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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #167180
Title: PHENOLIC PROFILING OF CAFFEIC ACID O-METHYLTRANSFERASE-DEFICIENT POPLAR REVEALS NOVEL BENZODIOXANE OLIGOLIGNOLS

Author
item MORREEL, KRIS - GENT U., BELGIUM
item LU, FACHUANG - UW MADISON
item Ralph, John
item GOEMINNE, GEERT - GENT U., BELGIUM
item BUSSON, ROGER - LEUVEN U., BELGIUM
item HERDEWIJN, PIET - LEUVEN U., BELGIUM
item GOEMAN, JAN - GENT U., BELGIUM
item VAN DER EYCKEN, JOHAN - GENT U., BELGIUM
item BOERJAN, WOUT - GENT U., BELGIUM
item MESSENS, ERIC - GENT U., BELGIUM

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2004
Publication Date: 10/29/2004
Citation: Morreel, K., Lu, F., Ralph, J., Goeminne, G., Busson, R., Herdewijn, P., Goeman, J., Van Der Eycken, J., Boerjan, W., Messens, E. 2004. Phenolic profiling of caffeic acid o-methyltransferase-deficient poplar reveals novel benzodioxane oligolignols. Plant Physiology. 136:4023-4036.

Interpretive Summary: Lignin is a polymer that is mainly present in plant cell walls, where it provides strength and impermeability, allowing transport of water and solutes through the vascular system. There is wide interest in understanding the process of lignin biosynthesis and deposition because of its economic relevance: during chemical pulping, lignin needs to be extracted from the wood chips, a process that is expensive and environmentally hazardous. In addition, lignin limits the digestibility of forages. Hence, plant varieties with altered lignin contents may have improved performance as fodder crops or in the production of paper and pulp. The lignin polymer is made essentially from building blocks called monolignols. In addition, a variety of other phenolic compounds may be co-polymerized into the lignin polymer. In a previous paper we characterized the methanol-soluble, low molecular weight fraction of poplar xylem, a tissue which is heavily lignified. This fraction was severely depleted in transgenic poplars. Here we have identified the differences in the profile when a crucial lignin gene, COMT, is down-regulated. In addition to other differences, we identified high levels of 4 compounds that were exclusively detected in the COMT-deficient plants. These compounds reveal important clues to the biochemical changes that are occurring in these plants, and explain the novel structures we find in the lignin polymer from these plants. All products are consistent with a current theory for lignification involving 'combinatorial' chemical coupling reactions. Such studies are ultimately aimed at improving the utilization of valuable plant resources.

Technical Abstract: Caffeic acid O-methyltransferase (COMT) catalyzes preferentially the methylation of 5-hydroxyconiferaldehyde to sinapaldehyde in monolignol biosynthesis. Here, we have compared HPLC profiles of the methanol-soluble phenolics fraction of xylem tissue from COMT-deficient and control poplars, using statistical analysis of the peak areas. COMT down-regulation results in significant concentration differences for 25 of the 91 analyzed peaks of which the identity of 10 could be resolved. All of the differentially accumulating oligolignols involving sinapyl units were either reduced in abundance or became undetectable. Eight peaks were exclusively detected in COMT-deficient poplar of which 4 could be purified for further identification using MS/MS, NMR and spiking of synthesized reference compounds. These new compounds were derived from 5-hydroxyconiferyl alcohol or 5-hydroxyconiferaldehyde and were characterized by benzodioxane moieties, a structural type that is also increased in the lignins of COMT-deficient plants. One of these four benzodioxanes amounted to the most abundant oligolignol in the HPLC profile. The concentration levels of all identified oligolignols were in agreement with the relative supply of monolignols and with their chemical coupling propensities. For the benzodioxane oligolignols, both enantiomers were present in equal amounts, indicating that they were formed by radical coupling reactions under simple chemical control, rather than dirigent protein-guided.