Structural and functional analyses of the plant host proteins associated with viral infection.

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1. A tobacco translation elongation factor 1A (eEF1A) that binds to TMV RNA polymerase was demonstrated to be an essential host factor of TMV replication complex by overexpression or suppression of eEF1A gene in the infected plants. While, a tobacco ringfinger protein PHF15 that also binds to TMV RNA polymerase was indicated to be an inhibitory factor for TMV infection by the same experiments as the above.2. A tobacco co-chaperon NtDnaJ-3 that binds to TMV movement protein (MP) and a tobacco transcription factor NtKN1 that binds to NtDnaJ-3 were both indicated to be essential for stable MP accumulation which leads the infected cell to facilitate the viral3. To elucidate the interaction between MPs and host proteins required for viral movement, yeast two-hybrid screening using cDNA library clones from plant mRNA was performed. The partial or full-length sequences of TGBpl,-2,-3, and CP of a potexvirus (Tulip virus X, TVX), or the MP and CP of a capillovirus (Apple stem grooving virus, A … More SGV) were used as bait. The ankyrin-repeat domain containing protein (ARD) was identified as a TGBp2-interacting protein. In planta ARD knock-down experiments indicated that ARD promotes TVX cell-to-cell movement. By contrast, ASGV MP did not interact with ARD. These data suggest that plant viruses require different host factors for cell-to-cell movement depending on the type of MP.4. Formation of RNA replication complexes of Soil-borne wheat mosaic virus was examined using Rep RNA1 consisting 5'-and 3'-untranslated regions and p152/p211 replicase genes as an inoculum and barley mesophyll protoplasts as host cells. Replication of Rep RNA 1 reached the maximum at 9 hours post-inoculation (hpi) while p152/p211 translation continued until 24 hpi. p152/p211 at 12 hpi were detected in soluble fractions of P1 and S15 whereas those at 24 hpi were mostly detected in an insoluble P1 fraction. These results suggest that Rep RNA 1 replicates at the early stages of infection in membrane-bound soluble RNA replication complexes and that p152/p211 complexes accumulated at the late stages of infection are insoluble and inactive in RNA replication. The molecular ratio of p152 to p211 was approximately 4 : 1. Less