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Genomic Science Program

2006 Awardee

Systematic Modification of Monolignol PathwayGene Expression for Improved LignocelluloseUtilization

INVESTIGATORS: Dixon, R.A.; Chen. F.

INSTITUTION: Samuel Roberts NobleFoundation

NON-TECHNICAL SUMMARY: Plant cell wallsare 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 phenylpropaneunits (monolignols) that is recalcitrant to degradation.There are two stages involved in bioethanol production fromlignocellulosic biomass: hydrolysis of the cell wallpolysaccharides to their component hexose and pentosesugars, derived from cellulose/hemicellulose andhemicellulose respectively, and subsequent fermentation ofthe sugars to ethanol. The presence of lignin reducesaccess of enzymes and chemicals to hemicellulose andcellulose, thus reducing the efficiency of hydrolysis.

OBJECTIVES: The objectives of thisproposal are 1) to determine which features of thelignocellulosic material (lignin content, lignincomposition or other factors) are most detrimental to thefermentation of biomass to ethanol and 2) to develop thecrop plant alfalfa ( Medicago sativa ) as a modelsystem for genomic studies on biomass utilization..

APPROACH: Obj. 1. We have already generated transgenic alfalfa linesindependently down-regulated in most (ten) of the enzymaticsteps believed to be required for monolignol biosynthesis.Lignin content and composition have been determined in mostof these lines (and cover a broader range of values thancould be found in natural populations). The chemicalanalyses of the lignins will be completed, and the plantmaterials subjected to cell wall hydrolysis (acid andenzymatic) and fermentation. Yields of released sugars andbioethanol will be measured. We can then determine whichfeatures of the lignin polymer (content, composition,linkage types, etc) are most detrimental to sugar releaseand fermentation during bioethanol production, and designthe optimal strategy for genetic modification of the plantfeedstock for biofuel processing.

Obj. 2. Using genomic approaches (DNA microarray andinformatics), we will discover additional genes necessaryfor lignin accumulation in alfalfa. These will be evaluatedby down-regulation in transgenic plants as described above We will develop approaches for non-biased discovery ofgenes impacting lignocellulose processing in Medicagotruncatula , a model legume closely related to alfalfa,utilizing a large population of plants generated at theNoble Foundation that harbor transposon insertions. Theselines will be screened for altered lignin properties bynear infrared reflectance spectroscopy and simple stainingprocedures


Name: Dixon, R.A.
Phone: 580-224-6601
Fax: 580-224-6692



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