Replication of cauliflower mosaic virus and transcription of its genome in turnip leaf protoplasts

Abstract

The replication of cauliflower mosaic virus (CaMV) was studied in turnip leaf protoplasts infected in culture with virus and in protoplasts isolated from infected plants. Production of mature virus in protoplasts infected in culture was synchronous but slow, requiring more than 4 days following infection. Virus assembly time in asynchronously infected cells (protoplasts from infected plants) was much shorter (10–15 hr), the difference considered to be the time in synchronous infection needed for the completion of replication cycle events prerequisite to virus assembly. About 2.5 days following synchronous infection in culture, a stable RNA species (apparent molecular weight of 1.5-1.8 × 10 6) coded by the CaMV genome appeared in infected protoplasts. The RNA species represented the coding capacity of a considerable portion (50–80%) of the CaMV genome as demonstrated by RNA-driven RNA-DNA hybridization reactions and by the hybridization of the viral RNA to EcoRI restriction fragments of the CaMV genome. The viral-coded RNA was the apparent product of asymmetrical transcription of the CaMV genome since it hybridized to only one DNA strand, the strand with one discontinuity. Other properties of the large viral-coded RNA suggest that it may serve a messenger function.