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Title: Small deletions in the potato leafroll virus readthrough protein affect particle morphology, aphid transmission, virus movement and accumulation

item Peter,, Kari
item Liang,, Delin
item Palukaitis,, Peter
item Gray, Stewart

Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2007
Publication Date: 6/1/2007
Citation: Peter,, K., Liang,, D., Palukaitis,, P., Gray, S.M. 2007. Small deletions in the potato leafroll virus readthrough protein affect particle morphology, aphid transmission, virus movement and accumulation. Journal of General Virology. 88:1821-1830.

Interpretive Summary: Potato leafroll virus is a major economic disease of potatoes worldwide. Host resistance is only available in limited cultivars and the disease is difficult to control in the field. This research is aimed at understanding how one virus protein is able to influence the ability of the virus to cause disease in plant hosts as well as control the transmission of the virus by aphid vectors. We have shown previously that a minor structural protein of potato leafroll virus is able to influence both the movement of virus in a plant host as well as an aphid vector. The work reported here identifies that one particular portion of the protein is required for the virus to move into the salivary glands of the aphid. If this step is blocked the aphid cannot transmit the virus. Another portion of the virus protein is required for the virus to be able to move efficiently in the vascular tissues of the plant. If this portion of the protein is changed or deleted the virus is restricted to the site of inoculation or moves very slowly to other parts of the plant. Understanding how this virus protein works has identified potential mechanisms to target for novel control strategies that would either prevent transmission of the virus or prevent the virus from easily infecting the entire plant. Localized infections are less damaging to the plant and the virus cannot be easily transmitted to other plants.

Technical Abstract: Potato leafroll virus (PLRV) capsid comprises 180 coat protein (CP) subunits, with some percentage containing a readthrough domain (RTD) extension located on the particle’s surface. The RTD N-terminus is highly conserved in luteovirids and this study sought to identify biologically active sites within this region of the PLRV RTD. Fourteen three amino-acid-deletion mutants were generated from a cloned infectious PLRV cDNA and delivered to plants by Agrobacterium-inoculations. All mutant viruses accumulated locally in infiltrated tissues and expressed the readthrough protein (RTP) containing the CP and RTD sequences in plant tissues; however, when purified, only three mutant viruses incorporated the RTP into the virion. None of the mutant viruses were aphid transmissible, but the viruses persisted in the aphid for a period sufficient to allow for virus transmission. Several mutant viruses were examined further for systemic infection in four host species. All mutant viruses, regardless of RTP incorporation, moved systemically in each host, although they accumulated at different rates in systemically infected tissues. The RTP biological properties are sensitive to modifications in both the RTD conserved and variable region.