DIFFERENCES AND SIMILARITIES IN TOMATO DEFENSE RESPONSE TO NECROGENIC AND NON-NECROGENIC STRAINS OF CUCUMBER MOSAIC VIRUS

An early plant response to pathogen infection is an oxidative burst characterized by the production of reactive oxygen species (ROS) such as hydrogen peroxide. The increase of these ROS has been found in plant tissues in response to infection of various pathogens, including viruses, and enzymatic and not-enzymatic antioxidant systems are activated by the host in order to prevent potential cell damages. The analysis of some enzymatic defence components such as superoxide dismutases, catalases, total peroxidases and ascorbate peroxidases allowed to evaluate their contribution to the tomato defense response to infections of different Cucumber mosaic virus (CMV) strains. In particular, these enzymes were examined in tomato (Solanum lycopersicum) cv. UC82 plants inoculated with the aggressive strain CMV-Fny and with the same strain co-inoculated with a necrogenic variant of satellite RNA (CMV-Fny/77-satRNA), a combination inducing systemic necrosis and plant death. Analyses included both the transcriptional activation and the enzymatic activity of such antioxidant components. Additionally, gene expression analysis was performed on genes involved in ethylene biosynthesis and signaling, in general defense responses and in programmed cell death processes. The results obtained demonstrated that some scavengers of ROS and other defense responses were commonly activated by the two viral strains despite the different disease phenotype induced. Peculiar responses to either specific CMV inoculum were also evidenced, and their possible roles in the determination of the disease phenotypes are discussed.