Potyvirus-induced gene silencing: the dynamic process of systemic silencing and silencing suppression.

Potato virus A (PVA; genus Potyvirus) was used for virus-induced gene silencing in a model system that included transgenic Nicotiana benthamiana (line 16c) expressing the gfp transgene for green fluorescent protein (GFP) and chimeric PVA (PVA-GFP) carrying gfp in the P1-encoding region. Infection of the 16c plants with PVA-GFP in five experiments resulted in a reproducible pattern of systemic gfp transgene silencing, despite the presence of the strong silencing-suppressor protein, HC-Pro, produced by the virus. PVA-GFP was also targeted by silencing, and virus-specific short interfering RNA accumulated from the length of the viral genome.

In vitro recombinants of two nearly identical potyviral isolates express novel virulence and symptom phenotypes in plants.

Six novel chimeric viruses were constructed by sequentially exchanging segments of the viral genomes between the infectious cDNA clone (pPVA-B11) of Potato virus A (isolate PVA-B11) and pUFL, an almost identical infectious cDNA of PVA (isolate U) made in this study. The infectious in vitro transcripts of pUFL and pPVA-B11 caused similar severe mosaic and leaf malformation phenotypes in systemically infected leaves of Nicotiana benthamiana. In contrast, one chimera induced a unique phenotype of yellow vein chlorosis without leaf malformation with viral titres that were equivalent to those of the parental viruses.