Abstract
Interspecific exchange of RNA1 or RNA2 between the cucumoviruses cucumber mosaic virus (CMV) and tomato aspermy virus (TAV) was reported to be non-viable in plants previously. Here we investigated viability of the reassortants between CMV and TAV in Nicotiana benthamiana plants by Agrobacterium-mediated viral inoculation. The reassortants were composed of CMV RNA1 and TAV RNA2 plus RNA3 replicated in the inoculated leaves, while they were defective in viral systemic movement at the early stage of infection. Interestingly, the reassortant containing TAV RNA1 and CMV RNA2 and RNA3 infected plants systemically, but produced RNA4A (the RNA2 subgenome) at an undetectable level. The defect in production of RNA4A was due to the 1a protein encoded by TAV RNA1, and partially restored by replacing the C-terminus (helicase domain) in TAV 1a with that of CMV 1a. Collectively, exchange of the replicase components between CMV and TAV was acceptable for viral replication, but was defective in either directing transcription of subgenomic RNA4A or facilitating viral long-distance movement. Our finding may shed some light on evolution of subgenomic RNA4A in the family Bromoviridae.
Highlights
Natural interspecific reassortant viruses containing heterologous replicase components have not been reported in viruses so far
Our work demonstrates that the exchange of RNA1 or RNA2 between cucumber mosaic virus (CMV) and tomato aspermy virus (TAV) was
Our work demonstrates that the exchange of RNA1 or RNA2 between CMV and TAV was acceptable for viral RNA replication in plants
Summary
Natural interspecific reassortant viruses containing heterologous replicase components have not been reported in viruses so far. One explanations could be that the heterologous replicase components are incompatible (e.g. with an absence of interaction) in directing the replication of viral RNAs in vivo. It is still unknown whether there are other factors limiting survival of such a reassortant. Proteins 1a and 2a are viral replicase components that form viral replication complex with host factors [5]. Among the six genera of Bromoviridae, only the members of Cucumovirus and Ilarvirus express the 2b protein that is translated from RNA4A, the subgenomic RNA of RNA2 [9,10,11]. The CMV 2b protein is one of the best-studied RNA silencing
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