Methylenetetrahydrofolate reductase modulates methyl metabolism and lignin monomer methylation in maize.
Methylenetetrahydrofolate reductase modulates methyl metabolism and lignin monomer methylation in maize.
复制标题
亚甲基四氢叶酸还原酶调节玉米中的甲基代谢和木质素单体甲基化。
DOI：
10.1093/jxb/ery208
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发表时间：
2018
影响因子：
6.9
通讯作者：
Fu Chunxiang
中科院分区：
文献类型：
--
作者：
Wu Zhenying;Ren Hao;Xiong Wangdan;Roje Sanja;Liu Yuchen;Su Kunlong;Fu Chunxiang
玉米的棕色中脉2（bm2）突变体具有改良的木质素成分，含有亚甲基四氢叶酸还原酶（MTHFR）基因的突变。在这里，我们发现 MITE 转座子插入导致 MTHFR 下调，伴随着 bm2 突变体中 5-甲基-四氢叶酸的减少以及 5, 10-亚甲基-四氢叶酸和四氢叶酸的增加。此外，MTHFR突变并没有改变参与愈创木基和紫丁香基木质素生物合成的甲基供体S-腺苷甲硫氨酸(SAM)的含量，但增加了SAM的去甲基化产物S-腺苷高半胱氨酸(SAH)的水平。此外，还发现SAH对玉米咖啡酰CoAO-甲基转移酶（CCoAOMT）和咖啡酸O-甲基转移酶（COMT）酶活性的竞争性抑制，表明SAH/SAM比率而不是SAM浓度调节木质素中间体的转甲基反应。酚谱分析显示咖啡酰醇葡萄糖衍生物在 bm2 突变体中积累，表明木质素单体的 3-O-甲基化受损。突变体中异常儿茶基木质素的显着增加表明MTHFR下调主要影响愈创木基木质素生物合成，这与CCoAOMT比COMT对SAH抑制更敏感的观察结果一致。这项研究揭示了木质素生物合成的一种新的调控机制，可能为未来利用木质纤维素原料提供一种有效的方法。
Thebrown 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 ofMTHFR, with an accompanying decrease in 5-methyl-tetrahydrofolate and an increase in 5, 10-methylene-tetrahydrofolate and tetrahydrofolate in thebm2mutant. Furthermore,MTHFRmutation did not change the content ofS-adenosyl methionine (SAM), the methyl group donor involved in the biosynthesis of guaiacyl and syringyl lignins, but increased the level ofS-adenosyl homocysteine (SAH), the demethylation product of SAM. Moreover, competitive inhibition of the maize caffeoyl CoAO-methyltransferase (CCoAOMT) and caffeic acidO-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 thebm2mutant, indicating impaired 3-O-methylation of monolignols. A remarkable increase in the unusual catechyl lignin in the mutant demonstrates thatMTHFRdown-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.