VIRAL VECTORS

Disclosed are nucleic acid vectors which comprise: (a) a transfer nucleotide sequence comprising (i) a plant active promoter, operably linked to (ii) a recombinant tobacco rattle virus (TRV) cDNA (preferably derived from TRV RNA2) which includes at least cis acting elements permitting replication of said cDNA; a subgenomic promoter operably linked to a sequence encoding a TRV coat protein; and a heterologous nucleotide sequence which is foreign to said virus;(b) border sequences which permit the transfer of the transfer nucleotide sequence into a plant genome. Such vectors may be used as expression vectors or for achieving viral induced gene silencing (VIGS) of a target gene, wherein the heterologous nucleotide sequence is a targeting sequence which corresponding to that gene. Example vectors include pTV00 and vectors which are derived from pTV00 and have the characteristics thereof. Also disclosed are associated processes, methods, viruses or viral particle, kits, host cells and plant tissues.