AtNSE1 and AtNSE3 are required for formation of embryo pattern and maintenance of cell viability during Arabidopsis embryogenesis.

Embryogenesis is an essential process during seed development in higher plant. Our previous work has showed that mutations of AtNSE1 or AtNSE3 would lead to early embryo abortion, and their proteins could interact with each other directly. However, the crucial regions of these proteins in this interaction, and how the proteins are cytologically involved in Arabidopsis embryo development are unknown. Here, we found that AtNSE1 can interact with the N-terminal of AtNSE3 by the C-terminal including the Ring-like motif, and only the Ring-like motif is essential for binding with three α motifs of AtNSE2/AtMMS21. Furthermore, by genetic assays and analyzing the molecular markers of cell fate decisions (STM, WOX5 and WOX8) in nse1 and nse3 embryos, we found that AtNSE1 and AtNSE3 worked non-redundantly in early embryo development, and the differentiation of apical meristem and the hypophysis was failed in the mutants which have disrupted auxin response and transportation. Besides that, the upper cells of suspensor in the mutants seem to have embryo proper cell identity. Cytological evidences showed that cell death occurred from early embryo stage, and the vacuolar programmed cell death and necrosis, occurred in nse1 and nse3 mutant embryos led to ovule aborted. As a result, AtNSE1 and AtNSE3 are essential for maintaining cell viability and growth during early embryogenesis. Our finding shed light on our understanding of the functions of SMC5/6 complex on early embryogenesis in Arabidopsis.