Summary auto-generated
This study demonstrates that the 2b gene is a conserved and expressed feature of the Cucumovirus genus. The researchers detected in vivo expression of the overlapping 2b gene in two additional cucumovirus strains: tomato aspermy virus V strain (V-TAV) and cucumber mosaic virus WAII strain (WAII-CMV). Using Northern blot analysis, they confirmed accumulation of RNA 4A (the mRNA encoding the 2b gene) in infected plants. For V-TAV, they produced antiserum against the 2b protein and detected protein accumulation in infected Nicotiana glutinosa plants via Western blotting, with the protein showing unusual solubility properties suggesting membrane or cell wall association. For WAII-CMV, RNA 4A accumulated in plants but was minimally encapsidated in virions, contrasting with Q-CMV and V-TAV where RNA 4A was robustly packaged. Since the 2b gene is conserved across all 10 sequenced cucumoviral species or strains and expression is now confirmed for three viruses, the authors conclude that 2b is a common feature of the Cucumovirus genus.
Key findings
- The 2b overlapping gene is expressed in vivo in V-TAV and WAII-CMV, confirmed by detection of RNA 4A mRNA and 2b protein in infected plants
- RNA 4A encodes the complete 2b open reading frame and is 702 nt in V-TAV and 690 nt in WAII-CMV
- V-TAV and WAII-CMV RNA 4A show different encapsidation patterns: V-TAV RNA 4A is robustly packaged in virions while WAII-CMV RNA 4A accumulates in plants but is minimally encapsidated
- The 2b gene is conserved in all 10 cucumoviruses sequenced to date, making it a common genomic feature of the genus
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Abstract
We recently reported the molecular characterization and functional analysis of an overlapping gene 2b encoded by RNA 2 of the Q strain of cucumber mosaic cucumovirus (Q-CMV). We show here that the homologous gene encoded by the V strain of tomato aspermy cucumovirus (V-TAV) and the WAII strain of CMV (WAII-CMV), which is in a different subgroup to Q-CMV, is also expressed in vivo by demonstrating the accumulation of the mRNA (RNA 4A) and its protein in infected plants. Interestingly, RNA 4A of V-TAV is encapsidated in virions as found previously for Q- CMV whereas WAII-CMV contains very little RNA 4A in virions. As the 2b gene is conserved in all 10 cucumoviral species or strains sequenced to date and the 2b gene is expressed for three of these viruses, we conclude that the 2b gene is a common feature of the Cucumovirus genus.