细胞分裂素调控杨树木材发育的分子机制研究

树干次生维管组织发育是木材生产的生物学基础，但其精细调控机制目前还很不清楚，尤其是细胞分裂素（Cytokinin, CK）在该过程中的具体作用仍知之甚少。为此，本项目拟以杨树为材料：①克隆次生维管组织特异性启动子以控制报告基因表达，构建各维管组织的转基因报告株系；②采用荧光免疫技术准确表征CK在次生维管组织中的分布模式，搞清CK积累与木材发育之间内在联系；③外施CK和采用转基因技术改变维管形成层中內源CK含量，明确其对于木材发育的调控作用；④利用遗传及生化技术鉴定CK信号通路调控次生维管形成层的下游靶标基因，建立其与CLE-WOX4调控通路之间的联系，阐明CK在次生维管组织中的分子机制；⑤此外，通过组织特异性改变次生维管组织中内源CK和生长素（Auxin）的浓度梯度，探究两者在次生维管组织发育中的协作机制。本项目将为最终揭示林木次生维管发育的分子机理奠定基础，为木材的材性改良提供理论依据。

Wood (also termed secondary xylem) is the most abundant biomass produced by woody plants. Wood development begins with the differentiation of lateral meristem and vascular cambium into secondary xylem mother cells followed by cell expansion, secondary wall deposition, programmed cell death, and finally heartwood formation. In the past decade, significant progress has been achieved in understanding the molecular mechanisms of wood formation in tree species. Hormonal signalling has been shown to play critical roles in vascular cambium cell proliferation. But it is still unclear the regulatory role of cytokinin in the vascular development during wood formation in poplar. In this project, we will isolate these vascular-specific promoters and fuse them into GUS/GFP reporter genes. After transformation, transgenic plants with vascular-specific promoter driven reporter genes will be obtained for exactly distinguishing different vascular tissues. We will further demonstrate the regulation of cytokinin on the differentiation of vascular cambium into xylem mother cells and identify the function of their downstream transcription factors in response to cytokinin signaling in poplar. And also we will figure out the mechanism about cytokinin signalling in phloem transducting into vascular cambium and demonstrate the transcription network encompassing secondary wall regulatory factors and their downstream transcription factors. In addition, we will determine the synergistic regulation of auxin and cytokinin signallings on vascular cambium activity during wood formation. Uncovering the molecular mechanisms of cytokinin regulating vascular development will greatly accelerate our understanding of the molecular control of wood formation in poplar.