Two MADS-box proteins, AGL9 and AGL15, recruit the FIS-PRC2 complex to trigger the phase transition from endosperm proliferation to embryo development in Arabidopsis

Spatiotemporal regulation of gene expression by Polycomb Repressive Complex 2 (PRC2) is critical for animal and plant development. Arabidopsis FIS-PRC2 complex functions uniquely during plant reproduction from gametogenesis to seed development. After a double fertilization event, triploid endosperm proliferates early followed by the growth of a diploid embryo to replace the endosperm in Arabidopsis and many dicots. Key genes critical for endosperm proliferation such as IKU2 and MINI3 are activated after fertilization. Here we report that two MADS-box AGL proteins associate with the key endosperm proliferation loci and recruit the FIS-PRC2 repressive complex at 4 to 5 days after pollination (DAP). Unique to this phase transition, AGL9 and AGL15 only accumulate toward the end of endosperm proliferation at 4 to 5 DAP and promote the deposition of H3K27me3 marks at the key genomic loci. Knockouts of AGL9 and AGL15 or overexpression of AGL9 or AGL15 significantly influence endosperm proliferation and cellularization. Genome-wide analysis with CUT&Tag seq and RNA-seq reveals the landscape of endosperm H3K27me3 marks and gene expression profiles in Col-0 and agl9 agl15. CUT&Tag qPCR also demonstrates the occupancy of the two MADS-box proteins and FIS-PRC2 with a few representative target loci. Our studies suggest that MADS-box proteins could potentially recruit PRC2 to regulate various developmental processes in many other plant species or even fungi and animals.