Abstract: It is a common phenomenon that recombination of heterogeneous replicases cannot efficiently replicate recombinant virus in Bramoviridae. Here, the effects of heterogeneous combination of viral replicases on viral replication was investigated using cucumber mosaic virus(CMV) and tomato aspermy virus(TAV) as the research objectives, which are the typical species of the genus Cucumovirus, Bromoviridea. CMV RNA1 (C1) and TAV RNA2 (T2) were heterogeneously combined, mixed with either CMV RNA3 (C3) or TAV RNA3 (T3), and then inoculated onto Nicotiana benthamiana plants by agroinfiltration. At 10 days post-infiltration, no obvious viral symptoms were observed on the plants inoculated with C1T2C3 or C1T2T3. Moreover, mild viral bands were detected in the upper systemic leaves of the plants by Northern blot. These results demonstrate that C1T2 heterogeneous combination could not support viral replication/infection efficiently. When C1T2C3 was passaged three times, the infected plants showed obvious viral symptoms and a high accumulation level of viral progeny RNAs. Sequencing data of viral genomic RNAs showed that C1 had a mutation at the position 1 390, and T2 had a mutation at the position 1 695. Moreover, the 3' end of C3 was tagged with the whole 3' UTR of T2. Taken together, the recombinant virus C1T2C3 could overcome defects in virus replication conferred by the heterogeneous combination of their replicases by in vivo mutation and recombination.

Key words: Cucumber mosaic virus, Tomato aspermy virus, replicase, mutation, recombination