Polycomb group (PcG) protein complexes, which function in the epigenetic regulation of gene expression, control numerous developmental processes in plants and animals. For instance, the Arabidopsis PcG protein FERTILIZATION INDEPENDENT ENDOSPERM (AtFIE) regulates the transition of the haploid female gametophyte to the diploid sporophyte phase. Nir Ohad and co-workers now report that FIE function is evolutionarily conserved from mosses to flowering plants (see ). They identify a FIE homologue, PpFIE, in the moss Physcomitrella patens,which is expressed only in apical gametophytic cells and in stem cells that undergo fate transition. Deleting PpFIE leads to disrupted gametophytic cell differentiation, indicating that the function of PpFIE is similar to that of AtFIE. The fact that AtFIE can partially rescue the PpFIE loss-of-function phenotype (and vice versa) and that PpFIE can interact with other PcG proteins further support this notion. Thus, the role of the FIE PcG complex in regulating gametophytic differentiation appears to have been established early in plant evolution.
