Mechanism of Disease Production by a Satellite of Turnip Crinkle Virus

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We propose to investigate how the virulent satellite RNA C intensifies the symptoms of its helper virus, Turnip Crinkle Virus (TCV). RNA C differs from the TCV avirulent satellites RNA D and RNA F primarily by the presence of a 3'TCV-homologous domain. We will analyze whether this 3' domain is responsible for satellite symptom production by infecting turnip with chimeric transcripts composed of the avirulent satellites linked to the 3' domain of RNA C, and assaying for infectivity and symptoms. We will also create a comprehensive set of site- specific mutations throughout RNA C in order to further specify the region(s) of the satellite involved in symptom production. By determining the secondary structure of RNA C, we will correlate disruption of secondary structure with satellite replication and plant disease morphology. We will test two models for RNA C's mode of action: l) RNA C binds to cellular factor(s) thereby acting to titrate out these factors necessary for basic cellular metabolism or, 2) RNA C aneals to putative plant U7 RNA and thereby interfers with histone mRNA processing leading to plants with a diseased morphology. This second model is based on the observation that RNA C is complementary to 83% of sea urchin U7 RNA. This study will lay the groundwork for establishing the molecular basis of disease production in plants by small non-protein coding RNAs.