The readthrough domain of pea enation mosaic virus coat protein is not essential for virus stability in the hemolymph of the pea aphid
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A fraction of the coat protein (CP) subunits in virions of members of the family Luteoviridae contain a C-terminal extension called the readthrough domain (RTD). The RTD is necessary for persistent aphid transmission, but its role is unknown. It has been reported to be required for virion stability in the hemolymph. Here, we tested whether this was the case for pea enation mosaic virus (PEMV) virions in the pea aphid (Acyrthosiphon pisum) using RNA1Δ, a natural deletion mutant lacking the middle portion of the RTD ORF, and CPΔRTD, in which the entire RTD ORF was deleted. In infected plants, RNA1Δ virions were as abundant and stable as wild-type (WT) virions, while CPΔRTD virions were unstable. No RTD of any size was translated from artificial subgenomic mRNA of CPΔRTD or RNA1Δ in vitro. Thus, only the major CP was present in the mutant virions. Using real-time RT-PCR to detect virion RNA, no significant differences in the concentration or stability of WT and RNA1Δ virions were detected in the aphid hemolymph at much longer times than are necessary for virus transmission. Thus, the RTD is not necessary for stability of PEMV RNA in the aphid hemolymph, and it must play another role in aphid transmission.
The authors thank the late Dr. Gus A. de Zoeten for generously providing the infectious clones of the PEMV genome, and Dr. Robert L. Harrison for making the anti-PEMV antiserum. This work was funded by the USDA North Central Biotechnology Program 97-34340-39087 to BCB and WAM, and USDA grant number 2005-35607-15233 to WAM and BCB. This journal paper of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project No. 6651, was supported by Hatch Act and State of Iowa funds.
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