Loss of function of cinnamyl alcohol dehydrogenase 1 leads to unconventional lignin and a temperature-sensitive growth defect in Medicago truncatula

There is considerable debate over the capacity of the cell wall polymer lignin to incorporate unnatural monomer units. We have identified Tnt1 retrotransposon insertion mutants of barrel medic (Medicago truncatula) that show reduced lignin autofluorescence under UV microscopy and red coloration in i...

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Bibliographic Details
Published in:	Proceedings of the National Academy of Sciences - PNAS 2013-08, Vol.110 (33), p.13660-13665
Main Authors:	Zhao, Qiao, Tobimatsu, Yuki, Zhou, Rui, Pattathil, Sivakumar, Gallego-Giraldo, Lina, Fu, Chunxiang, Jackson, Lisa A., Hahn, Michael G., Kim, Hoon, Chen, Fang, Ralph, John, Dixon, Richard A.
Format:	Article
Language:	eng
Subjects:	Acrolein - analogs & derivatives Acrolein - analysis Alcohol Oxidoreductases - deficiency Alcohol Oxidoreductases - genetics Alcohol Oxidoreductases - metabolism Alcohols Alfalfa Beans Biological Sciences Biosynthesis Cell Wall - chemistry Cell walls Cloning, Molecular Computational Biology Dehydrogenases Enzymes Genetic aspects Genotype & phenotype Greenhouses Growth Legumes Lignin Lignin - chemistry Lignin - metabolism Magnetic Resonance Spectroscopy Medicago truncatula - enzymology Medicago truncatula - growth & development Microarray Analysis Microscopy, Ultraviolet Mimosaceae Mutagenesis Mutation NMR Nuclear magnetic resonance Optical Imaging Pectin Phenotypes Physiological aspects Plant cells Plant genetics Plant growth Plants Retroelements - genetics Temperature
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Summary:	There is considerable debate over the capacity of the cell wall polymer lignin to incorporate unnatural monomer units. We have identified Tnt1 retrotransposon insertion mutants of barrel medic (Medicago truncatula) that show reduced lignin autofluorescence under UV microscopy and red coloration in interfascicular fibers. The phenotype is caused by insertion of retrotransposons into a gene annotated as encoding cinnamyl alcohol dehydrogenase, here designated M. truncatula CAD1 . NMR analysis indicated that the lignin is derived almost exclusively from coniferaldehyde and sinapaldehyde and is therefore strikingly different from classical lignins, which are derived mainly from coniferyl and sinapyl alcohols. Despite such a major alteration in lignin structure, the plants appear normal under standard conditions in the greenhouse or growth chamber. However, the plants are dwarfed when grown at 30 °C. Glycome profiling revealed an increased extractability of some xylan and pectin epitopes from the cell walls of the cad1-1 mutant but decreased extractability of others, suggesting that aldehyde-dominant lignin significantly alters cell wall structure.
ISSN:	0027-8424 1091-6490