Synthesis, Accumulation and Encapsidation of Individual Brome Mosaic Virus RNA Components in Barley Protoplasts

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Abstract
The rates of virus RNA synthesis and virion accumulation were investigated in brome mosaic virus-infected barley protoplasts. Single-stranded virus RNAs could be detected as early as 6 h after inoculation. Only RNA components 1 and 2 were detected at this time, suggesting that their synthesis is initiated relatively early in infection. The RNAs were synthesized at similar rates from 16 to 35 h post inoculation with maximal synthesis until approx. 25 h after inoculation. Double-stranded replicative forms of the four virus RNAs were observed. Their synthesis was first detectable at 6 h post inoculation and followed a time course similar to that of the single-stranded RNA species. Analysis of RNA encapsidation and infectivity assays of protoplast homogenates revealed that virion formation was greatest between 10 and 25 h after inoculation. All four RNAs were present in virions at 10 h post inoculation. Particles containing RNA 3 and RNA 4 accumulated at a faster rate than particles containing RNA 1 or RNA 2.