Two Distinct Roles of ARABIDOPSIS HOMOLOG OF TRITHORAX1 (ATX1) at Promoters and within Transcribed Regions of ATX1-Regulated Genes  

Abstract

The Arabidopsis thaliana trithorax-like protein, ATX1, shares common structural domains, has similar histone methyltransferase (HMT) activity, and belongs in the same phylogenetic subgroup as its animal counterparts. Most of our knowledge of the role of HMTs in trimethylating lysine 4 of histone H3 (H3K4me3) in transcriptional regulation comes from studies of yeast and mammalian homologs. Little is known about the mechanism by which ATX1, or any other HMT of plant origin, affects transcription. Here, we provide insights into how ATX1 influences transcription at regulated genes, playing two distinct roles. At promoters, ATX1 is required for TATA binding protein (TBP) and RNA Polymerase II (Pol II) recruitment. In a subsequent event, ATX1 is recruited by a phosphorylated form of Pol II to the +300-bp region of transcribed sequences, where it trimethylates nucleosomes. In support of this model, inhibition of phosphorylation of the C-terminal domain of Pol II reduced the amounts of H3K4me3 and ATX1 bound at the +300-nucleotide region. Importantly, these changes did not reduce the occupancy of ATX1, TBP, or Pol II at promoters. Our results indicate that ATX1 affects transcription at target genes by a mechanism distinct from its ability to trimethylate H3K4 within genes.

SIP1 participates in regulation of flowering time in rice by recruiting OsTrx1 to Ehd1

“…Defects in OsTrx1 might disrupt Ehd3′s ability to repress Ghd7 , resulting in late flowering (Choi et al ., 2014). Given that the H3K4me3 level is correlated with transcriptional activation (Ding et al ., 2011b; Fromm & Avramova, 2014), the induced transcription levels and reduced H3K4me3 levels of Ghd7 suggest that Ghd7 might not be the direct target of OsTrx1. A recent study has indicated that OsWDR5a interacts with the Win motif of OsTrx1 and directly binds to histone H3 (Jiang et al ., 2018).…”

“…Arabidopsis thaliana ecotype WS plants were grown at 22°C under an LD photoperiod (16 h : 8 h, light : dark cycle). Seeds from the atx1‐1 mutant have been described previously (Alvarez‐Venegas et al ., 2003; Ding et al ., 2011a,b). …”

“…Yeast SET1 is the sole methyltransferase acting on lysine 4 of histone H3, and is responsible for the mono, di‐ and tri‐methylation of H3K4 (Bernstein et al ., 2002; Santos‐Rosa et al ., 2002). Arabidopsis ATX1 tri‐methylates H3K4 at specific genes involved in multiple biological processes, such as flowering time regulation, dehydration stress responses and flower organ development (Alvarez‐Venegas et al ., 2003; Saleh et al ., 2007; Pien et al ., 2008; Ding et al ., 2011a,b, 2012a,b). In addition to development, ATX1 and WDR5a are also associated with RNA polymerase II enrichment, which promotes the transcription initiation at the promoter region and transcription elongation at the gene body (Ding et al ., 2011b, 2012b).…”

Multiple exposures to drought 'train' transcriptional responses in Arabidopsis

“…As Arabidopsis Trithoraxlike 1 (ATX1) regulates a large number of dehydration stressresponse genes [19][20][21] , its potential role in the memory responses was investigated here. Dehydration-induced transcript levels were strongly diminished in atx1 plants, consistent with its activating role at these genes ( Fig.…”

Dynamic regulation of Polycomb group activity during plant development

“…First, ATX1 recruits the TATA binding protein (TBP) and RNA Polymerase II (Pol II) to the target gene promoter. Subsequently, ATX1 is recruited by a phosphorylated form of Pol II to the transcribed region, where it places the H3K4me3 marks, associated with active chromatin [37]. The SAND-domain DNA binding protein ULTRAPETALA1 (ULT1) was identified as a second trxG protein in Arabidopsis.…”