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Abstract
Down-regulation of the gene encoding 4-coumarate 3-hydroxylase (C3H) in angiosperms massively but predictably increased the proportion of p-hydroxyphenyl (P) units relative to the normally dominant syringyl (S) and guaiacyl (G) units. Alfalfa stem levels of up to ~65% P (from wild-type (WT) levels of ~1%) resulting from down-regulation of C3H were measured by traditional degradative analyses as well as 2D 13C– 1H correlative NMR methods. Such levels put these transgenics well beyond the P:G:S compositional bounds of normal plants. NMR also revealed structural differences in the interunit linkage distribution that characterizes a lignin polymer. Less severely elevated P-levels were also detected in C3H-downreulated poplar and in HCT-downregulated P. radiata tracheid cultures, but with different structural effects. The compositional and structural changes remain consistent with the existing theory of lignification based on combinatorial radical coupling reactions under simple chemical control. Such structural differences form a basis for explaining differences in digestibility and pulping performance of C3H/HCT-deficient plants.
Keywords
Biosynthesis,
enzymes,
biotechnology,
nuclear magnetic resonance spectroscopy,
lignin analysis,
genetic engineering,
coumarins,
lignification,
pulping,
alfalfa,
transgenic plants,
poplar,
Pinus radiata,
down-regulation,
pulp and paper processes,
guaiacyl,
syringyl,
coumarate 3-hydroxylate,
hydroxyphenyl
Citation
Ralph, John; Akiyama, Takuya; Kim, Hoon; Lu, Fachuang; Ralph, Sally A.; Chapple, Clint; Nair, Ramesh B.; Wagner, Armin; Chen, Fang; Reddy, M.S. Srinivasa; Dixon, Richard A; Coleman, Heather D.; Mansfield, Shawn D. 2006. Lignification in transgenics deficient in 4-coumarate 3-hydroxylase (C3H)or the associated hydroxycinnamoyl transferase (HCT). Polyphenols communications 2006 : XXIII International Conference on Polyphenols, Winnipeg, Manitoba, Canada, August 22-25, 2006. [Winnipeg] : University of Manitoba, [2006]: ISBN: 0978158903: 9780978158903: [2] pages.
