Characterization of synergy between Cucumber mosaic virus and Tobacco necrosis virus in Nicotiana benthamiana

Mixed infections of Nicotiana benthamiana plants by Cucumber mosaic virus (CMV) and Tobacco necrosis virus (TNV) exhibit a synergistic interaction and result in symptom enhancement. Accumulation of CMV(+) RNA as well as capsid protein (CP) in mixed infection was considerably higher than that of singly-infected plants. There was also a slight increase in TNV(+) RNA and CP levels in doubly infected plants. Synergistic infection by CMV- and TNV-induced higher increase in the levels of malonyldialdehyde, hydrogen peroxide (H2O2) and more decline in the activities of catalase than singly infected ones. Both peroxidase and superoxide dismutase activities increased rapidly for the first 10 days post inoculation (dpi) in doubly-Infected plants and then declined, whereas the enzyme activities continued to increase after 10 dpi in singly infected plants and had higher enzyme activities in the late stages than that of co-infected plants. These results suggest that synergistic infection by CMV and TNV produced severes oxidative stress in N. benthamiana plants and the synergy between the two viruses was mutual.