一个短日照条件特异表达FT调控植物开花的分子机制

The appropriate timing of floral transition is crucial for plant reproductive success. Florigen, encoded by the FLOWERING LOCUS T (FT) gene, functions as a integrated signal to induce flowering in plants. FT protein interacts with scaffold protein 14-3-3s and the basic leucine zipper (bZIP) transcription factor FD to form a flowering initiation complex, stimulating flowering by activation of downstream floral genes. In long-day plants, it is generally thought that FT is induced by long-day conditions, while whether it can be induced and what the roles of it in short-day conditions remains elusive. Recently, we interestingly identified an FT homolog (FT9) that is specially expressed under short-days in Brachypodium distachyon. We found that over-expression of FT9 in transgenic plants is able to cause early flowering under short-day conditions, but not in long-day environments. Furthermore, we found that FT9 can interact with an untypical basic leucine zipper (bZIP) transcription factor FIB (FT interacting bZIP) rather than FD. More intriguingly, we found that FIB was also specially induced in short-days. In this project, through genetics and biochemistry approaches, we will explore the biological significance for FT9-FIB interactions and search for the upstream and downstream regulator of FT9. Our deep investigation of FT9 action mechanism will provide novel insights into the photoperiod-mediated flowering pathway in plants.

适时开花对于植物生长发育至关重要。成花素是诱导植物开花的信号分子，由FT基因编码。长日照植物中，通常认为FT蛋白随光照时间表达增加，并与骨架蛋白14-3-3和转录因子FD相互作用，形成开花复合物，在长日照条件下诱导植物开花，但FT是否直接参与短日照条件下的开花过程并不清楚。以二穗短柄草作为模式，我们发现了一个受短日照条件特异诱导表达的FT (FT9)，过量表达FT9的转基因植株在短日照条件下提早开花，但长日照条件开花时间并不提前。酵母双杂交文库筛选发现，FT9与一个并非是典型FD的bZIP家族转录因子FIB相互作用；有意思的是，进一步发现FIB同样受到短日照条件诱导表达。本项目在以上研究基础上，将通过遗传学和生物化学手段，研究FT9和FIB相互作用的生物学意义，并寻找调控FT9基因的上下游作用因子。揭示FT9的分子作用机制将为深入解析植物光周期途径介导的植物开花提供新启示。

开花是植物生命周期中重要的生物学过程。光周期是影响植物开花的重要环境信号。依据植物对光周期的响应，可将其分为长日照和短日照植物。长日照植物在短日照条件下开花延迟，但最终还是能够开花，其中的调控机制尚不清楚。FT（FLOWERING LOCUS T）编码成花素，是植物开花的关键整合因子。二穗短柄草属于典型的长日照植物，本研究鉴定了FT基因家族中唯一在短日照特异表达的FTL9基因。ftl9突变体在短日照条件下开花延迟，而过量表达FTL9则提早开花。FTL9能够与14-3-3s以及转录因子FD1互作，形成开花复合体（Florigen activation complex, FAC）激活下游VRN1与FUL2基因表达，这些遗传与生化证据表明FTL9在短日照下促进植物开花。有趣的是，FTL9过表达在长日照条件下导致植物晚花。研究发现，FTL9-FAC活性弱于FT1-FAC，FTL9竞争性干扰FT1-FAC形成，最终抑制植物开花。.CO1是光周期途径的核心调控因子，其蛋白在长日照下积累，本研究发现CO1能够抑制FTL9表达。而短日照条件下，由于CO1蛋白被降解无法积累，其对FTL9的转录抑制也随之解除，因此FTL9特异性在短日照下表达。.本研究揭示了长日照植物为何仍能在短日照条件下诱导开花的分子机理，为理解光周期途径调控植物开花提供了新的见解。