State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiamen 361102, China; Rice Research Institute, Sichuan Agricultural University, Chengdu, Sichuan 611130, China.
State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiamen 361102, China.
Mol Plant. 2017 Jul 5;10(7):948-961. doi: 10.1016/j.molp.2017.05.006. Epub 2017 May 23.
Photoperiodic flowering is one of the most important pathways to govern flowering in rice (Oryza sativa), in which Heading date 1 (Hd1), an ortholog of the Arabidopsis CONSTANS gene, encodes a pivotal regulator. Hd1 promotes flowering under short-day conditions (SD) but represses flowering under long-day conditions (LD) by regulating the expression of Heading date 3a (Hd3a), the FLOWERING LOCUS T (FT) ortholog in rice. However, the molecular mechanism of how Hd1 changes its regulatory activity in response to day length remains largely unknown. In this study, we demonstrated that the repression of flowering in LD by Hd1 is dependent on the transcription factor DAYS TO HEADING 8 (DTH8). Loss of DTH8 function results in the activation of Hd3a by Hd1, leading to early flowering. We found that Hd1 directly interacts with DTH8 and that the formation of the DTH8-Hd1 complex is necessary for the transcriptional repression of Hd3a by Hd1 in LD, implicating that the switch of Hd1 function is mediated by DTH8 in LD rather than in SD. Furthermore, we revealed that DTH8 associates with the Hd3a promoter to modulate the level of H3K27 trimethylation (H3K27me3) at the Hd3a locus. In the presence of the DTH8-Hd1 complex, the H3K27me3 level was increased at Hd3a, whereas loss of DTH8 function resulted in decreased H3K27me3 level at Hd3a. Taken together, our findings indicate that, in response to day length, DTH8 plays a critical role in mediating the transcriptional regulation of Hd3a by Hd1 through the DTH8-Hd1 module to shape epigenetic modifications in photoperiodic flowering.
光周期开花是调控水稻（Oryza sativa）开花的最重要途径之一，其中Heading date 1（Hd1）是拟南芥CONSTANS 基因的同源物，编码一个关键的调控因子。Hd1 在短日照条件下（SD）促进开花，但在长日照条件下（LD）抑制开花，通过调节水稻FT 同源物Heading date 3a（Hd3a）的表达。然而，Hd1 如何根据日照长度改变其调节活性的分子机制在很大程度上仍不清楚。在本研究中，我们证明了 Hd1 在 LD 中对开花的抑制依赖于转录因子 DAYS TO HEADING 8（DTH8）。DTH8 功能丧失导致 Hd1 激活 Hd3a，从而导致早期开花。我们发现 Hd1 直接与 DTH8 相互作用，并且 DTH8-Hd1 复合物的形成是 Hd1 在 LD 中对 Hd3a 转录抑制所必需的，这表明 Hd1 功能的转换是由 DTH8 在 LD 中而不是在 SD 中介导的。此外，我们揭示了 DTH8 与 Hd3a 启动子结合，以调节 Hd3a 基因座处 H3K27 三甲基化（H3K27me3）的水平。在存在 DTH8-Hd1 复合物的情况下，Hd3a 处的 H3K27me3 水平增加，而 DTH8 功能丧失导致 Hd3a 处的 H3K27me3 水平降低。总之，我们的研究结果表明，在响应日照长度时，DTH8 通过 DTH8-Hd1 模块在介导 Hd1 对 Hd3a 的转录调控中发挥关键作用，从而塑造光周期开花中的表观遗传修饰。
