Molecular analysis of the interaction between Olea europaea and the biotrophic fungus Spilocaea oleagina

The mitosporic fungus Spilocaea oleagina is an obligate biotroph of olive (Olea europaea) causing a scab disease associated with leaf fall and substantial losses in production. Using differential display we have identified 162 cDNA fragments corresponding to transcripts that show altered abundance during the defence response of a resistant olive cultivar to S. oleagina. Detailed analyses of 21 selected genes by real-time quantitative RT-PCR revealed different kinetics of induction. Genes involved in signalling, transcriptional control, oxidative stress, biotic and abiotic stress, and several genes with unknown function were found to be induced rapidly after infection. In contrast, genes involved in metabolism and cellular maintenance showed delayed induction. The induction of the selected genes in a susceptible cultivar was delayed and/or reduced during the response to S. oleagina. Interestingly, the basal expression of some genes in the uninfected resistant cultivar was higher than in the susceptible one, suggesting a constitutive activation of defence responses. Expression of these genes in response to salicylic acid, methyl jasmonate, a mixture of both, ethephon, hydrogen peroxide, menadione and wounding was also investigated. The results are discussed in relation to the molecular bases and signalling events involved in this biotrophic interaction.