Structural and compositional modifications in lignin of transgenic alfalfa down-regulated in caffeic acid 3-O-methyltransferase and caffeoyl coenzyme A 3-O-methyltransferase.
Isolated lignins from alfalfa deficient in caffeic acid 3-O-methyltransferase contained benzodioxanes resulting from the incorporation of the novel monomer, 5-hydroxyconiferyl alcohol. Due to the high level incorporated into the soluble lignin fraction and the use of sensitive NMR instrumentation, unique structural features were revealed. A new type of end-unit, the 5-hydroxyguaiacyl glycerol unit, was identified. It was possible to establish that coniferyl alcohol, sinapyl alcohol, and the novel 5-hydroxyconiferyl alcohol can cross-couple with the 5-hydroxyguaiacyl units that are formed in the lignin, the latter giving rise to extended chains of benzodioxane units. There is also evidence that 5-hydroxyconiferyl alcohol couples with normal (guaiacyl or syringyl) lignin units. Lignin in the alfalfa deficient in caffeoyl CoA 3-O-methyltransferase was structurally similar to the control lignin but the transgenic exhibited a dramatic decrease in lignin content (approximately 20%) and modest increase in cellulose (approximately 10%) reflecting a 30% increase in cellulose:lignin ratio. The compositional changes in both transgenics potentially allow enhanced utilization of alfalfa as a major forage crop by increasing the digestibility of its stem fraction.
Marita
Jane M
JM
US Dairy Forage Research Center, USDA-Agricultural Research Service, 1925 Linden Drive West, Madison, WI 53706-1108, USA.
Ralph
John
J
Hatfield
Ronald D
RD
Guo
Dianjing
D
Chen
Fang
F
Dixon
Richard A
RA
D015536:Down-Regulation; D008031:Lignin / Q000032:analysis / Q000096:biosynthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D000455:Medicago sativa / Q000737:chemistry* / Q000201:enzymology* / Q000235:genetics; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D015394:Molecular Structure; D030821:Plants, Genetically Modified
D008031:Lignin; D008780:Methyltransferases; C059825:caffeoyl-CoA O-methyltransferase; C019608:caffeate O-methyltransferase