Synchronizing the Panicle: A Spatiotemporal Network View of Phytohormones in Rice Grain Filling and Agronomic Regulation

The grain-filling stage is crucial for determining yield and quality in rice. This process, and the pronounced disparity in development between superior and inferior grains, is orchestrated by a dynamic network of endogenous phytohormones. However, an integrated synthesis of their synthesis, transport, signaling, and crosstalk—particularly in the context of modern high-yield cultivation—is lacking. This review comprehensively analyzes the roles of auxin, cytokinin, gibberellin, abscisic acid, ethylene, brassinosteroids, and polyamines, with emphasis on their spatiotemporal dynamics and interactions in shaping grain fate. We explicitly link these hormonal mechanisms to agronomic and chemical regulation practices, such as nitrogen management and alternate wetting-drying irrigation. By synthesizing this knowledge, we aim to propose a unified model of grain filling regulation. This framework provides an actionable theoretical foundation for designing precise strategies to manipulate hormonal balances, thereby improving grain filling uniformity, yield, and quality in rice.