Powdery mildew (PM) caused by Podosphaera xanthii poses a continuous threat to the performance and yield of the cucumber (Cucumis sativus L.). Control in the initial stages of infection is particularly important. Here, we studied the differential physiological and transcriptomic changes between PM-resistant strain B21-a-2-1-2 and PM-susceptible strain B21-a-2-2-2 at the early stage of P. xanthii attack. When challenged with P. xanthii, the tolerant line can postpone the formation of the pathogen primary germ. Comparative transcriptomic analysis suggested that DEGs related to the cell wall and to pathogen and hormone responses were similar enriched in both cucumber lines under P. xanthii infection. Notably, the number of DEGs triggered by P. xanthii in B21-a-2-1-2 was quintuple that in B21-a-2-2-2, revealing that the success of defense of resistant cucumber is due to rapidly mobilizing multiple responses. The unique responses detected were genes related to SA signaling, MAPK signaling, and Dof and WRKY transcription factors. Furthermore, 5 P. xanthii -inducible hub genes were identified, including GLPK, ILK1, EIN2, BCDHβ1, and RGGA, which are considered to be key candidate genes for disease control. This study combined multiple analytical approaches to capture potential molecular players and will provide key resources for developing cucumber cultivars resistant to pathogen stress.

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Aims: The aim of the paper was to isolate and characterize the promoters of two cucumber TCTP genes (CsTCTP1 and CsTCTP2) and evaluate their active domains. Study Design: CsTCTP1 and CsTCTP2 promoter activity were analyzed under treatments with different exogenous hormones. Place and Duration of Study: In 2017, these experiments were conducted in College of Bioscience and Biotechnology of Shenyang Agricultural University (Lab 240). Methodology: CsTCTPpro::GUS constructs were generated by using double digests method. Transient expression was mediated by Agrobacterium tumefaciens GV3101. Histochemical and Fluorometric GUS Assays were follow by the biochemical method. Results: Bioinformatics analysis revealed some hormone- and defense-related response elements. Histochemical and fluorometric GUS assays demonstrated that the 0.7-kb CsTCTP1 promoter (proT1-0.7kb) and 0.7-kb and 1.3-kb CsTCTP2 promoters (proT2-0.7kb and proT2-1.3kb) had strong transcriptional activity. In addition, we used exogenous hormones (abscisic acid [ABA], salicylic acid [SA], and ethylene [ETH]) for treatment. The results showed that proT1-0.7kb and proT2-1.3kb activity were upregulated in the ABA treatment group, suggesting that these promoter sequences may contain ABA-related response elements. However, in the SA and ETH treatment groups, the activity of all the promoter fragments of CsTCTP1 and CsTCTP2 declined to different degrees, suggesting that SA and ETH may have negative regulatory effects on CsTCTP1 and CsTCTP2 promoters. Conclusion: Taken together, these results suggest that the proT1-0.7kb promoter of CsTCTP1 and proT2-1.3kb promoter of CsTCTP2 may contain ABA-related response elements, and SA and ETH may have negative regulatory effects on the CsTCTP1 and CsTCTP2 promoters. This study will help to further understand the expression patterns and the regulatory mechanism of gene transcriptional regulation.