Abstract

Both anthocyanins and lignins are essential secondary metabolites in plant growth and development. Their biosynthesis is metabolically interconnected and diverges in the central metabolite 4-coumaroyl CoA of the phenylpropanoid pathway. Considerable progress has been made in understanding transcriptional regulation of genes involved in lignin and anthocyanin synthesis pathways, but the concerted regulation of these pathways is not yet fully understood. Here, we functionally characterized PtrMYB120, a R2R3-MYB transcription factor from Populus trichocarpa. Overexpression of PtrMYB120 in a hybrid poplar (i.e., 35S::PtrMYB120) was associated with increased anthocyanin (i.e., cyanidin 3-O-glucoside) accumulation and upregulation of anthocyanin biosynthetic genes. However, transgenic poplars with dominant-suppression of PtrMYB120 function achieved by fusing the ERF-associated Amphiphilic Repression motif to PtrMYB120 (i.e., 35S::PtrMYB120-SRDX) had a dramatic decrease in not only anthocyanin but also Klason lignin content with downregulation of both anthocyanin and lignin biosynthetic genes. Indeed, 35S::PtrMYB120-SRDX poplars had irregularly-shaped xylem vessels with reduced S-lignin content in stems, which was proportionally related to the level of the introduced PtrMYB120-SRDX gene. Furthermore, protoplast-based transcriptional activation assay using the PtrMYB120-GR system suggested that PtrMYB120 directly regulates genes involved in both anthocyanin and lignin biosynthesis, including chalcone synthase and ferulate-5 hydroxylase. Interestingly, the saccharification efficiency of line #6 of 35S::PtrMYB120-SRDX poplars, which had slightly reduced lignin content with a normal growth phenotype, was dramatically enhanced (> 45%) by NaOH treatment. Taken together, our results suggest that PtrMYB120 functions as a positive regulator of both anthocyanin and lignin biosynthetic pathways, and can be targeted to enhance saccharification efficiency in woody perennials.

中文翻译：

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PtrMYB120 作为杂种杨树花青素和木质素生物合成途径的正调节因子

摘要

花青素和木质素都是植物生长发育中必不可少的次生代谢产物。它们的生物合成在代谢上相互关联，并在苯丙素途径的中心代谢物 4-香豆酰 CoA 中发散。在了解参与木质素和花青素合成途径的基因的转录调控方面已经取得了相当大的进展，但尚未完全了解这些途径的协同调控。在这里，我们在功能上表征了PtrMYB120 ，一种来自毛果杨的 R2R3-MYB 转录因子。PtrMYB120在杂交杨树（即 35S::PtrMYB120）中的过表达与花青素（即花青素 3- O-葡萄糖苷）花青素生物合成基因的积累和上调。然而，通过将 ERF 相关的两亲性抑制基序与 PtrMYB120（即 35S::PtrMYB120-SRDX）融合来实现 PtrMYB120 功能显性抑制的转基因杨树不仅花青素显着下降，而且 Klason 木质素含量显着下降，两者均下调花青素和木质素生物合成基因。事实上，35S::PtrMYB120-SRDX 杨树的木质部血管形状不规则，茎中 S-木质素含量降低，这与引入的PtrMYB120-SRDX基因水平成正比。此外，使用 PtrMYB120-GR 系统的基于原生质体的转录激活测定表明 PtrMYB120 直接调节参与花青素和木质素生物合成的基因，包括查尔酮合酶和阿魏酸5羟化酶。有趣的是，35S::PtrMYB120-SRDX 杨树的第 6 行的糖化效率通过 NaOH 处理显着提高（> 45%），其木质素含量略有降低，具有正常的生长表型。总之，我们的研究结果表明，PtrMYB120 作为花青素和木质素生物合成途径的正调节剂，可用于提高多年生木本植物的糖化效率。