Maternally expressed OsFIE1 regulates endosperm-imposed dormancy and aleurone development by modulating gibberellin biosynthesis in rice

Seed dormancy, an essential trait for plant adaptation, is determined by the embryo itself and the tissues covering it, through complicated physiological and physical mechanisms. Here, we found that rice FERTILIZATION INDEPENDENT SEED1 (OsFIE1) regulates endosperm-imposed dormancy and the dorsal aleurone thickness, in a manner dependent on the parent of origin. The maternally expressed OsFIE1 suppresses gibberellin (GA) biosynthesis in the endosperm by depositing trimethylation of lysine 27 on histone H3 (H3K27me3) marks on the genes involves in such biosynthesis, to inhibit germination and aleurone differentiation. Knockout of OsGA20ox1 alleviated the defects in osfie1. The aleurone-positive determinant Crinkly 4 is another target of the OsFIE1-containing polycomb repressive complex 2 (PRC2). We also found that OsFIE1 plays an important role in genomic imprinting, particularly for the paternally expressed genes associated with H3K27me3, in the endosperm of germinating seed. Increased aleurone thickness of osfie1 significantly improves grain nutritional quality. Introducing osfie1 into late-heading varieties may reconcile the conflicts between attenuated dormancy and improved nutrition, indicating that the osfie1 gene is useful for rice improvement.