Replication of Cucumber Mosaic Virus Satellite RNA from Negative-sense Transcripts Produced Either in Vitro or in Transgenic Plants

Both positive [(+)] and negative [(-)] sense versions of two satellite RNA (satRNA) genes from cucumber mosaic virus (CMV), the necrogenic I17N and the non-necrogenic R, have been introduced into the genome of tobacco plants. On infection with satRNA-free CMV, satRNA was amplified in plants expressing each of the four genes. All four genes confer protection against CMV infection. However, co-inoculation of plants with viral RNA and CMV satRNA transcripts synthesized in vitro showed that (-) sense transcripts were less active than the corresponding (+) sense transcripts. This is the first report that (-) sense CMV satRNA transcripts can serve as a template for satRNA replication.