INVESTIGATORS: Dixon, R.A.; Chen. F.
INSTITUTION: Samuel Roberts Noble Foundation
NON-TECHNICAL SUMMARY: Plant cell walls are made of three types of sugar polymer, cellulose, hemicellulose and pectin, and, as the cell wall develops, these are reinforced by lignin, a polymer of phenylpropane units (monolignols) that is recalcitrant to degradation. There are two stages involved in bioethanol production from lignocellulosic biomass: hydrolysis of the cell wall polysaccharides to their component hexose and pentose sugars, derived from cellulose/hemicellulose and hemicellulose respectively, and subsequent fermentation of the sugars to ethanol. The presence of lignin reduces access of enzymes and chemicals to hemicellulose and cellulose, thus reducing the efficiency of hydrolysis.
OBJECTIVES: The objectives of this proposal are 1) to determine which features of the lignocellulosic material (lignin content, lignin composition or other factors) are most detrimental to the fermentation of biomass to ethanol and 2) to develop the crop plant alfalfa (Medicago sativa) as a model system for genomic studies on biomass utilization.
APPROACH: Obj. 1. We have already generated transgenic alfalfa lines independently down-regulated in most (ten) of the enzymatic steps believed to be required for monolignol biosynthesis. Lignin content and composition have been determined in most of these lines (and cover a broader range of values than could be found in natural populations). The chemical analyses of the lignins will be completed, and the plant materials subjected to cell wall hydrolysis (acid and enzymatic) and fermentation. Yields of released sugars and bioethanol will be measured. We can then determine which features of the lignin polymer (content, composition, linkage types, etc) are most detrimental to sugar release and fermentation during bioethanol production, and design the optimal strategy for genetic modification of the plant feedstock for biofuel processing.
Obj. 2. Using genomic approaches (DNA microarray and informatics), we will discover additional genes necessary for lignin accumulation in alfalfa. These will be evaluated by down-regulation in transgenic plants as described above. We will develop approaches for non-biased discovery of genes impacting lignocellulose processing in Medicago truncatula, a model legume closely related to alfalfa, utilizing a large population of plants generated at the Noble Foundation that harbor transposon insertions. These lines will be screened for altered lignin properties by near infrared reflectance spectroscopy and simple staining procedures
Name: Dixon, R.A.