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The N-terminal Region of the Plantago asiatica mosaic virus Coat Protein Is Required for Cell-to-Cell Movement but Is Dispensable for Virion Assembly

¹Laboratory of Plant Pathology, Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo; ²Department of Clinical Plant Science, Faculty of Bioscience and Applied Chemistry, Hosei University, Koganei, Tokyo

Potexvirus cell-to-cell movement requires coat protein (CP) and movement proteins. In this study, mutations in two conserved in-frame AUG codons in the 5′ region of the CP open reading frame of Plantago asiatica mosaic virus (PlAMV) were introduced, and virus accumulation of these mutants was analyzed in inoculated and upper noninoculated leaves. When CP was translated only from the second AUG codon, virus accumulation in inoculated leaves was lower than that of wild-type PlAMV, and the viral spread was impaired. Trans-complementation analysis showed that the leucine residue at the third position (Leu-3) of CP is important for cell-to-cell movement of PlAMV. The 14-amino-acid N-terminal region of CP was dispensable for virion formation. Immunoprecipitation assays conducted with an anti-TGBp1 antibody indicated that PlAMV CP interacts with TGBp1 in vivo and that this interaction is not affected by alanine substitution at Leu-3. These results support the concept that the N-terminal region of potexvirus CP can be separated into two distinct functional domains.