Fig. 4. Nuclear targeting and silencing suppression. Completely silenced (+) N.benthamiana plants were infected with in vitro RNA transcripts (A) or sap derived from transcript-inoculated plants (B). Total RNAs were extracted from the new leaves that had emerged after systemic infection was established at the days post-inoculation indicated above each lane, and analyzed by Northern blotting. The specificities of the ³²P-labeled riboprobes used are indicated next to the panels. Equivalent loading [5 μg for (A) and 4 μg for (B)] of the total plant RNA for each lane was determined by methylene blue staining and densitometry of the 28S rRNA. (–), RNA extracted from an unsilenced GFP transgenic plant.