Molecular characterization of a tomato isolate of impatiens necrotic spot virus.

Impatiens necrotic spot virus (INSV) has a range of hosts that includes primarily ornamental plants. Recently this virus has been detected in cucumber, chicory lettuce and pepper. Tomato was reported as an experimental host but in 2000 INSV was found in mixed infection with Tomato spotted wilt virus (TSWV) in field crops for canning. Here we report the complete nucleotide sequence of an isolate of INSV, denoted INSV-AG, obtained from soilless tomato plants cv Concita grown near Bari (Apulia, Southern Italy). The primary structure of INSVAG comprises 16,720 nt, distributed in two ambisense (S, M) and one negative-sense (L) RNA species encoding six putative proteins. RNA-S is 2,978 nt long, with a positive-sense ORF that encodes a polypeptide of 50,514 Da (protein NsS) and a negative-sense ORF that encodes a polypeptide of 28,831 Da (protein NcS). RNA-M is 4,962 nt long, with a positive-sense ORF that encodes a polypeptide of 34,023 Da (protein NsM) and a negative-sense ORF that encodes a polypeptide of 125,007 Da (G1-G2 precursor protein). RNA-L is 8,780 nt long, with a negative-sense ORF that encodes a polypeptide of 330,586 Da, which shows identity to the RNA-dependent RNA polymerises. Analysis of the 5'-end showed the presence of extranucleotides of plant host origin suggesting that INSV-AG uses a cap-snatching-like mechanism to initiate transcription of its mRNAs. The possible involvement of point mutations in the amino acid sequence of NsS and G1-G1 proteins in the change of virus-host-vector relationships is discussed.