Mutations in the coat protein-binding cis-acting RNA motifs debilitate RNA recombination of Brome mosaic virus

We have previously described the efficient homologous recombination system between 5′ subgenomic RNA3a (sgRNA3a) and genomic RNA3 of Brome mosaic virus (BMV) in barley protoplasts (Sztuba-Solińska et al., 2011a). Here, we demonstrated that sequence alterations in the coat protein (CP)-binding cis-acting RNA motifs, the Bbox region (in the intercistronic RNA3 sequence) and the RNA3 packaging element (PE, in the movement protein ORF), reduced crossover frequencies in protoplasts. Additionally, the modification of Bbox-like element in the 5′ UTR region strongly debilitated crossovers. Along the lines of these observations, RNA3 mutants not expressing CP or expressing mutated CPs also reduced recombination. A series of reciprocal transfections demonstrated a functional crosstalk between the Bbox and PE elements. Altogether, our data imply the role of CP in sgRNA3a-directed recombination by either facilitating the interaction of the RNA substrates and/or by creating roadblocks for the viral replicase.

► We model the role of coat protein (CP) during RNA recombination between RNA3 and sgRNA3a in Brome mosaic virus (BMV). ► Mutations in cis-acting RNA motifs responsible for CP binding debilitate recombination. ► Mutations in CP domains responsible for RNA binding debilitate recombination. ► Both, the recombination frequency and distribution of crossover sites are affected by mutations. ► Recombination mechanisms are suggested where CP molecules bring recombining RNAs together during (+) or (−) strand syntheses.