Wheat, Sorghum and Forage Research Unit, USDA-ARS, Lincoln, NE, 68583, USA.
Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, NE, 68583, USA.
Plant Mol Biol. 2020 Jun;103(3):269-285. doi: 10.1007/s11103-020-00991-3. Epub 2020 Mar 13.
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.
阿魏酸 5-羟化酶（F5H）催化松柏醇、松柏醛和阿魏酸的羟化反应，生成 5-羟基松柏基部分，进而形成芥子酸和丁香基（S）木质素单体。相比之下，另一种主要的木质素单体愈创木基（G）木质素则来源于松柏醇的聚合。本研究评估了高粱（Sorghum bicolor）中单宁生物合成的调控效果。在 CaMV 35S 启动子的控制下，过量表达高粱 F5H（SbF5H），既增加了 S-木质素水平，又提高了 S/G 木质素的比例，同时植物的生长和发育相对不受影响。对 SbF5H 过表达系的茎秆和叶片中脉切片进行 Maüle 染色，表明木质素组成发生了改变。SbF5H 的异位表达并未影响其他木质素途径基因的表达。此外，通过杂交授粉，将高粱咖啡酸 O-甲基转移酶（COMT）的无义突变 brown midrib 12-ref（bmr12-ref）与 35S::SbF5H 相结合，以检查其对木质素合成的影响。bmr12 35S::SbF5H 植物的秸秆成分比 bmr12 秸秆更接近 35S::SbF5H 或野生型（WT）秸秆；与 WT 或 35S::SbF5H 相比，S-木质素和总木质素浓度降低。同样，bmr12 和 bmr12 35S::SbF5H 中上游木质素生物合成基因的表达均高于 WT 或 35S::SbF5H。总的来说，这些结果表明，SbF5H 的过表达不能弥补 COMT 活性的丧失。主要结论：高粱中 F5H 的过表达增加了 S-木质素，而不增加总木质素含量或影响植物生长，但它不能弥补木质素合成中单宁醇途径中 COMT 活性的丧失。
