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.
摘要：
花色苷和木质素都是植物生长发育过程中必需的次生代谢产物。它们的生物合成在代谢上相互关联，并在类苯丙烷途径的中心代谢物4-香豆酰基CoA中发散。在了解木质素和花色苷合成途径相关基因的转录调控方面取得了相当大的进展，但是这些途径的协调调节尚未完全理解。这里,我们对毛果杨的R2R3-MYB转录因子PtrMYB120进行了功能表征。PtrMYB120在杂交杨树中的过表达(即，35S::PtrMYB120)与花色苷增加(即，花青素3-O-葡萄糖苷）积累和花青素生物合成基因的上调。然而,通过将ERF相关的两亲性抑制基序与PtrMYB120融合而实现的具有PtrMYB120功能的显性抑制的转基因杨树（即，35S::PtrMYB120-SRDX）不仅花色苷含量急剧下降，而且花色苷和木质素生物合成基因的下调也使Klason木质素含量急剧下降。的确,35S::PtrMYB120-SRDX杨树具有不规则形状的木质部血管，茎中的S-木质素含量降低，这与引入的PtrMYB120-SRDX基因的水平成比例相关。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#6生产线的糖化效率，木质素含量略有降低，生长表型正常，通过NaOH处理显著增强(>45%)。一起来看,我们的结果表明，PtrMYB120作为花青素和木质素生物合成途径的正调节剂，可以有针对性地提高木质多年生植物的糖化效率。
