Abstract
BackgroundDifferentiation and copy number of repetitive sequences affect directly chromosome structure which contributes to reproductive isolation and speciation. Comparative cytogenetic mapping has been verified an efficient tool to elucidate the differentiation and distribution of repetitive sequences in genome. In present study, the distinct chromosomal structures of five Cucumis species were revealed through genomic in situ hybridization (GISH) technique and comparative cytogenetic mapping of major satellite repeats.ResultsChromosome structures of five Cucumis species were investigated using GISH and comparative mapping of specific satellites. Southern hybridization was employed to study the proliferation of satellites, whose structural characteristics were helpful for analyzing chromosome evolution. Preferential distribution of repetitive DNAs at the subtelomeric regions was found in C. sativus, C hystrix and C. metuliferus, while majority was positioned at the pericentromeric heterochromatin regions in C. melo and C. anguria. Further, comparative GISH (cGISH) through using genomic DNA of other species as probes revealed high homology of repeats between C. sativus and C. hystrix. Specific satellites including 45S rDNA, Type I/II, Type III, Type IV, CentM and telomeric repeat were then comparatively mapped in these species. Type I/II and Type IV produced bright signals at the subtelomeric regions of C. sativus and C. hystrix simultaneously, which might explain the significance of their amplification in the divergence of Cucumis subgenus from the ancient ancestor. Unique positioning of Type III and CentM only at the centromeric domains of C. sativus and C. melo, respectively, combining with unique southern bands, revealed rapid evolutionary patterns of centromeric DNA in Cucumis. Obvious interstitial telomeric repeats were observed in chromosomes 1 and 2 of C. sativus, which might provide evidence of the fusion hypothesis of chromosome evolution from x = 12 to x = 7 in Cucumis species. Besides, the significant correlation was found between gene density along chromosome and GISH band intensity in C. sativus and C. melo.ConclusionsIn summary, comparative cytogenetic mapping of major satellites and GISH revealed the distinct differentiation of chromosome structure during species formation. The evolution of repetitive sequences was the main force for the divergence of Cucumis species from common ancestor.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1877-6) contains supplementary material, which is available to authorized users.
Highlights
Differentiation and copy number of repetitive sequences affect directly chromosome structure which contributes to reproductive isolation and speciation
Five Cucumis species including C. sativus, C. hystrix, C. melo, C. metuliferus and C. anguria which are of Asia or African origin (Fig. 1) were investigated [11]
The signal patterns revealed sGISH at the pericentromeric heterochromatin regions colocalized with those from 45S rDNA and Type III (Additional file 1: Figure S1)
Summary
Differentiation and copy number of repetitive sequences affect directly chromosome structure which contributes to reproductive isolation and speciation. The distinct chromosomal structures of five Cucumis species were revealed through genomic in situ hybridization (GISH) technique and comparative cytogenetic mapping of major satellite repeats. The distribution and copy number of repetitive DNA affect directly the genomic organization and chromosome structure through forming constitutive heterochromatin [2]. Tandem repetitive sequence (or called as satellite repeats) can yield species-specific patterns on chromosomes through fluorescence in situ hybridization (FISH) technology which could be used for karyotyping and phylogenetic analysis [2,3,4,5]. Genomic in situ hybridization (GISH) and comparative cytogenetic analysis provide powerful tools to study chromosome structure through the distribution pattern of characterized and uncharacterized gDNA sequences along chromosomes [2]. The GISH banding pattern correlated with evolutionary distance and has been used to study the evolution of some species [2, 10]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
