Page 119 - PC2019 Program & Proceedings

PLANT CANADA 2019

S23. Plant proteases: a continuous battle in molecular farming
Varennes-Jutras, P.; I. Dodds; R. van der Hoorn
University of Oxford

Over the past decade, clear evidence has uncovered the role of proteases in unwanted protein proteolysis
in plant molecular farming. Proteolytic degradation remains a significant problem and restricts industrial
viability of plant-based expression platforms. Controlling plant protease activity is an effective approach
to improve the accumulation of recombinant proteins. However, the molecular functions of many
proteases, including their regulators and their natural substrates, are mostly unknown. Hundreds of genes
code for proteolytic enzymes of various classes involved in many biological processes in plants.
Recombinant proteins are thus exposed to a large and complex proteolytic network. A better
characterization of the plant protease repertoire is essential to identify the principal constituents of the
recombinant protein degradation machinery. We here present the diversity of unrelated plant protease
families and discuss the recent developments towards a solution to the proteolytic degradation problem.
We exemplify the role of activity-based protein profiling to identify proteases and reveal candidate
proteases for depletion strategies.

Philippe Varennes-Jutras (philippe.varennes-jutras@plants.ox.ac.uk)

S24. Development of LED light quality to optimise recombinant protein expression in Nicotiana
benthamiana
Ratcliffe, S. *
University of Guelph

Valuable recombinant proteins such as those used in medical therapies can be mass produced in cost
efficient plant-based systems. Plantform Corporation has developed a platform for expressing
recombinant therapeutic antibodies based on transient expression of genes encoding therapeutic proteins
introduced into Nicotiana benthamiana host plants by Agrobacterium tumefaciens. One therapeutic that
the company has been developing production procedures for is trastuzumab, an IgG antibody used in
breast cancer treatment and marketed under the name of Herceptin®. Environmental growth parameters
can be manipulated to alter a plant’s physiology. Among these, light quality is a key driver of metabolic
pathways. Controlled environment chambers and tunable LED arrays were used to create eight separate
spectral environments. The available LEDs used for this study were; (1) Red [655 nm], (2) Blue [448 nm]
(3) Green [568 nm] (4) White [5650 K] and (5) Far-Red [735 nm]. Four visible mono-chromatic spectra
and four mixed spectra were selected as the eight treatment groups. At the end of the plant production
cycle, morphology was assessed, and biomass was analysed for total soluble protein and amount of IgG.
Morphological parameters such as leaf biomass, leaf area and total biomass showed up to a 20%
difference between treatments. The difference in IgG expression between treatment groups was shown to
be up to 30%. Light quality can alter transient protein expression in plant-based systems.

Sean Ratcliffe (sratclif@uoguelph.ca)

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