Double-stranded RNAs isolated from plant tissue infected with red clover necrotic mosaic virus correspond to genomic and subgenomic single-stranded RNAs

Abstract

Red clover necrotic mosaic dianthovirus (RCNMV) has a genome of two ssRNA species, RNA 1 (4.0 kb) and RNA 2 (1.4 kb). Double-stranded RNA was isolated from Phaseolus vulgaris plants infected separately with five isolates of RCNMV from Czechoslovakia, Sweden, Scotland and England. In each case three species of dsRNA, designated A, B and C in order of increasing mobility, were resolved by gel electrophoresis in non-denaturing conditions. The mobilities of dsRNA species A and B were similar for all the isolates, but the mobilities of the different species of dsRNA C showed some variation. Southern blotting followed by hybridization with cloned probes showed that dsRNA species A and B are related to RNA 1, whereas dsRNA C is related to RNA 2. In gel electrophoresis in denaturing conditions, RNA from dsRNA A had the same mobility as ssRNA 1, whereas RNA from dsRNA species B and C had the same mobility as ssRNA 2. It is concluded that dsRNAs A and C are the doublestranded forms of the genomic RNA 1 and RNA 2 respectively and that dsRNA B is the double-stranded form of a subgenomic RNA which is derived from RNA 1 and has the same size as RNA 2.