Timing of the maternal-to-zygotic transition during early seed development in maize. Plant Cell 17

In animals, early embryonic development is largely dependent on maternal transcripts synthesized during gametogenesis. Recent data in plants also suggest maternal control over early seed development, but the actual timing of zygotic genome activation is unclear. Here, we analyzed the timing of the maternal-to-zygotic transition during early Zea mays seed de-velopment.We show that for 16genes expressedduring early seeddevelopment, onlymaternally inherited alleles are detected during 3dafter fertilization inboth theembryoand theendosperm.Microarray analyses ofprecocious embryonicdevelopment in apomictic hybrids between maize and its wild relative, Tripsacum, demonstrate that early embryo development occurs without significant quantitative changes to the transcript population in the ovule before fertilization. Precocious embryo development is also correlated with a higher proportion of polyadenylated mRNA in the ovules. Our data suggest that the maternal-to-zygotic transition occurs several days after fertilization. By contrast, novel transcription accompanies early endosperm development, indicating that different mechanisms are involved in the initiation of endosperm and embryo development