S-methylmethionine contributes to enhanced defense against Maize dwarf mosaic virus infection in maize

The beneficial and protective effects of S-methylmethionine (SMM) were investigated in Maize dwarf mosaic virus (MDMV) infected maize (Zea mays L.). Response reactions and alterations in the physiological state of the plants were monitored by following changes in the values of chlorophyll a fluorescence and chlorophyll content, and differences in the expression patterns of the stress-related genes S-adenosylmethionine synthase (SAMS) and the 14-3-3-like protein gene G-box factor 14-6 (GF14-6). Infection was validated using the ELISA technique. A pronounced decrease in the red to far-red chlorophyll a fluorescence ratio, indicative of chlorophyll content, was observed in infected plants, which was tempered by SMM pretreatment. A noticeable decrease in the photochemical quenching of photosystem II and the thermal dissipation of the antennae was observed, together with a notable increase in other non-photochemical energy dissipation parameters in response to MDMV infection. SMM treatment enhanced blue fluorescence in both uninfected and MDMV-infected plants (probably due to the production of protective phenolic compounds), while infection characteristically increased green fluorescence emission. SMM treatment was found to elevate the rate of gene expressions of SAMS and GF14-6. The results suggest that SMM pretreatment enhances the stress response reactions that protect maize plants against MDMV infection.