杨树转录因子PtrHB7调控次生维管组织分化的分子机理解析

A key process of wood formation is secondary vascular differentiation in which cambium cells differentiate inwards forming secondary xylem tissue and outwards forming secondary phloem tissue in a highly ordered manner. Our previous work demonstrated an HD-zipIII gene, PtrHB7, plays a critical role in modulating a balanced secondary vascular differentiation in Populus. However, the molecular mechanism underlying the PtrHB7 function is still unclear. This study aims to identify the target genes of PtrHB7 and further investigate their function which will facilitate illustration of how PtrHB7 regulates secondary vascular differentiation process. One candidate gene, named PtrSVDR (Secondary Vascular Differentiation related Gene), has been identified through RNA-seq analysis of the PtrHB7 mutant. In PtrSVDR promoter, an predicated HD-zipIII transcription factor binding site was found. Genetic evidence indicated vascular differentiation was significantly enhanced in PtrSVDR overexpressed Arabidopsis plants. These results indicate PtSVDR may be regulated by PtrHB7 and involved in vascular differentiation process. Further validation and investigation of PtrSVDR and other candidate target gene of PtrHB7 is critical for illustrating the mechanism of secondary vascular differentiation in wood plants.

木材形成的关键过程是次生维管组织的分化，即形成层细胞如何高度有序地向内分化为次生木质部，向外分化为次生韧皮部。我们的研究证明木本植物杨树HD-zipIII转录因子PtrHB7在平衡次生维管组织分化过程中发挥关键的作用，但其调控次生维管组织分化的分子机制目前还不清楚。本研究将主要通过鉴定PtrHB7的下游目标基因并分析其功能来阐释PtrHB7作用的分子机制。目前已经利用RNA-seq方法筛选到一个PtrHB7候选下游基因PtrSVDR。预测发现它的启动子上具有HD-zipIII转录因子结合位点。在拟南芥中过表达PtrSVDR可以显著促进维管组织的分化。这些结果暗示了PtrSVDR可能受PtrHB7的调节，并参与维管组织的分化。进一步验证和研究PtrSVDR与其它PtrHB7下游候选目标基因的功能对于阐明木本植物次生维管组织分化的独特分子机制具有关键意义。

木材形成关键的调控机制之一是形成层细胞如何高度有序地向内分化为次生木质部，向外分化为次生韧皮部。本项目通过研究木本植物杨树HD-ZIPIII关键转录因子PtrHB7的下游基因，为揭示PtrHB7调控形成层细胞的分化过程提供了新的证据。本项目利用转录组学的方法，鉴定了PtrHB7下游调控基因。并利用生物信息学的方法构建完成了PtrHB7的转录调控网络。进一步通过遗传学的方法深入解析了一个关键的调控基因PtrSVDR，发现它可能是通过影响形成层细胞的属性（identity）来调节形成层的形成以及分化过程。为解析HD-ZIPIII家族基因在木本植物中如何调控形成层细胞的形成与分化提供了新理论。较好地完成了项目的预期任务和目标。