Oryza Sativa Baby Boom1 Converts the Developmental Fate of Rice Egg Cells from Gametic into Somatic Status.

Oryza sativa BABY BOOM 1 (OsBBM1), a member of the AP2/ERF family of transcription factors, plays a crucial role in the initiation of the early development of rice zygotes; however, how OsBBM1 is involved in the conversion of cellular and developmental fates of egg cells to zygotes remains unclear. Egg cells isolated from transgenic rice plants expressing OsBBM1 under the egg cell-specific promoter showed nuclear and cellular divisions, suggesting that OsBBM1 functions in the conversion of the cell fate of egg cells from a quiescent to a proliferative state. Ectopically expressed OsBBM1 regulates the expression profiles of genes related to cell cycle and division and microtubule-related machinery. Moreover, although cell wall formation generally occurs around zygotes after gamete fusion, egg cells expressing OsBBM1 formed cell walls around the cells before fertilization. These suggest that OsBBM1 plays roles in egg cell-zygote conversion and the subsequent proliferative growth of zygotes.