Project description:Virus resistances that are recessively inherited are associated with loss-of-susceptibility resistance alleles. Resistance to Watermelon mosaic virus (WMV) of melon accession TGR-1551 is expressed as a drastic reduction of the virus titer, and is recessively inherited. In this work, viral RNA accumulation was measured in TGR-1551 and in susceptible WMV-infected melon plants by real time quantitative PCR (qPCR), and gene expression of 17,443 unigenes represented in a melon microarray was monitored in a time-course experiment. Virus accumulation was higher in inoculated cotyledons of the resistant genotype up to 7 days post-inoculation; from this time on, virus accumulation was much higher in plants of the susceptible genotype. Microarray experiments were carried with samples from inoculated cotyledons at 1 and 3 dpi to monitor early changes in response to virus infection, and at 7 dpi. Samples from systemically infected leaves harvested at 15 dpi were also included in the analysis. Results showed much more profound transcriptomic alterations in resistant plants compared to susceptible ones. Analyses of gene expression profiles reveal deep and extensive transcriptomic alterations in TGR-1551 plants, many of them involving pathogen response-related genes. Overall, data suggested that resistance to WMV in TGR-1551 is associated with a defense response, contrasting with its recessive nature. Two melon genotypes have been used to analyse transcriptomic responses to infection by Watermelon mosaic virus: Tendral (susceptibel to WMV) and TGR-1551 (resistant to WMV). For each genotype, 60 melon seedlings were inoculated with WMV-M116 and another 60 were mock-inoculated. Cotyledons of 10 plants were harvested at 1, 3, 5, 7, 9 and 15 dpi. At 15 dpi, the systemically infected second true leaf was also harvested. To reduce variability, each biological replicate used in this study was prepared by mixing the RNA extracts from 2 or 4 mock or WMV-inoculated cotyledons, respectively, or from 3 melon leaves. Samples (WMV infected and mock inoculated) corresponding to cotyledons at 1, 3 and 7 dpi, and leaves at 15 dpi were used for microarray hybridisations, three biological replicates for each one, leading to a total of 48 samples.