Fusarium oxysporum f. Sp. melonis-melon interaction: Effect of grafting combination on pathogen gene expression

This work is part of a comprehensive study addressed to gain new insights into Fusarium oxysporum f. sp. melonis (FOM)-melon interaction and understand molecular mechanisms of disease control by grafting. Grafting vegetable is primarily used to provide resistance to soilborne diseases. In this study, the effect on FOM race 1 and race 1,2 gene expression was investigated by quantitative PCR (qPCR), during infection of both resistant and susceptible grafted melon scion-rootstock combinations. Eleven fungal genes related to pathogenicity were considered. The expression of the selected genes varied according to race, susceptible or resistant interaction, and time clustering into six profiles. Classical infection related genes, including Zn-Cys transcription factor FOW2, xylanase, and its relative transcriptional activator were highly induced particularly in the resistant combination when infected by race 1,2 at any time point. In turn, ROS degrading catalase/peroxidase enzyme and actin binding protein were upregulated only at the early stage of infection, in both resistant and susceptible combinations. Genes such as E3 ubiquitin-protein ligase and UTP-glucose-1-phosphate uridylyl transferase showed significant differences between both FOM races in both grafting combinations. Whereas MADS-box transcription factor and acyl-CoA synthetase were essentially unmodulated in race 1, but induced in race 1,2. The only gene significantly dependent on fungal race, resistant/susceptible interaction, and time, was a histidine kinase. Temporal transcription profiles were consistent with the capacity of race 1,2 to grow in the resistant host without inducing wilting symptoms being race 1,2 host colonization independent from virulence. In general, single FOM gene transcription profiles showed no evident differences between rootstock and scion confirming at a molecular level that a melon grafted plant reacts to the pathogen as a single genotype ruled by the rootstock.