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Defective tobamovirus movement protein lacking wild-type phosphorylation sites can be complemented by substitutions
Shigeki Kawakami1, Koichi Hori, Daijiro Hosokawa
1Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Japan.
Abstract:
We reported previously that the movement protein (MP) of tomato mosaic tobamovirus is phosphorylated, and we proposed that MP phosphorylation is important for viral pathogenesis. Experimental data indicated that phosphorylation enhances the stability of MP in vivo and enables the protein to assume the correct intracellular location to perform its function. A mutant virus designated 37A238A was constructed; this virus lacked two serine residues within the MP, which prevented its phosphorylation. In the present study, we inoculated plants with the 37A238A mutant, and as expected, it was unable to produce local lesions on the leaves. However, after an extended period, we found that lesions did occur, which were due to revertant viruses. Several revertants were isolated, and the genetic changes in their MPs were examined together with any changes in their in vivo characteristics. We found that reversion to virulence was associated first with increased MP stability in infected cells and second with a shift in MP intracellular localization over time. In one case, the revertant MP was not phosphorylated in vivo, but it was functional.
Insights
Phosphorylation of tomato mosaic tobamovirus movement protein (MP) is crucial for its function. Revertant viruses regained virulence, showing increased MP stability and altered intracellular localization, even without phosphorylation.
Area of Science:
- Plant virology
- Molecular biology
- Biochemistry
Background:
- The movement protein (MP) of tomato mosaic tobamovirus is phosphorylated, a process hypothesized to be vital for viral pathogenesis.
- Phosphorylation enhances MP stability and facilitates its correct intracellular localization for function.
Purpose of the Study:
- To investigate the role of MP phosphorylation in tomato mosaic tobamovirus pathogenesis.
- To analyze the characteristics of revertant viruses that regain virulence after initial non-phosphorylation.
Main Methods:
- Construction of a mutant virus (37A238A) lacking phosphorylatable serine residues in MP.
- Inoculation of plants with the mutant virus and isolation of revertant viruses.
- Genetic and in vivo characterization of revertant MPs, including stability and intracellular localization.
Main Results:
- The non-phosphorylatable mutant virus initially failed to produce local lesions.
- Revertant viruses emerged, regaining the ability to cause local lesions.
- Reversion to virulence correlated with increased MP stability and altered intracellular localization.
- One revertant MP was functional in vivo despite lacking phosphorylation.
Conclusions:
- MP phosphorylation is important but not strictly essential for tomato mosaic tobamovirus virulence.
- MP stability and intracellular localization are key factors in viral pathogenesis, potentially compensating for lack of phosphorylation.
- The study provides insights into the complex mechanisms governing tobamovirus infection and host interaction.