Background The cytogenomic study of repetitive regions is fundamental for the understanding of morphofunctional mechanisms and genome evolution. Passiflora edulis a species of relevant agronomic value, this work had its genome sequenced by next generation sequencing and bioinformatics analysis performed by RepeatExplorer pipeline. The clusters allowed the identification and characterization of repetitive elements (predominant contributors to most plant genomes). The aim of this study was to identify, characterize and map the repetitive DNA of P. edulis , providing important cytogenomic markers, especially sequences associated with the centromere. Results Three clusters of satellite DNAs (69, 118 and 207) and seven clusters of Long Terminal Repeat (LTR) retrotransposons of the superfamilies Ty1/Copy and Ty3/Gypsy and families Angela, Athila, Chromovirus and Maximus-Sire (6, 11, 36, 43, 86, 94 and 135) were characterized and analyzed. The chromosome mapping of satellite DNAs showed two hybridization sites co-located in the 5S rDNA region (PeSat_1), subterminal hybridizations (PeSat_3) and hybridization in four sites, co-located in the 45S rDNA region (PeSat_2). Most of the retroelements hybridizations showed signals scattered in the chromosomes, diverging in abundance, and only the cluster 6 presented pericentromeric regions marking. No satellite DNAs and retroelement associated with centromere was observed. Conclusion P. edulis has a highly repetitive genome, with the predominance of Ty3/Gypsy LTR retrotransposon. The satellite DNAs and LTR retrotransposon characterized are promising markers for investigation of the evolutionary patterns and genetic distinction of species and hybrids of Passiflora .

BackgroundA great interest exists in the production of hybrid plants of the genus Passiflora given the beauty and exotic features of its flowers which have ornamental value. Hybrid paternity confirmation is therefore important for assuring germplasm origin, and is typically carried out by molecular marker segregation. The aim of this study was to karyotypically characterize the chromosome heritance patterns of the progeny resultant from a cross of P. gardneri and P. gibertii using classical cytogenetics, chromosome banding, and molecular cytogenetics.ResultsAll analyzed genotypes showed the same diploid chromosome number as the genitor species: 2n = 18. Classical and CMA3 and DAPI staining allowed for chromosome counting and satellite identification (secondary constrictions). Fluorescence in situ hybridization (FISH) and genomic in situ hybridization (GISH) were used to characterize subgenomes by either identifying rDNA-specific genome patterns or parental genomes, respectively.ConclusionsThe heritance of chromosomal markers presenting rDNA sites from each parent for genome identification confirmed that all obtained plants were hybrids. These results will improve breeding programs involving the species of this genus. Apart from confirming hybridization, GISH allowed the visualization of recombination between the homeologous chromosome and the introgression of sequences of interest.Electronic supplementary materialThe online version of this article (10.1186/s12863-018-0612-0) contains supplementary material, which is available to authorized users.

Passiflora edulis f. flavicarpa is the most economically important species in the genus Passiflora. However, the origin of this yellow form of passion fruit remains unclear, being suggested as a hybrid (P. edulis f. edulis × P. ligularis) or wild mutant. Here, the origin and genomic relationships of P. edulis f. flavicarpa with some related species in the genus Passiflora (subgenera Decaloba and Passiflora) were investigated using genomic in situ hybridization (GISH). Genomic DNA of 18 species was used as probe, which was hybridized onto chromosomes of P. edulis f. flavicarpa. Of all genomic DNA probes tested, none allowed us to identify a specific chromosome set in P. edulis f. flavicarpa. Conversely, probes from the subgenus Passiflora, P. edulis f. edulis, P. alata, P. cincinnata, P. coccinea, P. nitida and P. vitifolia, produced intense and uniform hybridizations on all chromosomes of P. edulis f. flavicarpa. Moreover, probes from P. ligularis, P. foetida and P. sublanceolata produced more intense hybridizations in the terminal region of four chromosomes, corresponding to the DNAr 45S locus, and also dispersed, less intense, hybridization across all chromosomes. Probes from the subgenus Decaloba, P. biflora, P. capsularis, P. cervii, P. coriacea, P. micropetala, P. morifolia, P. rubra and P. suberosa, produced hybridizations restricted to the DNAr 45S sites. The hybrid origin of P. edulis f. flavicarpa could not be supported based on the GISH results, and it is suggested that this species is conspecific with P. edulis f. edulis, because the probe with DNA of this form hybridized strongly throughout the target genome. The other putative parent species, P. ligularis, showed only a distant relationship with the target genome. The results also suggest that species of the subgenus Passiflora share many repetitive sequences and that the relationship between subgenera Decaloba and Passiflora is very distant.

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Cucumis melo (melon) is a species from the Iberian Peninsula and is included in the family Cucurbitaceae. Despite the knowledge about the physical structure of melon chromosomes, little is known about the intraspecific karyotype diversity of the species. To study karyotype diversity in eight melon accessions, the following methods were used: Giemsa 3% staining; application of CMA3/DAPI fluorochromes; and location of 45S and 5S rDNA sequences by fluorescence in situ hybridization. Conventional staining analysis revealed stability in the chromosome number, with accessions presenting 2n = 24. There were significant variations in the mean chromosome size between accessions, ranging from 0.98 μm to 1.46 μm for accessions A26 and A18, respectively. Scott-Knott clustering distributed the accessions into two groups. GC-rich heterochromatic blocks (CMA3 + /DAPI-) were observed in pericentromeric regions of all chromosomes in the complement. CMA3 + /DAPIblocks were also located in terminal regions, being specific to satellite regions. Hybridization sites of 45S rDNA probes revealed the presence of a chromosome pair with this locus. In addition, 5S rDNA sites revealed a labeled chromosome pair. No quantitative variation was observed in rDNA sites between the accessions analyzed, indicating these markers as ideal for the verification of karyotypic stability in C. melo.