Abstract:
Conversion of lignocellulosic biomass to biofuels and biomaterials suffers from high production costs
associated with biomass pretreatment and enzymatic hydrolysis. In-planta expression of lignocellulosedigesting
enzymes is a promising approach to reduce these cost elements. However, this approach
faces a number of challenges, including auto-hydrolysis of developing cell walls, plant growth and
yield penalties, low expression levels and the limited stability of expressed enzymes at the high
temperatures generally used for biomass processing to release fermentable sugars. To overcome these
challenges we expressed codon-optimized recombinant hyperthermophilic endoglucanase (EG) and
xylanase (Xyn) genes in A. thaliana. Transgenic Arabidopsis lines expressing EG and Xyn enzymes at
high levels without any obvious plant growth or yield penalties were selected for further analysis.
The highest enzyme activities were observed in the dry stems of transgenic lines, indicating that the
enzymes were not degraded during stem senescence and storage. Biomass from transgenic lines
exhibited improved saccharification efficiency relative to WT control plants. We conclude that the
expression of hyperthermophilic enzymes in plants is a promising approach for combining pretreatment
and enzymatic hydrolysis processes in lignocellulosic digestion. This study provides a valid foundation
for further studies involving in planta co-expression of core and accessory lignocellulose-digesting
enzymes.
