Escape of a plant virus from amplicon-mediated RNA silencing is associated with biotic or abiotic stress.

Strong RNA silencing was induced in plants transformed with an amplicon consisting of full-length cDNA of potato leafroll virus (PLRV) expressing green fluorescent protein (GFP), as shown by low levels of PLRV-GFP accumulation, lack of symptoms and accumulation of amplicon-specific short interfering RNAs (siRNAs). Inoculation of these plants with various viruses known to encode silencing suppressor proteins induced a striking synergistic effect leading to the enhanced accumulation of PLRV-GFP, suggesting that it had escaped from silencing. However, PLRV-GFP escape also occurred following inoculation with viruses that do not encode known silencing suppressors and treatment of silenced plants with biotic or abiotic stress agents.

Evidence for RNA-mediated defence effects on the accumulation of Potato leafroll virus.

In plants infected with Potato leafroll virus (PLRV), or other luteoviruses, infection is very largely confined to cells in the vascular system. Even in tobacco plants transformed with PLRV full-length cDNA, in which all mesophyll cells should synthesize infectious PLRV RNA transcripts, only a minority of the mesophyll cells accumulate detectable amounts of virus. We have explored this phenomenon further by transforming a better PLRV host, Nicotiana benthamiana, with the same transgene, by superinfecting transformed plants with Potato virus Y and by producing tobacco plants in which cells contained both PLRV cDNA and DNA encoding the P1/HC-Pro genes of the potyvirus Tobacco etch virus.

Transformation of tobacco and potato with cDNA encoding the full-length genome of potato leafroll virus: evidence for a novel virus distribution and host effects on virus multiplication.

A full-length cDNA copy of the genome of Potato leafroll virus (PLRV) was introduced into the genome of tobacco and potato plants by Agrobacterium tumefaciens-mediated transformation. Transgenic lines were obtained in which the transgene was readily detected by PCR with DNA extracted from T(1) tobacco seedlings and clonally multiplied potato plants. PLRV-specific genomic and sub- genomic RNAs, coat protein antigen and virus particles were detected in transgenic plants.