Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2004
Publication Date: 1/1/2005
Citation: Lee, L., Kaplan, I., Ripoll, D., Liang, D., Palukaitis, P., Gray, S.M. 2005. A surface loop of the potato leafroll virus coat protein is involved in virion assembly, systemic movement and aphid transmission. Journal of Virology. 79:1207-1214. Interpretive Summary: The Luteoviridae family is one of the most economically important groups of plant viruses affecting many of the world's staple food crops. Natural or engineered host plant resistance has not been identified for many of the viruses despite intensive efforts. Other control measures are generally ineffective or economically prohibitive. An alternative control strategy, and the underlying goal of this research, is to disrupt the transmission of the virus by its aphid vector. This might be accomplished by preventing or reducing the ability of the virus to circulate through an aphid or by limiting the virus available to the aphid as it feeds. Our research identified specific amino acids in the virus capsid protein that regulate the movement of virus through aphids and plants. These findings could promote the development of specific compounds that block circulative transmission of viruses in aphids and/or virus movement and accumulation in plants. These compounds could possibly be expressed in transgenic plants and provide an alternate strategy to control virus epidemics. Furthermore, the mechanisms of transmission of luteoviruses have many similarities to the transmission mechanisms of numerous other arthropod-borne plant, animal and human viruses. The fundamental knowledge gained from this system and the techniques developed to study these interactions are likely to be applicable to other systems allowing a more rapid advancement in the development of strategies to control other arthropod-borne viruses.
Technical Abstract: Two acidic domains of the potato leafroll virus (PLRV) coat protein, separated by 55 amino acids and predicted to be adjacent surface features on the virion, were the focus of a mutational analysis. Eleven site-directed mutants were generated from a cloned infectious cDNA of PLRV and delivered to plants using Agrobacterium-mediated mechanical inoculation. Alanine substitutions of any of the three amino acids of the sequence EWH (amino acids 170-172) or of D177 disrupted the ability of the coat protein to assemble stable particles and the ability of the viral RNA to move systemically in four host plant species. Alanine substitution of E109, D173 or E176 reduced the accumulation of virus in agroinfiltrated tissues, the efficiency of systemic infection, and the efficiency of aphid transmission relative to wild-type virus, but the mutations did not affect virion stability. A structural model of the PLRV capsid predicted that the amino acids critical for virion assembly were located within a depression at the center of a coat protein trimer. The other amino acids that affected plant infection and/or aphid transmission were predicted to be located around the perimeter of the depression. Virions of PLRV play key roles in phloem-limited virus movement in plant hosts, as well as in transport and persistence in the aphid vectors. These results identified amino acid residues in a surface orientated loop of the coat protein that are critical for virus assembly and stability, systemic infection of plants, and movement of virus through aphid vectors.