This domain is Embryo surrounding factor 1 (ESF1) protein present in Arabidopsis thaliana. Maternally contributed central cell ESF1 peptides play an important role in suspensor formation and pro-embryo development. The biological activity of ESF1 depends on structural topology, which is stabilized by disulfide bonds [1].

1: Central cell-derived peptides regulate early embryo patterning in flowering plants. Costa LM, Marshall E, Tesfaye M, Silverstein KA, Mori M, Umetsu Y, Otterbach SL, Papareddy R, Dickinson HG, Boutiller K, VandenBosch KA, Ohki S, Gutierrez-Marcos JF; Science. 2014;344:168-172. PMID:24723605