HSI2/VAL1 and HSL1/VAL2 function redundantly to regulate seed dormancy by controllingDOG1expression in Arabidopsis

Abstract

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...

Histone deacetylase HDA19 interacts with histone methyltransferase SUVH5 to regulate seed dormancy in Arabidopsis

“…These studies suggested that the transcriptional repressors HSL1 and its homologue HSI2 could cooperate with different HDACs to participate in the regulation of gene expression. Interestingly, a recent study showed that HSI2 and HSL1 function redundantly to regulate seed dormancy by controlling DOG1 expression in Arabidopsis (Allen et al 2019). In the present work, although no interaction was found between SUVH4 and HDA19, it cannot rule out that SUVH4 might interact with another HDAC to regulate gene expression.…”

VALgenes regulate vegetative phase change via miR156-dependent and independent mechanisms

“…VAL1 has previously been found to physically interact with VAL2, multiple PRC1 and PRC2 components, and the transcriptional repressor SAP18 (Chen et al, 2018(Chen et al, , 2020Chhun et al, 2016;Jing et al, 2019;Qüesta et al, 2016;Xie et al, 2018;Yang et al, 2013a;Yuan et al, 2016). However, these studies do not provide information about VAL1's in planta protein interactions over time.…”

“…These results demonstrate that all five RY-sites are important for the expression of MIR156C, and that they function additively. Individual RY-sites have also been shown to interact additively to repress the VAL1-PRC2 targets FLC and DOG1 (Chen et al, 2020;Yuan et al, 2016).…”

“…In addition to their roles in vegetative phase change, VAL genes regulate multiple nodes of the flowering time (Jing et al, 2019;Qüesta et al, 2016;Yuan et al, 2016) and seed development (Chen et al, 2018(Chen et al, , 2020Suzuki et al, 2007;Yang et al, 2013a) networks. The co-option of VAL activity throughout genetic networks thus appears critical to coordinating plant developmental transitions.…”

“…There are three VAL genes in Arabidopsis, of which VAL1 and VAL2 (also known as HSI2 and HSL2 respectively) are the most functionally important (Suzuki et al, 2007). VAL proteins repress their targets by binding to 6 base pair RY-sequence motifs (CATGCA) via their B3 domain (Chen et al, 2018(Chen et al, , 2020Guo et al, 2013;Jing et al, 2019;Qüesta et al, 2016;Suzuki et al, 1997;Yuan et al, 2016).…”