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Methylenetetrahydrofolate Reductase Modulates Methyl Metabolism and Lignin Monomer Methylation in Maize

Methylenetetrahydrofolate Reductase Modulates Methyl Metabolism and Lignin Monomer Methylation in Maize

Zhenying Wu, Hao Ren, Wangdan Xiong, Sanja Roje, Yuchen Liu, Kunlong Su, Chunxiang Fu

J Exp Bot. 2018 Jul 18;69(16):3963-3973.

PMID: 29860438

Abstract:

The brown midrib2 (bm2) mutant of maize, which has a modified lignin composition, contains a mutation in the methylenetetrahydrofolate reductase (MTHFR) gene. Here, we show that a MITE transposon insertion caused down-regulation of MTHFR, with an accompanying decrease in 5-methyl-tetrahydrofolate and an increase in 5, 10-methylene-tetrahydrofolate and tetrahydrofolate in the bm2 mutant. Furthermore, MTHFR mutation did not change the content of S-adenosyl methionine (SAM), the methyl group donor involved in the biosynthesis of guaiacyl and syringyl lignins, but increased the level of S-adenosyl homocysteine (SAH), the demethylation product of SAM. Moreover, competitive inhibition of the maize caffeoyl CoA O-methyltransferase (CCoAOMT) and caffeic acid O-methyltransferase (COMT) enzyme activities by SAH was found, suggesting that the SAH/SAM ratio, rather than the concentration of SAM, regulates the transmethylation reactions of lignin intermediates. Phenolic profiling revealed that caffeoyl alcohol glucose derivatives accumulated in the bm2 mutant, indicating impaired 3-O-methylation of monolignols. A remarkable increase in the unusual catechyl lignin in the mutant demonstrates that MTHFR down-regulation mainly affects guaiacyl lignin biosynthesis, consistent with the observation that CCoAOMT is more sensitive to SAH inhibition than COMT. This study uncovered a novel regulatory mechanism in lignin biosynthesis, which may offer an effective approach to utilizing lignocellulosic feedstocks in the future.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP3598263	Caffeoyl alcohol		3598-26-3	Price

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