|Kovacs, Frank -|
Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 7, 2013
Publication Date: January 3, 2014
Repository URL: http://handle.nal.usda.gov/10113/58285
Citation: Tatineni, S., Kovacs, F., French, R.C. 2014. Wheat streak mosaic virus infects systemically despite extensive coat protein deletions: identification of virion assembly and cell-to-cell movement determinants. Journal of Virology. 88:1366-1380. Interpretive Summary: Wheat streak mosaic virus (WSMV) is the most economically important wheat virus in the Great Plains region. Previous investigations have developed resistance against WSMV based on host-plant expression of coat protein gene. Viral coat proteins have multiple roles in the life-cycles of viruses. Understanding the roles of coat protein in the virus life-cycle could provide important clues in identifying vulnerable sites in the disease cycle that can be used for the development of new management strategies. In this study, we found that WSMV is able to cause disease in wheat with shorter versions of coat protein. In addition, the coat protein regions that are required for virus to spread in wheat and form virus particles were identified. WSMV is able to infect wheat even when missing 30% of amino acids from its coat protein. The availability of WSMV mutants with shorter versions of coat protein will facilitate defining the roles of coat protein in wheat curl mite transmission and disease development. These results indicate that developing resistance based on viral coat protein antagonism should proceed with caution as such resistance will likely be overcome by WSMV after deployment to the field.
Technical Abstract: Viral coat proteins function in virion assembly and virus biology in a tightly coordinated manner with a role for virtually every amino acid. In this study, we demonstrated that the coat protein (CP) of Wheat streak mosaic virus (WSMV) (genus Tritimovirus; family Potyviridae) is unusually tolerant of extensive deletions with continued virion assembly and/or systemic infection. A series of deletion and point mutations were created in the CP cistron of wild-type and/or GFP-tagged WSMV and examined for their effects on cell-to-cell and systemic transport and virion assembly. Mutants with overlapping deletions comprising amino acids (aa) N-terminal 6 to 27, 36 to 100, or the C-terminal 17 aa systemically infected wheat with different efficiencies; however, mutation of conserved aa in the core domain abolished virion assembly and cell-to-cell movement. The N-terminal aa 6 to 27 and 85 to 100 are required for efficient virion assembly and cell-to-cell movement, while the C-terminal 65 aa are dispensable for virion assembly but required for cell-to-cell movement, suggesting that the C-terminus of CP functions as a dedicated cell-to-cell movement determinant. In contrast, aa 36 to 84 are dispensable with no obvious effects on systemic infection and virion assembly. In total, 152 aa (aa 6 to 27, 36 to 100 and 65 aa at the C-terminus end) of 349 aa of CP are dispensable for systemic infection and/or virion assembly, which is rare for multifunctional viral CPs.