The Prolonged Endosperm Filling and Embryo Enlargement Phases Contribute to the Impaired Development of Inferior Grains in Japonica Rice

In both syn-DW024 and asyn-DW179, the duration of the endosperm/embryo morphogenesis phase was identical in superior and inferior grains. The inferior grains of asyn-DW179 exhibited a 10-day prolongation in the endosperm filling phase and a 20-day extension in the embryo enlargement phase as compared with the superior grains. The endosperm of inferior grains exhibited higher contents of sugars and free amino acids, along with slower accumulation of storage compounds, which is associated with the down-regulation of genes for starch synthesis and ABA signaling.

In addition, transporters for nutrient exchanges between endosperm and embryo were down-regulated, suggesting a potential role of the embryo in adjusting the endosperm filling process. Collectively, our results reveal that the prolonged phases of endosperm filling and embryo enlargement may underlie the impaired development of inferior grains, offering a new perspective for breeding or cultivating rice with uniform grain quality.