Analysis of Differentially Expressed Genes in Cucumber Interspecific Introgression Line with Resistance to Downy Mildew

Downy mildew (DM), caused by Pseudoperonospora cubensis (Berk. et Curt.) Rostov. is currently the most important disease of cucumbers worldwide. The polygenic nature of genes conferring resistance to this pathogen, coupled with the development of new virulent races has made this pathogen difficult to control. An introgression line, IL-52, derived from the progenies of an interspecific hybridization between wild sour cucumber, C. hystrix, and cultivated cucumber ‘Beijingjietou’, was identified with high resistance to P. cubensis. By using a cucumber microarray containing 26,146 gene probe sets, gene expression in the leaves of IL-52 and susceptible ‘Changchunmici’ were evaluated at early stage with hourly intervals of 0 h, 12 h, 24 h, 48 h after inoculation. Results from co-expression analysis and gene-ontology analysis showed that the key regulatory factors with dynamic changes in IL-52 were involved in many functional categories, i.e., synthesis of pathogenesis-related (PR) proteins, cellular membrane reinforcement, and response processes to abiotic/biotic stimulus and stress. DEGs associated with ethylene (ET) and salicylic acid (SA) acted coordinately and were presumed to play an important role in IL-52, while jasmonic acid (JA) signaling pathways showed a weak down-regulated response. In conclusion, this study brings us more knowledge on early stage interactions between P. cubensis and the introgression line IL-52.