水稻光周期开花网络调控机制是描述水稻与环境因素光周期相互作用的分子机理。它对于水稻品种的引种、制种和产量至关重要。Hd1是水稻光周期开花网络的核心元件。与拟南芥的同源基因CO在长日照下正调控FT的转录不同，Hd1的转录活性能被光周期反转。在短日照下，Hd1激活FT的同源基因Hd3a的表达。相反，在长日照下，Hd1抑制Hd3a的表达。目前，光周期调控Hd1功能转换的分子机制依然未知。我们前期的研究发现DTH8在长日照下与Hd1形成复合体抑制Hd3a的表达。当DTH8无功能时，Hd1在长日照下转变为Hd3a的激活子。进一步我们通过常微分方程建模预测日照长度通过调控DTH8和Hd1的相互作用改变Hd1的功能。本课题将结合计算生物学，分子生物学与遗传学的研究方法。首先，利用实验手段证明光周期可以调控DTH8和Hd1的相互作用；最终，结合数学模型阐明光周期调控 Hd1功能转换的分子机理。

Photoperiodic flowering is one of the most important flowering pathways in rice (Oryza sativa). Short day (SD) conditions can induce rice flowering, whereas long day (LD) conditions repress it. Photoperiodic flowering can affect variety introduction, seed production and yield. Heading date 1 (Hd1), a CONSTANS ortholog from rice, acts as a so-called “Janus” regulator in response to day length during rice photoperiodic flowering. Under SD, Hd1 positively regulates Heading date 3α (Hd3α), the rice FLOWERING LOCUS T (FT) ortholog, to accelerate flowering. Under LD, however, Hd1 instead represses flowering. Our previous works demonstrate that the Hd1 flowering repression activity is dependent on a functional DAYS TO HEADING 8 (DTH8) allele in LD. In a background with non-functional DTH8, Hd1 activates Hd3α to promote flowering in LD. Further, we demonstrate that physical and functional association of Hd1 and DTH8 to compose a DTH8-Hd1 complex is necessary for the inhibitory activity of Hd1 in LD. Moreover, we used an Ordinary Differential Equation (ODE)-based model to predict photoperiod can switch Hd1 function by regulation the interaction between Hd1 and DTH8. In this project, we will use a systems-biology approach to investigate the dynamic behaviors and relationships between flowering activators and repressors. We will define a mathematical representation of the photoperiodic flowering network at a temporal scale. Firstly,, we will use experiments to prove photoperiod can regulate the interaction between Hd1 and DTH8 to switch Hd1 function. Together, the experimental validation, computational modeling and statistical data in this work will demonstrate the mechanism of Hd1 function conversion in rice photoperiodic flowering.