Abstract
Cucumber (Cucumis sativus L.) target leaf spot (TLS), which is caused by the fungus Corynespora cassiicola (C. cassiicola), seriously endangers the production of cucumber. In this assay, we performed comprehensive sequencing of the transcriptome and microRNAs (miRNAs) of a resistant cucumber (Jinyou 38) during C. cassiicola inoculation using the Illumina NextSeq 500 platform. The possible genes related to the response to C. cassiicola were associated with plant hormones, transcription factors, primary metabolism, Ca2+ signaling pathways, secondary metabolism and defense genes. In total, 150 target genes of these differentially expressed miRNAs were predicted by the bioinformatic analysis. By analyzing the function of the target genes, several candidate miRNAs that may be related to the response to C. cassiicola stress were selected. We also predicted 7 novel miRNAs and predicted their target genes. Moreover, the expression patterns of the candidate genes and miRNAs were tested by quantitative real-time RT-PCR. According to the analysis, genes and miRNAs associated with secondary metabolism, particularly the phenylpropanoid biosynthesis pathway, may play a major role in the resistance to C. cassiicola stress in cucumber. These results offer a foundation for future studies exploring the mechanism and key genes of resistance to cucumber TLS.
Highlights
Rate of lignin production in the resistant variety was faster under C. cassiicola stress than that of the susceptible variety
The response time is critical for cucumber resistance to C. cassiicola infection, as the results of reactive oxygen species (ROS) and lignin staining suggested that the resistant variety Jinyou 38 showed a faster response to pathogen stress
At the early stages of infection, we obtained many DEGs from the resistant variety that were involved in the response to C. cassiicola
Summary
Plant growth and C. cassiicola inoculation.The cucumber varieties used in the experiments were Jinyou 38(preliminary experiments showed that this variety was resistant to TLS) and Ludixianfeng (TLS susceptible), which were planted in a greenhouse at 28 °C under 16:8 light/dark cycles. The cucumber varieties used in the experiments were Jinyou 38. (preliminary experiments showed that this variety was resistant to TLS) and Ludixianfeng (TLS susceptible), which were planted in a greenhouse at 28 °C under 16:8 light/dark cycles. C. cassiicola was obtained from the Agricultural Culture Collection of China. The true leaves of 6-week-old plants were sprayed with spore suspensions (2 × 105 sporangia/ml). The inoculated materials were kept at 100% relative humidity to ensure spore germination. The inoculated leaves were harvested at seven time points (i.e., 0, 3, 6, 12, 24, 48 and 72 h post-inoculation), frozen in liquid nitrogen and stored at −80 °C. All experiments were performed in three independent replicates for each time point
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