluster analyses to compare quantitative differences in FISH signals within these groups. The results of these analyses were consistent with recent systematic interpretations and resolved differences among existing taxonomic systems based on diverse methodologies. Our results indicate that FISH signal patterns reflect the history of species differentiation and that comparative FISH karyotyping has potential as an important tool for studying the taxonomy or phylogeny of Pinus.