PtrOBP1转录调控杨树次生细胞壁形成分子机制研究

The hierarchical gene transcriptional regulation network (HGRN), encompassing transcriptional factors (TFs) and secondary cell wall (SCW) biosynthesis genes, has been proposed to control SCW formation in plants. However, numerous new TFs involved in wood formation are continuously identified, suggesting the HGRN of wood formation is still not perfect up to now. In previous study, a HGRN, whose top level TF is AtOBP1 belonged to Dof family of Arabidopsis and regulate SCW formation, was constructed through analysis the gene expression profile dates of Arabidopsis. It was proven that AtOBP1 and PtrOBP1 were expressed prominently in secondary growth tissues in Arabidopsis thaliana and Populus trichocarpa, respectively. The analysis of the Arabidopsis thaliana obp1 mutant and Populus trichocarpa OBP1(PtrOBP1) overexpression transgenic tobacco demonstrated that the thickness and main component of SCW, and the expression levels of TFs involved in SCW formation and SCW biosynthesis genes shown notable alternations compared to wild-type Arabidopsis and tobacco, respectively. These resulted suggested the regulation of SCW formation may be a new biological function of PtrOBP1. However, it is not clear whether PtrOBP1 is involved in the regulation of wood formation in tree species. In this project, through the molecular biology, bioinformatics, and biochemistry methods, the biological function of PtrOBP1 in the Populus trichocarpa SCW biosynthesis will be analyzed, the HGRN regulated by the PtrOBP1 will be constructed and verified, and the biological function and transcriptional regulation mechanism of PtrOBP1 in Populus wood formation will be illustrated lastly. Our identification of PtrOBP1 as a new regulators of SCW formation will potentially provide evidence to improve the molecular transcriptional regulation mechanism of wood formation in Populus.

木材形成受转录因子和功能基因组成的层次化基因转录调控网络控制。目前已知的木材形成转录调控机制并不完善，不断有新的转录因子被鉴定。前期研究在拟南芥次生组织表达谱数据中鉴定出一个以Dof 家族基因AtOBP1为顶点的层次化基因转录调控网络，而且AtOBP1和 PtrOBP1在次生组织中表达丰度最高，obp1突变体和PtrOBP1过表达烟草次生细胞壁厚度与主要组分含量、次生细胞壁转录因子与功能基因表达均发生显著变化，这表明参与次生细胞壁形成是PtrOBP1的生物学新功能。然而，PtrOBP1在树木木材形成中功能仍然不清。本项目采用分子生物学、生物信息学与生物化学等技术研究PtrOBP1在毛果杨次生细胞壁形成中的生物学功能，构建并验证以PtrOBP1为顶点的次生细胞壁形成层次化基因转录调控网络，阐明PtrOBP1在树木木材形成中的生物学功能和转录调控机制，为完善树木木材形成转录调控机制奠定基础。

在植物中，Dof转录因子在许多生物过程中发挥着重要作用。迄今为止，尚无关于木本植物Dof TFs在木本形成过程中的参与和作用的报道。本研究发现了毛果杨转录因子PtrOBP1的功能特征，该转录因子编码一个核定位转录激活因子，主要在发育中的木质部组织中表达。PtrOBP1的过表达不仅抑制了大部分表型性状的生长和生物量积累，而且改变了与次生细胞壁有关的部分主TFs和通路基因的表达，导致转基因株系茎中SCW成分发生变化。此外，PtrOBP1直接与PtrPAL4、PtrCAld5H2、PtrGT8F、PtrGT47C、PtrGA2oxA、PtrGA20ox2A、PtrGA20ox2B、PtrERF110、PtrLBD30、PtrMYB108、PtrSND1-A1、PtrSND1-B2、PtrMYB152和PtrMYB156一系列TFs和通路基因的启动子结合并激活它们。综上所述，我们的结果表明PtrOBP1通过直接和间接地控制SCW形成的分级转录网络的TFs和下游通路基因，对SCW组分的生物合成途径进行协调调控。