Improving molecular pharming with pathogen-derived effectors

The transient expression of proteins in plants offers unprecedented opportunities for the fast, safe, cheap and flexible production of vaccines, therapeutic antibodies and proteins for research purposes. Many proteins can be expressed in planta within days upon infiltrating leaves of the tobacco relative Nicotiana benthamiana (Nb) with Agrobacterium tumefaciens (agroinfiltration) carrying genes-of-interest on a transfer-DNA. Several companies use the agroinfiltration platform to produce vaccines (MedicaGo, Canada), antibodies (iBio, USA) and research proteins (LES, UK). However, although transiently expressed GFP can reach 50% of the total protein content, most recombinant proteins accumulate to a much lower level caused by e.g. immune responses induced by agroinfiltration, by mRNA degradation (silencing), and by bottlenecks in protein folding, secretion and post-translational modifications. The PROJECT AIM is to overcome these bottlenecks by identifying novel pathogen-derived effector proteins that boost recombinant protein expression levels. Plant pathogenic bacteria, fungi and oomycetes secrete hundreds of proteins that modify the host to suppress immunity and alter protein expression levels. Examples of these effectors are inhibitors of silencing, proteases, glycosidases and immune regulators. Silencing inhibitor P19, for instance, is an effector that is routinely used in agroinfiltration assays to boost recombinant protein expression through suppression of gene silencing.