Figure 4.

Severe symptoms and suppression of PTGS caused by PVX expressing the RYMV P1 protein. (A) UV illumination of a GFP-silenced N. benthamiana infected with PVX-mP1 at 14 DPI. (B) UV illumination of a GFP-silenced N. benthamiana infected with PVX-P1 at 14 DPI. Reversion of silencing occurs in both new emerging tissues and old leaves (indicated by an arrow). (C) Mild mosaic symptoms caused by PVX-mP1 at 14 DPI. (D) Severe necrotic symptoms caused by PVX-P1 at 14 DPI. (E) Northern blot analysis of RNA extracted at 14 DPI from either mock-infected, nonsilenced (NS), or silenced (S) N. benthamiana infected with PVX-P1 or PVX-mP1. RNA samples were taken from either old leaves (OL) or new emerging leaves (NL). Equal amounts of each RNA sample (10 μg) were assayed by RNA gel blotting by using a ³²P-labeled GFP cDNA as probe. Ethidium bromide staining of ribosomal RNA (rRNA) shows equal loading of the samples.