Fornalé Silvia, Rencoret Jorge, García-Calvo Laura, Encina Antonio, Rigau Joan, Gutiérrez Ana, Del Río José Carlos, Caparros-Ruiz David
Centre for Research in Agricultural Genomics (CRAG) Consorci CSIC-IRTA-UAB-UB Edifici CRAG Campus de Bellaterra de la UAB, Cerdanyola del Valles, Barcelona, Spain.
Instituto de Recursos Naturales y Agrobiología de Sevilla, CSIC, Av. Reina Mercedes, Seville, Spain.
Plant Cell Physiol. 2017 Feb 1;58(2):240-255. doi: 10.1093/pcp/pcw198.
Caffeoyl coenzyme A 3-O-methyltransferase (CCoAOMT) and caffeic acid-O-methyltransferase (COMT) are key enzymes in the biosynthesis of coniferyl and sinapyl alcohols, the precursors of guaiacyl (G) and syringyl (S) lignin subunits. The function of these enzymes was characterized in single and double mutant maize plants. In this work, we determined that the comt (brown-midrib 3) mutant plants display a reduction of the flavonolignin unit derived from tricin (a dimethylated flavone), demonstrating that COMT is a key enzyme involved in the synthesis of this compound. In contrast, the ccoaomt1 mutants display a wild-type amount of tricin, suggesting that CCoAOMT1 is not essential for the synthesis of this compound. Based on our data, we suggest that CCoAOMT1 is involved in lignin biosynthesis at least in midribs. The phenotype of ccoaomt1 mutant plants displays no alterations, and their lignin content and composition remain unchanged. On the other hand, the ccoaomt1 comt mutant displays phenotypic and lignin alterations similar to those already described for the comt mutant. Although stems from the three mutants display a similar increase of hemicelluloses, the effect on cell wall degradability varies, the cell walls of ccoaomt1 being the most degradable. This suggests that the positive effect of lignin reduction on cell wall degradability of comt and ccoaomt1 comt mutants is counteracted by changes occurring in lignin composition, such as the decreased S/G ratio. In addition, the role of the flavonolignin unit derived from tricin in cell wall degradability is also discussed.
咖啡酰辅酶A 3 - O - 甲基转移酶（CCoAOMT）和咖啡酸O - 甲基转移酶（COMT）是松柏醇和芥子醇生物合成中的关键酶，而松柏醇和芥子醇分别是愈创木基（G）和紫丁香基（S）木质素亚基的前体。在单突变和双突变玉米植株中对这些酶的功能进行了表征。在本研究中，我们确定comt（棕色中脉3）突变体植株中源自小麦黄素（一种二甲基化黄酮）的黄酮木脂素单元减少，这表明COMT是参与该化合物合成的关键酶。相比之下，ccoAomt1突变体中小麦黄素的含量与野生型相当，这表明CCoAOMT1对于该化合物的合成并非必需。基于我们的数据，我们认为CCoAOMT1至少在中脉中参与木质素的生物合成。ccoAomt1突变体植株的表型没有变化，其木质素含量和组成保持不变。另一方面，ccoAomt1 comt双突变体表现出与已报道的comt突变体相似的表型和木质素变化。尽管这三种突变体的茎中半纤维素含量均有类似增加，但对细胞壁可降解性的影响各不相同，ccoAomt1突变体的细胞壁最易降解。这表明木质素减少对comt和ccoAomt1 comt突变体细胞壁可降解性的积极影响被木质素组成的变化（如S/G比值降低）所抵消。此外，还讨论了源自小麦黄素的黄酮木脂素单元在细胞壁可降解性中的作用。
