Updated project metadata. In Arabidopsis mature seeds, the onset of the embryo-to-seedling transition is nonautonomously controlled, being blocked by endospermic abscisic acid (ABA) release under unfavorable conditions. Mature embryos lack an impermeable cuticle, unlike seedlings, consistent with their endospermic ABA uptake capability. Seedling cuticle formation occurs after germination rather than during embryogenesis. Mature endosperm removal prevents seedling cuticle formation and seed reconstitution by endosperm grafting onto embryos shows that the endosperm promotes seedling cuticle development. Grafting different endosperm and embryo mutant combinations, together with biochemical, microscopy and mass spectrometry approaches, reveals that endospermic release of Tyrosyl Sulfate Transferase (TPST)-sulfated CIF2 and PSY1 peptides promotes seedling cuticle development. Endosperm-deprived embryos produced nonviable seedlings bearing numerous developmental defects, in a manner unrelated to embryo nourishment, all restored by exogenously provided endosperm. Hence, seedling establishment is nonautonomous, requiring the mature endosperm.