HSI2/VAL1 PHD-like domain promotes H3K27 trimethylation to repress the expression of seed maturation genes and complex transgenes in Arabidopsis seedlings

Abstract

BackgroundThe novel mutant allele hsi2-4 was isolated in a genetic screen to identify Arabidopsis mutants with constitutively elevated expression of a glutathione S-transferase F8::luciferase (GSTF8::LUC) reporter gene in Arabidopsis. The hsi2-4 mutant harbors a point mutation that affects the plant homeodomain (PHD)-like domain in HIGH-LEVEL EXPRESSION OF SUGAR-INDUCIBLE GENE2 (HSI2)/VIVIPAROUS1/ABI3-LIKE1 (VAL1). In hsi2-4 seedlings, expression of this LUC transgene and certain endogenous seed-maturation genes is constitutively enhanced. The parental reporter line (WTLUC) that was used for mutagenesis harbors two independent transgene loci, KanR and KanS. Both loci express luciferase whereas only the KanR locus confers resistance to kanamycin.ResultsHere we show that both transgene loci harbor multiple tandem insertions at single sites. Luciferase expression from these sites is regulated by the HSI2 PHD-like domain, which is required for the deposition of repressive histone methylation marks (H3K27me3) at both KanR and KanS loci. Expression of LUC and Neomycin Phosphotransferase II transgenes is associated with dynamic changes in H3K27me3 levels, and the activation marks H3K4me3 and H3K36me3 but does not appear to involve repressive H3K9me2 marks, DNA methylation or histone deacetylation. However, hsi2-2 and hsi2-4 mutants are partially resistant to growth inhibition associated with exposure to the DNA methylation inhibitor 5-aza-2′-deoxycytidine. HSI2 is also required for the repression of a subset of regulatory and structural seed maturation genes in vegetative tissues and H3K27me3 marks associated with most of these genes are also HSI2-dependent.ConclusionsThese data implicate HSI2 PHD-like domain in the regulation of gene expression involving histone modifications and DNA methylation-mediated epigenetic mechanisms.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0293-4) contains supplementary material, which is available to authorized users.

HSI2/VAL1 Silences AGL15 to Regulate the Developmental Transition from Seed Maturation to Vegetative Growth in Arabidopsis

“…In previous reports, we showed that expression of AGL15 is strongly upregulated in both hsi2-2 knockout Arabidopsis plants and in hsi2-4 plants that carry a C-to-Y substitution in the HSI2 PHD motif (Veerappan et al, 2012). This change in expression is associated with a dramatic loss of histone 3 lysine 27 trimethylation (H3K27me3) at the AGL15 locus (Veerappan et al, 2014).…”

“…Since expression of AGL15 is strongly upregulated and H3K27me3 enrichment is reduced in hsi2 mutants (Veerappan et al, 2012(Veerappan et al, , 2014, we hypothesize that the AGL15 locus is a direct regulatory target of HSI2. To determine if HSI2 interacts with AGL15 in vivo, an epitope-tagged HSI2-rescued Arabidopsis line was generated by the introduction of HSI2-HA coding sequence under control of the native HSI2 promoter (HSI2pro:HSI2-HA) into hsi2-2 knockout plants that contain the GSTF8pro:LUC (hsi2-2 LUC ) reporter gene (Veerappan et al, 2012(Veerappan et al, , 2014.…”

“…To determine if HSI2 interacts with AGL15 in vivo, an epitope-tagged HSI2-rescued Arabidopsis line was generated by the introduction of HSI2-HA coding sequence under control of the native HSI2 promoter (HSI2pro:HSI2-HA) into hsi2-2 knockout plants that contain the GSTF8pro:LUC (hsi2-2 LUC ) reporter gene (Veerappan et al, 2012(Veerappan et al, , 2014. Expression of the luciferase reporter gene and selected seed-specific major transcriptional regulator genes in plants of the rescued line was reduced from the high levels seen in hsi2-2 LUC plants to levels similar to that in wildtype plants, indicating that HSI2-HA is functional ( Figures 1A to 1C).…”

“…The PHD finger is a zinc finger domain that is reported to recognize histone 3 trimethylated at lysine 4 (H3K4me3) and di-or trimethylated lysine 27 (H3K27me2/ 3) (Chakravarty et al, 2009;Zeng et al, 2010;Yuan et al, 2016). Genetic disruption of the HSI2-PHD domain in Arabidopsis results in decreased H3K27me2/3 and increased H3K4me3 enrichment at certain seed-related genes, correlating with ectopic expression of those genes in seedlings (Veerappan et al, 2012(Veerappan et al, , 2014Yuan et al, 2016). The CW domain also recognizes H3K4me2 and H3K4me3 in vitro (Hoppmann et al 2011) and the HSL1-CW domain interacts with HISTONE DEACETYLASE19 (HDA19) in vivo to downregulate a subset of seed maturation genes by alteration of histone acetylation at the target gene loci during seed germination (Zhou et al, 2013).…”

Transport and transcriptional regulation of oil production in plants

“…Double mutants of highlevel expression of sucrose inducible gene2 (HSI2)/VAL1 and HSI2-Like/VAL2 produce seedling expressing embryo specific genes, AFL clade genes, and accumulate high seed storage compounds. [93] Researchers recently found that a MYB and basic helix-loop-helix TFs, Transparent Testa 2 and 8 (TT2 and 8), respectively, inhibits FA biosynthesis in seed embryo by interacting with and inhibiting the FUS3 and LEC1, thereby repressing KASII and BIOTIN CARBOXYL CARRIER PROTEIN2 (BCCP2); a subunit of ACCase. [94] Arabidopsis six-b-interacting protein 1-like 1 (ASIL1) is a regulator of seed filling.…”