Abstract: Grain size is a pivotal agronomic trait that determines rice yield and grain quality. It is genetically regulated by multiple genes and interconnected signaling pathways. Numerous grain size‑related genes have been identified in rice, but relevant findings regarding regulatory pathways, natural gene variations, signaling crosstalk and breeding applications remain poorly systematically integrated. This review summarizes recent advances in regulatory mechanisms of rice grain size genes, integrates regulatory pathways and signaling crosstalks. We further discussed the multi-gene interaction, trade-offs between these genes and practical breeding application, as well as current major challenges in this field and propose future research directions. The overall aim is to offer a reliable theoretical reference and actionable guidance for the targeted optimization of grain size traits and the development of novel high-yielding, high-quality rice cultivars.

Key words: rice, grain size-related gene, molecular regulation, breeding application