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Tobamovirus replicase coding region is involved in cell-to-cell movement
1Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan.
Abstract:
Tobacco mosaic virus (TMV) encodes a 30-kDa movement protein (MP) which enables viral movement from cell to cell. It is, however, unclear whether the 126- and 183-kDa replicase proteins are involved in the cell-to-cell movement of TMV. In the course of our studies into TMV-R, a strain with a host range different from that of TMV-U1, we have obtained an interesting chimeric virus, UR-hel. The amino acid sequence differences between UR-hel and TMV-U1 are located only in the helicase-like domain of the replicase. Interestingly, UR-hel has a defect in its cell-to-cell movement. The replication of UR-hel showed a level of replication of the genome, synthesis, and accumulation of MP similar to that observed in TMV-U1-inoculated protoplasts. Such observations support the hypothesis that the replicase coding region may in some fashion be involved in cell-to-cell movement of TMV.
Insights
The replicase proteins of Tobacco mosaic virus (TMV) may play a role in cell-to-cell movement, a function previously attributed only to the movement protein (MP). This study investigated a chimeric virus with defects in movement, suggesting a broader role for TMV replicase.
Area of Science:
- Plant Virology
- Molecular Biology
- Genetics
Background:
- Tobacco mosaic virus (TMV) cell-to-cell movement is facilitated by its 30-kDa movement protein (MP).
- The specific roles of TMV replicase proteins (126- and 183-kDa) in viral movement remain largely uncharacterized.
Purpose of the Study:
- To investigate the potential involvement of TMV replicase proteins in viral cell-to-cell movement.
- To analyze the movement defect of a chimeric TMV strain, UR-hel, with sequence differences in the replicase helicase-like domain.
Main Methods:
- Construction and characterization of a chimeric TMV strain (UR-hel) derived from TMV-R and TMV-U1.
- Comparative analysis of viral replication, genome synthesis, and movement protein (MP) accumulation between UR-hel and TMV-U1 in protoplasts.
Main Results:
- The chimeric UR-hel virus exhibited a defect in cell-to-cell movement compared to the wild-type TMV-U1.
- Replication, genome synthesis, and MP accumulation levels were comparable between UR-hel and TMV-U1 in inoculated protoplasts.
- Amino acid sequence differences between UR-hel and TMV-U1 were localized to the helicase-like domain of the replicase.
Conclusions:
- The observed movement defect in UR-hel, despite normal replication and MP levels, suggests a role for the replicase coding region in TMV cell-to-cell movement.
- These findings challenge the exclusive role of MP in TMV cell-to-cell transport and implicate the replicase in this process.