Egg Cell Signaling by the Secreted Peptide ZmEAL1 Controls Antipodal Cell Fate

Unlike in animals, female gametes of flowering plants are not the direct products of meiosis but develop from a functional megaspore after three rounds of free mitotic divisions. After nuclei migration and positioning, the eight-nucleate syncytium differentiates into the embryo sac, which contains two female gametes as well as accessory cells at the micropylar and chalazal pole, respectively. We report that an egg-cell-specific gene, ZmEAL1, is activated at the micropylar pole of the eight-nucleate syncytium. ZmEAL1 translation is restricted to the egg cell, resulting in the generation of peptide-containing vesicles directed toward its chalazal pole. RNAi knockdown studies show that ZmEAL1 is required for robust expression of the proliferation-regulatory gene IG1 at the chalazal pole of the embryo sac in antipodal cells. We further show that ZmEAL1 is required to prevent antipodal cells from adopting central cell fate. These findings show how egg cells orchestrate differentiation of the embryo sac. ► The egg cell regulates antipodal cell fate ► Antipodal cells are able to adopt central cell fate ► The proliferation factor IG1 gene is regulated by ZmEAL1 ► Gametophytic expression of ZmEAL1 appears to be largely auxin independent The mechanisms by which plant gametes influence neighboring somatic accessory structures have been unclear. Krohn et al. identify a peptide—ZmEAL1, secreted by maize egg cells—that is required for somatic antipodal cell development. When this egg-derived signal is depleted, antipodal cells adopt a different (central cell) fate.