siRNA accumulation in 10.6.1 amplicon plants. A: Schematic representation of the two kind of 10.6.1 plants. Green and red patterns indicate expression and lack of expression of GFP, respectively. B: RNA was extracted from the leaf samples indicated in panel A, and subjected to Northern analysis with probes corresponding to the PPV NIb and P1 coding sequences. RNA samples from a 10.1.7 transgenic plant, expressing the PPV-NK-GFP amplicon from germination, and from wild type N. benthamiana plants manually infected with PPV-NK-GFP (PPV-GFP) or non-infected (NI-wt) were used as controls. The upper panel shows tRNAs and 5S RNAs stained with ethidium bromide.