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Fruit expansion is an essential and very complex biological process. Regulatory roles of microRNAs (miRNAs) and miRNA–mRNA modules in the cucumber fruit expansion are not yet to be investigated. In this work, 1253 known and 1269 novel miRNAs were identified from nine cucumber fruit small RNA (sRNA) libraries through high-throughput sequencing. A total of 105 highly differentially expressed miRNAs were recognized in the fruit on five days post anthesis with pollination (EXP_5d) sRNA library. Further, expression patterns of 11 differentially expressed miRNAs were validated by quantitative real-time PCR (qRT-PCR). The expression patterns were similar to sRNAs sequencing data. Transcripts of 1155 sequences were predicted as target genes of differentially expressed miRNAs by degradome sequencing. Gene Ontology (GO) enrichment showed that these target genes were involved in 24 biological processes, 15 cell components and nine molecular functions. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis demonstrated that these target genes were significantly enriched in 19 pathways and the enriched KEGG pathways were associated with environmental adaptation, signal transduction and translation. Based on the functional prediction of miRNAs and target genes, our findings suggest that miRNAs have a potential regulatory role in cucumber fruit expansion by targeting their target genes, which provide important data for understanding the miRNA-mediated regulatory networks controlling fruit expansion in cucumber. Specific miRNAs could be selected for further functional research and molecular breeding in cucumber.

Cucumber is one of the most important vegetable crops in the world. To establish an efficient genetic transformation system in cucumber, the role of different factors such as pre-cultivation time, acetosyringone concentration, infection time and cocultivation time that can influence the transformation, was evaluated. In addition, Csexpansin 10 (CsEXP10) gene was transformed into the cucumber genome to produce transgenic lines. The results showed that various optimal parameters such as 100 mg L -1 of kanamycin concentration for selection of transformants, 2 d of pre-cultivation time, 100 μmol L -1 of acetosyringone concentration, 15 min of infection time and 2 d of co-cultivation time were obtained using cotyledonary node explants. The rooting frequency observed on Murashige and Skoog (MS) medium supplemented with 0.2 mg L -1 indole acetic acid and 400 mg L -1 cefotaxime was found to be 100.00%. The positive transgenic cucumber lines were identified using PCR analysis and GUS staining assay. It suggests that the genetic transformation system developed using cotyledonary node explants is efficient and successful in cucumber.

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