Enhanced virus infection in Nicotiana benthamiana transiently overexpressing MDP92, encoding a tobacco MYB transcription factor

Transcription factors including MYB proteins are involved in plant resistance to viruses. However, the information on the role and function of MYB proteins during plant virus infection is limited. In this study, we found the trend that the expression of a tobacco MYB gene (MDP92) is temporarily be downregulated in tobacco cultivars with and without the virus resistance gene N during tobacco mosaic virus infection. To test a possible involvement of MDP92 in the regulation of virus infection, we investigated the effect of the transient overexpression of the MDP92 coding sequence alone or in combination with the N genomic sequence on infection with GFP-encoding tomato mosaic virus in Nicotiana benthamiana. Overexpression of MDP92 promoted virus intercellular movement in leaves in the presence of N and enhanced virus accumulation in leaves and protoplasts in the absence of N. Gene expression analysis of four selected resistance-related genes (NbPR1a, NbPR4, NbHin1, and NbHsr203j) showed that compared to control leaves, only NbHsr203j expression was significantly downregulated in MDP92-overexpressing leaves with N, and the expression of NbPR4 and NbHin1 was significantly upregulated in MDP92-overexpressing leaves without N. In contrast, NbPR1a expression was not affected by MDP92 overexpression. Transient overexpression of MDP92 without N also resulted in enhanced accumulation of potato virus X with upregulation of NbPR4 and NbHin1 expression during early virus infection. Based on these results, we discuss the role of the transcription factor MDP92 during virus infection.