Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2009
Publication Date: 11/30/2009
Citation: Hammond, R., Hammond, J. 2009. Maize rayado fino virus capsid proteins assemble into virus-like particles in Escherichia coli. Virus Research. 147:208-215. Interpretive Summary: The leafhopper-borne Maize rayado fino virus (MRFV) is restricted to the Americas and is widespread over several ecological conditions and vegetation zones. MRFV may cause up to 100% mature ear weight loss in recently introduced cultivars of maize. MRFV is the type member of a group of not well characterized plant viruses that have the ability to multiply both in their plant and insect hosts. Unlike other viruses that can multiply in their plant and insect hosts and whose genomes are large and complex, MRFV has a small and simple genome and presents a unique opportunity to investigate the molecular interactions between the virus and its hosts with implications for disease control. In the present study, we have addressed the lack of knowledge of the genome expression strategy of MRFV by determining the requirements for capsid protein assembly in a bacterial system and in plants. The capsid proteins were found to self-assemble into non-infectious, uniform, spherical virus-like particles (VLPs) that are either empty or are capable of incorporating RNA, and they appear to be stabilized by protein-protein interactions. These results will be of interest to plant and animal virologists who are studying virus genome expression and particle assembly. In addition, the VLPs would have potential use as biotemplates for applications in nanotechnology.
Technical Abstract: Maize rayado fino virus (MRFV; genus Marafivirus; family Tymoviridae) is a small spherical plant virus that contains two components: empty shells and complete virus particles (encapsidating the 6.3 kb genomic RNA). Virions are approximately 30 nm in diameter and composed of two serologically related, carboxy co-terminal, unglycosylated coat proteins (CP) of apparent molecular mass 22 kDa (CP2) and 28 kDa (CP1), and found in a molar ratio of 3:1, respectively. Recombinant CP1 and CP2 were each found to self-assemble into virus-like particles (VLPs) in Escherichia coli and Nicotiana benthamiana, using plasmid vectors based on pET or pGD, respectively. Expression of each protein alone in E. coli resulted in VLPs that appeared either empty (CP2) (stain penetrated particles) or complete (CP1) in electron microscopy. In N. benthamiana, expression of CP1 resulted in translation of both CP1 and CP2, in contrast to what was found in E. coli, and production of VLPs that appear to be complete. Co-expression of CP1 and CP2 in the pDUET vector resulted in the assembly of VLPs which were found to encapsidate the CP mRNA, suggesting that the N-terminal 37 amino acid residues of CP1 may be involved in RNA-protein interactions in the assembly of complete virion particles.