Cell-to-cell movement of potato virus X revealed by micro-injection of a viral vector tagged with the β-glucuronidase gene

The replication and cell-to-cell movement of potato virus X (PVX) has been studied using a PVX vector construct which expressed the β-glucuronidase (GUS) reporter gene in infected cells. Nicotiana clevelandii leaf trichome cells were micro-injected with the PVX-GUS vector and histochemical staining was used to locate GUS activity. The distribution of GUS activity revealed that PVX had moved from the injected cell into other trichome cells and into the cells along the leaf margin. GUS activity was always restricted to the cells at the edge of the leaf suggesting that PVX was unable to move out of the marginal cells. At the infection front, scattered along the leaf margin, there were isolated groups of cells staining for GUS activity. The absence of GUS activity in the intervening cells suggests that PVX had moved through several cells without replicating within them. This latter observation is consistent with previously reported observations that viral movement proteins are capable of moving between cells.