In vivo expression of an overlapping gene encoded by the cucumoviruses.

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.