Researchers Modifying Corn With Genes to Produce Enzymes to Enable Simpler Production of Cellulosic Ethanol
Researchers at Michigan State University (MSU) are modifying the corn genome to enable the production of enzymes, within the corn biomass, needed to convert cellulose into fermentable sugar. This capability reduces the need for pretreatment of the biomass for the production of cellulosic ethanol. The transgenic corn plants produce these enzymes only in their leaves and stalk, and store them in sub-cellular compartments (the vacuoles).
The most recent version of the engineered corn—Spartan Corn III—now uses three enzymes from different sources: the thermophilic Acidothermus cellulolyticus E1 endo-cellulase; the fungal Trichoderma reesei (CBH1) exo-cellulase; and, the most recent addition, the microbial Butyrivibrio fibrisolvens H17c beta-glucosidase. MSU professor of crop and soil science Mariam Sticklen is presenting a talk on her team’s work at the 235th national meeting of the American Chemical Society this week in New Orleans, Louisiana.
The fact that we can take a gene that makes an enzyme in the stomach of a cow and put it into a plant cell means that we can convert what was junk before into biofuel.—Mariam Sticklen
The first version of the corn—Spartan Corn I—added the endo-cellulase enzyme that cuts the cellulose into large pieces. Spartan Corn II added an exo-cellulase enzyme that breaks the cellulose pieces created by the first enzyme into sugar pairs.
Spartan Corn III uses the beta-glucosidase enzyme produced by a gene from the microbe in a cow’s rumen to separate pairs of sugar molecules into simple sugars. These single sugars are then readily fermentable into ethanol.
The DNA assembly of the animal stomach microbe required heavy modification in the lab to make it work well in the corn cells.
There are a lot of changes. We have to increase production levels and even put it in the right place in the cell.—Mariam Sticklen
If the cell produced the enzyme in the wrong place, then the plant cell would not be able to function, and, instead, it would digest itself. One of the targets for the enzyme produced in Spartan Corn III is the vacuole of the cell. The enzyme will collect in the vacuole with other cellular waste products.
Because it is only in the vacuole of the green tissues of plant cells, the enzyme is only produced in the leaves and stalks of the plant, not in the seeds, roots or the pollen.
Sticklen’s research was funded by the US Department of Energy and Edenspace Systems Corp., the Consortium for Plant Biotechnology Research, and MSU Research Excellence Funds. The work will also be presented in the article “Plant Genetic Engineering for Biofuel Production: Towards Affordable Cellulosic Ethanol” in the June edition of Nature Reviews Genetics.
Modifying the corn genome to meet the US biofuel agenda (ACS National Meeting, CINF 66)