SUMMARY SPLAYED (SYD) is a SWItch/Sucrose Non‐Fermentable (SWI/SNF)‐type chromatin remodeler identified in Arabidopsis thaliana (Arabidopsis). It is believed to play both redundant and differential roles with its closest homolog BRAHMA (BRM) in diverse plant growth and development processes. To better understand how SYD functions, we profiled the genome‐wide occupancy of SYD and its impact on the global transcriptome and trimethylation of histone H3 on lysine 27 (H3K27me3). To map the global occupancy of SYD, we generated a GFP‐tagged transgenic line and used it for chromatin immunoprecipitation experiments followed by next‐generation sequencing, by which more than 6000 SYD target genes were identified. Through integrating SYD occupancy and transcriptome profiles, we found that SYD preferentially targets to nucleosome‐free regions of expressed genes. Further analysis revealed that SYD occupancy peaks exhibit five distinct patterns, which were also shared by BRM and BAF60, a conserved SWI/SNF complex component, indicating the common target sites of these SWI/SNF chromatin remodelers and the functional relevance of such distinct patterns. To investigate the interplay between SYD and Polycomb‐group (PcG) proteins, we performed a genome‐wide analysis of H3K27me3 in syd‐5. We observed both increases and decreases in H3K27me3 levels at a few hundred genes in syd‐5 compared to wild type. Our results imply that SYD can act antagonistically or synergistically with PcG at specific genes. Together, our SYD genome‐wide occupancy data and the transcriptome and H3K27me3 profiles provide a much‐needed resource for dissecting SYD’s crucial roles in the regulation of plant growth and development.

The endosperm provides nutrients and growth regulators to the embryo during seed development. LEAFY COTYLEDON1 (LEC1) has long been known to be essential for embryo maturation. LEC1 is expressed in both the embryo and the endosperm; however, the functional relevance of the endosperm-expressed LEC1 for seed development is unclear. Here, we provide genetic and transgenic evidence demonstrating that endosperm-expressed LEC1 is necessary and sufficient for embryo maturation. We show that endosperm-synthesized LEC1 is capable of orchestrating full seed maturation in the absence of embryo-expressed LEC1. Inversely, without LEC1 expression in the endosperm, embryo development arrests even in the presence of functional LEC1 alleles in the embryo. We further reveal that LEC1 expression in the endosperm begins at the zygote stage and the LEC1 protein is then trafficked to the embryo to activate processes of seed maturation. Our findings thus establish a key role for endosperm in regulating embryo development.

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