ESD1 Affects Seed Setting Rate in Rice by Controlling Embryo Sac Development

Seed setting rate is one of the critical factors that determine rice yield. Grain formation is a complex biological process, whose molecular mechanism is yet to be improved. Here we investigated the function of an OVATE family protein, Embryo Sac Development 1 (ESD1), in the regulation of seed setting rate in rice ( Oryza sativa ) by examining its loss-of-function mutants generated via CRISPR/Cas9 technology. ESD1 was predominantly expressed at stage 6 of panicle development, especially in the ovules. esd1 mutants displayed reduced seed setting rates with normal stamen development and pollen tube growth but abnormal pistil group. Investigation of embryo sacs revealed that during the mitosis of functional megaspores, some egg cells degraded during differentiation in esd1 mutants, thereby hindering subsequent fertilization process and reducing seed setting rate. In addition, the transcriptional level of OsAPC6, a reported embryo sac developing gene, was found to be significantly reduced in esd1 mutants. These results support that ESD1 is an important modulator of embryo sac development and seed setting rate in rice. Together, this finding demonstrates that ESD1 positively regulates the seed setting rate by controlling embryo sac development in rice, and has implications for the improvement of rice yield.