Plant molecular farming provides a safe, inexpensive, and scalable platform for producing high-value recombinant proteins. Plant-based expression of pharmaceuticals, such as vaccines in the form of virus-like particles (VLPs), has demonstrated the capacity of such systems to produce therapeutic proteins at industrial scale [1]. Other self-assembling heterologous proteins, such as carboxysomes and ferritins, have also been successfully expressed in plants [2, 3]. These examples demonstrate the ability of plants to correctly assemble recombinant nanoscale protein complexes.
Antimicrobial peptides (AMPs) provide an exciting class of therapeutic for tackling the rising spread of antimicrobial resistance. The biophysical properties of AMPs, with high positive charge and membrane-lytic activity, make them notoriously difficult to produce recombinantly [4]. As such, AMPs are typically manufactured by environmentally costly chemistry. Plant molecular farming offers a great alternative to these approaches, however a versatile platform for expressing AMPs in plants is yet to be developed.
Here, we explore the use of VLPs as tools for expanding the biosynthetic range of Nicotiana benthamiana. We find that transient expression of Salmonella typhimurium P22 bacteriophage coat proteins facilitates VLP assembly in planta. Through co-expression of cargo proteins which direct packaging within P22 VLPs and various protein engineering approaches, we investigate the capacity of this platform to enable AMP expression in plants. To our knowledge, this is the first report of VLPs from bacteriophage being expressed in plants and opens future possibilities for applications of these proteins in plant synthetic biology.