The Polycomb Group (PcG) proteins form two protein complexes, PcG Repressive Complex 1 ( PRC 1) and PRC 2, which are key epigenetic regulators in eukaryotes. PRC 2 represses gene expression by catalyzing the trimethylation of histone H3 lysine 27 (H3K27me3). In Arabidopsis ( Arabidopsis thaliana ), CURLY LEAF ( CLF ) and SWINGER ( SWN ) are two major H3K27 methyltransferases and core components of PRC 2, playing essential roles in plant growth and development. Despite their importance, genome‐wide binding profiles of CLF and SWN have not been determined and compared yet. In this study, we generated transgenic lines expressing GFP ‐tagged CLF / SWN under their respective native promoters and used them for Ch IP ‐seq analyses to profile the genome‐wide distributions of CLF and SWN in Arabidopsis seedlings. We also profiled and compared the global H3K27me3 levels in wild‐type ( WT ) and PcG mutants ( clf , swn , and clf swn ). Our data show that CLF and SWN bind to almost the same set of genes, except that SWN has a few hundred more targets. Two short DNA sequences, the GAGA ‐like and Telo ‐box‐like motifs, were found enriched in the CLF and SWN binding regions. The H3K27me3 levels in clf , but not in swn , were markedly reduced compared with WT ; and the mark was undetectable in the clf swn double mutant. Further, we profiled the transcriptomes in clf , swn , and clf swn, and compared that with WT . Thus this work provides a useful resource for the plant epigenetics community for dissecting the functions of PRC 2 in plant growth and development.

SPT6 is a conserved elongation factor that is associated with phosphorylated RNA polymerase II (RNAPII) during transcription. Recent transcriptome analysis in yeast mutants revealed its potential role in the control of transcription initiation at genic promoters. However, the mechanism by which this is achieved and how this is linked to elongation remains to be elucidated. Here, we present the genome-wide occupancy of Arabidopsis SPT6-like (SPT6L) and demonstrate its conserved role in facilitating RNAPII occupancy across transcribed genes. We also further demonstrate that SPT6L enrichment is unexpectedly shifted, from gene body to transcription start site (TSS), when its association with RNAPII is disrupted. Protein domains, required for proper function and enrichment of SPT6L on chromatin, are subsequently identified. Finally, our results suggest that recruitment of SPT6L at TSS is indispensable for its spreading along the gene body during transcription. These findings provide new insights into the mechanisms underlying SPT6L recruitment in transcription and shed light on the coordination between transcription initiation and elongation.

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.