Gene 3 in the genomes of several plant-infecting rhabdoviruses, including rice transitory yellowing virus (RTYV), has been postulated to encode a cell-to-cell movement protein (MP). Transcomplementation experiments using a movement-defective tomato mosaic virus and the P3 protein of RTYV, encoded by gene 3, facilitated intercellular transport of the mutant virus. In transient-expression experiments with the GFP-fused P3 protein in epidermal leaf cells of Nicotiana benthamiana, the P3 protein was associated with the nucleus and plasmodesmata. Immunogold-labelling studies of thin sections of RTYV-infected rice plants using an antiserum against Escherichia coli-expressed His6-tagged P3 protein indicated that the P3 protein was located in cell walls and on virus particles. In Western blots using antisera against E. coliexpressed P3 protein and purified RTYV, the P3 protein was detected in purified RTYV, whilst antiserum against purified RTYV reacted with the E. coli-expressed P3 protein. After immunogold labelling of crude sap from RTYV-infected rice leaves, the P3 protein, as well as the N protein, was detected on the ribonucleocapsid core that emerged from partially disrupted virus particles. These results provide evidence that the P3 protein of RTYV, which functions as a viral MP, is a viral structural protein and seems to be associated with the ribonucleocapsid core of virus particles.
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