拟南芥FHY3/FAR1与SPL互作调控分枝数和开花时间的分子机理

Branch (tiller) number and flowering time are key determining factors of plant architecture and regional adaptation, respectively, and they greatly influence the final yield of crops. Increasing the planting density is a key measurement of increasing crop yield per unit land area. However, high density planting causes a reduction in the red:far-red ratio, thus inducing shade avoidance syndrome, including reduction of branch number and early flowering. The molecular genetic mechanisms governing these processes remain poorly understood. We found that in Arabidopsis, FHY3 and FAR1, a pair of homologous genes required for phytochromeA signaling, are involved in shade regulation of branching and flowering. In addition, FHY3 and FAR1 physically interact with multiple members of the SPL gene family. Moreover, we found that multiple SPL proteins can directly bind to the promoters of BRC1 and FUL, which are known key regulatory factor of branching and flowering respectively. Thus, we propose that FHY3/FAR1 and SPL proteins coordinately regulate the expression of BRC1 and FUL, which in turn regulate branching and flowering. In this project, we will verify this working hypothesis. Specifically, we will: 1) Verify the in vivo and in vitro interaction between FHY3/FAR1 and SPLs; 2) Elucidate the molecular mechanisms of FHY3/FAR1-SPL interaction in regulating the expression of BRC1 and FUL; 3) Establish the genetic regulatory network of FHY3/FAR1-SPL interaction in regulating branching and flowering in response to high density or shade conditions. The expected results will greatly enhance our understanding of the molecular mechanisms regulating plant architecture and flowering time in plants, but also help to guide breeding of high density-tolerant crop cultivars.

分枝(分蘖)数目和开花时间分别是作物株型和生态区适应性的关键决定因素，并最终影响作物产量。密植栽培条件会诱发植物的避荫反应，导致分枝数降低和开花提早，但其遗传和分子调控机理尚不清楚。前期研究发现拟南芥光信号转导因子FHY3和FAR1参与植株分枝数和开花时间的调控，并可与多个SPL转录因子直接互作，后者可与调控分枝关键基因BRC1和开花关键基因FUL的启动子直接结合。本项目将从三个方面验证FHY3/FAR1通过与SPL蛋白互作协同调控BRC1和FUL的表达，从而调控植株分枝数和开花时间的假说。1）验证FHY3/FAR1与SPL蛋白体内和体外互作；2）解析FHY3/FAR1与SPL协同调控BRC1和FUL表达的分子机制；3）建立FHY3/FAR1与SPL互作响应遮荫条件调控分枝数和开花时间的遗传网络。研究成果将加深对我们对植物株型和开花时间调控机理的的理解，并为耐密植作物新品种培育提供指导。

分枝（分蘖）数目和开花时间是影响植株产量和生物量的关键因素。但在密植栽培条件下，植物间的相互遮荫会诱发植物产生避荫反应（Shade Avoidance Response），引起植株分枝（分蘖）数目急剧减少、开花显著提前，最终导致植株单产和单位面积作物总产量下降。目前植株密植栽培条件下分枝（分蘖）减少和开花提早的分子机制尚不清楚。我们前期研究发现植物可通过光敏色素信号途径调控miR156-SPL分子模块，进而控制植物的避荫反应 (Xie et al., 2017, Nature Communications)。在本研究中，研究人员发现作为光敏色素A (phyA) 信号通路中的两个重要信号传导因子FHY3和FAR1能和独脚金内酯信号途径重要因子SMXL6/7/8共同与miR156-SPL分子模块控制分枝调控途径的重要成员SPL9/15蛋白直接互作，并抑制了SPL9/15对下游分枝关键负调控因子BRC1的转录，从而促进植株分枝分蘖的产生；而且FHY3和FAR1能直接促进SMXL6和SMXL7的转录；遮荫和密植栽培条件则引起FHY3和FAR1蛋白水平下降，引起SMXL6和SMXL7的转录本下降，使SPL9/15蛋白被释放出来，导致其下游基因BRC1的转录水平升高，从而抑制了植株分枝的产生。同时，研究发现FHY3和FAR1能与miR156-SPL分子模块控制的年龄开花调控途径中的三个重要成员SPL3/4/5蛋白直接互作，并抑制了SPL3/4/5对下游开花关键正调控因子FUL、LFY、AP1和MIR172C的转录，从而抑制开花；而遮荫和密植栽培条件则引起FHY3和FAR1蛋白水平下降，使SPL3/4/5蛋白被释放出来，导致其下游基因的转录水平升高，从而促使植株开花提前。这些研究首次从蛋白互作层面阐明了FHY3和FAR1通过整合植物外部光信号途径能够整合植物自身年龄信号途径和内部独脚金内酯信号途径协同调控植株响应环境变化的分子机制，完善了植物避荫反应的调控机理，进一步为耐荫、耐密植作物新品种的培育提供了理论指导。