Nitric oxide delays floral transition in Arabidopsis by inhibiting histone deacetylases HDA5 and HDA6.

Nitric oxide (NO), a reactive small molecule, plays a critical role in various developmental and physiological processes in living organisms. Previous studies by our group revealed that NO delays flowering in Arabidopsis by increasing transcript levels of the flowering repressor FLOWERING LOCUS C (FLC). In this study, we further investigated the molecular mechanism by which NO regulates FLC expression. Genetic experiments demonstrated that NO-induced delayed flowering specifically depends on elevated FLC transcript levels. Chromatin Immunoprecipitation assays revealed that NO significantly enhances histone H3 acetylation at the FLC locus. Biochemical analyses further showed that NO reduces total histone deacetylase activity through S-nitrosylation of histone deacetylases HDA5 and HDA6. Additionally, we identified and evaluated potential S-nitrosylation sites on HDA5 and HDA6, revealing their effects on deacetylase activity and floral regulation. Collectively, our findings uncover a novel mechanism by which NO mediates epigenetic modification to modulate flowering in Arabidopsis. This study sheds light on the functional network linking NO signaling, epigenetic modification, and flowering.