Summary auto-generated
This study investigated how groundnut rosette umbravirus (GRV) satellite RNA (sat-RNA) variants produce different disease symptoms in infected plants. The researchers used sat-RNA variant YB3b, which induces distinctive yellow blotch symptoms in Nicotiana benthamiana, as a model system. Through molecular analysis, they found that symptom production does not require sat-RNA accumulation levels or GRV replication rates to differ from symptom-neutral sat-RNA variants. Using mutagenesis and deletion analysis, the researchers demonstrated that symptom induction does not depend on any protein products encoded by sat-RNA, despite the presence of open reading frames. Instead, they identified three untranslated RNA elements: element R (nucleotides 47-281) required for sat-RNA replication in cis, and elements A (280-470) and B (629-849) required for symptom production that can function in trans. Significantly, complementation experiments showed that the two trans-acting elements can work together to induce symptoms even when separated on different sat-RNA molecules. The research reveals a novel mechanism where two independent untranslated RNA sequence elements interact with host factors to produce disease symptoms, representing an unusual form of viral symptom determination independent of viral protein expression.
Key findings
- Sat-RNA YB3b induces yellow blotch symptoms independent of altered viral RNA accumulation levels or helper virus replication
- Symptom production does not require any sat-RNA-encoded proteins, as demonstrated by mutating all open reading frames
- Three untranslated RNA elements control sat-RNA function: element R is required for replication in cis; elements A and B are required for symptom production and can function in trans
- Elements A and B can complement each other in trans to restore symptom production when present on separate sat-RNA molecules
- The symptom phenotype is determined by a novel interaction between two untranslated RNA elements that interact with host factors
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Abstract
Isolates of groundnut rosette umbravirus (GRV) contain a satellite RNA (sat-RNA), about 900 nucleotides (nt) in length, different variants of which are responsible for the symptoms of different forms of rosette disease in groundnuts and, in the particular instance of sat-RNA YB3b, for the production of yellow blotch symptoms in Nicotiana benthamiana. Sat-RNA YB3b does not affect the accumulation of GRV genomic or subgenomic RNAs in infected plants. Replication of sat-RNA YB3b and induction of yellow blotch symptoms do not require the production of any sat-RNA-encoded proteins. Experiments with deletion mutants identified three functional untranslated elements in sat-RNA YB3b. One (designated R) comprises nt 47-281, is essential for sat-RNA replication and appears to be cis-acting. The other two (designated A and B) comprise nt 280-470 and 629-849, respectively, are both involved in yellow blotch symptom production and can act in trans. Element A contains the determinant that is unique to sat-RNA YB3b. The process of symptom induction by sat-RNA YB3b apparently involves a novel type of specific interaction of two untranslated RNA elements, which can complement each other, with a host factor or factors.