Pokeweed antiviral protein (PAP) increases plant systemic resistance to Tobacco mosaic virus infection in Nicotiana benthamiana

Abstract

Pokeweed antiviral protein (PAP) isoforms are members of the type I ribosome inactivating proteins (RIPs) that are isolated from the extracts of pokeweed plant leaves (Phytolacca americana) and show many biological activities. However, the antiviral potential of the PAP in plants and its potential role in plant systemic resistance has been rarely reported. Therefore, in this report, we investigated the role of PAP in plant systemic resistance response against virus infection in Nicotiana benthamiana. N. benthamiana plants pre-treated with 0.1 mg/mL PAP three days before inoculation with green fluorescent protein (GFP)-tagged tobacco mosaic virus (TMV) showed less symptoms and less reactive oxygen species (ROS) accumulation compared to PBS-treated plants inoculated with TMV-GFP. Exogenous application of PAP yielded a significant reduction in GFP fluorescence in non-inoculated upper leaves. Furthermore, quantitative real-time PCR analysis revealed that the accumulation levels of TMV were significantly reduced in the systemic leaves of PAP-treated N. benthamiana plants compared with the levels observed in PBS-treated plants. In addition, some antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) were activated after PAP treatment. Taken together, our results suggest that exogenous application of PAP enhances N. benthamiana systemic resistance to TMV infection by regulating ROS levels. Furthermore, we concluded that PAP might be acting as a strong antioxidant that does not allow the induction/accumulation of harmful ROS on virus infection.