Molecular regulation mechanisms of seed development in rice (Oryza sativa L.)

Rice seed development is a complex and precisely orchestrated process that progresses through multiple critical stages from fertilization to maturity, involving intricate spatiotemporal gene regulatory networks and the coordinated interplay of multiple hormonal signaling pathways. As direct products of double fertilization, the embryo and endosperm fulfill distinct biological roles: the embryo transmits genetic information for progeny propagation, while the endosperm serves as a nutrient reservoir. Morphologically, embryo development is categorized into four stages-proembryo, globular embryo, scutellum formation, and coleoptile emergence-whereas endosperm development sequentially transitions through syncytial nuclear proliferation, cellularization, storage substance accumulation, and maturation. The embryo and endosperm exhibit distinct gene expression profiles and regulatory patterns at different developmental stages. In addition, with the advancing research in epigenetics, an increasing body of evidence demonstrates that under both normal developmental conditions and environmental stress, seeds dynamically reprogram the three-dimensional chromatin structure and alter gene expression patterns via epigenetic mechanisms such as DNA methylation, histone modification, and non-coding RNA regulation, thereby modulating the adaptability of seed development. Phytohormones also play pivotal roles in rice seed development: auxin polar distribution during early embryogenesis is essential for establishing the apical-basal axis, while its synergistic interaction with cytokinin coordinates cell division and organ differentiation. In this review, we conducted a systematic analysis of the key genes and their regulatory mechanisms involved in embryo and endosperm development in rice seeds. Additionally, we explored the epigenetic regulation during seed development as well as the roles of plant hormones. Finally, we highlighted that numerous unresolved questions remain regarding the molecular mechanisms underlying rice embryo and endosperm development, and outlined potential directions for future research.