Summary Lignin, a major wood component, is the key limiting factor for wood conversion efficiency. Its biosynthesis is controlled by transcriptional regulatory networks involving transcription factor (TF)–DNA interactions. However, the epigenetic mechanisms underlying these interactions in lignin biosynthesis remain largely unknown. Here, using yeast one‐hybrid, chromatin immunoprecipitation, and electrophoretic mobility shift assays, we identified that PtrbZIP44‐A1, a key wood‐forming TF, directly interacts with the promoters of PtrCCoAOMT2 and PtrCCR2, genes involved in the monolignol biosynthetic pathway. We used yeast two‐hybrid, bimolecular fluorescence complementation, biochemical analyses, transient and CRISPR‐mediated transgenesis in Populus trichocarpa to demonstrate that PtrHDA15, a histone deacetylase, acts as an epigenetic inhibitor and is recruited by PtrbZIP44‐A1 for chromatin histone modifications to repress PtrCCoAOMT2 and PtrCCR2, leading to reduced lignin deposition. In transgenic lines overexpressing PtrbZIP44‐A1 or PtrHDA15, histone acetylation at the promoters of PtrCCoAOMT2 and PtrCCR2 decreased, reducing their expression and lignin content. Conversely, in loss‐of‐function ptrbzip44‐a1 and ptrhda15 mutants, histone acetylation levels at PtrCCoAOMT2 and PtrCCR2 promoters increased, enhancing target gene expression and lignin content. Our study uncovered an epigenetic mechanism that suppresses lignin biosynthesis. This finding may help fill a knowledge gap between epigenetic regulation and lignin biosynthesis during wood formation in Populus.

中文翻译：

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木材形成中木质素生物合成的表观遗传调控


总结木质素是木材的主要成分，是木材转化率的关键限制因素。它的生物合成受涉及转录因子 （TF）-DNA 相互作用的转录调控网络控制。然而，木质素生物合成中这些相互作用背后的表观遗传机制在很大程度上仍然未知。在这里，使用酵母单杂交、染色质免疫沉淀和电泳迁移率变化测定，我们发现 PtrbZIP44-A1 是一种关键的木材形成 TF，直接与 PtrCCoAOMT2 和 PtrCCR2 的启动子相互作用，这些基因参与木质素生物合成途径。我们在毛果杨中使用酵母双杂交、双分子荧光互补、生化分析、瞬时和 CRISPR 介导的转基因来证明 PtrHDA15（一种组蛋白脱乙酰酶）作为表观遗传抑制剂，并被 PtrbZIP44-A1 募集用于染色质组蛋白修饰，以抑制 PtrCCoAOMT2 和 PtrCCR2，导致木质素沉积减少。在过表达 PtrbZIP44-A1 或 PtrHDA15 的转基因品系中，PtrCCoAOMT2 和 PtrCCR2 启动子处的组蛋白乙酰化降低，从而降低了它们的表达和木质素含量。相反，在功能丧失的 ptrbzip44-a1 和 ptrhda15 突变体中，PtrCCoAOMT2 和 PtrCCR2 启动子的组蛋白乙酰化水平增加，从而增强靶基因表达和木质素含量。我们的研究揭示了抑制木质素生物合成的表观遗传机制。这一发现可能有助于填补杨树木材形成过程中表观遗传调控和木质素生物合成之间的知识空白。