Comparative transcriptomics of cucumber cultivars reveals defense mechanisms against Pseudoperonospora cubensis infection
Cucumber downy mildew, caused by Pseudoperonospora cubensis, severely reduces cucumber yield across the world. Chemical fungicides are commonly used for disease control, yet they raise risks of pathogen resistance and environmental harm. Mining host resistance genes offers a sustainable strategy to combat this disease.This study performed comparative transcriptome sequencing on a downy mildew resistant cucumber cultivar '115' and a susceptible cultivar 'XTMC' at 48 h and 72 h after Pseudoperonospora cubensis inoculation. In total, 6667 differentially expressed genes (DEGs) were detected in resistant '115', and 6601 DEGs were found in susceptible 'XTMC'. KEGG enrichment analysis showed major DEGs were enriched in plant-pathogen interaction and plant hormone signal transduction pathways. qRT-PCR validated the expression patterns of candidate defense related genes. Among these candidates, the jasmonate-zim-domain gene CsJAZ8 was down-regulated in resistant '115' after pathogen infection. Transgenic experiments further demonstrated that over-expression of CsJAZ8 increases cucumber susceptibility to downy mildew, indicating CsJAZ8 acts as a negative regulator of disease resistance.This work characterizes transcriptomic differences between resistant and susceptible cucumber materials under downy mildew stress and identifies CsJAZ8 as an important susceptibility associated gene. These results provide candidate genetic resources for dissecting molecular mechanisms of cucumber downy mildew resistance and support molecular assisted breeding for disease resistant cucumber varieties.