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Nanotechnology is an expanding interdisciplinary field concerning the development and application of nanostructured materials derived from inorganic compounds or organic polymers and peptides. Among these latter materials, proteinaceous plant virus nanoparticles have emerged as a key platform for the introduction of tailored functionalities by genetic engineering and conjugation chemistry. Tobacco mosaic virus and Cowpea mosaic virus have already been developed for bioimaging, vaccination and electronics applications, but the flexible and filamentous Potato virus X (PVX) has received comparatively little attention. The filamentous structure of PVX particles allows them to carry large payloads, which are advantageous for applications such as biomedical imaging in which multi-functional scaffolds with a high aspect ratio are required. In this context, PVX achieves superior tumor homing and retention properties compared to spherical nanoparticles. Because PVX is a protein-based nanoparticle, its unique functional properties are combined with enhanced biocompatibility, making it much more suitable for biomedical applications than synthetic nanomaterials. Moreover, PVX nanoparticles have very low toxicity in vivo, and superior pharmacokinetic profiles. This review focuses on the production of PVX nanoparticles engineered using chemical and/or biological techniques, and describes current and future opportunities and challenges for the application of PVX nanoparticles in medicine, diagnostics, materials science, and biocatalysis.

Plant viruses are suitable as building blocks for nanomaterials and nanoparticles because they are easy to modify and can be expressed and purified using plants or heterologous expression systems. Plant virus nanoparticles have been utilized for epitope presentation in vaccines, for drug delivery, as nanospheres and nanowires, and for biomedical imaging applications. Fluorescent protein fusions have been instrumental for the tagging of plant virus particles. The monomeric non-oxygen-dependent fluorescent protein iLOV can be used as an alternative to green fluorescent protein. In this study, the iLOV sequence was genetically fused either directly or via a glycine-serine linker to the C-terminus of the Tobacco mosaic virus (TMV) coat protein (CP) and also carried an N-terminal Foot-and-mouth disease virus (FMDV) 2A sequence. Nicotiana benthamiana plants were inoculated with recombinant viral vectors and a systemic infection was achieved. The presence of iLOV fusion proteins and hybrid particles was confirmed by western blot analysis and transmission electron microscopy. Our data suggest that TMV-based vectors are suitable for the production of proteins at least as large as iLOV when combined with the FMDV 2A sequence. This approach allowed the simultaneous production of foreign proteins fused to the CP as well as free CP subunits.