Characterization of a vector-non-transmissible isolate of Tomato spotted wilt virus

The characteristics of a thrips-non-transmissible isolate of Tomato spotted wilt virus (TSWV), designated TSWV-M, were compared with those of a thrips-transmissible isolate, designated TSWV-T. TSWV-M showed a narrower host range than TSWV-T. Adult thrips failed to transmit TSWV-M, although the vector acquired the virus during the larval stages. TSWV-M was detected by RT-PCR in adult thrips bodies, but not in thrips heads, suggesting that loss of thrips transmissibility was the result of the absence of virus in adult thrips salivary glands. Whereas N (nucleoprotein), NSs (non-structural protein) and G C (the C-terminal portion of the glycoprotein precursor protein) were present in similar amounts in leaf tissue from TSWV-Mor TSWV-T-infected plants, G N (the N-terminal portion of the glycoprotein precursor protein) was present at much lower amounts in TSWV-Mthan in TSWV-T-infected plants. SDS-PAGE and immunoblotting analysis of TSWV-M and TSWV-T virion preparations with G N and G C -specific antibodies revealed similar amounts of the G N and G C glycoproteins in TSWV-T virions, but lower amounts of G N than G C in TSWV-M virions. This resulted in a statistically significant reduction in the G N /G C ratio in TSWV-M virions. In affinoblots, the G C and G N glycoproteins of TSWV-M exhibited weak binding with lectins showing affinity for N-linked oligosaccharide structures. Sequence analysis of M RNA (medium segment of the TSMV genome) revealed no deletions or frameshift mutations in the G N /G C precursor of TSWV-M. However, five amino acid changes were detected in the G N /G C precursor. A single, relatively conservative amino acid substitution (V → I) was observed in the NSm protein. Sequence analysis of S RNA (small portion of the TSMV genome) revealed a large intergenic region with no changes in the N protein and with three amino acid changes in the NSs protein.