Histone acetylation affects numerous cellular processes, such as gene transcription, in both plants and animals. However, the posttranslational modification-participated regulatory networks for crop-yield-related traits are largely unexplored. Here, we characterize a regulatory axis for controlling rice grain size and yield, centered on a potent histone acetyltransferase (chromatin modifier) known as HHC4. HHC4 interacts with and forms a ternary complex with adaptor protein ADA2 and transcription factor bZIP23, wherein bZIP23 recruits HHC4 to specific promoters, and ADA2 and HHC4 additively enhance bZIP23 transactivation on target genes. Meanwhile, HHC4 interacts with and is phosphorylated by GSK3-like kinase TGW3. The resultant phosphorylation triggers several functional impairments of the HHC4 ternary complex. In addition, we identify two major phosphorylation sites of HHC4 by TGW3—sites which play an important role in controlling rice grain size. Overall, our findings thus have critical implications for understanding epigenetic basis of grain size control and manipulating the knowledge for higher crop productivity.

组蛋白乙酰化影响植物和动物中的许多细胞过程，例如基因转录。然而，翻译后修饰参与的作物产量相关性状的调控网络在很大程度上尚未被探索。在这里，我们描述了控制水稻籽粒大小和产量的调控轴，以称为 HHC4 的有效组蛋白乙酰转移酶（染色质修饰剂）为中心。HHC4与接头蛋白 ADA2 和转录因子 bZIP23相互作用并形成三元复合物，其中 bZIP23 将 HHC4 募集到特定启动子，ADA2 和 HHC4 额外增强 bZIP23对靶基因的反式激活。同时，HHC4 与 GSK3 样激酶 TGW3 相互作用并被其磷酸化。由此产生的磷酸化会引发 HHC4 三元复合物的多种功能损伤。此外，我们还确定了 TGW3 对 HHC4 的两个主要磷酸化位点，这些位点在控制水稻籽粒大小方面发挥着重要作用。总的来说，我们的研究结果对于理解粒度控制的表观遗传基础和操纵知识以提高作物生产力具有重要意义。