27 28 DELAY OF GERMINATION1 (DOG1) represents a major quantitative locus for the genetic 29 regulation of seed dormancy in Arabidopsis. Accumulation of DOG1 in seeds leads to deep 30 dormancy and delayed germination. Here, we report that the conserved B3 DNA binding 31 domains of the transcriptional repressors HIGH-LEVEL EXPRESSION OF SUGAR 32 INDICIBLE GENE2/ VIVIPAROUS-1/ABSCISIC ACID INSENSITIVE 3-LIKE1 33 (HSI2/VAL1) and HSI2-LIKE1/ VIVIPAROUS-1/ABSCISIC ACID INSENSITIVE 3-LIKE2 34(HSL1/VAL2), which play critical roles in the developmental transition from seed maturation to 35 seedling growth, interact with RY elements in the DOG1 proximal promoter leading to 36 repression of DOG1 transcription during germination and seedling establishment. DOG1 37 expression is partially de-repressed in hsi2/val1 (hsi2-2) but not in hsl1/val2 (hsl1-1) knockout 38 mutants and is strongly upregulated in a hsi2/val1 hsl1/val2 double mutant, indicating that 39 HSI2/VAL1 and HSL1/VAL2 act redundantly to repress DOG1 expression. HSI2/VAL1 and 40 HSL1/VAL2 form homo-and hetero-dimers in vivo, and dimerization is dependent on the 41 HSI2/VAL1 PHD-like domain. Complementation of hsi2-2 with HSI2/VAL1 harboring a 42 disrupted plant homeodomain (PHD)-like domain results in stronger de-repression of DOG1 43 expression than the hsi2-2 knockout, indicating that the PHD-like domain plays a critical role in 44 mediating functional interactions between HSI2/VAL1 and HSL1/VAL2. Both HSI2/VAL1 and 45 HSL1/VAL2 interact with components of polycomb repressive complex 2 (PRC2), including 46 CURLY LEAF and MULTICOPY SUPPRESSOR OF IRA1 (MSI1), along with LIKE 47 HETERCHROMATIN PROTEIN 1 (LHP1), which are involved in the deposition and expansion 48 of histone H3 lysine 27 trimethylation (H3K27me3) marks in repressive chromatin. Thus, 49 HSI2/VAL1 HSL1/VAL2-dependent recruitment of PRC2 leads to silencing of DOG1 through 50 the deposition of H3K27me3.51 52 Transcriptional repression 54 55 109 to positively recruit PRC2 to chromatin for the deposition of H3K27me3 (Derkacheva et al., 110 2013). LHP1 also directly interacts with RING-RAWUL proteins and EMBRYONIC 111 FLOWER1 (EMF1, a component of PRC1), suggesting LHP1 can be present in several PRC1-112 like complexes and may act as a bridge between PRC1 and PRC2 (Xu et al., 2008; Bratzel et al., 113 2010). In Arabidopsis, LHP1 co-localizes with H3K27me3 across the genome, and is responsible 114 for the expansion of H3K27me3 associated with the stabilization of transcriptional repression 115 ( Turck et al., 2007; Zhang et al., 2007; Exner et al., 2009). Expression of many tissue specific 116 genes is upregulated in lhp1 loss-of-function mutants (Lafos et al., 2011; Libault et al., 2005), 117 5 with decreased levels of H3K27me3 seen at direct target gene loci, including FLC ( Yuan et al., 118 2016; Veluchamy et al., 2016), indicating that LHP1-dependent gene repression correlates with 119 deposition of H3K27me3. Molitor et al. (2014) reported that DOG1 is negatively regulated by 120 ALFIN1-like prot...