Figure 4

Evidence for RNA silencing suppression by the SBWMV 19K CRP. (A) nontransgenic N. benthamiana under a UV lamp exhibits red fluorescence due to chlorophyll. (B) GFP-transgenic N. benthamiana (line 16C) exhibits green fluorescence under a UV lamp. (C) GFP was systemically silenced in the 16C transgenic N. benthamiana following infiltration with Agrobacterium. Here in the upper most leaves GFP silencing is vein centric. Systemic GFP silencing is detected initially within 2 weeks. (D) Within 3 weeks, GFP expression is completely silenced in the upper leaves. (E) GFP silenced plant inoculated with PVX.GUS. Emerging tissues of the infected plant remain silenced. (F, G, and H) GFP expression was observed in the emerging tissues of plants that were inoculated with PVX.19K. (I) Northern analyses of total RNAs from nontransgenic tissues (lanes 1, 2) and GFP transgenic tissues (lanes 4 – 7) probed with a labeled GFP sequence probe. Lane 3 is blank. Lanes under the northern blot show ribosomal RNAs on an ethidium bromide stained gel. (J) Northern analysis of total RNAs from 16C plants infiltrated with Agrobacterium containing GFP constructs and probed with a labeled GFP sequence probe. Lanes 1–4 are RNA samples taken from plants that were also inoculated with PVX.19K. Lanes 5–8 are RNA samples taken from plants inoculated with PVX.GUS. Lanes under the northern blot show ribosomal RNAs.