Transient Overexpression of the Pepper WRKY2 Gene in Nicotiana benthamiana Markedly Delays the Systemic Necrosis Caused by Tobacco Mosaic Virus

The role of WRKY transcription factor proteins in plant defense reactions against fungal and bacterial pathogens is well studied, but less information is available about plant–virus interactions. We observed the rapid and strong activation of the transcription factor gene, CaWRKY2, in pepper leaves following inoculation with Obuda pepper virus (ObPV). In contrast, CaWRKY2 was only weakly induced by pepper mild mottle virus (PMMoV) inoculation. To carry out a functional analysis of CaWRKY2, the gene was transiently overexpressed in Nicotiana benthamiana leaves by agroinfiltration. Four days later, CaWRKY2-overexpressing and empty vector control leaves were inoculated with tobacco mosaic virus (TMV). Transiently overexpressing CaWRKY2 did not affect the replication rate of TMV in the inoculated leaves. However, TMV inoculation up-regulated the expression of a pathogenesis-related gene (NbPR-1b) and a lipoxygenase (NbLOX1) gene significantly more strongly in N. benthamiana leaves overexpressing CaWRKY2 than in empty vector control leaves. Intriguingly, CaWRKY2 overexpression delayed (by 3 days) the development of systemic necrosis and plant death caused by TMV in N. benthamiana. These results suggest that CaWRKY2 is able to hinder the spread of TMV from inoculated leaves towards vascular tissues and systemic leaves in N. benthamiana.