Transcriptome profiling analysis reveals distinct resistance response of cucumber leaves infected with powdery mildew

Powdery mildew is the main disease affecting cucumber cultivation and causes severe economic loss. So far, research on cucumber resistance to powdery mildew has not yielded feasible solutions. This study selected two inbred cucumber lines, XY09-118 (resistant) and Q10 (susceptible) and investigated their responses to powdery mildew infection (harvested 24 and 48 h after inoculation) using RNA sequencing. More than 20,000 genes were detected in cucumber leaves both with and without powdery mildew infection at the above two time points. Among these, 5478 genes were identified as differently expressed genes (DEGs) between XY09-118 and Q10. Based on the databases GO and KEGG, the functions of DEGs were analysed. Moreover, the complex regulatory network for powdery mildew resistance was assessed, which involves plant hormone signal transduction, phenylpropanoid biosynthesis, plant-pathogen interaction and the MAPK signalling pathway. In particular, genes encoding WRKY, NAC and TCP were highlighted. In addition, genes involved in plant hormone biosynthesis, metabolism and signal transduction, pathogen resistance and abiotic stress response were analysed. Co-expression analysis indicated that the transcription factors correlated with plant hormone signal pathway and metabolism, defence and abiotic response. The expression of several genes was validated by qRT-PCR. The pathogen resistance regulatory network was identified by comparing resistant and susceptible inbred lines infected with powdery mildew. The transcriptome data provide novel insights into cucumber response to powdery mildew infection and the identified pathogen resistance genes will be highly useful for breeding efforts to enhance the resistance of cucumber to powdery mildew.