CONSTANS, CONSTANS-LIKE, and TIMING OF CAB EXPRESSION1 (CCT) domain-containing proteins are a large family unique to plants. They transcriptionally regulate photoperiodic flowering, circadian rhythms, vernalization, and other related processes. Through their CCT domains, CONSTANS and HEADING DATE1 (HD1) coordinate with the NUCLEAR FACTOR Y (NF-Y) B/C dimer to specifically target a conserved ‘CCACA’ motif within the promoters of their target genes. However, the mechanism underlying DNA recognition by the CCT domain remains unclear. Here we determined the crystal structures of the rice (Oryza sativa) NF-YB/YC dimer and the florigen gene Heading date 3a (Hd3a)-bound HD1^CCT/NF-YB/YC trimer with resolutions of 2.0 Å and 2.55 Å, respectively. The CCT domain of HD1 displays an elongated structure containing two α-helices and two loops, tethering Hd3a to the NF-YB/YC dimer. Helix α2 and loop 2 are anchored into the minor groove of the ‘CCACA’ motif, which determines the specific base recognition. Our structures reveal the interaction mechanism among the CCT domain, NF-YB/YC dimer, and the target DNA. These results not only provide insight into the network between the CCT proteins and NF-Y subunits, but also offer potential approaches for improving productivity and global adaptability of crops by manipulating florigen expression.

含有 CONSTANS、CONSTANS-LIKE 和 TIMING OF CAB EXPRESSION1 (CCT) 结构域的蛋白质是植物特有的一个大家族。它们通过转录调节光周期开花、昼夜节律、春化和其他相关过程。通过其 CCT 结构域，CONSTANS 和 HEADING DATE1 (HD1) 与 NUCLEAR FACTOR Y (NF-Y) B/C 二聚体协调，特异性靶向其靶基因启动子内的保守“CCACA”基序。然而，CCT 结构域识别 DNA 的机制仍不清楚。在这里，我们确定了水稻 ( Oryza sativa ) NF-YB/YC 二聚体和成花基因Heading date 3a ( Hd3a ) 结合的 HD1 ^CCT /NF-YB/YC 三聚体的晶体结构，分辨率分别为 2.0 Å 和 2.55 Å 。 HD1 的 CCT 结构域显示出包含两个 α 螺旋和两个环的细长结构，将Hd3a束缚到 NF-YB/YC 二聚体。螺旋 α2 和环 2 锚定在“CCACA”基序的小沟中，这决定了特定的碱基识别。我们的结构揭示了 CCT 结构域、NF-YB/YC 二聚体和靶 DNA 之间的相互作用机制。这些结果不仅提供了对 CCT 蛋白和 NF-Y 亚基之间网络的深入了解，而且还提供了通过操纵成花素表达来提高作物生产力和全球适应性的潜在方法。