A scientific publication has appeared describing our initial work on producing cellulase in chloroplasts, providing useful information to the scientific community.
impact statement issue
The cellulases that are currently utilized for cellulose breakdown are produced by microbial fermentation, adding considerably to the cost of bioenergy production. Production of cellulases in plants may be more cost-effective, especially if the plant material left after extraction of soluble cellulases can itself be used as feedstock for sugar production. Because chloroplast genomes are present in multiple copies in the plant cell, many copies of the cellulase gene can be obtained in the plant. Protein yields in the range of 5 to 20 percent total soluble protein should be feasible, given proper environmental conditions for plant growth.
impact statement response
While some proteins have been expressed at high levels in chloroplasts, the only products of transgenic plants that are currently sold commercially are those with nuclear-encoded transgenes. An advantage of chloroplast transgenes is their lack of transmission through pollen in most species. We have learned how to introduce genes into the chloroplasts of nicotine-free tobacco. We plan to insert transgenes encoding cellulases into the chloroplast under a variety of gene-regulatory signals. We will evaluate how much cellulase can be produced per fresh weight of plant tissue at different times in development under different plant-growth regimens and evaluate enzymatic activity and protein stability. Several bacterial cellulases have already been produced in plants at levels of 1 to 3 percent total soluble protein. Improvements in design of cellulase constructs have been made, resulting in increases in yield of cellulase.
impact statement summary
More information is needed about how best to design genes and plants that will allow high yield of novel commercial enzymes and pharmaceutical products. One valuable protein that could be produced in plants is cellulase, an enzyme that is needed to digest cellulose-containing biomass into sugar, which can be fermented into ethanol. We plan to focus on chloroplasts as prospective sites for synthesis of useful proteins.
