Accumulation of Cellulase in Transgenic Maize Seeds

One of the key steps in producing bioethanol from lignocellulosic biomass is the digestion of the polysaccharide components of plant cell walls into simple sugar molecules. The step is being catalyzed by the enzyme cellulases. Current enzyme production systems, mostly based on extraction from microorganisms, however, are not cost-effective. Cellulose is degraded by a synergistic action of two cellulase enzymes: an endonuclease responsible for cleaving the cellulose chain internally and an exonuclease which is responsible for further cutting the polymer streams.

A group of US scientists successfully produced transgenic maize lines expressing both enzymes. The ratio of these enzymes, 1 endonuclease: 4 exonuclease, is necessary for efficient digestion of cellulose. Whereas other transgenic systems prove to be problematic in obtaining the correct ratio, the maize seed production system was found to overcome this difficulty. The expression of the exonuclease was found to be nearly 1000-fold higher than the expression in any other plant reported in the literature. The expression of the cellulase enzymes was found to be stable for a number of generations. Subcellular targeting proves to be important in obtaining the desired ratio of the two enzymes. The vacuole and the endoplasmic reticulum were found to support large-scale accumulation of the enzymes.

Read the abstract http://www.blackwell-synergy.com/doi/abs/10.1111/j.1467-7652.2007.00275.x or the full paper http://www.blackwell-synergy.com/doi/full/10.1111/j.1467-7652.2007.00275.x