Alteration of S‐adenosylhomocysteine levels affects lignin biosynthesis in switchgrass

First author: Zetao Bai; Affiliations: Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences (中科院青岛生物能源与过程研究所): Qingdao, China

Corresponding author: Chunxiang Fu (付春祥)

Methionine (Met; 甲硫氨酸) synthesized from aspartate (天冬氨酸) is a fundamental amino acid needed to produce S‐adenosylmethionine (SAM; S-腺苷蛋氨酸) that is an important cofactor (辅因子) for the methylation of monolignols. As a competitive inhibitor (竞争性抑制剂) of SAM‐dependent methylation, the effect of S‐adenosylhomocysteine (SAH; S-腺苷同型半胱氨酸) on lignin biosynthesis, however, is still largely unknown in plants. Expression levels of Cystathionine γ‐synthase (PvCGS; 胱硫醚-γ-合酶) and S‐adenosylhomocysteine hydrolase1 (PvSAHH1; S-腺苷同型半胱氨酸水解酶) were downregulated by RNAi technology, respectively, in switchgrass (柳枝稷), a dual‐purpose forage and biofuel crop. The transgenic switchgrass lines were subjected to studying the impact of SAH on lignin biosynthesis. Our results showed that downregulation of PvCGS in switchgrass altered the accumulation of aspartate‐derived and aromatic amino acids (芳香族氨基酸), reduced the content of SAH, enhanced lignin biosynthesis, and stunted (阻碍…发育) plant growth. In contrast, downregulation of PvSAHH1 raised SAH levels in switchgrass, impaired (损害) the biosynthesis of both guaiacyl and syringyl lignins (愈创木基木质素和紫丁香基木质素), and therefore significantly increased saccharification efficiency (糖化效率) of cell walls. This work indicates that SAH plays a crucial role in monolignol methylation in switchgrass. Genetic regulation of either PvCGS or PvSAHH1 expression in switchgrass can change intracellular SAH contents and SAM to SAH ratios and therefore affect lignin biosynthesis. Thus, our study suggests that genes involved in Met metabolism are of interest as new valuable targets for cell wall bioengineering in future.

甲硫氨酸由天冬氨酸合成，是合成S-腺苷蛋氨酸SAM基础的氨基酸，而SAM又是木质素单体甲基化的重要辅因子。S-腺苷同型半胱氨酸SAH作为SAM依赖性甲基化的竞争抑制剂，我们关于其对植物木质素生物合成的影响了解得还不多。作者通过RNAi技术在重要饲料和生物燃料作物柳枝稷中分别下调表达了胱硫醚-γ-合酶PvCGS基因和S-腺苷同型半胱氨酸水解酶PvSAHH1基因。柳枝稷转基因株系用于研究SAH对于木质素生物合成的影响。本文研究显示下调表达柳枝稷PvCGS基因会改变源自天冬氨酸和芳香族氨基酸的积累，减少SAH的含量，增强木质素的生物合成，延缓植株的生长发育。相反，下调表达柳枝稷PvSAHH1基因则会增加SAH的水平，减少愈创木基（G型）和紫丁香基（S型）两种木质素的生物合成，因此显著增强了细胞壁的糖化效率。本文的工作揭示了柳枝稷中SAH在木质素单体甲基化上所起到的重要作用。通过对于PvCGS或者PvSAHH1基因表达的遗传调控能够改变细胞内SAH含量和SAM/SAH比例，进而影响木质素的生物合成。本文的研究表明参与甲硫氨酸代谢的基因可以作为未来细胞壁生物工程的新的候选靶标。

通讯：付春祥 (http://sourcedb.cas.cn/sourcedb_qibebt_cas/zw/zjrc/201404/t20140401_4084317.html)

个人简介：2007年，中科院植物研究所，博士；2007-2011年，美国The Samuel Roberts Noble Foundation，能源植物和牧草的遗传改良和分子设计，博士后。

研究方向：1）能源植物和重要农业经济作物（包括玉米、柳枝稷、芒草及其他能源草、牧草与草坪草）的遗传改良和分子设计；2）植物酚酸类生物活性物质的代谢工程和开发利用；3）先进生物技术在转基因作物生物安全性中的应用。 

doi: https://doi.org/10.1111/pbi.12935

Journal: Plant Biotechnology Journal

First Published date: 28 April, 2018

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