PtFCA在柑橘成花转变中的功能及调控机制研究

Transition from vegetative to reproductive growth and juvenile to adult period are two essential processes for realizing economic value ofcitrus adult trees. The long juvenile stage is the biggest handicapt in citrus trees breeding and important economic traits research. The internal cues and environmental factors activate a series of signaling processes targeting shoot and axillary meristems, which culminate in the emergence of flowers. FCA which is a key gene for flowering was involved in the ambient temperature and autonomous pathways. Our research shows that, The alternative processing of FCA has divergence between citrus and model plants. Gene expression analysis in different development stages and shoots showed that PtFCA may be involved in flowering development. Ectopic expression of these altematively spliced transcripts in Arabidopsis caused different or even totally opposite ability of regulating flowering time, implying that PtFCA may play an important role during flowering transition in citrus. This project plans to study the function and regulatory mechanism of PtFCA during flowering transition in precocious and normal trifoliate orange via Real-time PCR, RNA-seq, genetic transformation, yeast two/one-hybrid, different temperature and hormone treatments. These results will provide an importent theoretical and practical basis for shortening the juvenile phase and regulating flowering time in the citrus genetic engineering breeding.

柑橘进入成年期实现经济价值需要经历童期向成年期、营养枝向结果枝等重要转变过程。其中漫长的童期，极大的阻碍了柑橘育种进程和重要经济性状的研究。植物成花转变是外界环境因子和植物内部发育信号协同作用的结果，过去研究表明FCA是植物自主成花途径与响应外界温度调控植物成花转变的关键基因。我们前期研究发现：PtFCA在柑橘中具有与模式植物不同的剪切模式，在早实枳与普通枳不同的发育阶段和成花能力的枝条中表达与成花转变密切相关，且不同剪切本在拟南芥中异位表达后呈现出不同甚至相反的成花能力，表明PtFCA可能在柑橘的成花转变过程中充当重要的角色。本项目拟以普通枳和早实枳为材料，采用实时定量、转录组测序、遗传转化、酵母单双杂交及温度和激素处理等手段研究PtFCA在柑橘成花转变过程中调控规律及其功能角色，揭示 PtFCA在柑橘成花调控网络中的作用机理，为通过遗传改良缩短果树童期和调控花期提供理论和实践依据。

柑橘实生苗从播种到初次开花前需要经历长达6-20年的童期，成年后的柑橘具有季节性开花的特点。研究柑橘长童期及季节性成花转变的分子机理，进而改良和培育童期短、花期不同的新品种，对提高柑橘的经济效益具有重要的意义。本项目从早实枳和普通枳中分离PtFCA选择性剪切产生三个转录本。实时定量PCR检测发现PtFCA1和PtFCA2表达模式相反，且与柑橘成花发育密切相关；转化模式植物表明PtFCA1和PtFCA2调控开花时间功能相反，PtFCA3没有调控成花的功能；采用酵母双杂交、双分子荧光互补、GST pull-down技术获得了PtFCA互作蛋白，PtFCA1通过WW结构域与具有延迟开花功能的PtNY-FA7和PtFCA2互作，且PtFCA1的功能部分依赖于PtNF-YA7的表达；双荧光素酶报告实验表明PtNF-YA7通过抑制成花转变关键基因PtFT转录推迟植株开花时间，PtFCA2和PtNF-YA7竞争性与PtFCA1互作，正负调控PtFT转录表达，从而调控开花时间；环境温度影响PtFCA选择性剪切，通过调节PtFCA1与PtFCA2的动态平衡调控成花；基于这些发现，提出了一个柑橘响应季节性环境温度调控季节性成花转变的模型和新的分子机制。