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 nonnecrogenic 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.