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Title: DUAL METHYLATION PATHWAYS IN LIGNIN BIOSYNTHESIS

Author
item ZHONG, RUIQIN - UNIVERSITY OF GEORGIA
item Morrison Iii, Wiley
item NEGREL, JONATHAN - LAB DE PHYS VEGETALE
item YE, ZHENG-HUA - UNIVERSITY OF GEORGIA

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Although the lignin biosynthetic pathway has been relatively well studied, there still are some unanswered questions regarding the steps in methoxylation. Standard pathways do not answer all the questions that arise with plants including tobacco, alfalfa, soybeans and tomatoes. This work clearly demonstrated an alternative methylation pathway and its affect ton lignin formation and the types of lignin (guaiacyl or syringyl lignin) produced and retarded as a result of engineered changes in pathways. This information opens new avenues and knowledge to the pulping industry because lignins with higher S/G ratios require fewer chemicals in the Kraft pulping.

Technical Abstract: Caffeoyl-coenzyme A (CoA) O-methyltransferase (CCoAOMT) has been proposed to be involved in an alternative methylation pathyway of lignin biosynthesis. However, no direct evidence has been available to confirm that CCoAOMT is essential for lignin biosynthesis. To understand further the methylation steps in lignin biosynthesis, we used an antisense approach hto alter O-methyltransferase (OMT) gene expression and investigated the consequences of this alteration. We generated transgenic tobacco plants with a substantial reduction in CCoAOMT as well as plants with a simultaneous reduction in both CCoAOMT and caffeic acid O-methyltransferase (CAOMT). Lignin analysis showed that the reduction in CCoAOMT alone resulted in a dramatic decrease in lignin content. The reduction in CCoAOMT also led to a dramatic alteration in lignin composition. Both guaiacyl lignin and syringyl lignin were reduced in the transgenic plants. However, guaiacyl lignin was preferentially reduced, which resulted in an increase in the S/G ratio. We have also analyzed lignin content and composition in transgenic plants having a simultaneous reduction in both CCoAOMT and CAOMT. The reduction in both OMT's resulted in a further decrese in total lignin content. This is in sharp contrast to the effect that resulted from the reduction in CAOMT alone, which only decreased the syringyl lignin units without a reduction in overall lignin content. These results unequivocally demonstrate that methylation reactions in lignin biosynthesis are catalyzed by both CCoAOMT and CAOMT.