A Satellite RNA of Groundnut Rosette Virus that Is Largely Responsible for Symptoms of Groundnut Rosette Disease

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Abstract
Groundnut (Arachis hypogaea) plants with rosette disease contain a manually transmissible virus, groundnut rosette virus (GRV), which depends on a luteovirus, groundnut rosette assistor virus (GRAV), for transmission by the aphid Aphis craccivora. No virus-like particles have been reported for GRV but infected plants yield infective ssRNA. Infected leaves also contain dsRNA with a prominent electrophoretic species of 4.6 kbp (dsRNA-1) and 1.3 kbp (dsRNA-2), a very abundant species of 900 bp (dsRNA-3), and numerous minor species of intermediate mobility. In studies with GRV(C), an isolate from groundnut plants with a chlorotic form of rosette, cDNA to dsRNA-1 reacted with ds RNA-1 and dsRNA-2 but not with dsRNA-3 or any of the minor dsRNA species. In contrast, cDNA to dsRNA-3 reacted with dsRNA-3 and several of the minor dsRNA species but reacted only weakly or not at all with dsRNA-1 or dsRNA-2. An isolate lacking dsRNA-3 (isolate G96) was derived from GRV(C) by passage through Gomphrena globosa. When dsRNA-3 recovered from agarose gels was melted and inoculated to Nicotiana benthamiana plants, it was not infective on its own but multiplied in plants that were also infected with G96. Similar results were obtained with sucrose density gradient fractions containing RNA molecules of the size expected for ssRNA-3. These results show that dsRNA-3 represents a satellite RNA. Addition of dsRNA-3 to the G96 culture resulted in slight amelioration of symptoms in N. benthamiana and N. clevelandii. However, only cultures containing RNA-3 induced rosette symptoms in groundnut, though the symptoms were intensified by further addition of GRAV. The results show that the satellite RNA is largely responsible for rosette disease symptoms in groundnut.