Promoter-associated histone acetylation is involved in the osmotic stress-induced transcriptional regulation of the maize ZmDREB2A gene.

Epigenetic modifications play a key role in the transcriptional regulation of stress-induced gene expression in plants. In this study, we showed that the overall acetylation levels of histone H3 lysine 9 (H3K9) and H4 lysine 5 (H4K5) in the genome were increased in maize seedlings after mannitol treatment (to mimic osmotic stress). Mannitol treatment significantly induced the upregulation of the maize osmotic stress responsive gene Zea mays dehydration-responsive element binding protein 2A (ZmDREB2A), whereas abscisic acid (ABA) did not result in the induction of this gene. The application of exogenous ABA under osmotic stress conditions strongly repressed the induction of the ZmDREB2A gene. Chromatin immunoprecipitation and chromatin accessibility by real-time PCR experiments revealed that the promoter region of the ZmDREB2A gene was quickly hyperacetylated and decondensed after the mannitol treatment, suggesting that the promoter region is poised for histone acetylation to allow for fast induction of the ZmDREB2A gene. However, under osmotic stress conditions, the ABA treatment decreased the acetylation status and chromatin accessibility to micrococcal nuclease. These results suggest that osmotic stress activates the transcription of the ZmDREB2A gene by increasing the levels of acetylated histones H3K9 and H4K5 associated with the ZmDREB2A promoter region.