Summary auto-generated
This study examined genome organization of nematode-transmissible tobravirus isolates to understand how viral structure determines vector specificity. Researchers sequenced RNA2 of tobacco rattle virus (TRV) isolate TpO1, a newly identified nematode-transmissible strain transmitted by Trichodorus primitivus—the same vector nematode that transmits pea early-browning virus (PEBV) TpA56, but not the other nematode vector of TRV PpK20 (Paratrichodorus pachydermus). The TpO1 RNA2 contained 3216 nucleotides encoding four proteins: coat protein (CP), a 9K protein, a 2b protein, and a 2c protein. Amino acid sequence comparisons revealed that TpO1 CP and 2b proteins more closely resembled those of PEBV TpA56 than TRV PpK20. Additionally, TpO1 possessed a 9K protein similar to PEBV, which is absent in PpK20. The C-terminal region of the CP, predicted to extend from the viral surface, showed sequence similarities between the two T. primitivus-transmitted viruses. These findings suggest that viral coat protein and 2b protein sequences, along with the presence of a 9K protein, may be important determinants in recognizing and binding to specific nematode vector species.
Key findings
- TRV TpO1 is transmitted by T. primitivus but not P. pachydermus, sharing vector specificity with PEBV TpA56 despite being serologically distinct
- TpO1 coat protein and 2b protein sequences are more similar to PEBV TpA56 than to TRV PpK20, correlating with vector nematode identity rather than viral species designation
- TRV TpO1 encodes a 9K protein located downstream of the coat protein gene, similar to PEBV TpA56 but absent in TRV PpK20
- The C-terminal flexible domain of the coat protein differs in size among isolates and may serve as a recognition domain for vector specificity
- Genome organization features appear to be determined by nematode vector compatibility rather than strict taxonomic classification between TRV and PEBV
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Abstract
Although sequence data have been obtained for several tobravirus isolates, only two of these isolates are nematode-transmissible. Tobacco rattle virus (TRV) PpK20 is transmitted by Paratrichodorus pachydermus, whereas pea early-browning virus (PEBV) TpA56 is transmitted by Trichodorus primitivus. To clarify whether differences in the genome structure of these isolates are relevant to the specificity of interactions with particular vector nematodes, or merely reflect a taxonomic difference between TRV and PEBV, we have sequenced RNA2 of a new isolate of TRV (TpO1) that is transmitted by the same vector nematode as PEBV TpA56 but is not transmitted by the nematode vector of TRV PpK20. TRV TpO1 RNA2 encodes, in 5' to 3' order, a coat protein (CP), a 9K protein, a 2b (29K) protein and a 2c (18K) protein. Amino acid sequence comparison shows that both the CP and 2b proteins of TRV TpO1 resemble more closely the analogous proteins from PEBV TpA56 than those from TRV PpK20. Also, the TRV TpO1 9K protein has similarities with the PEBV 9K protein whereas this protein is lacking in TRV PpK20.