Patterns and barriers of cell-to-cell movement and lack of systemic spread of tobacco etch potyvirus (TEV-GUS) in Solanum brevidens

Abstract

Movement of tobacco etch potyvirus (TEV) was monitored in the resistant wild potato species Solanum brevidens and susceptible tobacco ( Nicotiana tabacum cv. Samsun) using an engineered TEV (TEV-GUS) expressing the β-glucuronidase reporter gene (GUS). In mechanically inoculated leaves of S. brevidens and tobacco, single infected cells were observed on the basis of GUS expression at 2.5 h and 5 h after inoculation, respectively. Lesions up to 4–6 and 20 epidermal cells in diameter were observed in tobacco and S. brevidens, respectively, at 7 h after inoculation. At 24 h after inoculation, lesions in S. brevidens fused and could not be distinguished. Most epidermal cells, but few mesophyll cells, were infected in mechanically inoculated leaves of S. brevidens at 3 days after inoculation. In tobacco, cell-to-cell movement occurred concurrently from the initially infected epidermal cells to the neighbouring epidermal and mesophyll cells. TEV-GUS neither was transported systemically from mechanically inoculated leaves of S. brevidens nor established infection in graft-inoculated S. brevidens. These data indicated that resistance to TEV-GUS in S. brevidens is associated with restricted cell-to-cell movement in mesophyll tissue and lack of systemic spread. It is also suggested that the cell-to-cell movement of TEV-GUS between epidermal cells, between mesophyll cells, and possibly between epidermal and mesophyll cells have different requirements in S. brevidens.