Genetic variation is expressed by the presence of polymorphisms in compared genomes of individuals that can be transferred to next generations. The aim of this work was to reveal genome dynamics by predicting polymorphisms among the genomes of three individuals of the highly inbred B10 cucumber (Cucumis sativus L.) line. In this study, bioinformatic comparative genomics was used to uncover cucumber genome dynamics (also called real-time evolution). We obtained a new genome draft assembly from long single molecule real-time (SMRT) sequencing reads and used short paired-end read data from three individuals to analyse the polymorphisms. Using this approach, we uncovered differentiation aspects in the genomes of the inbred B10 line. The newly assembled genome sequence (B10v3) has the highest contiguity and quality characteristics among the currently available cucumber genome draft sequences. Standard and newly designed approaches were used to predict single nucleotide and structural variants that were unique among the three individual genomes. Some of the variant predictions spanned protein-coding genes and their promoters, and some were in the neighbourhood of annotated interspersed repetitive elements, indicating that the highly inbred homozygous plants remained genetically dynamic. This is the first bioinformatic comparative genomics study of a single highly inbred plant line. For this project, we developed a polymorphism prediction method with optimized precision parameters, which allowed the effective detection of small nucleotide variants (SNVs). This methodology could significantly improve bioinformatic pipelines for comparative genomics and thus has great practical potential in genomic metadata handling.

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Key message Transcriptome data and qPCR analysis revealed new insight into genes regulatory mechanism related to cucumber sex determination. Abstract Cucumber ( Cucumis sativus L.) is an economically important crop cultivated worldwide. Enhancing the genomic resources for cucumber may enable the regulation of traits relevant to crop productivity and quality. Sequencing technologies and bioinformatics tools provide opportunities for the development of such resources. The aims of this study were to identify and characterize the genes involved in sex determination and flower morphogenesis in cucumber isogenic lines that differed regarding flower sex type. We obtained transcripts for 933 genes related to shoot apex development, among which 310 were differentially expressed genes (DEGs) among the male, female, and hermaphroditic lines. We performed gene ontology and molecular network analyses and explored the DEGs related to already known processes like: hormone synthesis and signaling, lipid and sugar metabolism; and also newly discovered processes related to cell wall, membrane, and cytoskeleton modifications; ion homeostasis which appears to be important for ethylene perception and signaling, and genes expression mediated by transcription factors related to floral organ identities. We proposed a new model of regulatory mechanism network of sex development in cucumber. Our results may be useful for clarifying the molecular genetics and the functional mechanisms underlying the sex determination processes. Electronic supplementary material The online version of this article (10.1007/s00497-019-00362-z) contains supplementary material, which is available to authorized users.

Somaclonal variation during in vitro culture is often an undesirable phenomenon but may also be a source of genetic variation useful for breeders. The molecular mechanisms underlying this phenomenon remain uncertain. In this study, we analyzed the fruit transcriptome of three independent cucumber lines using RNA-sequencing technology and performed an extensive in silico study to determine how somaclonal variation altered gene expression. Comparison of the transcriptome profiles with the wild-type cucumber ‘Borszczagowski B10’ revealed 418, 364, and 273 genes that were differentially regulated. We performed bioinformatic functional analysis, gene ontology classification, molecular network analysis, and explored differentially expressed genes associated with processes such as protein and nucleic acid binding, enzyme activity, signaling, transport, sugar and lipid metabolism. We determined that the differential gene expression may be caused by polymorphism in the genic region and may also be a result of interaction among molecular networks, which triggers specific pathways.

Transgenic plants are commonly used in breeding programs because of the various features that can be introduced. However, unintended effects caused by genetic transformation are still a topic of concern. This makes research on the nutritional safety of transgenic crop plants extremely interesting. Cucumber (Cucumis sativus L.) is a crop that is grown worldwide. The aim of this study was to identify and characterize differentially expressed genes and regulatory miRNAs in transgenic cucumber fruits that contain the thaumatin II gene, which encodes the sweet-tasting protein thaumatin II, by NGS sequencing. We compared the fruit transcriptomes and miRNomes of three transgenic cucumber lines with wild-type cucumber. In total, we found 47 differentially expressed genes between control and all three transgenic lines. We performed the bioinformatic functional analysis and gene ontology classification. We also identified 12 differentially regulated miRNAs, from which three can influence the two targets (assigned as DEGs) in one of the studied transgenic lines (line 224). We found that the transformation of cucumber with thaumatin II and expression of the transgene had minimal impact on gene expression and epigenetic regulation by miRNA, in the cucumber fruits.

Snake melon (Cucumis melo subsp. melo L. var. flexuosus (L.) Naudin) is an ancient and traditional crop in the Mediterranean region. Nevertheless, there has been poor interest in assessing snake melon germplasm where its genetic resources have not been surveyed before despite their potential in adaptation to environmental changes. In this study, we assess the genetic diversity of snake melon landraces collected from different Lebanese regions at both morphological and molecular levels. Morphological characterization using a set of 18 descriptors revealed an important phenotypic variability among the landraces studied. Principle component analysis indicated that fruit hair and its consistency, fruit size, and skin color pattern were good criteria for discriminating among landraces. Based on the scatter plot diagram, landraces of snake melon formed five different groups with one being defined as typical var. flexuosus. Ten simple sequence repeat (SSR) markers were used for the molecular characterization. Fifty-six different alleles were detected, with an average of 5.6 alleles per locus. Polymorphism information content of SSR markers ranged from 0.06 to 0.84 (average 0.38). Cluster analysis based on molecular markers showed high genetic diversity and divided the landraces into five distinct genetic groups, confirming thereby the morphological variability. Findings of this study indicate a significant diversity for the Lebanese snake melon germplasm that must be further conserved and considered in improvement programs of this ancient crop.