title: Expression of UDP-glucose dehydrogenase reduces cell-wall polysaccharide concentration and increases xylose content in alfalfa stems.
abstract: The primary cell-wall matrix of most higher plants is composed of large amounts of uronic acids, primarily D-galacturonic acid residues in the backbone of pectic polysaccharides. Uridine diphosphate (UDP)-glucose dehydrogenase is a key enzyme in the biosynthesis of uronic acids. We produced transgenic alfalfa (Medicago sativa) plants expressing a soybean UDP-glucose dehydrogenase cDNA under the control of two promoters active in alfalfa vascular tissues. In initial greenhouse experiments, enzyme activity in transgenic lines was up to seven-fold greater than in nontransformed control plants; however, field-grown transgenic plants had only a maximum of 1.9-fold more activity than the control. Cell-wall polysaccharide content was lower and Klason lignin content was higher in transgenics compared to the nontransformed control. No significant increase in pectin or uronic acids in the polysaccharide fraction was observed in any line. Xylose increased 15% in most transgenic lines and mannose concentration decreased slightly in all lines. Because of the complexity of pectic polysaccharides and sugar biosynthesis, it may be necessary to manipulate multiple steps in carbohydrate metabolism to alter the pectin content of alfalfa.
authors.affiliation: USDA-ARS-Plant Science Research, 495 Borlaug Hall, 1991 Upper Buford Circle, University of Minnesota, St. Paul, MN 55108, USA. dasamac@umn.edu
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Samac
authors.forename: Lynn
authors.initials: L
authors.lastname: Litterer
authors.forename: Glena
authors.initials: G
authors.lastname: Temple
authors.forename: Hans-Joachim G
authors.initials: HJ
authors.lastname: Jung
authors.forename: David A
authors.initials: DA
authors.lastname: Somers
mesh_terms: D018533:Biomass; D001709:Biotechnology / Q000379:methods*; D002241:Carbohydrates / Q000737:chemistry; D002473:Cell Wall / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D000455:Medicago sativa / Q000378:metabolism*; D010368:Pectins / Q000737:chemistry; D030821:Plants, Genetically Modified; D011134:Polysaccharides / Q000737:chemistry*; D011401:Promoter Regions, Genetic; D012313:RNA / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014533:Uridine Diphosphate Glucose Dehydrogenase / Q000096:biosynthesis* / Q000737:chemistry*; D014994:Xylose / Q000737:chemistry*
chemical_list: D002241:Carbohydrates; D018076:DNA, Complementary; D011134:Polysaccharides; D012313:RNA; D010368:Pectins; D014994:Xylose; D014533:Uridine Diphosphate Glucose Dehydrogenase