合子通常经一次不均等分裂产生发育途径和命运截然不同的顶细胞和基细胞。顶细胞按特定的分裂模式和发育途径形成胚体，而基细胞则发育成胚柄。同一母细胞的两个子细胞为什么会具有截然不同的发育命运？何种机制决定了顶、基细胞进入不同的发育途径是发育生物学的核心问题，长期以来备受关注。但由于缺乏好的研究切入点，相关研究难以着手，以致迄今对其分子机制仍所知甚微。我们的前期工作发现了1个顶细胞系特异表达的Cystatin基因NtCYSb。当NtCYSb表达水平降低时，顶细胞不能进入胚胎发育途径，而是与基细胞一样，进入胚柄发育途径，这为我们研究顶、基细胞发育途径抉择的分子机制提供了难得的切入点。以此为契机，本项目拟通过解析NtCYSb及其上游转录因子、下游靶蛋白的功能，揭示NtCYSb在胚体/胚柄发育途径抉择过程中的作用及分子机制，以期对认识植物胚胎细胞发育命运决定的分子调控机理有新的突破。

Zygote usually undergoes an asymmetric division, giving rise to the formation of an apical cell and a basal cell with distinct developmental pathway and cell fate. The smaller apical cell will develop into the embryo proper, whereas the larger basal cell will form a suspensor. The molecular mechanism underlying cell fate determination of the apical and basal cell lineages has been considered as the central topic in developmental biology and has been paid great attention by scientists in this field. However, the molecular mechanism regulating developmental pathway of apical cell and basal cell is largely unknown, possibly due to the lack of the proper starting point for research. In our previous work, we found that a cysteine protease inhibitor, NtCYSb, is specifically expressed in the apical cell lineage. In NtCYSb-silencing plants, the apical cell can be switched into basal cell developmental pathway and develop into a suspensor-like structure, but can not develop into an embryo proper, which provides a unique opportunity for studying the molecular mechanism of apical cell and basal cell developmental pathway determination. In this project, we will focus on the revealing the upstream and downstream mechanism of NtCYSb in the determination of embryo proper and suspensor pathway. Hope to enhance our understanding of the molecular mechanism regulating embryonic cell fate determination in plants.