Abstract
Post‐translational modification of proteins by O‐linked β‐N‐acetylglucosamine (O‐GlcNAc) is catalyzed by O‐GlcNAc transferases (OGTs). O‐GlcNAc modification of proteins regulates multiple important biological processes in metazoans. However, whether protein O‐GlcNAcylation is involved in epigenetic processes during plant development is largely unknown. Here, we show that loss of function of SECRET AGENT (SEC), an OGT in Arabidopsis, leads to an early flowering phenotype. This results from reduced histone H3 lysine 4 trimethylation (H3K4me3) of FLOWERING LOCUS C (FLC) locus, which encodes a key negative regulator of flowering. SEC activates ARABIDOPSIS HOMOLOG OF TRITHORAX1 (ATX1), a histone lysine methyltransferase (HKMT), through O‐GlcNAc modification to augment ATX1‐mediated H3K4me3 histone modification at FLC locus. SEC transfers an O‐GlcNAc group on Ser947 of ATX1, which resides in the SET domain, thereby activating ATX1. Taken together, these results uncover a novel post‐translational O‐GlcNAc modification‐mediated mechanism for regulation of HKMT activity and establish the function of O‐GlcNAc signaling in epigenetic processes in plants.
Highlights
The O-linked b-N-acetylglucosamine (O-GlcNAc) modification of nuclear and cytoplasmic proteins is ubiquitous and essential for a number of biological processes
In the MCF7 cell line, O-GlcNAc transferases (OGTs) associates with the enhancer of zeste homolog 2 (EZH2) in the polycomb repressive complex 2 (PRC2), and O-GlcNAc modification of EZH2 at Ser75 plays a role in maintaining EZH2 stability to catalyze H3K27me3 (Chu et al, 2014)
To explore whether the O-GlcNAc transferase SECRET AGENT (SEC) is involved in flowering-time regulation in Arabidopsis, we identified two homozygous mutant lines in the Col-0 background, sec-4 and sec-5, which contain T-DNA insertions in the promoter region and in exon 2 of SEC, respectively (Fig 1A and B)
Summary
The O-linked b-N-acetylglucosamine (O-GlcNAc) modification of nuclear and cytoplasmic proteins is ubiquitous and essential for a number of biological processes. The dynamic addition and removal of O-GlcNAc at serine and threonine residues are catalyzed by two highly conserved types of enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively (Haltiwanger et al, 1990; Dong & Hart, 1994; Hart et al, 2007). Proteins modified with O-GlcNAc include transcription factors, polymerases, proteasomes, and RNA-processing proteins (Hart et al, 2007), indicating that protein O-GlcNAcylation has significant biological functions. Some proteins associated with chromatin remodeling are modified with O-GlcNAc. In the MCF7 cell line, OGT associates with the enhancer of zeste homolog 2 (EZH2) in the polycomb repressive complex 2 (PRC2), and O-GlcNAc modification of EZH2 at Ser plays a role in maintaining EZH2 stability to catalyze H3K27me (Chu et al, 2014). O-GlcNAcylation of MLL5b, an isoform of the mammalian trithorax histone lysine methyltransferase (HKMT) MLL5, is critical for recruitment and assembly of the MLL5b-AP-1 transcription activation complex (Nin et al, 2015)
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