Plant-infecting icosahedral viruses have recently provided a new class of bio-inspired architectures for non-genomic materials packaging.1–9
Virus-based nanoparticles (VNPs) are protein cages encapsulating a nanoscopic cargo that can be genetically engineered to achieve desired physical and chemical properties10–12
or can be used without any modification.4, 7, 9
Important features of VNPs include their monodisperse character, chemical addressability, and symmetric architecture that are potentially useful for targeted delivery.13
Until now, most such VNPs have been designed for biomedical applications such as vaccines, high-contrast functional imaging, and vascular delivery of therapeutic agents.11–12, 14–18
In certain cases, the VNP protein cage mimics the morphology and functional characteristics of wild-type virus capsids (VCs).9
Such constructs have promise as tools for studying virus-induced physiological responses.
In particular for plants, with their exact size and controllable surface chemistry, VNPs can be used for high-contrast functional imaging of vascular transport processes, making it possible to examine specific features such as determining the dimensions of the various pathway restrictions within plant vascular systems.19–23
Understanding vascular transport processes is crucial to environmental and agronomic concerns relating to biomass partitioning, water stress, and disease. Knowledge of the physical parameter(s) governing protein-based macromolecular movement in the plant vasculature is essential for researchers to better engineer plants (through either genetically engineered plants, breed crops for improved vascular flow, or nanotech engineering) for increased delivery of protein biomass to target tissues. Water stress is a crucial consideration in respect to the potential impact of climate change on rainfall and temperature, which are predicted to affect crop yields. With respect to disease, VNPs can be used to explore the fate of virion particles in host plants, and those vector interactions that result in the widespread dissemination of disease. When VNPs have magnetic properties imparted by their cargo, magnetic resonance imaging (MRI) can be employed for tracking VNP transit. To the best of our knowledge, there have been no attempts so far to explore these opportunities. In this paper, we report the first attempt towards comparing transport properties of VNPs made of Brome mosaic virus
(BMV) capsid proteins (CPs) and iron oxide NPs in a plant host (Nicotiana benthamiana
In a previous paper, we described the formation of VNPs around 20.1 nm iron oxide NPs coated with phospholipids containing a poly(ethyelene glycol) (PEG) tail of 2,000 Da with terminal carboxyl groups.7
The NPs were efficiently encapsulated by BMV VCs yielding 41 nm VNPs with narrow VNP size distribution (2.2% standard deviation).7
In the present work we report the formation of VNPs with cubic NP cores and the comparative study of the transit of cubic NPs functionalized with PEGylated phospholipids with and without viral coats in Nicotiana benthamiana leaves. We found that virus capsids influence both subcellular and long distance transport and that VNPs with magnetic cores can be transported across long distances and inside cells of different types.
Cubic iron oxide NPs of 18.6 nm in diameter were chosen for VNP formation because they can be unambiguously discriminated in a stained plant tissue from organelles and endogenous macromolecules and because they can carry adequate charge density for encapsulation.24
The MRI signature of cubic NPs was also studied to validate them as MRI contrast agents. We believe this work represents one of few examples that bridge bioinspired nano-architectures and phytology.25