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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #114725
Title: CHANGES IN LIGNIN AND IN VIVO ACCUMULATION OF PHENOLIC GLUCOSIDES IN POPLARXYLEM UPON DOWNREGUALTION OF CAFFEOYL-COENZYME A O-METHYLTRANSFERASE AN ENZYME INVOLVED IN LIGNIN BIOSYNTHESIS

Author
item Ralph, John
item MARITA, JANE - UNIV OF WISCONSIN MADISON
item MEYERMANS, HUGO - U GHENT BELGIUM
item MORREEL, KRIS - U GHENT BELGIUM
item LAPIERRE, CATHERINE - INRA FRANCE
item POLLET, BRIGITTE - INRA FRANCE
item DE BRUYN, ANDRE - U GHENT BELGIUM
item BUSSON, ROGER - U LEUVEN BELGIUM
item KERDEWIJN, PIET - U LEUVEN BLEGIUM
item DEVREESE, BART - U GHENT BELGIUM

Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: A major component in all plants, lignin is a complex component that limits digestion of plants by animals, and is removed from wood to make paper. There has been interest recently in using genetic biotechnologies to knock out specific genes that produce crucial precursors of lignin to determine the potential for improved utilization of the plant cell wall in various natural and industrial processes. Workers at the University of Ghent in Belgium have decreased the expression (down-regulated) a specific lignin-producing gene in poplar trees, CCoAOMT. In these down-regulated transgenic plants, the lignin has been reduced by about 12%. As with other enzymes early in the lignin pathway, there has been little change in the structure of the core lignin; studies at the Dairy Forage Research Center show this lignin to be very similar to that in the wild type plant. However one component attached to the lignin, p-hydroxybenzoate esters, is approximately doubled. Other components build up in the plant and allow insight into the pathways by which lignin precursors are biosynthesized. Likely favored pathways are proposed, and compounds previously thought as lignin precursors are now in doubt. Similar transformations in forage crop plants will eventually be evaluated in attempts to improve digestibility by ruminants, potentially reducing animal wastes. Such studies are at the hear of efforts to improve agricultural sustainability and maximize our plant resources.

Technical Abstract: Caffeoyl-coenzyme A O-methyltransferase (CCoAOMT) methylates, in vitro, caffeoyl-CoA and 5-hydroxyferuloyl-CoA, two possible precursors of lignin biosynthesis in vivo. To clarify the in vivo role of CCoAOMT in lignin biosynthesis, transgenic poplars with 10% residual CCoAOMT protein levels in the stem xylem were generated. Upon analysis of the xylem, the affected transgenic lines had a 12% reduction in Klason lignin content, a slight increase in the syringyl/guaiacyl ratio in the noncondensed lignin fraction, an increase in lignin-attached p-hydroxybenzoic acid, but otherwise a lignin composition similar to that of wild-type. Stem xylem of the CCoAOMT-downregulated lines had a pink-red coloration, which coincided with an enhanced fluorescence of mature vessel cell walls. The reduced production of CCoAOMT caused an accumulation of 04-beta-D-glucopyranosyl- sinapic acid, showing that endogenously produced sinapic acid is not committed to syringyl biosynthesis. This result supports the recently obtained in vitro enzymatic data that suggest that the hydroxylation of ferulic acid to 5-hydroxyferulic acid does not play a major role in lignin biosynthesis. In addition, an accumulation of 03-beta-D-glucopyranosyl- caffeic acid and 04-beta-D-glucopyranosyl-vanillic acid was observed, which is consistent with the function of CCoAOMT in menthylating caffeoyl-CoA.