Growing fuel and medicine: Advancing biofuels and plant-produced therapeutics

"The Many Reasons Why Plants Also Need Their Vitamin C!"

Argelia Lorence, PhD Assistant Professor of Metabolic Engineering, Arkansas Bioscience Institute, Arkansas State University

Humans and several other animals are unable to synthesize vitamin C (ascorbate, AsA) and thus they are dependent on dietary sources, mainly fresh fruits and produce, to fulfill their requirements for this nutrient. In plants, AsA is one of the major carbohydrates and antioxidants that play a role in essential physiological processes such as photosynthesis, cell division, and stress tolerance. Although ascorbate as a chemical entity is an old molecule, the elucidation of how plants make this vitamin is a recent discovery. Four different pathways are known to be functional in plants, one of them proposed by our group involving myo-inositol (MI) as the main precursor. We have engineered elevated AsA levels in Arabidopsis by over-expressing MI oxygenase (MIOX4) and L-gulono-1,4-lactone oxidase (GLOase), enzymes involved in the MI pathway to AsA. One of our current objectives is to study the stress tolerance and growth of these high AsA lines. MIOX4 and GLOase over-expressers were challenged with various types of abiotics stresses and their growth and performance was compared to the one of wild type controls. MIOX4 or GLOase lines containing higher AsA content (2 to 3-fold), were more tolerant to salt, cold, heat, high light, and methyl viologen when compared to controls. They also displayed enhanced growth of both aerial and underground tissues. In addition, these lines exhibited tolerance to common environmental pollutants such as trichloroethylene, a chlorinated hydrocarbon, and pyrene, a model polycyclic aromatic hydrocarbon. These broad stress-tolerance responses are most likely due to the ability of AsA to detoxify reactive oxygen species. In addition, I will also present our progress on the characterization of two novel enzymes involved in the MI pathway to AsA and well as our efforts in investigating how these high AsA mustard lines respond when challenged with herbivores. Engineering crops to have elevated vitamin C may lead to delayed senescence, increased biomass, stress tolerance, and enhanced phytoremediation capabilities.

"Cellulase enzymes for biomass conversion from the transgenic maize production system"

Elizabeth Hood, PhD, Associate Vice Chancellor for Research and Technology Transfer, Arkansas Bioscience Institute, Arkansas State University

One of the major constraints with production of lignocellulosic ethanol is the cost and volume of enzymes required to digest the feedstock. Enzymes produced in commodity crops can resolve both of these issues. We have developed transgenic maize plants that produce E1 -D-glucosidase and cellobiohydrolase I in seed. Enzyme amounts in the first generation seed for both enzymes were as high as17 percent of total soluble protein. Our results suggest that enzyme amount is affected by several factors including subcellular localization and the promoter used to drive gene expression. Southern hybridization analysis indicates that the gene is present at one copy per genome, simplifying breeding and regulatory issues. Protein accumulation can be increased several fold over multiple generations through breeding (Hood et al., 2003), thus it is our expectation that cellulase accumulation can be improved to 3-5 percent of dry weight. This concentration of cellulase can provide for a cost-effective enzyme supply for the developing biomass to ethanol industry.