Flowers are the core reproductive organ of plants, and flowering is essential for cross-pollination. Diurnal flower-opening time is thus a key trait influencing reproductive isolation, hybrid breeding, and thermostability in plants. However, the molecular mechanisms controlling this trait remain unknown. Here, we report that rice Diurnal Flower Opening Time 1 (DFOT1) modulates pectin methylesterase (PME) activity to regulate pectin methylesterification levels of the lodicule cell walls, which affect lodicule swelling to control diurnal flower-opening time. DFOT1 is specifically expressed in the lodicules, and its expression gradually increases with the approach to flowering but decreases with flowering. Importantly, a knockout of DFOT1 showed earlier diurnal flower opening. We demonstrate that DFOT1 interacts directly with multiple PMEs to promote their activity. Knockout of PME40 also resulted in early diurnal flower opening, whereas overexpression of PME42 delayed diurnal flower opening. Lower PME activity was observed to be associated with higher levels of pectin methylesterification and the softening of cell walls in lodicules, which contribute to the absorption of water by lodicules and cause them to swell, thus promoting early diurnal flower opening. Higher PME activity had the opposite effect. Collectively, our work uncovers a molecular mechanism underlying the regulation of diurnal flower-opening time in rice, which would help reduce the costs of hybrid breeding and improve the heat tolerance of flowering plants by avoiding higher temperatures at anthesis.

花是植物的核心生殖器官，开花对于异花授粉至关重要。因此，昼夜开花时间是影响植物生殖隔离、杂交育种和热稳定性的关键性状。然而，控制这一性状的分子机制仍然未知。在这里，我们报告水稻昼夜开花时间 1 (DFOT1) 调节果胶甲酯酶 (PME) 活性以调节浆片细胞壁的果胶甲基酯化水平，从而影响浆片肿胀以控制昼夜开花时间。DFOT1在浆片中特异表达，其表达随着接近开花而逐渐增加，但随着开花而减少。重要的是，淘汰DFOT1显示较早的昼夜开花。我们证明 DFOT1 直接与多个 PME 交互以促进它们的活动。PME40的敲除也导致早期的昼夜开花，而PME42的过表达延迟昼夜开花。观察到较低的 PME 活性与较高水平的果胶甲酯化和浆片中细胞壁的软化有关，这有助于浆片吸收水分并导致它们膨胀，从而促进早期昼夜开花。较高的 PME 活动具有相反的效果。总的来说，我们的工作揭示了调控水稻昼夜开花时间的分子机制，这将有助于降低杂交育种的成本，并通过避免花期较高的温度来提高开花植物的耐热性。