Commercial Plant-Produced Recombinant Cellulases for Biomass Conversion

Optimized expression of a hyperthermostable endoglucanase from Pyrococcus horikoshii in Arabidopsis thaliana

“…The endoglucanase Cel5A from Thermotoga maritima was expressed in tobacco targeted to different subcellular compartments, which showed no enzyme accumulation when it was targeted to cytosol but produced the highest endoglucanase activity when targeted to chloroplast (Mahadevan et al 2011). However, it was not evident which subcellular compartments were best for any particular protein (Hood and Requesens 2014). The endoglucanase E1 from A. cellulolyticus showed a low expression in plant cytosol (Ziegelhoffer et al 1999).…”

Transgene Biocontainment Strategies for Molecular Farming

“…Plants can also produce large volumes of industrial compounds. Examples of plant made industrial compounds (PMIs) include cellulases and amylases for bioethanol production, xylanases to enhance animal feed and oxidation/reduction enzymes such as laccases and peroxidases for paper manufacturing (Van Der Maarel et al, 2002;Bailey et al, 2004;Clough et al, 2006;Shen et al, 2012;Hood and Requesens, 2014). Currently, bioethanol is produced by using starch derived from corn.…”

Plant Molecular Farming: Much More than Medicines

“…Cell wall polymers such as lignocellulose and hemicellulose are abundant sources of fermentable sugars, but the sugars are not released as readily as they are from starch because the polymers tend to be cross-linked, structurally heterogeneous, and pseudocrystalline, making them recalcitrant to enzymatic hydrolysis without harsh and expensive pretreatments. A combination of several enzymes is then required to yield sugars from the recalcitrant biomass, and even conservative estimates suggest that up to 0.6 tons of pure enzyme would be needed to generate the 20 billion gallons of bioethanol that the United States has mandated for 2022, with an estimated infrastructure cost of nearly $30 billion to achieve this output using microbial fermentation (91).…”

“…Even so, the enzyme is expressed under the control of the embryo-preferred globulin-1 promoter, so defatted germ formulations can be used for industrial saccharification (91) as shown in Figure 2. Expression levels of >6% TSP were achieved (96) corresponding to 0.5% of the dry seed weight after seven backcrosses and two generations of selfpollination (91). Assuming that expression levels can be improved to 1% of the dry seed weight and that saccharification requires 30 g of enzyme per gallon of biofuel, a cultivation area of only 64 square miles for enzyme production would be sufficient to achieve an output of 20 million gallons of biofuel.…”