REGULATION OF TOMATO BUSHY STUNT VIRUS LONG-DISTANCE MOVEMENT
M CHU, J-W PARK, S GARCIA, J KUECKER, B DESVOYES, B WHITEHEAD and HB SCHOLTHOF
Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843, USA
Background and objectives
Results and conclusions
In related genetic studies on the involvement of host-specific interactions with the p19 protein, we mutated codons for clustered charged amino acids that were considered candidates to be exposed on the protein surface for specific interactions with host proteins. Bio-assays with several mutants revealed that amino-acid residues located towards the central domain of the p19 protein were required for TBSV to systemically invade spinach plants. Further analyses revealed that replication and cell-to-cell movement were not affected by these mutations, but the mutants were defective for long-distance spread. These results suggest that the central domain of the p19 protein may interact with specific host factors to stimulate a systemic invasion.
During time-course studies in spinach it became obvious that a systemic infection proceeded from the inoculated leaves downward to the roots prior to infection of upper leaves, and the p19 protein was the first virus protein to be detected in roots. Subsequent experiments revealed that a p19 mutant that previously was shown to be debilitated in its ability to invade spinach plants was defective for movement from inoculated leaves down into the roots.
The combined results of the above studies lead us to speculate that a functional p19 protein is required in abundance for interaction with host factors, to permit spread of virus out of the inoculated leaves into the vasculature and to permit transport to the roots and subsequently to the upper parts.