Ferulate 5-hydroxylase (F5H) of the monolignol pathway catalyzes the hydroxylation of coniferyl alcohol, coniferaldehyde and ferulic acid to produce 5-hydroxyconiferyl moieties, which lead to the formation of sinapic acid and syringyl (S) lignin monomers. In contrast, guaiacyl (G) lignin, the other major type of lignin monomer, is derived from polymerization of coniferyl alcohol. In this study, the effects of manipulating S-lignin biosynthesis in sorghum (Sorghum bicolor) were evaluated. Overexpression of sorghum F5H (SbF5H), under the control of the CaMV 35S promoter, increased both S-lignin levels and the ratio of S/G lignin, while plant growth and development remained relatively unaffected. Maüle staining of stalk and leaf midrib sections from SbF5H overexpression lines indicated that the lignin composition was altered. Ectopic expression of SbF5H did not affect the gene expression of other monolignol pathway genes. In addition, brown midrib 12-ref (bmr12-ref), a nonsense mutation in the sorghum caffeic acid O-methyltransferase (COMT) was combined with 35S::SbF5H through cross-pollination to examine effects on lignin synthesis. The stover composition from bmr12 35S::SbF5H plants more closely resembled bmr12 stover than 35S::SbF5H or wild-type (WT) stover; S-lignin and total lignin concentrations were decreased relative to WT or 35S::SbF5H. Likewise, expression of upstream monolignol biosynthetic genes was increased in both bmr12 and bmr12 35S::SbF5H relative to WT or 35S::SbF5H. Overall, these results indicated that overexpression of SbF5H did not compensate for the loss of COMT activity. KEY MESSAGE: Overexpression of F5H in sorghum increases S-lignin without increasing total lignin content or affecting plant growth, but it cannot compensate for the loss of COMT activity in monolignol synthesis.

中文翻译：

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阿魏酸5-羟化酶的过表达增加了双色高粱中的丁香基单位。

单木质醇途径的阿魏酸5-羟化酶（F5H）催化松柏油，松柏醛和阿魏酸的羟基化以产生5-羟松柏基部分，其导致芥子酸和丁香基（S）木质素单体的形成。相反，另一种主要类型的木质素单体愈创木基（G）木质素衍生自松柏油醇的聚合。在这项研究中，评估了操纵S-木质素在高粱（双色高粱）中的生物合成的作用。在CaMV 35S启动子的控制下，高粱F5H（SbF5H）的过表达增加了S-木质素水平和S / G木质素的比例，而植物的生长和发育仍然相对不受影响。来自SbF5H过表达株系的茎和叶中脉切片的Maüle染色表明木质素组成发生了变化。SbF5H的异位表达不影响其他monolignol途径基因的基因表达。此外，棕色中肋12-ref（bmr12-ref）是高粱咖啡酸O-甲基转移酶（COMT）中的无意义突变，通过交叉授粉与35S :: SbF5H结合使用，以检查对木质素合成的影响。bmr12 35S :: SbF5H植物的秸秆组成比35S :: SbF5H或野生型（WT）秸秆更类似于bmr12秸秆。相对于WT或35S :: SbF5H，S-木质素和总木质素浓度降低。同样，相对于WT或35S :: SbF5H，bmr12和bmr12 35S :: SbF5H中上游单木酚生物合成基因的表达均增加。总体而言，这些结果表明SbF5H的过表达不能补偿COMT活性的丧失。关键信息：