REPLICATION OF THE SATELLITE RNA OF PEA ENATION MOSAIC-VIRUS IS CONTROLLED BY RNA 2-ENCODED FUNCTIONS

The helper virus mediating replication of the satellite RNA (RNA 3) of pea enation mosaic virus (PEMV) consists of two autonomously replicat ing, taxonomically unrelated viral RNAs with ties to the luteovirus (R NA 1) and the newly proposed umbravirus (RNA 2) genera. The following study dissects the relative contribution of each of the genomic RNAs o f PEMV to the subsistence and dissemination of this satellite RNA. Inf ectivity assays in a pea protoplast system demonstrate that RNA 2 alon e is responsible for the replication of RNA 3, an observation that is supported in part by shared regions of sequence homology at the 5' and 3' termini of both RNAs. In pea seedlings, infectivity assays also de monstrated that the presence of RNA 2 alone is necessary for the syste mic invasion of RNA 3. In contrast, the luteovirus-like phase of PEMV (RNA 1) is solely responsible for the encapsidation and aphid transmis sion of both RNA 2 and the satellite RNA. In a manner comparable to se veral other virus-satellite systems, the satellite of PEMV also displa ys a differential response in its capacity to attenuate symptom expres sion in selected host species. Thus, the satellite RNA of PEMV exists in a trilateral arrangement with its host and two viral RNAs, comparab le in many respects to the satellite-virus-host interaction occurring with groundnut rosette disease.