Arabidopsis O ‐Glc NA c transferase SEC activates histone methyltransferase ATX 1 to regulate flowering

Post‐translational modification of proteins by O ‐linked β‐ N ‐acetylglucosamine ( O ‐Glc NA c) is catalyzed by O ‐Glc NA c transferases ( OGT s). O ‐Glc NA c modification of proteins regulates multiple important biological processes in metazoans. However, whether protein O ‐Glc NA cylation 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 TRITHORAX 1 ( ATX 1), a histone lysine methyltransferase ( HKMT ), through O ‐Glc NA c modification to augment ATX 1‐mediated H3K4me3 histone modification at FLC locus. SEC transfers an O ‐Glc NA c group on Ser947 of ATX 1, which resides in the SET domain, thereby activating ATX 1. Taken together, these results uncover a novel post‐translational O ‐Glc NA c modification‐mediated mechanism for regulation of HKMT activity and establish the function of O ‐Glc NA c signaling in epigenetic processes in plants.