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An inhibitor of viral RNA replication is encoded by a plant resistance gene

Ishibashi, Kazuhiro, Masuda, Kiyoshi, Naito, Satoshi, Meshi, Tetsuo, Ishikawa, Masayuki
Proceedings of the National Academy of Sciences of the United States of America 2007 v.104 no.34 pp. 13833-13838
tomatoes, protein binding, host-pathogen relationships, plant proteins, Tomato mosaic virus, amino acid sequences, resistance mechanisms, genes, disease resistance, DNA-binding proteins, viral proteins, virus replication, Solanum lycopersicum var. lycopersicum
The tomato Tm-1 gene confers resistance to tomato mosaic virus (ToMV). Here, we report that the extracts of Tm-1 tomato cells (GCR237) have properties that inhibit the in vitro RNA replication of WT ToMV more strongly than that of the Tm-1-resistance-breaking mutant of ToMV, LT1. We purified this inhibitory activity and identified a polypeptide of [almost equal to]80 kDa (p80GCR²³⁷) using LC-tandem MS. The amino acid sequence of p80GCR²³⁷ had no similarity to any characterized proteins. The p80GCR²³⁷ gene cosegregated with Tm-1; transgenic expression of p80GCR²³⁷ conferred resistance to ToMV within tomato plants; and the knockdown of p80GCR²³⁷ sensitized Tm-1 tomato plants to ToMV, indicating that Tm-1 encodes p80GCR²³⁷ itself. We further show that in vitro-synthesized Tm-1 (p80GCR²³⁷) protein binds to the replication proteins of WT ToMV and inhibits their function at a step before, but not after, the viral replication complex is formed on the membrane surfaces. Such binding was not observed for the replication proteins of LT1. These results suggest that Tm-1 (p80GCR²³⁷) inhibits the replication of WT ToMV RNA through binding to the replication proteins.