甘蔗开花关键基因FT的克隆及功能分析

Bad-induced flowering of sugarcane parents is a bigger "bottleneck" for sugarcane cross-breeding and innovation. Recently, a hypothetical of the gene network controlling floral induction under photoperiodic control was constructed by means of bioinformatics methods and it was predicted that FT-like genes may play an essential role in controlling the transition from vegetative to reproductive growth, but the gene function and expression patterns are remain unknown. In this study, we want to clone FT-like genes and its promoter from Saccharum spp., the gene expression patterns at different periods of duration, different tissues, and eight different times round the clock will be analyzed in the sugarcane floral induction process under different artifical and field photoperiod-controlled inducement conditions. Meanwhile, the FT-like gene which required for controlling flowering of sugarcane will be transfered into the Arabidopsis thaliana plants for functional analysis. Further, we want to analyse the structural features and detect the activity of the promoter of sugarcane FT-like gene. This study aims to clarify the role of sugarcane FT-like genes in the photoperiod-controlled flowering pathway. Finally, the result will provide a preliminary information for understanding the molecular mechanism of sugarcane induction flowering in photoperiod pathway, and it can provide good groundwork for developing a skill for regulating the flowering time of sugarcane accurately.

甘蔗亲本开花难且花期调控难是甘蔗杂交育种和新种质创制的“瓶颈”。甘蔗成花光周期调控途径假定的基因成员及其网络已经初步建立，生物信息学分析表明，FT基因在甘蔗成花过程中发挥重要作用，但其实际生物学功能和表达模式未知。项目组在前期研究基础上，拟克隆甘蔗FT基因及其启动子序列，研究其mRNA在人工光周期诱导和非诱导条件下从营养生长转向生殖生长不同时期、不同组织部位以及1天8个不同时间点的表达模式；同时拟通过转化模式植物拟南芥初步确认FT基因的功能；进一步拟对基因上游启动子序列进行结构分析和活性检测。本研究旨在阐明FT基因对甘蔗开花的调控作用，为后续甘蔗成花分子机制研究和花期精准调控技术研发奠定基础。

FT/TFL1基因是植物开花时间重要调控基因，本研究从甘蔗中克隆获得了3个ScFT基因（ScFT-1、ScFT-2和ScFT-3）；生物信息学分析和表达模式分析（含3个ScFT基因和1个ScTFL1基因）结果表明：ScFT-1和ScFT-2基因促进甘蔗开花；ScFT-1基因在光周期调控诱导开花甘蔗成花转变时期成熟叶中表达量增加，说明它很可能是甘蔗的“成花素”基因，具有启动和促进甘蔗开花的功能；ScFT-2基因在诱导开花甘蔗幼穗中表达量增加，说明可能参与甘蔗花序的发育和维持；相反，ScFT-3和ScTFL1基因可能抑制甘蔗开花，在诱导开花甘蔗成花转变时期表达量下调。ScFT-1和ScFT-3基因在孕穗早期幼叶中表达量均较高，二者具有相互平衡的作用。ScFT-1、ScFT-2和ScTFL1基因在对照（非诱导）甘蔗和田间自然开花的割手密中表达量变化不明显，推测它们可能不参与甘蔗属野生种割手密的开花调控。割手密可能不是严格的短日照植物，其开花可能不依赖于光周期调控途径，而是由其它调控途径的基因（或由其它FT基因）起作用。ScFT-3基因在对照甘蔗营养生长后期，诱导开花甘蔗和田间自然开花割手密成花转变时期表达量均下调，推测可能功能相似，存在较相似的调控网络。分别构建了3个ScFT基因过表达载体，遗传转化拟南芥验证基因的功能。从不同开花潜能种质（难诱导开花-拔地拉、田间自然光照易开花-割手密和可诱导开花-甘蔗品种）中克隆获得了ScFT基因的启动子序列，除含有启动子基本元件外，还含有大量光响应元件和植物激素响应元件，为后续开展启动子的功能分析奠定基础。此外，分析了光周期调控诱导开花对甘蔗表型的影响；完成了甘蔗花芽分化及花序发育过程的石蜡切片显微观察与分析，并将甘蔗开花过程划分为6个阶段。以上研究为后续开展ScFT基因调控甘蔗开花的作用机制研究奠定了重要的前期基础，对阐明甘蔗成花分子机理及花期调控的应用具有重要的参考意义。