Comparative transcriptome profiling of genes and pathways related to resistance against powdery mildew in two contrasting melon genotypes

Powdery mildew (PM) is a catastrophic disease of melon caused by Podosphaera xanthii (Px). However, there is limited information available at the molecular level regarding how the melon plant develops defense mechanisms against this pathogen. We studied melon mRNA transcripts from the resistant MR-1 and susceptible Topmark cultivars through comparative transcriptome analysis. Leaves inoculated with spores of P. xanthii were collected from 0 to 168 hpi to identify the candidate regulators for resistance to PM at different infection stages. We identified 1888 and 2842 melon genes in MR-1 and Topmark, respectively, that were differentially expressed during the plant-pathogen interaction. Gene function analysis of these differentially expressed genes (DEGs) classified them into seven functional groups: pathogen recognition, signal transduction, transcription factors (TFs), phytoalexin biosynthesis, other primary metabolite functions, Mildew Locus O genes (MLOs) and pathogenesis-related (PR) proteins. The expression of ten of these genes in both the MR-1 and Topmark cultivars was validated via qRT-PCR. Our results revealed both similar and differential patterns of gene expression between the two cultivars. This study may provide a new understanding of the molecular mechanisms of melon resistance to PM.