Cucumber, Cucumis sativus L., is an economically important vegetable crop which is processed or consumed fresh worldwide. However, the narrow genetic base in cucumber makes it difficult for constructing high-density genetic maps. The development of massively parallel genotyping methods and next-generation sequencing (NGS) technologies provides an excellent opportunity for developing single nucleotide polymorphisms (SNPs) for linkage map construction and QTL analysis of horticultural traits. Specific-length amplified fragment sequencing (SLAF-seq) is a recent marker development technology that allows large-scale SNP discovery and genotyping at a reasonable cost. In this study, we constructed a high-density SNP map for cucumber using SLAF-seq and detected fruit-related QTLs.

Background: Plant nucleotide-binding site (NBS)-leucine-rich repeat (LRR) proteins encoded by resistance genes play an important role in the responses of plants to various pathogens, including viruses, bacteria, fungi, and nematodes. In this study, a comprehensive analysis of NBS-encoding genes within the whole cucumber genome was performed, and the phylogenetic relationships of NBS-encoding resistance gene homologues (RGHs) belonging to six species in five genera of Cucurbitaceae crops were compared. Results: Cucumber has relatively few NBS-encoding genes. Nevertheless, cucumber maintains genes belonging to both Toll/interleukine-1 receptor (TIR) and CC (coiled-coil) families. Eight commonly conserved motifs have been established in these two families which support the grouping into TIR and CC families. Moreover, three additional conserved motifs, namely, CNBS-1, CNBS-2 and TNBS-1, have been identified in sequences from CC and TIR families. Analyses of exon/intron configurations revealed that some intron loss or gain events occurred during the structural evolution between the two families. Phylogenetic analyses revealed that gene duplication, sequence divergence, and gene loss were proposed as the major modes of evolution of NBS-encoding genes in Cucurbitaceae species. Compared with NBS-encoding sequences from the Arabidopsis thaliana genome, the remaining seven TIR familes of NBS proteins and RGHs from Cucurbitaceae species have been shown to be phylogenetically distinct from the TIR family of NBS-encoding genes in Arabidopsis, except for two subfamilies (TIR4 and TIR9). On the other hand, in the CC-NBS family, they grouped closely with the CC family of NBS-encoding genes in Arabidopsis. Thus, the NBS-encoding genes in Cucurbitaceae crops are shown to be ancient, and NBS-encoding gene expansions (especially the TIR family) may have occurred before the divergence of Cucurbitaceae and Arabidopsis. Conclusion: The results of this paper will provide a genomic framework for the further isolation of candidate disease resistance NBS-encoding genes in cucumber, and contribute to the understanding of the evolutionary mode of NBS-encoding genes in Cucurbitaceae crops.

Parthenocarpy is an important trait determining yield and quality of fruit crops. However, the understanding of the mechanisms underlying parthenocarpy induction is limited. Cucumber (Cucumis sativus L.) is abundant in parthenocarpic germplasm resources and is an excellent model organism for parthenocarpy studies. In this study, the transcriptome of cucumber fruits was studied using RNA sequencing (RNA-Seq). Differentially expressed genes (DEGs) of set fruits were compared against aborted fruits. Distinctive features of parthenocarpic and pollinated fruits were revealed by combining the analysis of the transcriptome together with cytomorphological and physiological analysis. Cell division and the transcription of cell division genes were found to be more active in parthenocarpic fruit. The study also indicated that parthenocarpic fruit set is a high sugar-consuming process which is achieved via enhanced carbohydrate degradation through transcription of genes that lead to the breakdown of carbohydrates. Furthermore, the evidence provided by this work supports a hypothesis that parthenocarpic fruit set is induced by mimicking the processes of pollination/fertilization at the transcriptional level, i.e. by performing the same transcriptional patterns of genes inducing pollination and gametophyte development as in pollinated fruit. Based on the RNA-Seq and ovary transient expression results, 14 genes were predicted as putative parthenocarpic genes. The transcription analysis of these candidate genes revealed auxin, cytokinin and gibberellin cross-talk at the transcriptional level during parthenocarpic fruit set.