Mechanisms controlling seed size by early endosperm development

Seed size is an important agronomic trait determining the yield potential of crops that is controlled by the growth and development of the endosperm, embryo, and seed coat. The seed coat and endosperm have been proposed to play primary roles in determining seed size. Extensive research has been carried out on the regulation of seed size by seed coat, whereas the molecular mechanism underlying the regulation of seed size by the endosperm is poorly understood. Recent studies have emphasized the central role of the endosperm in seed development. The proliferation of syncytial endosperm nuclei and the endosperm cell division during early endosperm development determine the number of endosperm cells, which plays a fundamental role in controlling seed size. Here, we summarize the recent progress in early endosperm development, emphasizing the roles and molecular mechanisms of the HAIKU pathway, phytohormones, and polycomb repressive complex 2 in the control of seed size.