Spatiotemporal Restriction of Expression by Class I BPCs Promotes Ovule Development and Coordinates Embryo and Endosperm Growth.

Spatiotemporal regulation of gene expression is critical for proper developmental timing in plants and animals. The transcription factor regulates developmental phase transitions by acting as a link between hormonal pathways in Arabidopsis (). However, the mechanisms governing its spatiotemporal expression pattern are poorly understood. Here, we show that is repressed in the ovule integuments and seed endosperm. repression requires class I BASIC PENTACYSTEINE (BPC) proteins, which directly bind GA/CT -elements in and restrict its expression pattern. During vegetative and reproductive development, derepression in () double mutant or misexpression in lines causes dwarf plants carrying defective flowers and aborted ovules. After fertilization, ectopic expression in endosperm or endosperm and endothelium increases endosperm nuclei proliferation and seed size, causing delayed or arrested embryo development. These phenotypes are rescued in Finally, class I BPCs interact with FIS-PRC2 (FERTILIZATION-INDEPENDENT SEED-Polycomb Repressive Complex2), which represses in the endosperm during early seed development. We propose that BPC1 and 2 promote the transition from reproductive to seed development by repressing in ovule integuments. After fertilization, BPC1 and 2 and FIS-PRC2 repress in the endosperm to coordinate early endosperm and embryo growth.