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

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Abstract
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 ≈80 kDa (p80 GCR237 ) using LC–tandem MS. The amino acid sequence of p80 GCR237 had no similarity to any characterized proteins. The p80 GCR237 gene cosegregated with Tm-1 ; transgenic expression of p80 GCR237 conferred resistance to ToMV within tomato plants; and the knockdown of p80 GCR237 sensitized Tm-1 tomato plants to ToMV, indicating that Tm-1 encodes p80 GCR237 itself. We further show that in vitro -synthesized Tm-1 (p80 GCR237 ) 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 (p80 GCR237 ) inhibits the replication of WT ToMV RNA through binding to the replication proteins.