Posttranscriptional control of gene expression can be achieved through RNA interference when the activities of Dicer-like (DCL), argonaute (AGO) and RNA-dependent RNA polymerase (RDR) proteins are significant. In this study, we analysed the expression of seven AGO, five DCL and eight RDR genes in cucumber under cold, heat, hormone, salinity and dehydration treatments using quantitative reverse-transcription PCR (qRT-PCR). All CsAGO, CsDCL and CsRDR genes were differentially expressed under abiotic stress treatment. In response to abiotic stress treatment, most genes were expressed at higher levels in flowers or stems than in other organs, whereas some CsAGOs (CsAGO1c, CsAGO6 and CsAGO7) and CsRDRs (CsRDR1d and CsRDR2) were highly expressed in roots during dehydration treatment. The expression patterns indicate that most CsDCLs, CsAGOs and CsRDRs respond to abiotic stress, and stems or flowers are the most sensitive organs, followed by roots. This is the first report of expression analysis of all CsDCL, CsAGO and CsRDR family genes in cucumber under abiotic stress, which provides basic information and insights into the putative roles of these genes in abiotic stress. The results of this study should serve as a basis for further functional characterization of these gene families in cucumber and related Cucurbitaceae species.

Dicer, Argonaute (AGO), and RNA-dependent RNA polymerase (RDR) comprise the core components of RNA-induced silencing complexes, which trigger RNA silencing. Here, we performed a complete analysis of the cucumber Dicer-like, AGO, and RDR gene families including the gene structure, genomic localization, and phylogenetic relationships among family members. We identified seven CsAGO genes, five CsDCL genes, and eight CsRDR genes in cucumber. Based on phylogenetic analysis, each of these genes families was categorized into three or four clades. The orthologs of CsAGOs, CsDCLs, and CsRDRs were identified in apple, peach, wild strawberry, foxtail millet, and maize, and the evolutionary relationships among the orthologous gene pairs were investigated. We also investigated the expression levels of CsAGOs, CsDCLs, and CsRDRs in various cucumber tissues. All CsAGOs were relatively higher upregulated in leaves and tendrils than in other organs, especially CsAGO1c, CsAGO1d, and CsAGO7. All CsDCL genes were relatively higher upregulated in tendrils, with almost no expression detected for CsDCL1, CsDCL4a, or CsDCL4b in other organs. In addition, CsRDR1a, CsRDR2, CsRDR3, and CsRDR6 had relatively higher upregulation in tendrils, whereas almost all CsRDRs were downregulation in other organs. The results of this study will facilitate further studies of gene silencing pathways in cucumber.