Chromosomal structures and repetitive sequences divergence in Cucumis species revealed by comparative cytogenetic mapping

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.

Divergence between<b><i> C. melo</i></b> and African <b><i>Cucumis</i></b> Species Identified by Chromosome Painting and rDNA Distribution Pattern

“…To date, the distribution of 5S and 45S rDNA loci has only been reported in C. sativus and C. melo of the genus Cucumis [Han et al, 2008;Liu et al, 2010]. The distribution of 45S rDNA loci has also been analyzed in C. hystrix, C. anguria , and C. metuliferus [Yang et al, 2014;Zhang et al, 2015]. Yang et al [2014] mapped the 45S rDNA loci to chromosomes 8, 10, and 12 of C. hystrix based on the syntenic relationships between chromosomes of cucumber, C. hystrix, and melon inferred from comparative genetic and physical mapping and whole genome alignment studies.…”

“…Yang et al [2014] mapped the 45S rDNA loci to chromosomes 8, 10, and 12 of C. hystrix based on the syntenic relationships between chromosomes of cucumber, C. hystrix, and melon inferred from comparative genetic and physical mapping and whole genome alignment studies. However, Zhang et al [2015] mapped the 45S rDNA loci to chromosomes 3, 4, and 8 of C. hystrix , chromosomes 4 and 10 of C. metuliferus , and chromosomes 1 and 2 of C. anguria based on chromosome sizes in the karyotype. The homeologous relationships of chromosomes with rDNA loci among different Cucumis species were unknown in the study of .…”

Genome composition and pollen viability of Jatropha (Euphorbiaceae) interspecific hybrids by Genomic In Situ Hybridization (GISH)

“…However, no terminal heterochromatic dots were found for J. integerrima or J. multifida chromosomes (Marinho et al, 2018), as was corroborated by the absence of dot sites by GISH for chromosomes of both species in F 1 hybrids in the present work and by Fukuhara et al (2016) for J. curcas x J. integerrima hybrids. Previous work with GISH on species with small chromosomes also showed preferential in situ hybridization in regions rich in repetitive DNA, as observed in Arachis (Seijo et al, 2007) and Cucumis (Zhang et al, 2015).…”

Karyomorphological Study of Taraxacum in Northeast China

“…The basic trend in karyotype evolution in higher plants is from a symmetrical to asymmetrical karyotype. Plants that are relatively old or evolutionarily primitive often harbor relatively symmetrical karyotypes, whereas asymmetrical karyotypes usually appear in more evolved or specialized plants [28]. The karyotypes of the 18 dandelion species were asymmetric, with the asymmetry coe cients approximately in the range of 60%-70%, i.e., they belonged to relatively evolved species.…”